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Guide to Tilt-Up Concrete
Construction
ACI 551.1R-14
Reported by ACI Committee 551
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ISBN: 978-0-87031-956-3
Guide to Tilt-Up Concrete Construction
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ACI 551.1R-14
Guide to Tilt-Up Concrete Construction
Reported by ACI Committee 551
Jeff Griffin, Chair
Iyad M. Alsamsam
William R. Braswell
Jerry D. Coombs
Darryl E. Dixon
Michael Fulton
John G. Hart
Robert P. Hirsch
James R. Baty II, Secretary
Brent E. Hungerford
Anthony I. Johnson
Philip S. Kopf
Kimberly Waggle Kramer
James S. Lai
John W. Lawson
Ed T. McGuire
Andrew S. McPherson
Trent C. Nagele
Craig J. Olson
Lance Osborne
Jayendra R. Patel
J. Edward Sauter
Nandu K. Shah
Consulting members
Hugh Brooks
David L. Kelly
3.2—Trends, p. 4
3.3—Sustainability, p. 4
Tilt-up concrete construction is commonly used in low- to mid-rise
building construction. This guide reviews the many issues related
to the planning and construction of tilt-up buildings to produce
a quality tilt-up project. Major topics include preconstruction
planning, foundations, special considerations for slab-on-ground
construction, wall panel forming and casting, panel erection,
connections and repairing, and painting. This guide also contains
sections on sustainability and insulation systems, as well as references to the relevant codes and standards including updated
Occupational Safety & Health Administration (OSHA) safety
regulations.
CHAPTER 4—PRECONSTRUCTION
PLANNING, p. 6
4.1—Introduction, p. 6
4.2—Site layout and crane access, p. 6
4.3—Review of drawings, p. 7
4.4—Production schedule, p. 7
4.5—Submittals, p. 7
4.6—Staging, p. 8
4.7—Crews, p. 8
4.8—Panel layout and erection, p. 8
4.9—Casting beds and stack casting, p. 8
4.10—Concrete placement and testing, p. 9
4.11—Panel orientation and bracing, p. 9
4.12—Safety planning, p. 10
Keywords: forming; finish; inserts; insulation; panel; precast; release
agent; sandwich panel; site cast; sustainability; tilt-up.
CONTENTS
CHAPTER 1—INTRODUCTION AND SCOPE, p. 2
1.1—Introduction, p. 2
CHAPTER 5—FOUNDATIONS, p. 11
5.1—Foundation systems, p. 11
5.2—Continuous footings, p. 11
5.3—Spread footings, p. 12
5.4—Foundation walls, p. 12
5.5—Deep foundations (piles and drilled piers), p. 12
5.6—Foundation elevation versus bottom of panel elevation, p. 13
5.7—Backfill at loading dock high panels, p. 14
CHAPTER 2—DEFINITIONS, p. 2
CHAPTER 3––HISTORY, TRENDS, AND
SUSTAINABILITY, p. 3
3.1—History of tilt-up construction, p. 3
ACI Committee Reports, Guides, and Commentaries are
intended for guidance in planning, designing, executing, and
inspecting construction. This document is intended for the use
of individuals who are competent to evaluate the significance
and limitations of its content and recommendations and who
will accept responsibility for the application of the material it
contains. The American Concrete Institute disclaims any and
all responsibility for the stated principles. The Institute shall
not be liable for any loss or damage arising therefrom.
Reference to this document shall not be made in contract
documents. If items found in this document are desired by
the Architect/Engineer to be a part of the contract documents,
they shall be restated in mandatory language for incorporation
by the Architect/Engineer.
ACI 551.1R-14 supersedes ACI 551.1R-05 and was adopted and published
November 2014.
Copyright © 2014, American Concrete Institute.
All rights reserved including rights of reproduction and use in any form or by any
means, including the making of copies by any photo process, or by electronic or
mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission
in writing is obtained from the copyright proprietors.
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Joseph J. Steinbicker
Jason A. Swagert
Gerry J. Weiler
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
CHAPTER 6—CONSIDERATIONS FOR SLAB-ONGROUND CONSTRUCTION, p. 14
6.1—Temporary construction loads, p. 14
6.2—Floor slab (casting bed) preparation, p. 14
6.3—Joints and openings, p. 15
6.4—Slab closure strips (pour strips), p. 16
6.5—Floor slab repair, p. 16
CHAPTER 7—WALL PANEL FORMING AND
CASTING, p. 17
7.1—Forming, p. 17
7.2—Architectural treatments, p. 20
7.3—Reinforcement placement, p. 26
7.4—Steel embedment plates, p. 27
7.5—Lifting and bracing inserts, p. 27
7.6—Concrete placement, finishing, and curing, p. 29
CHAPTER 8—PANEL ERECTION, p. 31
8.1—Before erection, p. 31
8.2—Rigging, p. 31
8.3—Panel erection sequence, p. 31
8.4—Safety, p. 33
CHAPTER 9—CONNECTIONS, p. 33
9.1—Design of connections, p. 33
9.2—Foundation and slab-on-ground connections, p. 33
9.3—Roof connections and supported floor connections,
p. 35
9.4—Panel-to-panel connections, p. 37
9.5—Connections for higher seismic design categories, p.
38
CHAPTER 10—FINISHING AND SEALING, p. 38
10.1—Surface preparation, p. 38
10.2—Repairs, p. 38
10.3—Joints, p. 39
10.4—Paints, p. 40
CHAPTER 11—INSULATED PANELS, p. 41
11.1—Insulated panels, p. 41
11.2––Sandwich panels, p. 41
11.3––Insulation, p. 42
CHAPTER 1—INTRODUCTION AND SCOPE
1.1—Introduction
Tilt-up concrete construction is a unique form of site-cast
precast construction where building elements commonly
referred to as panels are constructed in job-site conditions
and set in place within the building design. The conditions of
casting location and positioning within the building design,
therefore, necessitate tilt-up’s own specialized set of design
parameters and construction techniques. Tilt-up panels are
generally handled only once. They are lifted or tilted from
the casting slab and erected in their final position in one
continuous operation.
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ACI defines tilt-up as “a construction technique for casting
concrete elements in a horizontal position at the job site
and then tilting them to their final position in a structure.”
ACI 318 further states that tilt-up concrete construction is a
form of precast concrete. Several features make the tilt-up
construction method unique.
Tilt-up panels serve as many functions for building design
as markets in which they are constructed. Panels, or perhaps
better described as tilt-up elements are constructed with and
without openings, sometimes consisting of only a grid of
monolithic beams and columns. Wall panels are found flat,
ribbed, curved (with broad to tight radii), and even biaxially
curved. Elements have been constructed freestanding and
cantilevered, simply supported, and connected in a variety of
configurations. Elements have been taller than 96 ft (30 m)
(Lucky Street Parking Garage, Hollywood, FL) and building
façades have been stacked as high as 138 ft (42 m) (ASU
Student Housing, Phoenix, AZ). Not all tilt-up elements are
building panels, however. Although the majority produced
annually are designed as either load- or nonload-bearing
building envelope panels, tilt-up elements have also been
featured as signs, monuments and art, walkways, stadium
seat supports, spires, tanks, tunnels, and bridges.
1.2––Scope
This guide presents the basic concepts, techniques, and
procedures used in tilt-up construction. The design of
tilt-up wall panels, although not addressed in this guide,
is addressed in the companion design guide ACI 551.2R,
which is beneficial in content to both licensed design professionals and contractors. This guide includes a brief history
of tilt-up concrete and a discussion of planning; foundation
and floor slab construction; and wall panel forming, casting,
and erection. It briefly describes typical connections used to
attach the panels to the rest of the structure, and options for
panel finishes are briefly described.
CHAPTER 2—DEFINITIONS
ACI provides a comprehensive list of definitions through
an online resource, “ACI Concrete Terminology,” http://
www.concrete.org/Tools/ConcreteTerminology.aspx. Definitions provided herein complement that resource.
bolster strip––continuous reinforcement support device for
wire mesh or mat in a concrete slab or wythe element.
cribbing––wood blocking set under crane outriggers to
spread the point load over a larger area to prevent damage
to the supporting surface.
densifier––chemical applied to a concrete surface to fill
pores, increasing surface density.
elastomeric paint––paint consisting of a polymer with
elasticity, generally having low Young’s Modulus and high
yield strain compared with other materials that behave as
a rubber-like membrane on the concrete surface to span
cracks and decrease permeability.
hygrothermal analysis––analysis of the movement of heat
and moisture through buildings, particularly a building
envelope, component, or system.
membrane bond breaker––nonchemically active release
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
agent that prevents the bond of fresh concrete to the casting
surface that dissipates with time.
penetrating bond breaker––chemically active release
agent that prevents the bond of fresh concrete to the casting surface that requires cleaning methods to remove from
substrate.
polyisocyanurate––thermoset plastic typically produced as
foam and used as rigid thermal insulation.
polystyrene––rigid or foamed synthetic aromatic polymer
made from the monomer styrene, a liquid petrochemical for
use in extruded shapes or insulation boards.
polysulfides––sealants designed for joints that need to
withstand prolonged immersion in liquids. Typical applications include swimming pools, fountains, cooling towers,
fuel and chemical storage tanks, wastewater treatment, and
petrochemical plants.
reentrant––inward corner of a concrete element that is
typically recognized at windows and doors.
reveal––longitudinal recess in the surface of a concrete
element.
spud vibrator––vibrator with a vibrating casing or a
vibrating head used to consolidate freshly placed concrete
by insertion into the mass. Also commonly referred to as a
stinger.
thermal transmittance––measure of the rate of heat loss
of a building component expressed as watts per square meter, per degree Kelvin, W/m2K; U-value is calculated from
the reciprocal of the combined thermal resistances of the
materials in the element, air spaces and surfaces, also taken
into account is the effect of thermal bridges, air gaps, and
fixings (commonly known as the U-value).
urethanes––thermosetting polymer formed by reacting an
isocyanurate with a polyol, used in the manufacture of flexible, high-resilience foam seating, caulks, and rigid foam
insulation panels.
wythe––each continuous vertical section of a concrete wall
in monolithic thickness.
Fig. 3.1a—Front wall panel of Memorial United Methodist
Church on tilt table.
CHAPTER 3––HISTORY, TRENDS, AND
SUSTAINABILITY
3.1—History of tilt-up construction
Although precasting building elements is sometimes
considered an innovative concept in engineering, origins can
be traced to as early as 4700 BC to a small village in Jarmo,
Iraq, where the villagers made walls for their dwellings
from touf, a pressed mud. As cementitious materials became
available, the quality and durability of these precast materials improved. The Romans produced pozzolan cement,
which they used extensively in their building projects
around 25 BC. It was not until the nineteenth century and
the development of portland cement that concrete structures
became integral to the construction process. By 1890, portland cement was widely accepted as the standard cementing
material.
Early structures using portland-cement concrete were
usually cast-in-place. By 1914, cast-in-place concrete rein-
forced with mild steel reinforcing bars was second only to
structural steel as a building material.
Some builders in the United States developed an early
form of tilt-up construction in which a tilting platform was
used. Aiken (1909) described the innovative method where
walls for a building were constructed on a structural platform, then rotated or tilted upward by means of specially
designed mechanical jacks, setting the panel in its final position. This tilt table method was used on the Jewett Lumber
Company in Des Moines, IA, between 1906 and 1912, and
on several Army facilities, factory buildings, and churches.
The tilt table method was also used on the Memorial
United Methodist Church in suburban Chicago. The church
construction incorporated decorative precast elements that
were embedded in the tilt-up panels (Fig. 3.1a and 3.1b).
Collins (1958) states that railroads during the period
before World War I developed a technique for precasting
large sections of bridges from reinforced concrete and setting
them in place with their heavy cranes. The cranes, however,
were mounted on railroad cars and required additional track
to be laid to access the site.
The idea of precasting large structural units using reinforced concrete cast into molds or forms was hastened by
World War I. The shortage of steel and labor caused by the
war and the subsequent increase in building prices challenged engineers and contractors to develop new methods
of building. Most improvements in precasting methods
were developed in England and Western Europe. Precast
elements, however, were small and easily handled without
heavy equipment. In Russia, precast building elements
developed using alternative casting methods due to more
difficult conditions for fabrication and construction. There,
larger sections were constructed using techniques similar to
those now used in the United States. Erection was accomplished with stationary cranes.
In the United States, there was little advancement in the
use of precast concrete elements until World War II. Three
technological innovations, attributed to this era, made the
erection and connection of site-cast elements more practical.
The first two of these developments were the heavy-duty
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 3.1b—Memorial United Methodist Church, Zion City,
IL, built circa 1906.
truck crane and electric-arc welding. The third development that made site casting of concrete elements a mature
industry was transit- or ready-mixed concrete. The readymixed concrete concept made quality concrete available to
anyone in any quantity on short notice.
As a result of these innovations, the number of buildings
constructed with site-cast concrete elements increased significantly. There were construction projects incorporating new
technologies and ideas in local areas of the Midwest, Texas,
Pennsylvania, and the New England states. The most progress, however, was in southern California during 1945 and
1946. The dollar volume of work using this type of construction in southern California increased dramatically between
1946 and 1952. Other Sun Belt states soon followed.
Numerous surveys conducted by the Tilt-Up Concrete
Association (2013) have found that tilt-up concrete is most
prevalent in North America, with buildings constructed in
every state in the United States, every province in Canada,
and in many areas of Mexico. The strongest concentration of
tilt-up activity occurs from British Columbia, south along the
Pacific coast into Mexico, across the southern United States,
and north along the Atlantic coast through Newfoundland.
Pockets of strong activity can also be found throughout the
Midwest, Plains, and Rocky Mountain states. Strong tilt-up
industries have also developed in Australia, New Zealand,
and several countries in Central and South America, while
locations in Africa, Europe, the Caribbean, and southern
Asia have recently been added to the regions where tilt-up
is being used.
3.2—Trends
3.2.1 Building applications—Tilt-up construction was
first used for large, plain, simple structures—most notably
warehouses or distribution centers. This is still a common
building type in tilt-up construction. Familiarity with
tilt-up by licensed design professionals and the use of the
broadening array of innovative finishes, discussed in later
sections, have advanced tilt-up for use in many other types
of buildings. These include correctional facilities, schools,
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multi-story office buildings, retail structures, cold storage
buildings, industrial and manufacturing projects, recreational facilities, churches, and multi-family housing. Most
recently, applications for tilt-up construction have broadened to include smaller buildings and single-family residential structures.
3.2.2 Sandwich wall panels––Most model energy codes
have minimum thermal performance requirements that
can be met or exceeded using insulated sandwich wall
panels. Tilt-up sandwich wall panels have been successful
for more than half a century in controlling temperatures
and increasing the thermal efficiency of tilt-up structures.
Current increases in the minimum energy code requirements and the shift toward sustainable systems have helped
sandwich walls grow in popularity and frequency of use.
Whether it is schools, offices, correctional facilities, cold
storage, or religious buildings, tilt-up sandwich panels can
provide the durability, speed of construction, and design
flexibility of tilt-up while providing significant R-value and
moisture protection. In general, sandwich wall panels are
comprised of two layers, or wythes, of concrete separated by
a layer of rigid insulation, and are tied together with a series
of connectors or fasteners. The performance of the tilt-up
sandwich panel, both structurally and thermally, depends on
the capacity of the connector and the detailing of the insulation layer, as discussed in Chapter 11.
3.2.3 Aesthetics—Economy provided in the tilt-up
construction method has combined with the challenge of
architectural variety and upscale aesthetics, using creative
form and advanced finishes. Engineering creativity and
craftsmanship of the construction professional together have
delivered building form involving significant amounts of
glazing with long spandrel concrete sections (Fig. 3.2.3a),
deep recesses and graphics, extensive reveal patterns,
complex geometric shapes, and angles and curves both outof-plane and in-plane. The surface appearance and texture
of tilt-up panels has also inspired more upscale architectural
finishes. Exposed-aggregate finishes provide natural, durable
concrete surfaces with low maintenance (Fig. 3.2.3b). Direct
casting onto aggregate placed in a sand bed, sandblasting,
power-washing techniques, and chemical retarders are
some of the methods used to expose the aggregate in the
panel surface to varying depths. These techniques are more
dependable than in the past, producing more uniform aggregate exposure. Panel elevations fit into a broader variety of
traditional community vernacular with thin brick, block, and
stone finishes cast into the concrete (Fig. 3.2.3c).
3.3—Sustainability
Tilt-up construction offers several key characteristics to
the goal for sustainable construction. By definition, the use
of locally available materials to construct energy efficient
building elements on-site embodies the essence of sustainability. Cement is the only component of a standard panel
with high-embodied energy and CO2 output; however, efficiencies in the production of cement coupled with the long,
low maintenance life of the structure more than compensate
for this deficiency.
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Fig. 3.2.3a—Tilt-up spandrel panels.
Fig. 3.2.3b—Detailed exposed aggregate finish.
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Fig. 3.2.3c—Thin brick tilt-up façade.
