FUNDAMENTALS
OF
CONCRETE
A short presentation
by
K.Veerappan
VP&Head-EDRC-RBF
B&F IC
CONTENT

What is concrete?
 Properties of Concrete

Composition of concrete
 Cracking


Cement
 Dusting

Aggregates
 Blisters

Water

Chemical admixtures

Reinforcement
 Types of Concrete
Concrete production

Mixing Concrete

Workability

Curing
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What is concrete?
 Mixture of Portland cement, water, aggregates, and in some cases, admixtures.
 The cement and water form a paste that hardens and bonds the aggregates together.
 Versatile construction material, adaptable to a wide variety of agricultural and residential
uses.
 Strong, durable, versatile, and economical.
 Can be placed or molded into virtually any shape and reproduce any surface texture.
 The most widely used construction material in the world.
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COMPOSITION OF CONCRETE
Admixtures
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CEMENT
 Portland cement
Artificial cement. Made by the mixing clinker with gypsum in a 95:5 ratio.
 Blended cements
Mix of Portland cement with one or more SCM (supplementary cementitious materials)
like following additives.
 Pozzolana Cement
Flyash from Power plant
 Slag Cement
Slag from Steel plant
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AGGREGATES
 Aggregates occupy 60 to 80 percent of the
volume of concrete.
 Sand, gravel and crushed stone are the
primary aggregates used.
 All aggregates must be essentially free
of silt and/or organic matter.
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WATER
 Good water is essential for quality concrete.
 Should be good enough to drink--free of trash,
organic matter and excessive chemicals and/or
minerals.
 The strength and other properties of concrete
are highly dependent on the amount of water
and the water-cement ratio.
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WATER
 Advantage of Reducing Water content
 Increased strength
 Lower permeability
 Increased resistance to weathering
 Better bond between concrete and reinforcement
 Reduced drying shrinkage and cracking
 Less volume change from wetting and drying
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CHEMICAL ADMIXTURES
 Materials in the form of powder or fluids that are added to the concrete to give it
certain characteristics not obtainable with plain concrete mixes.
 In normal use, admixture dosages are less than 5% by mass of cement,and are
added to the concrete at the time of batching/mixing
The most common types of admixtures are:
 Accelerators
Speed up the hydration (hardening) of the concrete.
Typical materials used are CaCl2 and NaCl.
 Acrylic retarders
 Slow the hydration of concrete, and are used in large or difficult pours.
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WATER REDUCING ADMIXTURES
 Increase the workability of plastic or "fresh" concrete, allowing it be placed more
easily, with less consolidating effort.
 Increase workability
 Reduce the water content of a concrete.
 Improves its strength and durability characteristics.
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REINFORCEMENT
 Concrete is strong in compression, as the
aggregate efficiently carries the compression load.
 Concrete is weak in tension as the cement holding
the aggregate in place can crack, allowing the
structure to fail.
 Reinforced concrete solves these problems by
adding either metal reinforcing bars, steel fibers,
glass fiber, or plastic fiber to carry tensile loads.
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CONCRETE PRODUCTION
 This process develops physical and chemical properties like mechanical strength,
low moisture permeability, and chemical and volumetric stability.
 A properly proportioned concrete mix will provide
 Mixing concrete
 Workability
 Curing
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MIXING CONCRETE
 Essential for
The production of uniform concrete,High quality concrete.
 Equipment and methods should be capable of effectively mixing
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WORKABILITY
 The ease with which freshly mixed concrete can be
placed and finished without segregation.
 Important to accurately describe what the concrete is to
be used for, and how it will be placed.
 Factors affecting workability
 Method and duration of transportation
 % entrained air
 Quantity and characteristics of cementing
 Water content
materials
 Concrete consistency (slump)
 Concrete & ambient air temperature
 Admixtures
 Agg. grading, shape & surface texture
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CURING
 Maintenance of a satisfactory moisture content and
temperature in concrete for
a suitable period of time
immediately following placing & finishing so that the desired
properties may develop.
 Concrete that has been specified, batched, mixed, placed,
and finished "letter-perfect" can still be a failure if improperly
or inadequately cured.
 Usually the last step in a concrete project and, unfortunately,
is often neglected even by professionals.
 Curing has a major influence on the properties of hardened concrete such as durability,