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3.3.1 Carbon footprint reduction—On-site manufacturing, along with the use of locally available raw materials
such as sand, gravel, and water, can significantly contribute
to the sustainability of the structure by reducing fossil fuel
consumption and emissions related to transporting the materials. On site, the size of tilt-up elements results in fewer
lifts, fewer joints, and faster shell construction than many
competing construction methods such as masonry, wood,
steel, and cast-in-place, further reducing emissions and
fuel consumption. Reduced waste of production materials
and the ability to recondition unused or outdated buildings
further adds to the sustainability of tilt-up by reducing the
strain on landfills.
3.3.2 Energy efficiency—Tilt-up construction can be very
energy efficient despite the low material R-value of concrete.
Thermal mass, inherent in tilt-up and other concrete-based
building systems, is largely responsible for structures that
require less energy to heat and cool as well as providing
greater degrees of comfort for occupants, even when insulation is not present. This is particularly true in temperate
climates, and those with a dominant cooling load. Where
insulation is required by code, or for a specific building
program, the negligible concrete R-value of 0.08 ft2-F-hr/
BTU-in. = 0.014 m2-C/Watt-mm) is bolstered with many
options for continuous insulation on the interior or exterior
surface as well as in a configuration known as a sandwich
wall construction. Tilt-up insulation systems effectively
deliver a building envelope that meets minimum performance standards, significantly reducing thermal transfer and
protecting the interior space conditioning needs. The degree
of energy efficiency provided by these insulation system
choices combined with the thermal mass can reduce the size
of heating and cooling equipment required, further contributing to the sustainability of the system.
Another benefit to energy efficiency and a requirement
found in the latest energy codes is a continuous air barrier.
The low permeability of a solid concrete tilt-up panel
decreases air and moisture infiltration into the structure—
one of the major factors in equipment sizing and operation.
The International Energy Conservation Code (ICC 2012a)
defines such panels as a qualified air barrier envelope component. Additionally, the size of tilt-up panels results in fewer
system joints that must be sealed to meet the continuous air
barrier requirements. This results in building envelopes that
are much higher in air tightness. The recent development of
high emissivity wall coatings can further enhance the performance of tilt-up buildings in southern climates by reflecting
more of the sun’s energy, thus reducing cooling demand and
costs.
3.3.3 Longevity—Concrete buildings have a distinct
advantage in terms of building life because of the permanence and durability of concrete as a building material.
Concrete structures have been continually in service since
before 150 AD. Change of use is one of the most challenging
aspects to the practicality of building life span. Tilt-up
building structures, however, offer significant flexibility
for modifications to embrace these changes of use and/or
occupancy. Panels can be removed, reused, relocated, and
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
modified. Modifications can include both window and door
openings. If demolition is required, the wall panels can be
crushed, allowing the concrete and steel to be recycled.
3.3.4 Finishes—Tilt-up concrete structures can be painted,
unfinished with exposed aggregate, have other materials
embedded in the concrete, or left simply as unfinished
concrete. Exposed aggregate panels, in particular when
executed with retarders and unfinished concrete, provide a
low-maintenance surface. The reduction in maintenance and
elimination of coatings adds to the sustainable characteristics of the system. The use of form liners and the availability
of thin brick embedded in the face of panels has further
broadened the aesthetic variety for tilt-up, contributing to its
use for virtually any building type.
3.3.6
Recycle/reuse/replace—Tilt-up
construction
employs recycling at several levels. Lumber, if used for
side forms, is typically reused several times. When panels
are replaced or destroyed, standard methods for recycling
steel content as well as the concrete itself can be employed.
Recycled concrete can be used as fill under slabs, sidewalks,
road base, and as coarse aggregate in concrete mixtures.
Careful consideration should be given to the types and
source for recycled aggregate that may be used in panels.
Cement content can be reduced by supplementary cementitious materials such as fly ash, slag cement, and silica fume.
These products, formerly directed to landfills, can replace
cement content. Recycling reduces direct and indirect costs,
and lessens the production of CO2.
3.3.7 Resilience—Tilt-up structures are not subject to
attack by termites or other wood destroying organisms.
Tilt-up structures have proven to be resilient for forces of
nature including tornadoes and hurricanes and the wind born
debris produced by these violent storms. As recent as May
2013, tilt-up buildings have withstood the intensity of EF-4
and 5 tornados as seen in Moore, OK. In fact, tilt-up is the
building system of choice for many emergency shelters as
well as emergency operation centers. Fire stations in Florida
and Texas, for instance, are among the building types turning
to tilt-up to withstand the intense forces of hurricanes, maintaining safety zones and functional services.
Fire resistance is an important characteristic of tilt-up
building envelopes. Due to the height of so many of today’s
tilt-up buildings, an average panel thickness of 7 in. (178
mm) is common. Such panel thicknesses are rated at 4-hour
fire resistance (ICC 2012b). This is important for separation within larger structures and for buildings, which require
distance separations in urban settings. Tilt-up is also used
for stair and elevator towers because of its strength and fireresistive properties.
Resiliency is also expressed in the force-resistance from
man-made threats, such as explosives and progressive
collapse. Numerous tilt-up structures in Texas, California,
District of Columbia, Florida, and Louisiana have been
designed for progressive collapse using the structural efficiency and redundancy of tilt-up panels. Additionally, tilt-up
panels have been studied by the Air Force Research Laboratory (AFRL-RX-TY-TR-2008-4616) and proven to perform
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with substantial resistance to explosive charges without
enhanced engineering.
CHAPTER 4—PRECONSTRUCTION PLANNING
4.1—Introduction
Preconstruction planning is essential for the smooth
progression of events in the construction of a tilt-up
building. Efficient on-site production operation is important
to the economy of tilt-up construction. Successful production requires organization and planning.
Many projects are developed with a contractor as a member
of the design team. This facilitates the coordination of the
design with the construction process, thus enabling the coordination of construction logistics into the design process.
A meeting between the licensed design professionals and
contractor can address limitations and concerns such as slab
thickness, panel size (height, weight, width, thickness, and
configuration), temporary bracing requirements, finishes
and reveals, use of new techniques, materials, erection, and
crane access. This is of particular importance when team
members are not familiar with tilt-up construction. The
meeting should also address lead times and other logistical
items that may impact the construction schedule.
4.2—Site layout and crane access
During preliminary construction planning of the project,
it is important for the contractor to become familiar with the
building site. Building location on the site can greatly affect
many aspects of construction. Locating the building adjacent
to a property line will affect foundation design and construction, panel layout and erection, and panel repairing and
painting. A geotechnical engineer should determine the soil
bearing capacity and advise of any soil removal or replacement requirements in addition to compaction requirements
prior to the start of any construction activities.
Crane access in and around the site is critical to a smooth
panel erection process. Many owners do not want the crane
on the floor slab due to potential slab damage. As a result,
many specifications restrict the crane to the building exterior or to an uncast strip of floor. If panel erection is to
proceed from outside the building perimeter, the area should
be graded smooth and compacted so no soft spots or ruts
impede the crane’s progress. Utility trenches into or around
the building may restrict crane access. Lateral clearance
around the building should also be sufficient to allow the
crane to maneuver. This is especially critical in urban areas.
All overhead power lines within potential reach of
cranes or other equipment should be carefully evaluated.
The contractor should consult OSHA 29 CFR 1926.1408
for required safe working distance based on the voltage,
or deenergize and ground the overhead power lines within
the operating reach of construction equipment. Proximity to
airports can even require special permits for panel erection
activities. Early planning for these situations is critical to be
the least disruptive to surrounding property owners.
If crane access around the building is limited, some or
all of the panels may have to be erected from within the
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building perimeter. The panel erection crane is typically
much heavier than a framing erection crane. Consequently,
if the panel erection crane is required to drive on the slab, the
slab edge may need to be thickened where the crane enters
and exits the building. Slab recesses or other obstructions
may also restrict crane access. Panel size, weight, and lift
distance will dictate the required crane size. The crane’s
operation manual provides guidance on maximum reach.
A general rule of thumb is that the crane’s rated capacity
should be three times the maximum panel weight.
The slab should be investigated wherever construction
loads are to be placed, including loading applied from temporary wind bracing. If the crane is going to be placed on the
slab during erection, the subgrade and the building slab must
be able to withstand the loads applied during erection or slab
damage will occur. The loads will vary depending on crane
location and weight of the tilt-up panels. Also, placement of
crane outriggers near slab corners, edges, and control and
construction joints can contribute to floor damage. Timber
cribbing should be placed under outriggers to distribute the
load. For structural slabs, including those supported on deep
foundations, the Engineer of Record should be made aware
if the erection crane is going to be placed on these slabs. A
licensed design professional should review this temporary
construction loading condition.
For buildings with large plan areas, it may be beneficial to
cast only the perimeter bay of the floor slab, which is enough
to form and cast panels. This has the advantage of casting
the majority of the slab after the panels and roof have been
erected and casting in a relatively controlled environment.
This staging can avoid placing large construction loads on
the slab. Proper planning is required to designate traffic
access in and out of the building and to areas of the slab that
are to be cast.
Planning should consider which panels are to be used to
allow the crane to exit the building. If the framing erection
crane is scheduled to place the closure panel(s) into its final
position, it should have the capacity to do so.
4.3—Review of drawings
Construction planning should involve a thorough review
of the architectural and structural drawings. The contractor
should ensure that the design intent is fully understood.
Structural drawings should be compared with the architectural drawings to make sure reveals, chamfers, openings,
and other items are not in conflict and can be constructed
as intended without impeding on design concrete cover.
Discrepancies, or areas in doubt, should immediately be
brought to the attention of the licensed design professionals.
If a more efficient design is visualized, it also should be
brought to the attention of the licensed design professionals
before commencement of construction.
When calculating the lifting stresses, the licensed design
professional assumes an unreinforced panel and adds the
needed steel to address the stresses. If the engineer of record
has designed the same quantity and size of reinforcement in
the same plane (location) the added reinforcement may not
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7
be required but should be confirmed by the licensed design
professional completing the lifting and bracing design.
All necessary information should be assembled for panel
forming, casting, and erection. This information includes
panel dimensions, opening dimensions, reinforcing, embedment plates, connections, architectural features, and similar
items.
4.4—Production schedule
As with all construction projects, the contractor often uses
a flow chart, Gantt chart (bar graph), or other visual form
of planning depicting all stages and steps in the process,
including the sequence in which they should proceed; the
items that are dependent on other phases before they can
proceed; lead time; the time period for completion; and the
manpower, resources, and materials required for each task.
The task of putting this schedule together can highlight
problem or critical areas and provide a visual depiction of
the entire process. The production schedule should be coordinated with overall building occupancy schedule.
Planning should also include scheduling of subcontractor
start times and logistics for materials ordering. On large
warehouse buildings, panel forming, casting, and erection
may progress simultaneously with roof framing. Failure to
account for these activities can produce inefficiency or even
a safety hazard.
4.5—Submittals
Panel shop drawing submittals should include at least the
following (Fig. 4.5):
a) Openings and reveal locations
b) Reinforcing steel, including concrete cover
c) Lift and brace insert locations and product information
d) Embedments
e) Panel dimensions, including thickness
f) Panel weight and concrete strength at time of lifting
It is also suggested that panel shop drawings include
section cuts, the depth and shape of rustication, and the types
and locations of panel finishes (including form liners and
thin brick).
Material submittals should include at least the following:
a) Concrete mixture proportion and substantiated 28-day
compressive strength (prescriptive concrete requirements,
if any; water-cementitious material ratio; air content and
minimum lifting compressive or flexural strength)
b) Bond breakers and curing compounds to check
compatibility
c) Form liners, reveal details
d) Grouting and repairing materials
e) Aggregate samples if exposed aggregate is used
f) Any other materials integrated into the panel
g) Reinforcing supports
h) Finishes and coatings
Thorough construction planning also involves the
concrete supplier, who should be aware of approved mixture
proportions including flexural and compressive strengths,
and quantities of concrete required for each series of panel
castings.
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Fig. 4.5—Typical shop drawing excerpt.
If specifications require it, or if the architect has special
finishing requirements such as exposed aggregate, a sample
panel should be made for approval. This mock-up panel
should be a minimum of 32 ft2 (3.0 m2), using the same
materials and methods proposed for the finished building.
This panel will serve as the basis for acceptance and help
to establish the range of acceptable finishes on other panels.
Submittals should be approved before commencement of
any aspect of the work that is influenced by the respective
material or work item.
4.6—Staging
Job-site staging can begin when most of the submittals
have been approved. Staging involves selection of locations
for support structures and materials storage, fabrication
areas, and paths for movement of materials and heavy equipment such as concrete trucks, cranes, and concrete conveyance equipment.
All planning should be done with safety as an underlying
goal. Essential items should be placed in areas that will not
be affected by rain or other adverse weather. In winter conditions, provisions for removal or depositing of snow may be
advisable.
sequence. Additionally, the contractor should determine if
there is sufficient slab area to cast the panels and maneuver
equipment during construction. A planning session to review
these items should be held early in the planning phase and
should include the superintendent, concrete subcontractor,
panel crane operator, and framing erector if the closure
panel will be set. A typical casting and erection sequence
plan is shown in Fig. 4.8a. The plan shows where panels
are to be formed and cast, as well as their final erected positions. Crane access through the building and the panel erection sequence are also shown. Crane size and access in and
around the building, including whether or not the crane is
permitted on the slab, and site layout greatly affect the panel
casting layout.
Figure 4.8b shows variations in the forming locations for
panels near a corner, based on decisions such as temporary
casting slabs, stack casting and crane access, size, or reach
capacity. A proper layout plan should provide enough space
between the panel being erected and panels yet to be erected
to attach temporary braces to the slab. Corners require added
coordination due to the increased brace congestion compared
with elsewhere in a building.
A licensed design professional should verify the capacity
of the slab to support construction, casting, and bracing
loads.
Typically, all panels are erected during one crane mobilization. Phasing of panel erection can cost more if there is a
second crane mobilization fee. A second crane mobilization,
however, could accelerate the schedule by allowing the first
phase of panels to be erected before all panels are cast and
cured.
To optimize the construction schedule, panels should be
cast in nearly the same order as they are to be erected and as
close as possible to their final position. Time could be lost if
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4.7—Crews
Crew size, productivity, and tasks should be carefully
planned. Crew tasks should be sequenced to avoid overrunning production of the preceding crew. Typical crews
include floor preparation, panel layout, forming, reinforcement, inspection, concrete, preerection, erection layout, lift
and brace preparation, erection, and grouting or repair. To
reduce manpower, personnel from one crew can staff other
crews. If several tilt-up operations occur simultaneously,
additional personnel may be required.
4.8—Panel layout and erection
One of the more important items to discuss during
preconstruction planning is the panel-casting and erection
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Fig. 4.8a—Casting and erection sequence plan.
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9
Fig. 4.9—Stack-cast panels.
on the stack casting operation. Casting smaller or equal size
panels and openings that are easily aligned maximize the
effectiveness and simplify the method. However, creativity
and experience frequently allow contractors to broaden the
application. Additionally, the height of the stack is important. Maximum height is dependent on many variables and
is directly related to the thickness and type of panel (that
is, solid or sandwich). The casting surface inside the panel
face should be finished to the same quality as the primary
casting surface. Formwork should be properly braced if
stack casting is required.
the first panel to be erected is the last panel to be cast, or if the
panel is cast too far from where it is to be erected. If panels
are cast in the wrong location, they may have to be lifted
and temporarily braced while other panels are moved out of
the way or they may have to be walked to the correct location while attached to the crane. In addition to the increased
cost and time involved, safety concerns increase each time
panels are handled. Lifting insert manufacturers may require
increased safety factors if panels are handled more than
once. The applied bending stresses from additional handling
can also add to durability and performance concerns, which
derive from cracks occurring during erection and the possibility of damage to the panels. Panels should be arranged so
they are erected consecutively. It is difficult to break a panel
free when it is cast between two other panels. Lack of planning panel sizes and casting locations may require a larger
crane than anticipated or scheduled.
4.9—Casting beds and stack casting
If the required casting area exceeds that available, or if
the floor slab cannot be used for casting, temporary casting
slabs at the perimeter should be investigated. The proximity
to the floor slab should be planned to minimize crane sets
and movements while maintaining the safe maneuver of all
panels to their designed location.
Stack casting of panels (Fig. 4.9) can occur on the floor slab
(6.2) or on temporary casting slabs (6.2.5). It is recommended
that contractors understand the impact of panel configuration
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4.10—Concrete placement and testing
Limited site access for concrete trucks may necessitate the
use of a concrete pump for placement. Panels are often erected
within 7 days of being cast. Specified flexural and compressive strength tests should be conducted by an accredited
testing agency in accordance with ASTM C78/C78M and
C39/C39M before erection to verify concrete strengths meet
or exceed erection requirements. Tests should be conducted
on beams and cylinders cast from the same concrete used in
the panels and cured and stored on site in conditions similar
to those experienced by the panels. For accurate slump tests,
the concrete slump should always be taken at the point of
placement (end of chute or hose), not at the hopper, if placement equipment is being used. The testing agency should be
notified when panels are to be cast so they can fabricate test
specimens and perform other on-site quality tests such as
slump and air content of the fresh concrete.
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Fig. 4.8b—Alternative panel forming location.
4.11—Panel orientation and bracing
Another item to be addressed during preconstruction planning includes determining whether the panels should be cast
inside face-up (more common) or outside face-up, or if they
should be braced to the inside or outside of the building.
When panels are braced outside of the building, it may be
necessary to provide temporary helical ground anchors, or
deadman blocks, outside the building to anchor the braces.
Exterior bracing will not be possible if the building is located
adjacent to a property line or other site geometry restrictions, such as the grade on or proximity to other buildings or
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
structures on the site, or the proximity of other construction
activities. Alternatively, the panel can be lifted and braced
in a temporary location with braces initially attached to the
outside face of the panel. Additional braces should then be
attached to inserts on the inside face. At this point, the panel
can be moved to its final position and braced in the normal
manner to the floor slab. This will double or triple the time
required to erect the panels. Refer to Chapter 8 for panel
bracing.
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4.12—Safety planning
While all construction projects require safety planning,
tilt-up construction has specific safety issues that should be
addressed. The planning process should include a meeting
among the superintendent, crane operator, rigging foreman,
and all other personnel involved in the erection process before
panel erection begins. Crewmembers should be assigned
specific tasks for handling braces and hardware attachment.
Only individuals directly involved with the erection process
should be near the panel being erected. No one should be
permitted to walk under a panel while it is being tilted, on
the blind side of the panel when the crane is traveling with it,
or between the crane and the panel. The crew should remain
alert and look out for the safety of fellow workers.
The rigging foreman, who the crane operator looks to for
all signals, should be experienced in handling panels, have
received formal training, and be completely familiar with
the precise set of hand and arm signals used to communicate
with the crane operator. The rigging foreman should be able
to demonstrate proper use of all lifting hardware, bracing
hardware, and any tools or equipment that may be necessary.
Prior to arriving on site, the rigging foreman should review
rigging requirements as designed by the licensed design
professional responsible for the lifting and bracing design.
CHAPTER 5—FOUNDATIONS
5.1—Foundation systems
Foundations transfer loads from the structure to the soil or
rock supporting the structure. In the case of tilt-up building
envelopes, the foundations are loaded with 75 percent of
the dead load when the panels are erected. Therefore, it
is important to understand the relationship of foundation
design to the construction process and the assumptions made
in the design process that may or may not fully exist during
that process. An understanding of the variations in foundation types and how they impact the construction process is
equally as important to the tilt-up planning process.
Foundation systems can be categorized as shallow or
deep. Shallow foundations bear on a soil layer at a reasonable depth below the surface. These include continuous footings, spread footings, combined footings, and mats. Deep
foundations, such as piles and drilled piers, transmit loads
by friction or bearing at some depth below the surface. The
permissible soil-bearing capacity or pile-load capacity is
typically specified in the geotechnical report prepared for
the project. The geotechnical engineer is responsible for the
selection and design of any foundation element.
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Depending on site and building conditions, subgrade
preparation may be necessary. This can include excavation
and removal of poor soils, compaction of existing soils, or
importing engineered fill. The prepared subgrade should be
maintained throughout construction as it affects the designed
integrity of the supporting slab condition for panel erection.
5.2—Continuous footings
Where soil conditions are adequate for the use of shallow
foundations, continuous strip footings are typically used to
provide support to interior and exterior tilt-up wall panels
(Fig. 5.2a, b, and c). The engineer of record determines
the continuous footing size and reinforcement. How the
panel is set on the footing during erection should always be
considered during footing design and construction. Typically, panels will be set on shim packs in two locations
temporarily. This is a far greater load than the continuous
footing and is designed to support and may subject the
footing to cracking if the load is not distributed as promptly
Fig. 5.2a—“At grade” continuous strip footing.
Fig. 5.2b—Dock continuous strip footing.
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11
panels (Fig. 5.3). Panels are centered on the footing unless
property lines or similar restrictions exist and have been
accounted for in the design. At minimum, the bottom of the
footing should be at or below the foundation embedment
depth and also extend below frost depth as required by the
geotechnical engineering report and local building codes.
Provisions should be made to address frost heave under the
unsupported panel edge if it does not extend below frost
depth.
Spread footings are typically wider than continuous footings and therefore require placement before the slab, or a
generous slab closure strip should be provided.
Fig. 5.2c—Continuous foundation elevation.
as possible with grout (5.6.1 and 5.6.2). Continuous reinforcement in footings helps to distribute panel loads over
weak spots in the subgrade. Heavier reinforcement might be
required if the footing should span trenches, drain lines, or
other site features. Footing width is inversely proportional
to soil capacity, so wider footings are necessary for softer
soil conditions. Panels are usually centered on continuous
footings unless property lines or other restrictions exist. At
a minimum, the bottom of the footing should extend below
frost depth in accordance with the geotechnical engineering
report and local building codes.
Continuous footings can usually be installed before or
after the slab when a portion of the perimeter slab is left out.
When the slab has no closure strip, however, the continuous
footing should be installed prior to the slab so that the slab
can be turned down on top of the footing.
In some instances, the panels are placed directly on a
thickened edge cast integral with the slab-on-ground. This
is usually an integral beam to accommodate the additional
loads created by the direct bearing of the panel. This type of
direct bearing can cause cracks in the slab near the junction
of the thickened slab edge and slab due to the rotation of the
beam when the panel load is applied.
5.3—Spread footings
Where soil conditions permit, isolated spread footings at
panel joints may be used to provide support for tilt-up wall
Fig. 5.3—Spread foundation elevation.
5.4—Foundation walls
Site conditions or design considerations may necessitate
the use of foundation walls. Because these walls are formed
as cast-in-place walls, the formed wall area will require
more time, material, and labor than if the same wall area
is an integral part of the tilt-up panel. They also reduce the
weight from height and occasionally thickness reductions,
thus impacting the crane size. The footing is constructed as
a continuous element with reinforcement dowels projecting
vertically. Typically, reinforcement is placed horizontally
and vertically in the center of the foundation walls for
at-grade conditions. Using a foundation wall where the exterior grade is well below finished floor elevation requires the
wall to be designed as a cantilevered retaining wall resisting
the backfill pressure and may require reinforcement on both
faces or temporary construction bracing. Dowels projecting
horizontally from the top of the foundation wall may be
required for connection to the floor slab (Fig. 5.4). Panel
connections to the slab or foundation walls more commonly
found are described in 9.2.
Foundation walls generally favor the use of a perimeter
slab closure strip so that the construction of the foundation walls can occur at approximately the same time as the
construction of the tilt-up panels. Otherwise, the construction of the tilt-up panels should be delayed until the foundation walls and slab are complete.
Fig. 5.4—Foundation wall system.
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5.5—Deep foundations (piles and drilled piers)
Where soil conditions dictate the use of deep foundations,
continuous grade beams on piles or pile caps on groups of
piles may be used to provide support to tilt-up wall panels.
Grade beams or pile caps are constructed similar to continuous strip footings. Panel widths are centered on the continuous grade beam or pile cap unless property lines or similar
restrictions exist. If piles are centered on the grade beam
and not staggered, rotation of the grade beam due to accidental misalignment of the as-built components should be
prevented by bracing the top of the grade beam to the slab, or
by taking other appropriate measures. Floor slabs supported
on piles may not be adequate to support construction loads
from the panel erection crane. For this reason, panel erection
for pile-supported buildings often takes place with the crane
located outside the building perimeter.
Foundation systems for drilled piers are similar to those on
piles when grade beams or caps are used. If the drilled pier
is of sufficient diameter, however, panels may bear directly
on the drilled pier without the need for a grade beam or cap.
Because deep foundations require more time to construct
than conventional shallow foundations, the process of
installing piles or drilled piers should begin well in advance
of panel work. The decision to incorporate a slab closure
strip is based on whether the slab is at-grade or dock-high
and required timing of the slab placement. Dock-high conditions and early slab placement generally dictate the use of
a slab closure strip while at-grade conditions and delayed
slab placement can avoid a slab closure strip and realize the
benefits of not having to fill and compact the closure strip as
well as having to place and finish the closure strip slab.
5.5.1 Continuous grade beams—When panel widths can
be established before foundation construction, the panels
can be designed and constructed to span from pier to pier
with the piers centered on the panel joints. The purpose of
the grade beam then would be to prevent frost heave. The
licensed design professional may specify the reinforcement
of the grade beam. If panel widths cannot be established
before foundation construction, or if drilled pier capacity or
size does not permit placement only at panel joints, the grade
beam should be designed and constructed to span from pile
to pile and provide continuous support to the panels. Continuous horizontal reinforcement and reinforcement stirrups
should be provided as specified to permit the grade beam to
span from pile to pile. Grade beams should be sufficiently
wide to allow for staggered or slightly mislocated piles. Pile
embedment into the grade beam should be specified by the
engineer of record (Fig. 5.5.1).
5.5.2 Individual pile caps—Individual pile caps used to
support the panels are usually located under the joint of adjacent panels. Panel widths should be finalized before foundation construction. The pile cap size and reinforcement
as well as pile embedment into the cap should be specified
by the engineer of record (Fig. 5.5.2). Pile caps can usually
accommodate small tolerances of less than 3 in. (75 mm) in
pile location. As with individual spread footings, the bottom
of the cap should extend below frost depth as required by
local building codes. Provisions should also be made to
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Fig. 5.5.1—Pile/grade beam foundation.
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12
Fig. 5.5.2—Pile and pile cap foundation.
address frost heave under the unsupported edge of the panel
if it does not extend below frost depth.
5.6—Foundation elevation versus bottom of panel
elevation
It is common for the contractor and panel engineer to
shorten the panel height to accommodate setting or bearing
pads and provide for adjustment. This is accomplished by
removing panel height from the base of the panel during the
shop drawing phase. An adjustment of 1 to 2 in. (25 to 50
mm) is common for continuous footings, spread footings,
and piles or piers with grade beams. An adjustment of 1 in.
(25 mm) or less is common for foundation walls.
5.6.1 Setting (bearing) pads—Setting or bearing pads
are positioned on top of the foundation system to temporarily support the wall panel during the erection and bracing
process. Typically, two separate pads are placed 1 to 3 ft (0.3
to 0.9 m) in from each end of the panel to provide the most
effective bearing. Although a single pad can be used under
the joint of abutting panels, localized shear forces can be
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13
full weight supported by the setting pads. Panels should be
plumbed within specified tolerances in their final position
prior to grouting. Any adjustments to the panel’s position
after grouting will disturb the bearing of the panel at the
grout joint.
5.7—Backfill at loading dock high panels
Footings for panels used at a loading dock may be located
4 to 6 ft (1.2 to 1.8 m) below floor slab elevation. The floor
slab is typically held back 5 to 10 ft (1.5 to 3 m) to allow the
panel to be erected onto the footing. The base of the panel
may need to be braced before back-filling along dock high
panels. The contractor should avoid lateral displacement of
the panel due to soil pressures during backfill compaction.
The panel may require temporary bracing or welding of the
reinforcement dowels (Fig. 5.2b).
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CHAPTER 6—CONSIDERATIONS FOR SLAB-ONGROUND CONSTRUCTION
Fig. 5.6.1—Panel setting.
induced by restraint at the pad, creating a diagonal crack at
the panel corner. Additional setting pads composed of plastic
shims may be required for wider panels or for panels with
openings to evenly distribute the panel weight to the footing.
These pads can be placed during or immediately after panel
erection. Panel weight alone may account for 75 percent or
more of the total load to the footing, so proper distribution of
this load is essential (Fig. 5.6.1).
Plastic shims of varying thicknesses are frequently used
as bearing pads. These shims allow for adjustment when
vertical alignment of the panels is necessary at windows and
reveal strips. With excessively high plastic bearing pads,
pins or dowels into the footing may have to be added to
prevent the panel from sliding off the pads.
5.6.2 Panel grouting—Once the panels are set and aligned,
space between the footing and panel should be packed or
filled with grout as soon as practical, preferably within 24
to 48 hours, to provide continuous panel support onto the
footing. If this space is not grouted, the footing may settle
from the point loads if it has not been designed for such
loads and damage to the footing or alignment issues in the
panels may result. The construction crew may install grout
from both sides of the panel to provide full bearing or place
flowable grout from one side. Grout typically has a 3000
psi (21 MPa) minimum compressive strength with No. 89
aggregate (ASTM C33/C33M). Although it does not have
to be a nonshrink type, the grout should maintain continuous bearing. The footing under the panel remains elastic
just enough to deflect and close any gap that may develop
or exist in the grout joint. The most important aspect of
installing the grout is to do so as soon as possible to prevent
overload damage to either the panel or the footing as neither
is designed for the concentrated loads applied, due to the
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6.1—Temporary construction loads
Because tilt-up panels are typically cast directly on the
building floor slab, it is necessary to minimize the possibility of temporary construction loads damaging the slab.
Loads imposed on the slab by temporary panel braces or
stored construction materials such as reinforcement, form
materials, aggregate, bond breaker containers, and embedment steel are generally not a problem for slabs designed
for industrial use. These activities may result in damage to
thinner slabs that may be specified for shopping center or
office applications, or slabs placed on subgrade with a relatively low modulus of subgrade reaction (k value). Braces
attached to thin slabs, generally less than 5 in. (125 mm)
thick, should be reviewed by the licensed design professional
responsible for the bracing design for sufficient capacity of
the anchorage to the concrete section. Loads imposed by
cranes or concrete trucks are much heavier than most other
construction loads and will usually exceed the slab capacity
as designed for in-place use. If loads are to be placed on the
slab shortly after casting, recognize that early-age concrete
strength will be significantly less than the specified 28-day
strength.
If panel erection requires the crane be placed on the
floor slab, it could be necessary to improve the subgrade or
increase the slab thickness and reinforcement. Oftentimes,
crane outrigger loads substantially exceed the floor slab
capacity, posing a risk of slab cracking or differential movement. Under these circumstances, a strip of floor slab can be
omitted where the crane will travel during panel erection.
This strip of slab is cast after panel erection is completed.
Prebid instructions should address crane placement on the
slab for panel erection.
6.2—Floor slab (casting bed) preparation
6.2.1 General—Placing and finishing the slab should be in
accordance with ACI 302.1R. The floor slab should have a
smooth steel trowel finish because the panel face cast against
the slab will mirror all imperfections.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
The slab should resist uplift forces imposed by temporary wind braces as defined in ASCE 37 or by the Tilt-Up
Concrete Association (2012). For slabs-on-ground less than
5 in. (125 mm) thick, such as those often used in office
buildings or shopping centers, a portion of the slab at the
temporary wind brace anchorage location will often require
thickening, reinforcement, or both, to resist these forces, as
determined by a licensed design professional.
On the majority of tilt-up projects, the floor slab is used
as a casting bed and, therefore, cast before enclosing the
building with the roof system. Take proper precautions
during concrete placement to protect against the adverse
effects of weather such as wind, temperature extremes, and
relative humidity, as recommended in ACI 308.1 and ACI
308R. Because the floor slab is cast during early phases of
the project, it can be subjected to traffic and wear from all
trades, showing evidence of that activity if care is not taken
to minimum these impacts.
6.2.2 Bond breakers—Bond breaker is one of the most
critical materials used on a tilt-up project. As the name
suggests, the bond breaker will prevent the panel concrete
from adhering to the slab. Section 7.1.4 provides an in-depth
discussion of bond breakers.
A combination of curing compound and bond breaker
material can be used, meeting requirements of ASTM C309.
A separate curing compound and bond breaker are also
acceptable as long as the products are compatible. Slabs
should be cured in accordance with ACI 302.1R, ACI 308.1,
and ACI 360R.
Consideration should be given to the removal or cleaning
of bond breaker residue remaining on the slab once panels are
erected. Contact the bond breaker manufacturer for specific
cleaning recommendations. Bond breaker residue on casting
slab and wall panel surfaces can be difficult to remove
depending on the type of product used and how heavy it
was applied. Residue from wax-containing bond breakers is
virtually impossible to completely remove, which may result
in compatibility concerns with subsequently applied liquid
floor treatments, floor coverings, and wall paints and coatings. In general, some form of cleaning may be necessary to
ensure complete removal of all bond breaker residue.
6.2.3 Sloped floors and utility penetrations—Panels are
usually cast on flat surfaces or on floors with constant slope.
Areas where compound slopes occur should be avoided for
casting panels.
Electrical and plumbing penetrations should be capped at
least 0.75 in. (19 mm) below the finished floor level. Utility
penetrations above the floor slab interfere with screeding
operation and become an obstacle for crane movement.
These projections may also become a source of cracks in the
slab. It is imperative to coordinate utility penetrations with
the slab casting procedures, panel forming, and panel erection sequencing.