strength, water-tightness, wear resistance and volume stability
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CURING
 Proper concrete curing applications involves keeping newly placed concrete moist and
avoiding temperature extremes (above 32°C or below 10°C).
 Prevent the loss of the mixing water from concrete by sealing the surface.
 Begin the curing as soon as the concrete has hardened
sufficiently to avoid erosion or other damage to the freshly
finished surface.
 Usually within one to two hours after placement and finishing.
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METHODS OF CURING
 Ponding
 Sprinkling
 Wet coverings
 Sealing
 Steam curing
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PONDING
 Concrete for flat surfaces such as pavements, sidewalks, and slabs can be cured by
ponding However, it is often impractical except for small jobs. Furthermore, ponding
is undesirable if the concrete will be exposed to early freezing.
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SPRINKLING
 Sprinkling is an excellent method of curing. If it is done at intervals, care must be
taken to prevent the concrete from drying the applications of water.
 When a fine spray of water is continuously applied, the possibility of "crazing" or
cracking due to alternate cycles of wetting and drying can be minimized
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WET COVERINGS
 Wet coverings such as burlaps, cotton mats, or other moisture-retaining fabrics are
extensively used for curing. Treated burlaps that reflect light and are resistant to rot
and fire are available. Wet coverings of earth or sand are effective for curing, too.
However, it is expensive and may be useful only in small jobs.
Moist earth or sand  ~ 5cm (on previously moistened surface)
Moist hay or straw  ~ 15 cm (keep continuously wet)
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SEALING
 The concrete surface may be done by means of waterproof papers, plastic sheets,
liquid membrane-forming compounds, and forms left in place. One important
advantage of this group of methods is that periodic additions of water are not
required. These methods assure the hydration of cement by preventing loss of water
from the concrete. They should be applied as soon as the concrete has hardened
sufficiently to prevent surface damage, and after concrete has been thoroughly
moistened.
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STEAM CURING
 Can be used to advantage where early strength gain in concrete is important or
where additional heat is required to accomplish hydration, as in cold-weather
concreting. This method normally used in Pre casting
 Two methods of steam curing
curing in live steam at atmospheric pressure
(for enclosed cast in place structures and
manufactured precast units)
curing in high pressure steam autoclaves
(for small manufactured units)
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GRAPHS SHOWING IMPORTANCE OF CURING
Effect of Curing on
Strength Development
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Effect of Casting and
Curing
Temperature on Strength
Development
Concrete Strength Gain Versus Time
for Concrete Exposed to Outdoor
Conditions
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PROPERTIES OF CONCRETE
 Strength
 Elasticity
 Watertightness
 Permeability
 Cracking
 Shrinkage cracking
 Tension cracking
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STRENGTH
 Concrete has relatively
 High compressive strength,
 Low tensile strength
 Fair to assume that a concrete sample's tensile strength is about 10%-15%
of its compressive strength
 The ultimate strength of concrete is influenced by
 Water-cementitious ratio
 Design constituents
 Mixing
 Placement
 Curing methods
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COMPRESSIVE STRENGTH , W/CM & W/C RATIO
 is defined as the measured maximum resistance of a concrete or mortar
specimen to an axial load, usually expressed in MPa at an age of 28-days.
Most general use concrete
:
20 to 50 N/mm2
High-strength concrete by definition
:
70 N/mm2 or greater
 Water – cementing materials ratio (W/CM)
 ratio of mass of water to mass of cementing materials in a concrete mix
expressed as a decimal.
 Water – cement ratio (W/C)
 ratio of mass of water to mass of cement in a concrete mix expressed as a
decimal
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STRENGTH : W/C RATIO
With less
water more
the strength
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WATERTIGHTNESS & PERMEABILITY
 Watertightness
 The ability of concrete to hold back or retain water without visible leakage.
 Permeability
 Amount of water migration through concrete when the water is under
pressure or the ability of concrete to resist penetration by water or other
substances (liquids, gas, ions, etc.)
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CRACKING
 All concrete structures will crack to some extent.Normal concrete design is done
with 0.3 mm crack width. Liquid retaining structures are deigned with 0.1 mm crack
width which is water tight concrete.
 Cracks due to tensile stress induced by shrinkage or stresses occurring during
setting or use
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SHRINKAGE CRACKING