6.2.4 Fiber-reinforced floors—Synthetic fiber reinforcement can be used in floor slabs for tilt-up buildings. Some
fibers may protrude above the surface of the slab, even with
the best placing and finishing techniques. These are often
easily broken or burned off. Casting of tilt-up panels on
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Fig. 6.2.5—Panels formed on casting slab.
slabs with synthetic reinforcement has not been problematic,
either for lifting or finishing. Fibers left projecting from the
casting surface, however, will transfer to the tilt-up panel
face during casting. Consider removing the projecting fibers
if exposed aesthetic impact is a concern. Steel fibers may
also be used for floor slabs in tilt-up buildings. There are
fewer problems associated with steel fibers projecting above
the slab surface because their stiffness and weight ensures
that they are worked into the concrete surface during the
trowel operation.
6.2.5 Casting beds—Prior to panel layout and forming,
verify that the slab area is large enough to cast all panels
and allow room for construction equipment to maneuver.
A general rule of thumb is that the panel area should not
exceed approximately 70 to 85 percent of the floor slab
area for casting panels. Otherwise, stack casting or additional temporary casting beds may be required. If temporary
casting beds are employed, they may be located outside the
main floor slab (Fig. 6.2.5) or in an area where the final floor
will be placed at a later date once the panels are erected.
Temporary casting beds are typically 3 in. (75 mm) thick
and constructed of concrete with 2500 to 3000 psi (18 to
21 MPa) compressive strength. These should be cast on a
compacted subgrade, finished, and cured by similar procedures used for the floor slab. Casting beds are usually not
designed to support loads from the crane. After panel erection, casting beds are usually broken up and hauled away.
However, if located correctly, they may be left in place and
paved over. Contraction joints in casting beds are optional.
Random cracking can be dealt with by filling with latex
caulk, depending on crack width and location.
6.3—Joints and openings
6.3.1 Joint locations and treatments—Construction and
contraction joints are integral to most floor slab designs and
rarely completely eliminated. Because every imperfection
on the floor surface is reflected on the panel surface, the
contractor should plan for the impact that slab joints may have
on the finished surface. There are many options for reducing
the effects of mirror images. For example, joints are most
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Fig. 6.3.1a—Plastic slab joint inserts snapped into joints.
Fig. 6.3.1b—Caulking removal from common slab joint.
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Fig. 6.3.1c—Drywall compound applied to floor joints.
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15
often left untreated or unfilled resulting in fins on the surface
of the panel. These can be removed with light grinding.
Other options include filling the joints with a removable
rubber or plastic strip inserted into the joint (Fig. 6.3.1a),
latex caulk (Fig. 6.3.1b), sand, or a drywall compound (Fig.
6.3.1c). Filling with sand or drywall compound are probably
the least effective methods because they have an affinity to
absorb moisture from the concrete mixture. Also, caulking
has a tendency to come up with the panel and not come off
cleanly, leaving caulk that requires painting that will eventually fade. The joint, where affected by the caulk or drywall
compound, will also be different than the adjacent floor
panel area and may be inconsistent or irregular or have a
high, fine aggregate concentration. Using tape to cover the
joints is not recommended because it will leave a mark on
the panel that is difficult to remove or hide behind paint.
Because paint or coatings alone will not always eliminate
the visual effects of a treated joint, the grinding of fins, or
untreated joint impressions on panels should be considered
when making this decision. Slab joints left untreated will
fill with concrete slurry and require recutting to clean them.
6.3.2 Openings and slab recesses—When space is limited,
it may be necessary to cast panels over openings or recesses
in the floor slab that are required by other trades. These
may be isolated equipment pads, trenches, pits, recessed
computer floors, recessed tile areas, or column blockouts.
Slab blockouts may be filled with sand to within 2 to 3 in.
(50 to 75 mm) from the surface and then topped with a thin
concrete layer. After panel erection, the concrete layer is
sawcut around the perimeter, chipped out, and discarded or
recycled. An alternative method for deep depressions is to
use plywood on formwork and level with the slab. Spray
the plywood with bond breaker similar to that used on the
slab. Support for the plywood should be adequate to prevent
sag during construction activity. Use a high quality plyform
or finished plywood to minimize the aesthetic impact to the
panel surface. The plywood surface may also be depressed
2 or 3 in. (50 to 75 mm) to allow a layer of concrete to be
placed on top.
6.4—Slab closure strips (pour strips)
Slab closure strips are areas of the slab between the initial
slab pour and erected panels (Fig. 5.2b). These strips will
occur wherever the slab is left out from the initial pour, which
is most often around the building perimeter where a connection of the panel to footing or slab is to be made. The initial
slab pour will usually have reinforcement projecting through
the construction joint to be connected to the panel reinforcement dowels. For dock conditions, use polyethylene sheeting
to minimize the exposed subgrade from erosion during
construction. Once panels are erected, braced, and plumbed,
the area behind them is backfilled and compacted to the
same requirements as the building subgrade. The closure
strip is then cast per the drawing requirements with the same
materials and methods used for concrete and finishing, and
curing procedures used for the initial slab. Slab control joints
should continue across the closure strip to the panel. Due
to the high length-to-width ratio of the slab closure strips,
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
give extra attention to control joint design, as they will differ
from the main body of the slab.
CHAPTER 7—WALL PANEL FORMING AND
CASTING
6.5—Floor slab repair
If the bond breaker performance is adequate, then minimal
damage should occur to the slab underlying the panel. Avoid
the tendency during initial panel lifting to drag the base of
the panel along the slab surface before it is lifted clear; panel
dragging can cause abrasion damage to the slab and place
undue stress load on the panel surfaces. This damage can
easily be reduced or eliminated by casting a 1 x 2 strip of
lumber or a hard plastic component along the bottom outside
edge of the panel. As the panel is lifted, an embedded lumber
strip protects the edge, resulting in very little contact between
the concrete panel and slab.
Holes in the slab caused by temporary wind brace and
form anchors should be repaired (Fig. 6.5a and 6.5b).
Various repairing materials are available, which should meet
the same strength requirements specified for the slab.
7.1—Forming
As discussed in 4.10, one of the most important planning items is creating a panel casting and erection sequence
plan (Fig. 4.8a) that shows where panels are to be formed;
the orientation they are to be formed; their final position
in the structure; and their casting and erection sequences.
This allows the superintendent, concrete subcontractor, or
panel erection subcontractor to plan the sequence of panel
construction and erection. The most common method
used by contractors to plan the layout of panels is scaled
computer aided design (CAD) or computer-generated drawings. Another technique is the use of scaled paper cutouts
of the panels arranged on a scaled floor plan. Often times,
the contractor will use a scale model of a crane with marked
boom lengths and capacities with this paper cutout method.
Used for decades, it is not as fast as CAD but is a simple
method to accurately complete the panel plan. Using either
method the lifting capacity at given distances of the selected
crane should be known. Panels should be arranged so that
they are erected and braced consecutively and bracing will
not interfere with erection.
7.1.1 Forming preparations and layout—The slab surface
should be clean and free of dirt or other materials. All block
outs for columns should be addressed before placement of
edge forms. Slab curing chemicals should be thoroughly
dry before panel forms are placed. If the slab is cured with
a chemical different from the bond breaker, they should be
compatible (7.1.4).
All layout elements including architectural features, panel
edges, and openings should be marked before setting any
forms. Chalk lines are commonly used to mark the location of panel forms (Fig. 7.1.1). Methods of chalking vary
between contractors, such as outside of forms and panel
openings. Marking only one side of a form can lead to
forming mistakes. Contractors should mark both sides of the
form to eliminate confusion over the correct side of the line
Fig. 6.5a—Hole drilled in slab for brace feet bolt.
Fig. 6.5b—Holes in slab from forming cleat attachments.
Fig. 7.1.1—Chalk lines marking the location intended for
plywood recess.
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to which the form belongs. Be consistent in the method used
to avoid confusion. Chalk lines can be sprayed with bond
breaker to prevent them from washing away during rain and
to reduce fading from foot traffic. Forming tolerances should
adhere to the requirements in ACI 117.
7.1.2 Forming materials—Dimension lumber, such as 2
x 6 and 2 x 8, and engineered wood are the most common
forming materials. Dimensional lumber is modified to
achieve the project needs by cutting down to the desired
dimension or using additional pieces as necessary to achieve
the required forming thickness. Only straight and true lumber
should be used. Sandwich panels are cast with wider-forming
material to accommodate the insulation thickness and the
additional layer of fascia concrete. To provide the taller form
height, striated wood products such as a faced particleboard
are more commonly used (Fig. 7.1.2a). Modular aluminum
forms as well as steel channels or angles can be used as edge
forms as well. These can be effective edge forms but are
less common and may offer less dimensional flexibility (Fig.
7.1.2b).
7.1.3 Securing forms—Accurate layout of forms is critical because panel joints are typically only 1/2 to 3/4 in.
(13 to 19 mm) wide. Forms are typically secured to form
supports spaced 36 to 48 in. (0.9 to 1.2 m) on center if used
with nominal 2 in. (50 mm) lumber. Form supports may be
constructed on the job from lumber or shop fabricated from a
variety of materials including wood, steel angles, or tubing.
They can be attached to the floor slab with masonry screws
or by drilling small holes and inserting nails, forming spikes,
or nylon anchors. Holes in the floor from form attachment
anchors should be repaired after erection of the panels.
Forms can be attached to the supports in a similar fashion
using wood screws or nails (Fig. 7.1.3a). Minor bows in the
forming lumber can be corrected with the form supports,
although bowing is rare due to the low form pressures
created by the thickness of typical panels. Adhesive systems
may also be used to secure formwork (Fig. 7.1.3b). Adhesive
systems are gaining popularity because the casting slab does
not get marred with form holes. Most adhesive systems do,
however, cause a slight discoloration where the adhesive is
applied.
The joint between the form bottom and slab should be
sealed with a chamfer strip, caulk, or both. If concrete paste
seeps under the edge form, it will leave a ragged edge that
requires additional grinding or repair after panel erection.
It is good practice to lay out forms as continuous panels
separated by a common form (Fig. 7.1.3c). Common forms
may be of nominal 1 or 2 in. (25 or 50 mm) lumber construction. The advantages of a common form are that fewer form
boards are required and any inconsistency in straightness of
Fig. 7.1.2a—Panels formed with engineered wood product.
Fig. 7.1.2b—Aluminum tilt-up panel forms.
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Fig. 7.1.3a—Typical formwork connection practice.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 7.1.3b—Adhesive bracket systems.
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Fig. 7.1.3c—Common form separating two panels.
the form is in and matches the adjacent panel, assuming the
adjacent panel shares the common form. Additionally, the
use of a common form allows the contractor to use a double
chamfer, which saves time by cutting the chamfer installation time in half and helps to keep the bottom of the form
from kicking out. The main disadvantages are the difficulty
of securing the common form, the lack of reuse of the lumber
and the additional restraint generated during the erection of
the panel because the common form cannot be stripped until
one panel is erected. In addition, there is no place to wedge
the panel free from the casting bed if the need arises due to
suction or bond breaker problems.
7.1.4 Bond breakers—Selection and proper application of
the bond breaker in conjunction with proper slab finishing
and workmanship is critical to the success of any tilt-up
project. Bond breakers generally fall into one of two major
categories: penetrating or membrane. Penetrating bond
breakers should not be used as curing compounds as they
do not comply with ASTM C309. Membrane-forming bond
breakers do comply with ASTM C309 and can be used as
both a curing compound and a bond breaker.
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Membrane bond breakers will dissipate over time.
Although the rate of dissipation is dependent on a number of
environmental factors, it is prolonged in cool, dry, and shaded
exposures. If these bond breakers require removal prior to
their dissipation, a mechanical or chemical method can be
used. A light brushblast or light acid-based chemical application should be sufficient to remove the remaining product.
Penetrating bond breakers do not usually require chemical
removal from the tilt-up panel prior to exterior coating,
other than pressure washing. They do, however, require
chemical removal from the casting surface if subsequent
toppings such as chemical hardeners, densifiers, sealers,
or epoxies will be applied. When a subsequent topping is
specified for the slab and a penetrating bond breaker is to be
used, the subsequent topping, such as hardener, densifier, or
sealer, should be applied before bond breaker application, if
possible. Hardeners and densifiers are most efficient when
applied to water-cured slabs, as a preexisting, penetrating
bond breaker diminishes their penetration.
Curing compounds; bond breakers; and any chemical
hardeners, densifiers, or sealers should be obtained from
the same manufacturer. Always use a bond breaker from
a single manufacturer. Further, the chosen manufacturer
should be consulted on specific compatibility issues among
their products. Not all manufactures of subsequent toppings,
coatings, or treatments are compatible with bond breakers.
Confirm compatibility and manufacturers’ agreement if
bond breakers and subsequent toppings, coatings, or treatments are used from different manufacturers. Regardless of
the bond breaker chosen, the more stringent of the subsequent topping, coating, or treatment manufacturer’s exterior
and interior requirements or bond breaker manufacturer’s
requirements for surface preparation should always be
followed prior to coating application.
A hard steel-troweled slab finish is a prerequisite for any
applied treatments and quality panel surfaces. A higher
FF/FL for the casting slab will result in a more consistent
panel face with the least risk of shadows and irregularities
exposed by sunlight when the panels are vertical. Slabs that
are poorly finished or cured, or ones that have low strength at
the surface, will exhibit higher permeability, which increases
absorption of the bond breaker, reducing its effectiveness.
All casting slabs should be cured according to ACI 302.1R,
ACI 308.1, and ACI 360R. Most bond breaker manufacturers recommend their product be applied in two coats after
all reveal strips, chamfer strips, and blockouts are installed,
but before installation of reinforcement and embedments
(Fig. 7.1.4). These coats are sprayed at right angles to each
other to ensure complete coverage of the casting slab. A
simple test for adequate application is to sprinkle water over
the slab once the bond breaker has been applied and allowed
to dry. The water should form beads. High concentrations
of the material in the form of puddles can cause discoloration or a gluing effect or impact the hydration process at
the panel face behaving like a retarder. The panel concrete
in these areas will not set fully, resulting in a surface that
is soft and subject to abrasion during cleaning. If the bond
breaker coverage is deemed to be inadequate and a second
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Fig 7.1.4—Applying the bond breaker prior to the installation of any steel reinforcement.
19
Fig. 7.2a—Uncoated panel finish for a natural appearance.
application is needed, care should be taken to minimize bond
breaker overspray covering the reinforcement and embedded
items.
7.2—Architectural treatments
The development of new finishes, coatings, and construction techniques, along with improvements in methods for
traditional finishes, has given licensed design professionals
and contractors many options for aesthetic treatment of
tilt-up panels. Aesthetic enhancements are achieved using
form liners, applied elements, offset panels, panel shape
variations, blockouts, and recesses. Thin brick or block
inlays also can be cast with the panel (7.2.7).
Finishes are created using several processes. Color variations of the mixture are created with different cement types,
color admixtures (pigments), different coarse and fine aggregates, and adjusting the mixture proportioning. Applied
finishes offer an even broader opportunity to affect the color
with stains, paints, and coatings. Surface texture and appearance are developed through various mechanical methods,
by special forming techniques, or through application of
surface-retarding coatings.
Figure 7.2a illustrates an uncoated panel that gives a
natural appearance. Slight variations in color are to be
expected and are what give the finish its natural appearance.
To limit undue or extreme color variations, cement color,
colored admixtures, forming surfaces, release agents, watercementitious material ratio (w/cm), consolidation procedures, fly ash, blast furnace slag cement, course and fine
aggregate, and the amount of cement used should be closely
controlled.
Textured surfaces can be obtained with the use of form
liners, sandblasting, or exposing aggregates (Fig. 7.2b).
Form liners should be stiff enough to minimize displacement or distortion during concrete placement. An exposedaggregate finish can be obtained with the use of retarders,
sandblasting or waterblasting, mechanical abrasion or bushhammering, or embedding aggregate in a sand bed prior to
casting (Fig. 7.2c). Because coarse aggregate from some
Fig 7.2b—Panel sand blasting. Note: color/texture change
in panel as a result of the sand blasting.
Fig 7.2c—Oyster shells placed in a sand bed.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig 7.2.1a—Typical butt joint building corner.
Fig. 7.2.1b—Sandwich panel butt joint.
Fig 7.2.1c—Mitered corner.
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sources may have a low hardness and abrade at the same
pace or faster than the cement paste matrix, careful evaluation of the coarse aggregate is critical if mechanical means
is to be used to expose the aggregate.
Architectural treatments resulting in panel thickness
reduction should be checked by the licensed design professional and accommodated for by additional thickness if
required. Consideration should also be given to the minimum
outer wythe thickness for sandwich wall panels. Though
not affecting the structural integrity of the tilt-up panel, the
manufacturer will have recommendations for the minimum
thickness required to develop the pullout capacity of their
embedded wythe connectors. In particular, features such as
reveal strips, embedded elements, and recesses will impact
the intended performance.
7.2.1 Chamfers and corners—Exterior panel edges are
usually chamfered (Fig. 7.2.1a), resulting in fewer spalls
and a cleaner appearance. Chamfers are normally formed at
45-degree angles and are at least 3/4 in. (19 mm) wide. They
are made from wood or a plastic extrusion of vinyl or polystyrene. Any damage to the chamfer, in particular the leading
edges, will result in deformations or ragged edges, so use
caution to minimize damage to the softer forming surfaces.