 Occur when concrete members undergo restrained volumetric changes
(shrinkage) as a result of either drying or thermal effects.
 The number and width of shrinkage cracks that develop are influenced by
 The amount of shrinkage that occurs
 The amount of restraint present
 The amount and spacing of reinforcement provided
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PLASTIC SHRINKAGE
 After the fresh concrete has been placed in forms, concrete undergoes a volumetric contraction
while it is in plastic state (before the concrete has set). This is known as Plastic Shrinkage
 Quick drying of concrete at the surface results in shrinkage and as concrete in plastic state cannot
resist any tension, short cracks develop. These cracks occur within a few hours
(i.e. between one – two hours) of placing concrete
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PREVENTION OF PLASTIC SHRINKAGE
 The fresh concrete should be protected from direct sunrays and strong winds for at least 24 hours
 Concrete should not be placed on dry subgrade. It should be made wet by sprinkling water before the
concrete is placed.
 Avoid use of warm water and warm aggregates in order to keep the temperature of fresh concrete
low.
 Dampen the subgrade and formwork, ensuring that any excess water is removed prior to placing
concrete.
 Keep the aggregates under shade. In hot weather, lower the temperature of the fresh concrete by
using chilled mixing water or replacing some of this water with crushed ice
 Cover the freshly placed concrete with tarpaulins or plastic sheet to prevent evaporation of bleed water.
 Start curing as soon as possible after placing of concrete but before the surface water-sheen fully
disappears
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DRYING SHRINKAGE
 After hardening, concrete starts drying. The excess water (not consumed for hydration) leaves the
system causing contraction or shrinkage
 Under drying conditions, the gel water is lost progressively over a long time, as long as the concrete
is kept in drying conditions. Cement paste shrinks more than mortar and mortar shrinks more than
concrete. Concrete made with smaller size aggregate shrinks more than concrete made with bigger
size aggregate.
 The magnitude of drying shrinkage is also a function of the fineness of gel. The finer the gel the
more is the shrinkage
 The shrinkage that takes place after the concrete has set and hardened
is called Drying Shrinkage and most of it takes place in the first few months
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PREVENTION OF DRYING SHRINKAGE
 Use minimum water content (consistent with placing and finishing requirements). To compensate for
the reduction in workability, plasticizers can be used.
 Provide adequate and early curing to exposed surfaces, particularly on large flat areas.
 Provide reinforcement steel at closer spacing (generally 15cm in slabs) in order to control crack
width.
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CRAZING
 Crazing is the development of fine random cracks on the surface of the concrete caused by shrinkage
of the surface layer
 The cracks are shaped like irregular hexagon and are typically not more than 50 to 100 mm across
 They generally occur in the over floated or over troweled surface layers of concrete slabs and in the
formed surfaces of concrete
 The generally observed reasons for appearance of Crazing cracks are
 Poor or inadequate curing.
 ·Too wet a mix, excessive floating
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PREVENTION OF CRAZING
 Use of moderate slump (75mm to 125mm), Higher slump (up to 150 to 180mm) can be used,
provided the mixture is designed to produce the required strength without excessive bleeding and
segregation.
 Never sprinkle or trowel dry cement or a mixture of cement and fine sand into the surface of the
plastic concrete to absorb bleed water. Remove bleed water by dragging a hose pipe across the
surface
 DO NOT perform any finishing operation while bleed water is present on the surface
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DUSTING
 Powders under any type of traffic
 Easily scratched with a nail or even by sweeping
 Very weak wearing surface
CAUSES
 Finishing operation performed while bleed water is on the surface or before bleeding has finished
 Insufficient curing
 Placement of non-absorptive sub grade or polyethylene vapor barrier
 Floating/Troweling after the condensation of moisture from warm humid air is on cold concrete
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PREVENTION OF DUSTING
 Do not place concrete directly on polyethylene vapor barriers or non-absorptive sub grades
 Proper curing
 Cold weather concrete practices
 Vent exhaust to the outside to provide adequate ventilation
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BLISTERS
 An irregular hollow bump that appears on the surface
during or right after finishing operations
PREVENTION
 Delay final finish as long as possible
 Avoid surface drying
 Initial float done with flat blades
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TENSION CRACKING
• Most common in concrete elements where a transversely applied load will put one