Chamfers should be caulked if the joints are not tight.
Panels at building corners can be formed with either butt
joints or mitered corners. The butt joint may be the simplest
and least expensive to form (Fig. 7.2.1a). The detail shown
in Fig. 7.2.1a is much easier to form and less fragile to
handle, but far more difficult when the detail is applied to
a sandwich panel due to the reentrant section created by the
fascia and insulation layers (Fig. 7.2.1b). The mitered corner
should be accurately formed because the miter magnifies any inconsistency (Fig. 7.2.1c). Mitered edges can be
formed from an assembly of dimension lumber or by using
specially fabricated materials, such as extruded polystyrene
shapes or prefabricated metal forms (Fig. 7.2.1d). Mitered
corners rarely terminate in a point, which is very difficult to
form and erect without damage.
7.2.2 Reveal strips—The simplest method to divide the
visual expanse of a large tilt-up panel and hide casting slab
irregularities reflected in the panel is to use reveal strips
(Fig. 7.2.2a). Reveals may run vertical, horizontal, diagonal, or circular, and there may be one or several bands on
a building (Fig. 7.2.2b and 7.2.2c). Reveals are typically
1/2 to 3/4 in. (13 to 19 mm) deep and 2 to 4 in. (50 to 100
mm) wide with 22.5- or 45-degree beveled sides for ease of
stripping. Reveals with square edges (90-degree angles) are
not recommended unless they occur at a panel edge or form
liner (Fig. 7.2.2d), as they are difficult to strip and may result
in poor-quality edges. Chamfers and reveal strips should
have a consistent depth and angle. If a reveal is required,
its location and subsequent effect on the panel’s structural
performance should be considered. The reduction of overall
concrete thickness at a reveal weakens the cross section of
the concrete panel and may require additional reinforcement
or additional panel thickness to achieve the required structural performance.
Fig. 7.2.1d—Mitered corner formwork.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
21
Fig 7.2.2a—Reveal strip section.
Fig. 7.2.2b—Vertical and horizontal reveals.
Fig. 7.2.2d—Reveals at form liner edge.
Reveals can be fabricated from 1x white pine, poplar,
spruce, or fir lumber, or composite lumber. Wood reveals
may need to be coated with a sealer to reduce adhesion to
concrete and stabilize the wood. The reflection of grain
pattern from the wood to the concrete can be a problem. To
minimize this condition, a finished lumber or plyform reveal
is often used. Reveals can also be made of plastic extrusions
of vinyl or polystyrene. A smooth-faced surface is desired,
often plastic-coated or naturally formed, to minimize the
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Fig. 7.2.2c—Intricate reveal patterns.
bond to the concrete. With any plastic-based component,
the use of noncompatible solvents and chemicals should
be avoided. As with chamfers, the forming material for
reveals is softer and the exposed surfaces subject to damage.
Be careful to protect these surfaces to minimize the panel
surface finish. The effect of weather and moisture should be
considered when choosing the lumber for reveals.
Accurate placement of reveals is important, particularly
if the reveal continues from one panel to the next. Location of the reveals should be marked on the slab with chalk
lines and should be fastened, nailed, or adhered to the slab
with construction adhesives. Edges of the reveal strip should
be caulked with a silicon or latex caulk to produce a clean,
crisp edge when needed. Reveal strips should be thoroughly
coated with bond breaker after caulking and compatibility
of the chemical with the reveal components tested prior to
application.
7.2.3 Dimple finish—A dimple surface finish can be used
as an accent or to soften the appearance of an entire panel
(Fig. 7.2.3a). Although the concept of this treatment is
simple, exercise care in its application. The area to receive
the dimple finish is outlined or edged by a nominal 2 in. (50
mm) lumber strip, unless the entire panel is to be dimpled,
in which case it is then filled to the top of the nominal 2 in.
(50 mm) lumber strip with 3/4 to 1 in. (19 to 25 mm) crushed
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 7.2.3a—Dimple finish.
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Fig. 7.2.3b—Formed dimple finish.
stone (Fig. 7.2.3b). Clear, 6 mil (0.15 mm) (minimum)
polyethylene is then stretched over the stone and secured to
the nailing strip. All wrinkles and folds in the polyethylene
should be stretched out of the area to be cast, unless that is
part of the desired effect. A 3/4 in. (19 mm) reveal is then
added to the top of the nominal 2 in. (50 mm) lumber strip.
Foot traffic or other activities that could dislodge or move
the rock or puncture the polyethylene should be avoided.
Care should be taken when placing reinforcement for proper
location.
For an alternate dimple finish, a dimple formliner may be
used (7.2.5).
7.2.4 Exposed-aggregate and stone finishes—Exposedaggregate finishes can be achieved by using one of the
following techniques:
a) Exposing the surface aggregate by sandblasting
b) Exposing the aggregate by pressure washing, combined
with the use of a retarder
c) Bush hammering
d) Placing aggregate in a sand bed within the panel forms
and casting the concrete onto these aggregates
Exposed-aggregate finishes derive their appearance from
crushed graded aggregates, which normally vary between
3/4 and 1-1/2 in. (19 to 38 mm) A colored mortar can also
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enhance the finished product. A clean, durable aggregate
intended for use in an exposed concrete panel should be used.
Aggregates from a reliable and consistent source should be
chosen. Aggregates with iron sulphides or other impurities
may cause surface discoloration. Some types of aggregates
can cause popouts or deteriorate when exposed to alkalinity
or freezing-and-thawing cycles. If a specific color aggregate
is desired, it should be used throughout the concrete mixture.
Some stone may be more expensive than the regular coarse
aggregate used in the concrete, which should be considered
in the planning and cost-estimating stages. If an expensive
aggregate or cement is desired, a special fascia wythe may
be an option over using expensive components for the full
panel thickness. This fascia wythe, 2 to 3 in. (50 to 75 mm)
thick, requires a structural panel backup and adds to the total
panel thickness. Adequate bond between the two wythes
should be provided and differential shrinkage considered.
Shrinkage can be minimized by control of the w/cm, cement
content, and placement timing. This same effect could also
be achieved by constructing a sandwich panel, which would
eliminate any possible concrete compatibility issues that
may arise over time. Whichever method is used to obtain an
exposed-aggregate finish, or if plain concrete is the desired
look, panels should be cleaned and sealed with a nongloss,
non-membrane-forming, nonyellowing, penetrating silane/
siloxane blend complying with local volatile organic
compound (VOC) regulations. The penetrating sealer should
impart a breathable water-repellent barrier without changing
the appearance of the substrate.
A large-scale panel, a minimum of 4 x 8 ft (1.2 x 2.4 m),
should be cast for architect and building owner approval
with the provision that aggregate supplier test panels are
generally too small to show variations that typically occur
in large panels. Rather, supplier test panels are intended to
show characteristics of the exposed aggregate finish. Furthermore, the cement, casting technique, or curing conditions of
the test panel may vary from that used on the subsequently
produced full-size panels.
7.2.4.1 Sandblasting—Sandblasting is one typical method
to obtain an exposed-aggregate finish. The objective is to
abrade the concrete surface to remove the hardened cement
matrix surface and expose the underlying aggregate. Light
sandblasting will remove approximately 1/16 in. (1.5 mm)
of the surface while heavy sandblasting can remove up to
1/2 in. (13 mm), which in turn may require larger coarse
aggregate.
Sand or abrasive blasting with or without retarders may
change the appearance of aggregates by permanently
dulling them. The degree of change will vary depending
on aggregate type. Concrete matrix strength will affect the
final appearance and ease of sandblasting. Concrete matrix
strength in each panel should be approximately the same
when it is sandblasted. Ideally, concrete should be less than
14 days old. Diameter of the venturi nozzle, air pressure, and
type of sandblast sand used should be determined by a trial
procedure on concrete similar to that used in the actual tilt-up
panel. Once the sand is selected, the source and particle size
should not be altered during the course of the project.
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The degree of uniformity is generally in direct proportion
to the depth of exposure; therefore, the deeper the sandblast
exposure, the greater the uniformity. A brush or light sandblast finish may appear acceptable on a small sample, but
uniformity on a large panel is difficult to obtain. To mask
some nonuniformity or to allow for variation in the depth
of exposure of the sandblasted surface, reveal strips can be
used to divide the surface into smaller areas (Fig. 7.2b).
When casting panels that are to be sandblasted, the
contractor should be prepared to give extra attention to the
concrete placement, crack control, and the prevention of
other irregularities to the surface. The sandblasting process
will round the edges of all cracks and increase their visibility.
The sandblasting operator should use an aerial lift (Fig
7.2b) or have scaffolding sufficient to maintain a consistent
angle and constant distance from the concrete surface being
blasted to obtain the best results. Sandblasting is generally
more uniform if the nozzle is moved in a circular motion
rather than only vertically and horizontally. Wet sandblasting may be required for conformance with environmental regulations.
Sandblasted surfaces are normally classified as:
a) Brush—Removes the cement matrix and exposes the fine
aggregate—no projection of the coarse aggregate from the
matrix
b) Light—Sufficient to expose fine aggregate and occasional
exposure of coarse aggregate reveal 1/16 in. (1.5 mm)
c) Medium—Sufficient to expose coarse aggregate with a
slight reveal—maximum aggregate reveal 1/4 in. (6 mm)
d) Heavy—Sufficient to generally expose and reveal the
coarse aggregate to a maximum projection of 1/3 the
maximum size of coarse aggregate diameter with a reveal
of 1/4 to 1/2 in. (6 to 13 mm) and a surface that is rugged
and uneven
Careful selection of coarse aggregate is critical if a
mechanical means is being used to expose the aggregate.
This will provide greater uniformity and reduce sandblasting
time. When sandblasted surfaces are required, only 100
percent plastic, pointed chairs should be used to support the
reinforcing steel. Plastic tips on steel chairs can come off,
resulting in rust stains on the panel. The deeper the sandblast, the more coarse aggregate is required in the mixture
proportion. Deep exposure of coarse aggregate requires a
finer abrasive to obtain uniform results.
7.2.4.2 Pressure washing—Pressure washing, in combination with the retarder, gives similar results to sandblasting
by stopping the hydration process of the cement paste at the
surface, and then removing the cement and fine aggregate
on the panel surface to expose the coarse aggregate below.
Proper retarder application and concrete placement are critical to obtaining a uniform appearance with exposed-aggregate finishes. Once the panel forms are placed, the retarder
is applied to a properly sealed casting surface, eliminating
the possibility that the retarder is absorbed by the casting
surface. The retarder should be checked for compatibility
with the curing compound, sealer, or both. Care should be
taken to obtain a constant concentration of retarder that will
result in uniform aggregate exposure. Select a retarder with
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23
an etch depth compatible with the size of aggregate used.
Protection from the elements should be provided during the
time period after the retarder has been applied until concrete
is placed because the retarder is activated by water. Joints
and cracks should be covered or filled to prevent the absorption of retarder or moisture from the concrete mixture. The
material, however, should not have an affinity for water.
Care should also be taken when installing panel reinforcement, lifting inserts, and other items to avoid scraping the
retarder off the casting surface.
Concrete should be deposited as close as possible to its
final position in the panel and not moved about with the
vibrator. Otherwise, segregation may occur, resulting in a
nonuniform surface finish. Once panels have been cast, the
edges should be protected in the event of rain to prevent the
retarder from being diluted by the precipitation.
After the panel has been lifted into place, the retarded
surface is removed by light sandblasting or waterblasting.
Aggregate exposure should begin as soon as possible to
within 2 to 3 hours after lifting because the retarded surface
will start to harden from ultraviolet exposure. Use light etch
retarders in combination with medium or deep sandblasting
of exposed surfaces to minimize time and labor. Proper
procedures and trained personnel are critical in obtaining
desirable results.
7.2.4.3 Bush-hammering—Another type of exposed
aggregate surface, though less common than sandblasting,
is produced by bush-hammering. Bush-hammered surfaces
are produced by pneumatic tools fitted with a bush-hammer,
comb, chisel, or multiple-pointed attachment. The type
of tool is determined by the final surface desired. Bushhammering is normally applied to well-graded mixtures with
softer aggregates such as dolomite and marble. Most bushhammering will remove 3/16 in. (5 mm) of surface material. Bush-hammering works best with 4000 psi (28 MPa)
and higher concrete. To minimize loosening of the aggregate
during hammer operations, a minimum concrete age of 14
days is recommended. Bush hammering at corners tends to
cause damage unless special care is taken. Corners should be
completed with hand tools rather than pneumatic hammers.
7.2.4.4 Sand bed—The sand bed method involves handplacing aggregates on a 2 to 3 in. (50 to 75 mm) sand bed
within the forms. A low slump sand/cement grout is then
placed over the aggregates. This method has been successfully used with maximum sizes of coarse aggregate up to 6
in. (150 mm). These larger aggregates should be hand placed
in the sand. Large stone has also been used successfully
in sand bed casting (Fig. 7.2.4.4a) including thin slices of
facing stone, flagstone, limestone, and rounded river rocks.
The best results are obtained with dry masonry sand as the
sand bed. The color of the sand should be consistent with the
aggregates used in the concrete to avoid a mottled appearance. Sand is usually spread to a depth of 40 to 50 percent
of the stone diameter, but depth is dependent on the amount
of exposure desired. All aggregate to be exposed should be
of uniform size and gradation for best results. However,
smaller aggregate needs to be worked in to fill voids.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Special care should be taken to ensure that adequate
aggregate density is obtained around edges, corners, and
openings. This may require special tamping tools in these
areas. After aggregate distribution has been obtained, the
aggregate is pushed or hand tamped into the sand bed. The
aggregate can be rolled into the sand bed using a weighted,
smooth-face roller. Once a final adjustment in sand thickness has been made, a fine spray of water is then used to
settle the sand around the aggregates. Excessive use of water
from a normal nozzle may disturb the aggregate bedding
and promote cement migration into the sand bed. The grout
mixture is then placed over the aggregate. The surface is
mechanically roughened prior to setting to aid in bonding
with the structural wythe.
Reinforcement should then be placed in its proper position within the structural wythe of the concrete portion
of the panel. Chairs maintain this position similarly to a
normal reinforcement placement. When placed on top of
the stones or grout bed (Fig. 7.2.4.4b), however, the variation in aggregate thickness may make it difficult to maintain
the proper location. The licensed design professional should
be consulted for possible adjustments to the reinforcement
design to account for these variations.
With smaller aggregates or if a specific color of mortar is
desired, a 2 to 3 in. (50 to 75 mm) cement and sand grout can
be placed over the aggregate and allowed to harden to ensure
that the aggregate is not dislodged when the structural wythe
concrete is placed. Provisions should be made to cure the
grout. A curing compound should not be used as a bonding
agent to ensure bond with the concrete. The grout surface
should also be raked to promote bonding with the concrete.
After the tilt-up panels have been erected, the sand is hand
brushed or removed with water under low pressure, 1000 psi
(7 MPa) or less.
7.2.5 Form liners—Manufactured form liners are often
used to produce a special finish or create geometric shapes.
They can be used as an accent on a portion of the panel or
for the entire panel. Form liners are available in a variety
of materials and patterns (Fig. 7.2.5a). Liners designed for
a single use, manufactured from polystyrene or vacuumformed plastic, are most common on tilt-up projects. There
are, however, also multi-use form liners made out of highdensity plastic or rubber.
Corrugated siding, metal decking, and other commonly
available materials have been successfully used as form
liners, and other common materials like roughhewn wood
impart interesting surface textures (Fig. 7.2.5b).
7.2.6 Surface applied features—Accent features are used
extensively in construction because of their relatively low
price and the ability to form complex shapes on the panel
surface. These systems consist of cementitious coatings over
a base material or shape usually consisting of a rigid or foam
plastic shape.
Accent features and their finishing systems are used in
conjunction with tilt-up construction, either directly on the
tilt-up panel or in conjunction with tilt-up and other forms
of construction. Applications should be limited to fascia and
feature elements that are less susceptible to damage from
ground level such as projectiles and vandalism, unless a
system is selected with a higher durability. Affixed features
that cross tilt-up joints can be damaged due to the movement
of the panel. Care should be taken to address this movement. Simple reveals and patterns can be easily applied to
Fig. 7.2.4.4a—Hand-placed stone finish.
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Fig.7.2.4.4b—Flagstone concrete casting.
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Fig. 7.2.5a—Form liner finishes.
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--`,,,,```,`,`,`,,```,,`,```,``,-`-`,,`,,`,`,,`---
Fig. 7.2.5b—Rough wood exterior finish.
25
Fig. 7.2.7a—Thin brick application.
the panel, depending on the coatings used. Combining these
multiple elements can add new dimensions to the finished
building.
7.2.7 Thin cast brick/block—Thin cast bricks and blocks
are now widely used in tilt-up construction as architectural
features or to create an architectural style (Fig. 7.2.7a). Thin
bricks are used over the entire panel or an accent portion of
the panel. Thin bricks come in all colors and textures and
can be cast in the same types of courses as applied brick.
The brick area is laid out in the panel with special care to
be taken to keep the running pattern constant across panel
joints. Further, special return bricks are manufactured
for window and door openings so that the brick feature is
constant (Fig. 7.2.7b). Form liners or a snap system can be
used as the brick template. Both systems incorporate the
mortar joint into the system and provide a pattern to place
the thin bricks into. The thin bricks are scored on the back
to allow for a mechanical bond with the concrete. The front
of the thin brick can be waxed or nonwaxed. The waxed
front helps keep any mortar flow from sticking to or staining
the brick face (Fig. 7.2.7c). A hot water pressure washer is
needed to remove the wax from the brick face.
Fig. 7.2.7b—Special detailing options at corners.
7.3—Reinforcement placement
The engineer of record will determine the size, number, and
spacing of reinforcement for the in-place wall panel. In most
cases, another licensed design professional with the lift and
brace insert manufacturer or retained by the contractor will
provide the lifting analysis of the stresses created by lifting
and temporary bracing of the panel. This engineer may also
stipulate additional reinforcement to resist these forces. ACI
318 governs the placement of reinforcement (deformed bar
and welded wire) including cover, lap lengths, and spacing.
Steel reinforcement location is critical to the performance of
the panel, and all instructions and information relating to it
should be precisely followed (Fig. 7.3). Refer to ACI 117 for
reinforcement placement tolerances.
Fig. 7.2.7c—Erected panels with thin brick prior to washing.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 7.3—Reinforcement and shop drawings critical to panel
layout.
7.4—Steel embedment plates
Steel embedment plates (Fig. 7.4) are used to attach the
panel to other building components, such as roof or floor
framing members, or for panel-to-panel connections and
panel-to-foundation connections. They are fabricated from
plate steel with lugs, headed studs, or weldable deformed bar
anchors welded to the back. The embedment plate should be
exposed to facilitate ease of attachment. The plates may be
either flush with the surface or recessed. In structures where
appearance is a factor, or where a highly corrosive environment is anticipated, a recessed embedment is preferred
because it can be concealed. Galvanized or stainless steel
embedment plates should be used in corrosive environments
if they are to be exposed.
Welding is the most frequent form of connection to an
embedment plate. It gives maximum flexibility and allows
greater latitude to adjust for variations in height or dimension. All welding should be performed by certified welders
and in accordance with AWS D1.1/D1.1M and AWS D1.4/
D1.4M. Bolting can also be used but requires the use of
Fig. 7.4—Embedment plates set and tied to steel prior to
concrete placement.
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7.5—Lifting and bracing inserts
Inserts are required for lifting the panels and for the connection of temporary braces. Lifting inserts are the attachment
points of the crane to the panel through the rigging. Bracing
inserts are the attachment points of pipe braces that hold the
panels in place until the roof diaphragm and floor connections are made and the licensed design professional approves
their removal.
Lifting and bracing inserts are usually selected and
supplied by the hardware manufacturer based on panel
dimensions and configuration. The supplier analyzes each
panel to determine the number and location of lifting inserts
required. These requirements are a function of the panel
weight and stresses encountered during its lifting. The
lifting hardware manufacturer typically provides the lifting
analysis and lifting insert details along with any additional
requirements like strongbacks. Special or odd-shaped panels
may require strongbacks. Strongbacks may be required to
prevent panel cracking during lifting due to deflection and
should be installed as detailed by the licensed design professional for the lifting design.
Many factors are involved in the design of the lifting
inserts. They include:
a) Panel size, thickness, and weight
b) Insert type
c) Panel shape
d) Concrete compressive and flexural strengths at time of lift
e) Panel reinforcement
f) Panel openings
g) Panel finish
h) Panel lifting options, for example, edge or face lift
Concrete flexural strengths should be equal to or greater
than the lifting strength before panels are lifted. Higherstrength or high early-strength concrete can be used if early
panel erection is desired. Inserts properly sized for anticipated loading, panel thickness, and other characteristics
should be provided along with drawings detailing the exact
location for the inserts and any additional reinforcement
requirements. Lifting inserts should be installed to a plan
location tolerance of ±1 in. (±25 mm) unless otherwise specified by the supplier.
Inserts are supplied with a void form material designed to
prevent concrete from filling the insert during casting operations (Fig. 7.5a). Infill pieces are usually made of plastic and
have nubs that project after the troweling or finishing operation so that the insert can be easily located.
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slotted attachment members to account for dimensional
variations.
Steel embedment plates may be either galvanized or the
exposed surface may be painted to minimize rusting. The
embedded portion should not be painted. Welded areas
should be touched up with paint or galvanizing paint.
Contract documents often direct the presetting of embeds.
If not restricted, however, embed plates may be preset or
placed in the concrete prior to initial set, following the provisions of ACI 301. Consultation with the panel design engineer is recommended before proceeding with wet-setting.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
27
Fig. 7.5c—Panel braces attached prior to lifting.
Fig. 7.5a—Brace insert and lifting insert.
Fig. 7.5d—Brace foot bolted to the floor slab.
Fig. 7.5b—Releasing lifting clutch from inserts.
All lifting inserts used today can be connected to the
rigging apparatus with a ground-release mechanism. This
allows the insert to be disconnected at the appropriate time
without the need to climb ladders (Fig. 7.5b), as was the
method of the past.
The supplier of the bracing inserts analyzes each panel
to also determine the required number and location of these
inserts. These requirements are a function of the construction period wind load applied to the project and capacity
of the braces available to the project as well as the brace
foot anchorage condition. The calculated wind load may
be increased either as desired for greater protection or as
required based on the time of the year.
Braces are attached to panel inserts before lifting (Fig.
7.5c). After the panel has been erected and before the crane
is released, the braces are attached to the floor slab, or
temporary anchoring devices such as helical ground anchors
or deadmen. Floor attachments may be either cast-in or postdrilled (Fig. 7.5d). Manufacturer’s instructions should be
explicitly followed regarding attachment capacity based on
slab thickness, edge distance, and other parameters. Helical
ground anchor systems are an alternative to slab-based
anchors for attachment of the wind load bracing system.
They are installed into the surrounding grade (Fig. 7.5e) at
designed locations and the braces are attached to the exposed
anchor heads. The braces are attached to the exposed heads of
the anchors. Deadmen are premade or cast-in-place concrete
blocks wholly or partially buried into the grade to provide
attachment of the braces (Fig. 7.5f). Bolts and inserts should
--`,,,,```,`,`,`,,```,,`,```,``,-`-`,,`,,`,`,,`---
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--`,,,,```,`,`,`,,```,,`,```,``,-`-`,,`,,`,`,,`---
28
Fig. 7.5e—Brace feet attached to helical ground anchors.
Fig. 7.6.1—Pumping operation.
Fig. 7.5f—Brace foot to cast-in-place deadman.
be compatible and from the same manufacturer. A deviation
in threads, length, or strength could cause the insert or the
bolt to fail when subjected to load.
7.6—Concrete placement, finishing, and curing
Before placement of the concrete, the location of inserts,
embedments, and other critical components should be
checked. The floor slab may be misted with water to provide
cooling unless a retarder is used.
7.6.1 Pumping—Pumping is becoming increasingly
popular for placement of concrete (Fig. 7.6.1). It has several
advantages, including easier and quicker placement, especially on difficult sites and if pumped from the outside of the
building perimeter, the slab is not damaged due to concrete
trucks.
Pumped concrete requires special considerations to minimize shrinkage and resulting cracks. A concrete mixture
proportion formulated for pumping with appropriate aggregate size, w/cm, additives, maximum allowable slump
measured at point of placement, and minimum hose size
(preferably at least 5 in. [125 mm] system reduced to 4 in.
[100 mm] diameter) should be selected. Additional informaCopyright American Concrete Institute
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tion may be found in ACI 304.2R on the requirements for
placing concrete with pumps.
When pumping, the height of drop should be kept to a
minimum. The fresh concrete placement should always be
directed into an area of previously placed concrete. This
method absorbs the impact of pumping and minimizes abrasion of the bond breaker (or retarder for an exposed-aggregate panel) and aggregate segregation. Concrete placement
should progress across the panel beginning at one corner.
7.6.2 Bucket—A crane with a bucket is still used on some
projects. The bucket has few moving parts and no pumps.
Placement with a bucket also has the advantages of placing
concrete where it is needed and works well on difficult
or tight sites. No special mixtures are required. It can be
unwieldy, is slower than pumping, and requires a crane and
operator to transport the bucket. Placement should follow
the same procedures previously outlined for pumping.
7.6.3 Direct chute placement—Direct chute placement of
concrete (Fig. 7.6.3) is the most economical and dependable method of placement if the site conditions and building
layout are favorable. Access to at least two sides of the panel
is required. If access from the interior of the building is
desirable, a decision should be made as to whether concrete
truck traffic on the slab is permissible or if sections of the
slab should be omitted until the panels are cast.
7.6.4 Placement sequence—Regardless of the concrete
placement method used, it should proceed from one edge
of the panel to the opposite side, not from the perimeter to
the center, or vice versa. The concrete should not abrade
the bond breaker or retarders from the slab during placement. Use a shovel, piece of plywood, or other surface to
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 7.6.3—Concrete placement operation direct from chute.
Fig. 7.6.5a—Spud vibrator for vibration around inserts,
embeds, and reinforcement.
Fig. 7.6.4—Concrete placement maintained in fresh
concrete.
slow the first concrete volume to be placed. Freshly placed
concrete can then be used to break the impact from the chute
or nozzle (Fig. 7.6.4). Concrete should be placed as close
as is practical to its final location. It is acceptable to rake
concrete short distances. The vibrator should not be used to
move concrete.
If a common form is used between panels, concrete should
be evenly distributed on both sides of the form to reduce the
chances of form movement.
7.6.5 Consolidation—Vibration is critical to ensure
consolidation around reinforcement, inserts, and embedments, and to get a proper finish on the panel. A spud
vibrator is the method most commonly used (Fig. 7.6.5a).
The tubular end of the vibrator should be positioned as close
to parallel with the slab as possible and pulled through the
concrete without coming into contact with the slab (Fig.
7.6.5b). An attachment to hold the end of the vibrator can
be fabricated if one is not available. The vibrator should be
drawn through each successive deposit of fresh concrete
into the previous placement to ensure adequate blending.
The vibrator can also be placed in contact with the forms to
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Fig. 7.6.5b—Spud vibrator moved through concrete.
ensure flow at the edges. Secondary vibration will promote
the flow of concrete between reinforcement if two layers are
used. The use of vibrating screeds is another popular consolidation method currently in use with supplementary spud
vibrators at embedments (Fig. 7.6.5c). Refer to ACI 309R
for further information. A single-person, gas-operated truss
screed vibrator provides considerable ease with which strike
off and vibration become a one-person, one-step operation.
7.6.6 Finishing and curing—Interior finish of the panels
is often an owner’s preference. If the panels are to be left
exposed, a hard trowel finish may be desired. (Hard trowel
finish is required if panels are to be stack cast.) Many times, a
float finish is all that is required, especially when the interior
is to receive insulation or a furred wall with drywall finish.
For concrete to develop the desired properties for strength
and durability, it should be properly cured. ACI 308.1
discusses proper curing procedures.
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Fig. 7.6.5c—Vibrating screed or strike-float vibrates final
surface.
CHAPTER 8—PANEL ERECTION
8.1—Before erection
Any errors or miscalculations occurring during the planning stages will become obvious when the panels are erected.
Panels cast in the wrong location, crane inaccessibility to the
site or portions of the site, panels stack cast in the wrong
order, an inexperienced crane operator or crew, or inadequate
crane size will severely hinder the erection process. Safety
procedures are critical to the erection process and should be
reviewed in a safety meeting before panel erection.
8.1.1 Planning review—The panel erection process should
be reviewed before the start of panel erection. A preerection meeting should take place between the controlling
contractor and the steel or panel erection contractor. This
meeting confirms the panel layout and sequence. If panel
erection is from the outside of the building, careful attention to the crane movement should be in place accounting
for power lines, roads, excavations, and other obstacles. The
casting and erection sequence plan should be reviewed to
verify that all panels have been cast and are in their correct
locations. Items that have changed from the original plan
should be addressed.
8.1.2 Panel preparation—Panel preparation includes
removing formwork, locating and cleaning out lifting and
brace inserts, testing each lifting insert with the lifting hardware, attaching braces, and cleaning debris from around and
on the panels. Any standing water around the panels and
within openings should be removed. Standing water flows
between the casting surface and panel face, which results
in additional loading needed to break the bond. The additional loading can result in damage to the panel and create
a dangerous situation for the erection crew. Locations of
lifting and brace inserts should be checked with the erection manual. It is good practice to clean out blockouts for
framing connections before erecting panels because of the
easy access. Attachment of shelf angles and beam seats to
embedded plates is also easier at this stage.
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Panel concrete strengths, both flexural and compressive,
should be determined according to ASTM C78/C78M and
C39/C39M procedures before erection. These strengths are
obtained from tests performed by the testing agency in accordance with ASTM E329 on the cylinder and beam specimens
fabricated during casting of the panels. Field tests should be
performed by an ACI Certified Concrete Field Technician.
The erection manual should specify the strengths needed for
lifting panels. Panel erection should not occur until strengths
are equal to or above the requirement stated previously.
8.1.3 Site preparation—Ground conditions where cranes
are placed to lift panels should be verified for adequate
support. The controlling contractor should consult the
geotechnical engineer to determine ground conditions are
adequate to support the crane’s weight and load as required
by OSHA 29 CFR 1926.1402.
8.1.4 Footing preparation—Several items are required to
prepare footings for panel erection. Setting pads should be
properly located both in plan and elevation. Grout setting
pads (Fig. 8.1.4a) require sufficient time to reach their specified strength and, therefore, plastic shim stacks are the more
common method of setting elevation of the supported panel
base (Fig. 8.1.4b). High spots in continuous footings should
be ground down to allow panels to bear on the setting pads.
Fig. 8.1.4a—Grout setting pads prepared for panel
placement.
Fig. 8.1.4b—Panels being set on plastic shim stacks.
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31
Fig. 8.2—Rigging arrangements.
If the panel bears on a high spot in the footing, the panel may
not be plumb and the footing may be overloaded.
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8.2—Rigging
All rigging should be sized and verified that it will support
the intended loads per the minimum safety factor of 5
based on ultimate loads in compliance with OSHA 29 CFR
1926.704. All applications of the rigging should be used
in accordance with the manufacturer’s recommendations.
Cable lengths and rigging layout should be compatible with
the lifting design (Fig. 8.2).
8.3—Panel erection sequence
Panel erection should progress in one continuous and
smooth operation. The rigging should first be inspected for
proper alignment after the rigging and lifting hardware have
been attached to the panel and the slack has been taken out
of the cables, but before initial loading of the inserts. If the
cables twist or the hardware tries to rotate, the lift should
be halted and the hardware realigned. Lifting inserts should
not be subjected to a significant amount of side loading
unless they are specifically designed for that purpose. The
lifting hardware manufacturer’s recommendations should be
followed at all times.
The crane operator applies force to the panel through the
rigging until the load gauge reaches the weight of the panel
and rigging. The erection team should make sure that the
panel has broken free of anticipated suction, created when
the center of the panel moves prior to the edges as the panel
begins to flex, to avoid applying excessive force to lifting
hardware. Additional suction forces such as bond breaker
failures and water between the casting surface and panel face
can cause damage to tilt-up panels during erection, including
breaking of the tilt-up panel.
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If the panel does not readily break free from the casting
surface, use wedges and pry bars to help release the panel.
As the panel rotates and lifts off the slab, crewmembers
should support the free end of the braces above the slab
so the braces do not bind or hang up on other panels or
construction materials. The crane operator should lift the
panel without dragging the bottom edge along the slab or
striking any previously erected panels.
Once the panel is set on the setting pads, it can be roughly
plumbed with the crane before attaching the braces to the
slab. A 4 ft (1.2 m) level may be sufficiently accurate for
this initial plumbing. Adjustments in the plane of the panel
are accomplished by adding or removing plastic shims at the
setting pads. A transit is often used to verify that the vertical
edges of the first panel set are plumb. Subsequent panels can
be adjusted relative to the first panel by providing a uniform
joint width between panels. Minor panel adjustments in or
out can be accomplished with the brace’s threaded adjusting
mechanism, enabling the brace to be lengthened or shortened after it is attached to the slab and the rigging released.
The tilt-up contractor can make minor vertical adjustments until the panels are grouted or the roof and floor
diaphragm framing is erected. Once the panel is grouted and
connected at its base, its position cannot be adjusted. If a
panel supports another panel, which is often called a spandrel or lintel panel, the supporting panel should be vertically
straight before spandrel panel erection.
8.3.1 Temporary bracing of panels—Typically, the licensed
design professional designing the lifting inserts will also
design the temporary panel bracing. The number, size, and
placement of the braces are based on wind loads and panel
location and size with a minimum of two braces per panel
(Fig. 8.3.1). If knee braces are required, lateral bracing with
intermittent X-bracing is also needed to reduce the brace’s
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Because wind vibration may work connectors loose, connection bolts should be checked and torqued daily.