surface into compression and the opposite surface into tension due to induced
bending.
• The size and length of cracks is dependent on
 The magnitude of the bending moment
 The design of the reinforcing in the beam at the point under
consideration.
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TYPES OF CONCRETE
 Regular concrete
 High-strength concrete
 High-performance concrete
 Self-compacting concrete (SSC)
 Shotcrete
 Roller-compacted concrete
 Polymer concrete
 Rapid strength concrete
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TYPES OF CONCRETE
 High-strength concrete
 It has a compressive strength greater than 50 Mpa. High-strength concrete is made by
lowering the water-cement (W/C) ratio to 0.35 or lower
 High-performance concrete
 It is a relatively new term for concrete that conforms to a set of standards above those of the
most common applications.
 Some examples of such standards currently used in relation to HPC are: Compaction without
segregation, Early age strength, Toughness, Long life in severe environments, Heat of
hydration, Depending on its implementation, Environmental, Permeability & Density.
 Polymer concrete
Polymer concrete is concrete which uses polymers to bind the aggregate. Polymer concrete can
gain a lot of strength in a short amount of time. This type is extensively used in concrete repairs.
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TYPES OF CONCRETE
 Self compaction concrete-SCC
 Self-Compacting Concrete (SCC) which was cohesive, but flowable and took the shape of the formwork
without use of any mechanical compaction.
 The use of SCC has grown tremendously since its inception in the 1980s.
 Because of the material performance in its fresh state, the existing testing methods for conventional concrete
are no longer suitable for SCC.
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BENEFITS OF SSC
 Improved constructability
 Virtually flawless finish
 Homogenous and uniform concrete
 Better reinforcement bonding
 Flows easily into complex shapes and through congested
reinforcement
Wall with Normal concrete
 Superior strength and durability
 Allows for innovative architectural features
Wall with SSC
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TESTING PROCEDURED FOR SSC
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TYPES OF CONCRETE
 Shotcrete
 Shotcrete (also known by the trade name Gunite) uses compressed air to shoot concrete onto (or into) a
frame or structure. The greatest advantage of the process is that shotcrete can be applied overhead or
on vertical surfaces without formwork
 It is often used for concrete repairs or placement on bridges, dams, pools, and on other applications
where forming is costly or material handling and installation is difficult.
 Roller-compacted concrete
Roller-compacted concrete, sometimes called rollcrete, is a low-cement-content stiff concrete
placed using techniques borrowed from earthmoving and paving work.
 The concrete is placed on the surface to be covered, and is compacted in place using large heavy
rollers typically used in earthwork. The concrete mix achieves a high density and cures over time
into a strong monolithic block.
Normally used in pavements.
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CROSS SECTION OF HARDENED CONCRETE
Concrete made with siliceous rounded
gravel. Good for pumping of concrete
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Concrete made with crushed
limestone or sharp aggregates
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SLUMP TEST
 The concrete slump test measures the consistency of fresh concrete before it sets. It is
performed to check the workability of freshly made concrete, and therefore the ease with which
concrete flows. It can also be used as an indicator of an improperly mixed batch.
 The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is
used to ensure uniformity for different loads of concrete under field conditions
 A separate test, known as the flow table or slump-flow test, is used for concrete that is too fluid
(workable) to be measured using the standard slump test, because the concrete will not retain
its shape when the cone is removed.
Collapse
In a collapse slump
the concrete
collapses
completely.
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Shear
In a shear slump the
top portion of the
concrete shears off
and slips sideways.
True
In a true slump
the concrete
simply subsides,
keeping more or
less to shape.
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SLUMP TEST
EFFECT OF CASTING TEMPERATURE
ON SLUMP
Moderate slump : 75mm to 125mm
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BLEEDING AND SETTLEMENT
Higher slump : up to 150 to 180mm
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COMPACTION
HYDRATION
 is the chemical reaction between the cement
and water in which new compounds with
strength producing properties are formed
Properly compacted
 Heat of hydration
is the heat given off during the chemical
reaction as the cement hydrates
Poor compaction
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THANK YOU
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