8.3.5 Brace removal—Panel braces should remain in place
until the panel is fully connected to the roof diaphragm to
stabilize the building structure. The engineer of record
should verify when temporary wind braces can be removed.
Fig. 8.3.1—Temporary panel bracing.
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unsupported length. If a strip of floor slab is left out until
the panels are erected, deadmen for anchoring the braces
may be required until permanent connections are made. The
crane should not be released from the panel until the licensed
design professional’s bracing recommendations have been
satisfied. The Tilt-Up Concrete Association’s (2012) wind
bracing guidelines or ASCE 37 should be used.
It is good practice to have lifting and bracing equipment
on-site in addition to what is designed for the panel erection and bracing process, in the event that the primary hardware is missing, damaged, or malfunctions. This emergency
equipment often includes special lifting plates that can be
anchored to the panel face when an embedded lifting insert is
mislocated or knocked over during panel casting. The lifting
plate is bolted to the panel as near as possible to where the
insert should have been located. The plate and connection
bolts should have the same load capacity as the cast-in lifting
inserts and should be specified or otherwise approved by the
licensed design professional providing the lifting design.
Other equipment may include additional braces for replacement of braces damaged in shipment or staging.
8.3.2 Stack casting panels—When panels are cast atop
one another, additional time is required for panel erection. Forming lumber below the top panel erected should
be removed before erecting the next panel. Lifting inserts
should be located and cleaned out and panel braces attached.
This process will often double the time required to erect
these panels. In addition, the crane operator should exercise
caution when lifting stacked panels because the crewmembers supporting the braces may have to walk over the panel
on which the panel being erected was cast.
8.3.3 Panel connections—After the panel is shimmed
and plumbed, it should be grouted as soon as possible and
connected at the base as shown on the structural drawings.
The tilt wall contractor should verify the locations of embedment plates for permanent connections. Any discrepancies
should be brought to the engineer of record’s attention for
immediate resolution.
8.3.4 Panel brace maintenance—Panel brace connections
at the floor and panel should be checked daily and tightened
in accordance with the manufacturer’s recommendations.
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8.4—Safety
In addition to safety issues discussed in Chapter 4, special
attention should be given to the quality of the crane and
rigging. OSHA 29 CFR 1926.1402 requires that the crane
owner be responsible for documenting inspections. Annual,
monthly, and daily inspections should be readily available
for review by the controlling contractor, which means they
are to be kept with the crane at all times while it is on site.
Qualifications of the operators should be reviewed. Items
such as crane access and crane support, quality control of
placement, attachment of lifting inserts to lifting hardware,
and rigging should also be monitored.
CHAPTER 9—CONNECTIONS
9.1—Design of connections
This chapter introduces typical connections to the licensed
design professional and contractor who are new to tilt-up.
It does not recommend one connection over another nor
is it all-inclusive. The details shown are pictorial representations of connections that have been successfully used
in the construction of uninsulated and insulated sandwich
wall panels. This detailing is shown to illustrate the proper
structural, as well as thermal, connection between building
elements. Commonly, the licensed design professionals are
responsible for designing and detailing connections while
the contractors are responsible for proper execution. All
permanent connections should be made before the removal
of the temporary wind braces, or as directed by the engineer
of record. Several references are available on connection
design and construction for tilt-up buildings (PCI 1999; PCA
1987; Weiler 1986; Lemieux et al. 1998).
9.2—Foundation and slab-on-ground connections
Most tilt-up panels are connected to the floor slab with
bent reinforcement dowels cast into the panel and lapped
with reinforcement cast into the floor slab closure strip (Fig.
9.2a). Dowels can also be drilled and epoxied into the panel.
Welded embedment plates are another option (Fig. 9.2b) and
eliminate the need for the slab closure strip. In many cases,
if the panel is anchored to the floor slab, connections to the
footing are not required except for grout under the panels.
Additionally, use of a thickened slab edge is not required in
many cases, and often depends on construction sequence or
contractor preference.
Where a positive connection to the foundation is required,
foundation connections can be made by dowel between
the footing and panel, to the slab (Fig. 9.2c) or providing a
keyway (Fig. 9.2d). Alternatively, use a welded embedment
plate connection or a field-drilled mechanical connection
(Fig. 9.2e and 9.2f). Corrosion protection should be added
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to all connection elements exposed to potentially corrosive
environments. If analysis shows tension forces are present
at the base of the panel, a reinforcement bar or dowel can
be projected from the footing and spliced to the panel reinforcement (Fig. 9.2g). Embed plates with dowels can also
be provided on both sides of the panel and welded to corresponding embeds in the footing (Fig. 9.2h).
Steel embed plates cast into sandwich walls are very often
the same used in uninsulated panels (Fig. 9.2i); however, the
insulation may have to be thinned locally to accommodate
embed sizes. Sandwich wall panels placed on foundation
walls are set on shims beneath the interior bearing wythe
only; the grout joint between shims should also be limited
to the area beneath the structural wythe only, allowing the
nonstructural exterior concrete wythe to expand and contract
as needed. A closed-cell backer rod and caulk should be used
to impede the penetration of moisture and debris along this
horizontal joint.
When sandwich walls are attached to the floor with a
threaded dowel (Fig 9.2j), care should be taken to assure
that the reinforcing bar or doweling extending out from the
sandwich wall is contained within the interior-bearing wythe
only. Insulation removal is typically unnecessary and will
reduce the thermal efficiency of the wall panels.
Fig. 9.2c—Slab dowel connection.
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Fig. 9.2a—Panel to slab dowel connection.
Fig. 9.2d—Keyway dowel connection.
Fig. 9.2b—Panel to slab welded plate connection.
Fig. 9.2e—Welded plate connection.
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Fig 9.2h—Welded plate and dowel connection.
Fig. 9.2f—Field-drilled plate connection.
Fig 9.2j—Sandwich panel threaded dowel connection.
Fig. 9.2g—Foundation dowel connection.
Fig. 9.2i—Sandwich panel welded plate connection.
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9.3—Roof connections and supported floor
connections
Roof and supported floor connections usually consist of
embedment plates with headed studs or reinforcing bars. A
continuous angle or seat angle is welded to the embedment.
Seat angles can also be attached to the panel with expansion
or adhesive bolt fasteners. A recessed pocket with an embedment angle or plate is commonly used for heavy loads such
as joist girders, although embeds on the face of the panel can
also be used to support girders (Fig. 9.3a to 9.3g).
Wood roof systems and hybrid systems, which usually use
a combination of wood sheathing and subpurlins with steel
joists and girders, are also common in some areas, particularly in the western states. These systems often use wood
ledgers attached with anchor bolts to the wall for support of
wood subpurlins and wood sheathing attachment.
Where joist connections occur at a panel joint, a slip detail
that allows for panel shrinkage and thermal expansion should
Fig. 9.3a—Chord angle.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
35
Fig. 9.3e—Glulam beam seat.
Fig. 9.3c—Pocket for joist girder.
Fig. 9.3f—Wood joist ledger.
Fig. 9.3d—Steel beam connection plate.
be considered, particularly if the condition occurs at successive panel joints. One common method is to weld a seat or
plate to an embed on one side of the joint, and provide cast
bolts in horizontal slotted holes on the opposite panel.
An advantage of tilt-up, sandwich walls is the ability
to extend the exterior concrete wythe beyond the interior,
concrete-bearing wythe. This condition allows the wall and
roof insulation to be made continuous at the roof and wall
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Fig. 9.3g—Hollow core plank ledge.
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Fig. 9.3b—Seat angle for joist.
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
Fig. 9.3h—Sandwich panel roof deck connection.
9.4—Panel-to-panel connections
In the past, it was common practice to connect all panel
joints with rigid embedment plates welded together. Subsequent panel shrinkage and other panel movement resulted
in cracking or even total failure of these connections. Many
licensed design professionals avoid panel-to-panel connections except where required to meet structural requirements for wind or seismic loads (Fig. 9.4a). Joint alignment
is seldom an issue, except in outside corners where panel
bowing can result from temperature variations due to differential sun exposure.
When a licensed design professional requires a panelto-panel connection, they should provide some degree of
Fig. 9.3i—Sandwich panel joist pocket connection.
Fig. 9.4a—Panel joint connection.
Fig. 9.4b—Alternate panel joint connection.
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Fig. 9.3j—Sandwich panel tall parapet joist pocket
connection.
Fig. 9.3k—Sandwich panel low roof termination.
intersection (Fig. 9.3h). Joists being set on sandwich walls
can bear directly on top of the interior concrete wythe or be
pocketed (Fig. 9.3i to 9.3k), thus allowing for a more effective insulation transition at the roof line, which is considered
critical to the overall building envelope.
Fig. 9.4c—Reinforcing bar chord splice.
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Fig. 9.4d—Overlap corner connection.
Fig. 9.4h—Insulated and vapor-protected panel joint detail.
Fig. 9.4e—Mitered corner panel to panel joint.
Fig. 9.4f—Typical panel joint sealant.
ductility to accommodate panel shrinkage and thermal
expansion and contraction. For this purpose, reinforcing
bar anchors are preferred over short, headed studs. When
a rigid connection is required (for example, chords and
shear walls), however, welding of these connections should
be delayed as long as possible to allow for the majority of
panel shrinkage to occur. This reduces the risk of cracking
around the embeds (Fig. 9.4b and 9.4c). Recessed embeds
(Fig 9.4c) should be used with caution, as they tend to cause
unwanted panel cracks because of the reduced concrete
section and strain created around the embeds. Rigid panel
connections, however, can be provided at corner conditions
without significant risks of cracking (Fig. 9.4d and 9.4e).
All welding should be performed by a certified welder using
welding procedures specified in AWS D1.1/D1.1M or AWS
D1.4/D1.4M for reinforcing steel.
Panel-to-panel connections for sandwich panels will typically be made within the interior concrete wythe, allowing
insulation to extend the panel edges. Panel joints are typically sealed on the inside and outside with backer rod and
caulk to protect from moisture intrusion and provide for a
clean interior finish (Fig. 9.4f). In cases where a fire-rated
joint is required, mineral wool, along with fire-rated backers
and caulks, may be specified (Fig. 9.4g). Where special
moisture issues are of concern, poly-sheeting and spray
urethanes may be placed within the joint (Fig. 9.4h).
9.5—Connections for higher seismic design
categories
In areas of high seismic activity, connection design and
construction are especially critical to the integrity of the
structure. Wall anchorage to the roof structure is very important, as this is the typical area of failure in seismic events.
Careful attention should be given to the chords, drag struts,
and collectors.
CHAPTER 10—FINISHING AND SEALING
Fig. 9.4g—Fire-rated panel joint detail.
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10.1—Surface preparation
Before the repair of any blemishes on wall panels, they
should be thoroughly cleaned of all bond breakers, form
release agents, oils, dust, mold, and mildew. Any repair
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
material applied over the bond breaker and most paints
will not adhere to the panel surfaces with their presence.
Bond breaker manufacturers provide recommendations
for removal of their product and coatings manufacturers
provide the required surface preparation for their product.
Power washing, detergent washing, or wet blasting may
be required. After drying, concrete should change color
to a relatively uniform gray. If heavy applications of bond
breaker are present, additional cleaning may be necessary.
Panel joints should also be thoroughly cleaned. The same
factors that can prevent paint adhesion can also prevent
caulk or other joint sealants from adhering to the panel.
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Fig. 10.2a—Floor joint ridge.
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10.2—Repairs
Once panels are cleaned, surface defects can be repaired.
Almost every blemish in the floor slab or casting bed will
appear on the panel surface. Floor slab construction and
contraction joints, column blockouts, utility blockouts, and
any cracks or voids should be filled or concealed before
casting the panels (6.3.1 and 6.3.2).
Concrete panels cast over unfilled floor joints will have
fins projecting from the panel surface (Fig. 10.2a). These
fins should be ground smooth after panels are erected. A
rubbing stone generally works best for this operation, but
power grinding may also be necessary. Filling joints before
panel casting can greatly reduce the amount of repair
required. Refer to 6.3.1 for joint treatments. Fins left along
panel edges and reveal strips should be knocked off with a
rubbing stone.
Formed edges around doors and windows usually require
the most repairs, but care in forming these edges can eliminate much of this work. Caulking around formed edges
and reveal strips can also reduce the amount of subsequent
repairing and finishing (7.1.3).
The repairing or patching process involves filling
bugholes, cracks, or honeycombed areas on the panel surface
and exposed edges. Repair material is often hydraulic
cement or a specially manufactured patching compound.
The repair material should be applied to a dampened surface
with a rubber trowel and then scraped off flush. Steel troweling the repair material when it begins to dry will produce a
smooth surface. The repair material should also be allowed
to cure sufficiently before painting. When a textured paint is
to be used, small imperfections in the panel surface can be
ignored.
Cracks in concrete tilt-up panels are typically caused by
either shrinkage or lifting and generally do not affect the
structural integrity of the panel. If the w/cm of the concrete
mixture is too high or the panels are improperly cured,
cracking will occur due to restrained drying shrinkage.
Cracking can also occur at corners of openings (Fig. 10.2b) or
where contraction caused by drying shrinkage is restrained.
For example, wide spandrel panels rigidly attached to the
supports can crack diagonally at or near the support, unless
the design allows for some stress relief; for example, with
the use of bolts in slotted holes. Cracks occurring during
lifting usually occur at locations in the panel with reduced
section opening locations or reveals or at the lifting inserts.
Fig. 10.2b—Reentrant corner crack.
Causes of cracks during lifting include low concrete strength;
mislocation of lifting inserts, whether by design or construction; improper rigging configuration; or poor bond breaker
performance. The crack width determines the repair type.
Small cracks, less than 0.013 in. (0.33 mm), can be grouted
as previously described or filled with latex caulk by pressing
it in by hand. Caulk should be compatible with the paint to
be used. Elastomeric paint or quality primer can sometimes
be used to span the crack. The engineer of record should
examine all large or structural cracks wider than 0.013 in.
(0.33 mm) before any repair is attempted. Usually the crack
can be repaired by pressure injection with a structural epoxy
performed by a qualified applicator.
Cracking in the exterior panel face of sandwich panels may
also occur if the two layers of concrete become monolithic,
resulting from holding the insulation back from the panel
edge(s). During the curing process, the restraint created by
these monolithic areas further induces shrinkage cracking.
A sandwich panel, however, is also designed to maintain
unique temperature differences on opposing sides of the
wall and, therefore, will have large temperature differentials between the inside and outside concrete layers. Uncon-
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39
strained relative movement, due to temperature differentials
alone, can often be as great as 1/4 in. (7 mm). When fullthickness concrete connections exist, cracking and bowing
can result from the restraint.
Therefore, insulation should not be interrupted by any
monolithic concrete sections or restraints of any kind.
However, at a minimum the two layers of concrete should
be separated by insulation on three full edges to reduce the
likelihood of restraint cracking.
10.3—Joints
Many water infiltration problems are traced to failed
joints between panels. Caulking may become brittle and
crack from expansion and contraction, or the sealant may
pull away from the panel. The latter may be due to improper
preparation of the panel edge. Dirt, grease, paint, or form
release agent not cleaned from the panel edge will prevent
proper adhesion of the sealant. As mentioned in 10.1, power
washing, wire brushing, grinding, chemical cleansing, and
sandblasting may be required to prepare the surface.
Polyurethanes, polysulfides, silicones, and some specially
formulated acrylics are used as joint sealants for buildings.
Polyurethane and silicone sealants are most commonly
used in tilt-up construction. Also, many types of polyurethane do not require the panel surface to be primed. For best
results, use a sealant that conforms to ASTM C920 for Type
S (single-component) or Type M (multi-component); Grade
NS (nonsagging when applied between 40 and 122°F [4
and 50°C]); and Class 25, which withstands a 25 percent
increase or decrease in joint width.
At each sealant location, a foam backer rod of the appropriate size for the gap between the panels and the caulk is
set to the appropriate depth (Fig. 10.3a). Surface preparation
and installation requirements should follow the manufacturer’s recommendations and include backer rod type, size and
placement depth, conditions that warrant the use of a primer,
and temperature range for optimum application.
Joint sealants should not be installed in panel joints
smaller than 0.25 in. (6 mm) or larger than 2.5 in. (63 mm).
The sealant depth (thickness) should be half of the width
of the joint and no less than 0.25 in. (6 mm) or more than
0.5 in. (13 mm) thick. Closed cell backer rods are preferred
with most sealants and required with urethane sealants. The
backer rod should be 25 to 50 percent larger than the joint.
Installation procedures for installing joint sealants should
follow guidelines published by the Sealant, Waterproofing
and Restoration Institute (2013).
Most paint coatings and sealers do not adhere well to sealants. The recommended method for installing joint sealants
in painted concrete panels is to install the sealant prior to
painting (Fig. 10.3b), choosing a sealant to match the paint.
Another method is to first install the backer rod halfway into
the joint in a manner that protects the joint face at the adhesion plane of the sealant. After the panels are painted, push
the backer rod in to the appropriate depth and install sealant.
Do not install sealants in panel joints prior to attaching
panels permanently to the structure and adding roof, roof top
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Fig. 10.3a—Backer rod inserted to panel joint.
Fig. 10.3b—Sealant applied over backer rod to exterior
panel joint.
units, and roof loads. Panels can shift and tear or damage
the sealant.
Types of panel joint treatments are:
a) Exterior only––Joints comprised of backer rod and sealant
that only provide protection from the exterior elements; the
backer rod and sealant extend from the bottom of the panel
to the top (including the top and back of parapets) in a single,
uninterrupted line
b) Exterior and interior––Joints comprised of backer
rod and sealant on both faces of the concrete wall panel
to protect from the exterior elements while maintaining a
cleaner interior environment; the backer rod and sealant
extend fully from the bottom of the panel or exposure to the
top (including the top and back of parapets) in uninterrupted
lines
c) Two-stage (pressure equalized)––Joints most often used in
insulated wall panels that are based on rain screen principles
and comprised of two stages of backer rod and caulk; one
placed within the exterior, concrete wythe, and the other at
the intersection of insulation layer and the interior concrete
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
wythe. These joints are unique because the space between
the stages is vented and drained to the exterior.
In cases where a fire-rated joint is required, mineral wool,
other fire-rated backers, or both, and fire-rated sealants may
be specified (Fig. 9.4g). In cases where thermal or moisture
issues are of concern, poly-sheeting and spray urethanes and
precompressed foam fillers may be placed within the joint to
offer additional protestation (Fig. 9.4h).
Do not install sealants off of ladders. Follow OSHA 29
CFR 1926.501. When installing sealants below grade,
comply with OSHA 29 CFR 1926.651. Do not install sealants on panels that have not been permanently attached to
the structure unless temporary shoring has been reviewed by
a licensed design professional.
10.4—Paints
Recommendations of ACI 515.1R should be followed
when painting tilt-up panels. Painting should proceed after
the panels have been cleaned and allowed to dry a sufficient
period of time to allow as much excess water as possible
to leave the panel. Any dirt or dust blown onto the panels
from other construction operations should be removed with
wire brushes or compressed air before painting. Panel pH,
moisture content, and surface preparation should be checked
before painting for conformity to the paint manufacturer’s recommendations. Generally, a pH value of 7 to 10 is
preferred.
Paint systems should consist of a primer coat and at least
one finish coat. The primer coat should be approximately 3
mils (0.08 mm) thick and each finish coat should be 1.5 to 2
mils (0.04 to 0.05 mm), with the total paint thickness equal
to 5 mils (0.13 mm) minimum. Application of paint may be
by either sprayer or roller, as recommended by the coating
manufacturer.
The prime coat may be either latex- or solvent-based.
Solvent-based primers are more effective as an adhesion
promoter, but their use and production have all but been
eliminated due to the more stringent federal VOC laws. Many
contractors recommend a 100 percent acrylic latex topcoat.
Use of alkyd- and oil-based paint has declined because they
contain esters that react with alkalis in the concrete to form
water-soluble soaps. As a result, these paints have a strong
tendency to blister and lose adhesion, which is also known as
burning. Acrylic coatings will not burn, but they may allow
efflorescence to migrate through the paint. The paint and
joint caulk should also be compatible or the paint may not
adhere to the concrete surface. Some caulks are produced in
different colors to match the paint color.
A popular option for the exterior treatment is the use of
elastomeric paint systems. These are largely primerless
multiple coats that achieve the desired thickness systems,
and specially formulated to provide a weatherproof coating
over cured concrete surfaces. Their advantages are savings
in resources, time, and money from reduction of surface
preparation, including patch, rub, and surface cleaning
during the construction process. The systems are available
in several finishes including smooth, fine, coarse, and extra
coarse, which enhances the aesthetics of the building with
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color variety and texture. The systems are environmentally
friendly due to an extremely low VOC content and are resistant to fading, even in darker colors. Their use also facilitates
vapor impermeance of the building envelope environments
where significant temperature and humidity differential
occurs between the building interior and exterior (such as a
refrigerated structure or warm, humid climates).
CHAPTER 11—INSULATED PANELS
11.1—Insulated panels
Tilt-up panels can be insulated with either interior applied
systems or through use of sandwich panels. Several forms of
applied insulation systems are available. These systems may
be acceptable where a less durable interior finish is acceptable and where fire and moisture are not of concern. All interior systems isolate the thermal mass inherent in concrete
from the conditioned space, reducing the benefits of thermal
mass.
Interior systems are boards or blankets of fiberglass,
mineral wool, polyisocyanurate, or polystyrene. They may
also be metal-skinned panels with insulation cores. The first
two types, fiberglass and mineral wool, are typically backed
with some form of vapor-resistant coating. The coatings
range from a thin flexible plastic or paper liner to a rigid
plastic or metallic board. The insulation strips are usually
secured with some type of spline or cap that is attached to
the wall. The systems are inexpensive, quick to install, and
can be applied after the building is erected. By code, plastic
insulation should be covered by a thermal barrier to reduce
fire spread and smoke development. When using sandwich wall panels, the interior concrete layer serves as the
thermal barrier so no additional protection to the insulation
is required.
11.2––Sandwich panels
Sandwich panels consist of an inner and outer wythe
of concrete with an insulating material in between. These
panels may be fully composite, partially composite, or
noncomposite. In fully composite sandwich panels, the
two concrete wythes are structurally linked to perform as
a single unit. Partially composite sandwich panels display
some composite behavior between the concrete wythes.
Noncomposite panels have two wythes that behave structurally independent.
11.2.1 Fully composite sandwich panels—sandwich panels
constructed so that the two layers of concrete are rigidly
connected together as an integral unit using reinforcement
or monolithic concrete. The entire panel thickness behaves
structurally similar to a solid or uninsulated concrete panel.
Where the concrete layers are connected monolithically
with concrete or significantly with steel reinforcement, large
thermal bridges are created, resulting in increased thermal
conductivity or reduced insulating value. Fully composite
systems are subject to bowing brought about by differential
thermal expansion rates on the interior and exterior wythes
constrained by the rigid connections.
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11.2.2 Partially composite sandwich panels––sandwich
panels constructed so that insulation extends fully between
the two layers of concrete with rigid connections between
the layers. The rigid connections permit the total panel thickness to have a structural capacity greater than the individual
concrete wythes but less than the same thickness as an uninsulated panel. The interior and exterior wythes of concrete
are allowed to move relatively independently of one another
in response to thermal changes, reducing the potential for
bowing. Partially composite sandwich panels are most often
created with nonconductive structural connections that eliminate or substantially reduce thermal bridging.
11.2.3 Noncomposite sandwich panels—These are sandwich panels constructed with one structural wythe and
another architectural or nonstructural wythe separated fully
by continuous insulation. They are the most commonly used
form of tilt-up sandwich panels. Systems use fiber composite,
steel, or plastic injection-molded connectors pushed through
the insulating material and into the still fresh concrete below.
Some fiber composite systems use uniformly spaced connectors that are inserted into predrilled holes or placed between
insulation sheets. These systems are recognized as being
thermally efficient.
The inner concrete wythe is typically designed to carry
the structural loads for the panel. The outer wythe is usually
thinner (2 to 3 in. [50 to 75 mm]) and serves primarily as an
exterior skin to protect the insulation. The minimum recommended exterior wythe thickness of a sandwich wall panel
is 2 in. (50 mm), plus the depth of any reveal, rustication,
or architectural feature. Therefore, if incorporating a 3/4 in.
(19 mm) architectural reveal, the minimum exterior concrete
thickness is 2.75 in. (69 mm). The nonstructural, exterior
concrete layer of a sandwich wall panel is typically cast first
with the connectors installed while the concrete remains in a
plastic state. This concrete wythe is typically reinforced with
welded wire mats (ACI 318-11, 14.3). The mats are positioned on plastic bolster strips or chairs. A working slump
of 5 to 7 in. (125 to 175 mm) is recommended to ensure
proper consolidation around the connectors. Additionally,
maximum aggregate size is 3/4 in. (19 mm) and 3000 to
4000 psi (20.7 to 27.6 MPa) concrete is typical.
11.3––Insulation
The insulation thickness for sandwich wall panels is
a function of the desired R-value and interior condition
including ambient, cooler, and freezer. Ambient facilities,
where the interior space will remain at room temperature,
typically requires 2 in. (50 mm) of insulation, whereas
coolers require 3 to 4 in. (75 to 100 mm) and freezers use 6
in. (150 mm) or more.
To achieve a high R-value and consistent thermal and
moisture protection, edges of the insulation layers should
remain in contact along their entire length, separating the
two layers of concrete. If the insulation is not continuous,
thermal bridges occur, resulting in a loss of thermal integrity
and increasing the likelihood for moisture migration.
Several types of insulation are used successfully in
concrete sandwich panels. The most common type is
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41
extruded polystyrene, although expanded polystyrene and
polyisocyanurate are also used in sandwich wall designs.
These insulations are widely used because of their availability of thickness and rigidity, as well as durability and
ease of cutting during the construction process. However,
the physical and insulating properties of each are different.
11.3.1 Expanded polystyrene (EPS or beadboard) is
manufactured by compressing expanded polystyrene beads
under heat and pressure into a large block that is then sliced
into sheets. Densities of 1 to 1.5 lb/ft3 (16 to 24 kg/m3) are
common with R-values of 3.7 to 4.2 ft2·°F·hr/Btu per in.
(0.026 to 0.03 m2•K/W per mm) of thickness. EPS has a
relatively low moisture absorption and permeability but will
strongly adhere to the concrete. The effects of differential
thermal expansion between the inner and outer concrete
wythes should be considered, particularly in large panels.
11.3.2 Extruded polystyrene (XPS) is closed-cell and
manufactured to a specified sheet thickness. It has greater
and more uniform density with better physical properties
compared with EPS. Moisture absorption and permeability
are lower, the R-value is higher (5 per in.), and adhesion
to concrete is reduced if not eliminated over time. XPS is
also stronger and less compressible than EPS. Because sandwich tilt-up panel construction involves walking on top of
the insulation during the placement operation, the higherstrength XPS boards resist breakage and are preferred over
EPS, even though the initial price is higher.
11.3.3 Polyisocyanurate (PIR) insulations are closed-cell
and also manufactured to a specified sheet thickness. It has
density and physical properties similar to XPS insulation.
When the product is covered with a trilaminate polyester or
aluminum foil facer, however, the moisture absorption and
permeability rates are lower than XPS, but the R-value is
higher (6.5 ft2·°F·hr/Btu per in. [0.124 m2•K/W per mm]).
11.3.4 Other types of insulation used in sandwich panel
construction include polyurethanes and mineral wool
boards. Because of the high moisture absorption properties
of these types of insulation, they should not be considered
unless there is an integral and impervious facing material,
like that of a polyisocyanurate. Moisture absorbed from the
concrete into the insulation can adversely affect the insulation properties and the concrete.
CHAPTER 12––REFERENCES
ACI committee documents and documents published to
other organizations are listed first by document number and
year of publication followed by authored documents listed
alphabetically.
American Concrete Institute
ACI 117-10—Specification for Tolerances for Concrete
Construction and Materials and Commentary
ACI 301-10—Specifications for Structural Concrete
ACI 302.1R-04—Guide for Concrete Floor and Slab
Construction
ACI 304.2R-96—Placing Concrete by Pumping Methods
ACI 308.1-11—Specification for Curing Concrete
ACI 308R-01—Guide for Curing Concrete
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GUIDE TO TILT-UP CONCRETE CONSTRUCTION (ACI 551.1R-14)
ACI 309R-05—Guide for Consolidation of Concrete
ACI 318-11—Building Code Requirements for Structural
Concrete and Commentary
ACI 360R-10—Guide to Design of Slabs-on-Ground
ACI 515.1R-79—A Guide to the Use of Waterproofing,
Dampproofing, Protective, and Decorative Barrier Systems
for Concrete (Inactive)
ACI 551.2R-10—Design Guide for Tilt-Up Concrete
Panels
Air Force Research Laboratory
AFRL-RX-TY-TR-2008-4616—Precast/Prestressed
Concrete Experiments–Series 1 (V. 1)
ASTM International
ASTM C33/C33M-13—Standard Specification for
Concrete Aggregates
ASTM C39/C39M-12—Standard Test Method for
Compressive Strength of Cylindrical Concrete Specimens
ASTM C78/C78M-10—Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with ThirdPoint Loading)
ASTM C309-11—Standard Specification for Liquid
Membrane-Forming Compounds for Curing Concrete
ASTM C920-11—Standard Specification for Elastomeric
Joint Sealants
ASTM E329-11—Standard Specification for Agencies
Engaged in Construction Inspection, Testing or Special
Inspection
American Society of Civil Engineering
ASCE 37-10—Design Loads on Structures During
Construction
American Welding Society
AWS D1.1/D1.1M:2008—Structural Welding Code Steel
AWS D1.4/D1.4M:2011—Structural Welding Code–
Reinforced Steel
Occupational Health & Safety Administration (OSHA)
29 CFR 1926.501-1995—Safety and Health Regulations
for Construction, Fall Protection
29 CFR 1926.651-1994—Safety and Health Regulations
for Construction, Excavations
29 CFR 1926.704-1988 (89) —Requirements for precast
concrete
29 CFR 1926.1402-2010—Safety and Health Regulations for Construction, Cranes & Derricks in Construction,
Ground Conditions
29 CFR 1926.1408-2010—Safety and Health Regulations
for Construction, Cranes & Derricks in Construction, Power
Line Safety (up to 350kv) – Equipment Operations
Authored documents
Aiken, R., 1909, “Monolithic Concrete Wall Building—
Methods, Construction and Cost,” ACI Journal Proceedings, V. 5, No. 1, Jan., pp. 83-105.
Collins, F. T., 1958, Building With Tilt-Up, Know-How
Publications, 160 pp.
International Code Council, 2012a, “International Energy
Conservation Code,” ICC, Washington, DC, 90 pp.
International Code Council, 2012b, “International
Building Code,” ICC, Washington, DC, 690 pp.
Lemieux, K.; Sexsmith, R.; and Weiler, G., 1998,
“Behavior of Embedded Steel Connectors in Concrete
Tilt-Up Panels,” ACI Structural Journal, V. 95, No. 4, JulyAug., pp. 400-411.
PCA, 1987, “Connections for Tilt-Up Wall Construction,”
EB110.01D, Portland Cement Association, Skokie, IL, 39
pp.
PCI, 1999, PCI Design Handbook for Precast and
Prestressed Concrete, fifth edition, Precast/Prestressed
Concrete Institute, Chicago, IL, 630 pp.
Sealant, Waterproofing and Restoration Institute, 2013,
“Sealants: The Professionals Guide,” SWAI, 75 pp.
Tilt-Up Concrete Association, 2012, “Tilt-Up Concrete
Association’s Guideline for Temporary Wind Bracing of
Tilt-Up Concrete Panels During Construction,” Tilt-Up
Concrete Association, Mount Vernon, IA, Dec., 11 pp.
Tilt-Up Concrete Association, 2013, http://www.tilt-up.
org/resources/wind_bracing.php (accessed August 12,
2014).
Weiler, G., 1986, “Connections for Tilt-Up Construction,”
Concrete International, V. 8, No. 6, June, pp. 24-28.
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As ACI begins its second century of advancing concrete knowledge, its original chartered purpose
remains “to provide a comradeship in finding the best ways to do concrete work of all kinds and in
spreading knowledge.” In keeping with this purpose, ACI supports the following activities:
· Technical committees that produce consensus reports, guides, specifications, and codes.
· Spring and fall conventions to facilitate the work of its committees.
· Educational seminars that disseminate reliable information on concrete.
· Certification programs for personnel employed within the concrete industry.
· Student programs such as scholarships, internships, and competitions.
· Sponsoring and co-sponsoring international conferences and symposia.
· Formal coordination with several international concrete related societies.
· Periodicals: the ACI Structural Journal, Materials Journal, and Concrete International.
Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACI
members receive discounts of up to 40% on all ACI products and services, including documents, seminars
and convention registration fees.
As a member of ACI, you join thousands of practitioners and professionals worldwide who share
a commitment to maintain the highest industry standards for concrete technology, construction,
and practices. In addition, ACI chapters provide opportunities for interaction of professionals and
practitioners at a local level.
American Concrete Institute
38800 Country Club Drive
Farmington Hills, MI 48331
Phone: +1.248.848.3700
Fax: +1.248.848.3701
www.concrete.org
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38800 Country Club Drive
Farmington Hills, MI 48331 USA
+1.248.848.3700
www.concrete.org
The American Concrete Institute (ACI) is a leading authority and resource
worldwide for the development and distribution of consensus-based
standards and technical resources, educational programs, and certifications
for individuals and organizations involved in concrete design, construction,
and materials, who share a commitment to pursuing the best use of concrete.
Individuals interested in the activities of ACI are encouraged to explore the
ACI website for membership opportunities, committee activities, and a wide
variety of concrete resources. As a volunteer member-driven organization,
ACI invites partnerships and welcomes all concrete professionals who wish to
be part of a respected, connected, social group that provides an opportunity
for professional growth, networking and enjoyment.
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