INTERLOCKING CONCRETE PAVERS
Author(s): David R. Smith
Source: Landscape Architecture Magazine, Vol. 81, No. 8 (AUGUST 1991), pp. 72-74
Published by: American Society of Landscape Architects
Stable URL: https://www.jstor.org/stable/44674463
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INTERLOCKING CONCRETE PAVERS
GUIDELINES
FOR
DESIGN
Interlocking
seemingly
signing
areas,
the
INSTALLATION
concrete
simple
the
AND
product
pavement
especially
landscape
pavers'
with
is
and
regard
architect
appar
still
com
installin
to
pavem
design
and
BY
the Paving Product
formance is directly related to the quality of
Consider the paver thickness.
depth
of
a
the soilThe
and base material.
In most
situations,
David R. Smith
paver affects its ability
to
and prior
spread
the carry
soil should be compacted
to installing
loads to neighboring units when
set
in sand.
the base.
Compaction
typically is The
95 to 98 pergreater the depth, the greater
the
interlock
cent Proctor
density,
as described in ASTM
with adjacent units and theD698.
greater
theto loadFor pavements subject
vehicular trafcarrying capacity. For areas
to
vehicufic,subject
a qualified civil or
geotechnical
engineer
shouldbe
be consulted
assess the soaked
Calilar traffic, the paver should
at to
least
3.125
inches (80 mm) thick; for pedestrian
areas
and
fornia Bearing Ratio (CBR)
of the soil.
This test
residential driveways, 2.375-inch-thick
(60-mmmethod (ASTM D 1883) determines
the ability
thick) units are acceptable. of the soil to take loads and is a critical compoConsider the aspect ratio. The nent
aspect
ratio
is the
in determining
the thickness
of the base
materials.
ratio of the paving unit's length
to its depth.
Pavers subject to street traffic
should
an
Use high-quality
aggregatehave
base materials.
For
aspect ratio no greater than parking
3:1 lot
and
no
less than
and street
applications,
the fines
1.5:1. The American Society
ofparticles)
Testing
and
(very small
in the aggregate
passing
Materials (ASTM), in its standard
specification
through a Number
200 (75-micrometer) sieve
for concrete paving units (ASTM
should be kept atC936),
between 5 and 1 cur1 percent. This
rently defines a concrete ispaver
asmoisture,
having
a
because fines hold
thereby lubrimaximum dimension of 6.5 cating
inches
by
9.5
the largerwide
aggregate and
allowing
it to
inches long by 5.5 inches deepsettle.
(160
x traffic
240while
mm
When mm
placed under
satuX 140 mm), suggesting that
a with
concrete
paver
rated
moisture, premature
deformation of
should be capable of beingthegrasped
with
one
base and pavement surface
can occur.
hand for installation. Yet paving
slabs
exist
Base materials should
be compacted
to 95 to
with dimensions of 8 inches
inches
100 by
percent8
of modified
Proctorand
density, as
Selecting
describedratios
in ASTM D 1557.
In areas
with conlarger, and generally have aspect
of
5:1
to
9: 1 . Such slabs should only be
used
in orpedestrian
tinuously
wet soils
extremely heavy traffic,
areas
because,
if
interlock between slab units is minimal. Fur-
aspect
thermore, they are susceptible to bending and
cracking under vehicular traffic.
Doubling the depth of a slab increases its
resistance to bending four times. Unfortunately,
increasing the thickness of slabs makes them so
heavy that workers cannot easily lift or move
them around the site.
Pavement Design
Assess the strength of the soil. Pavement perLANDSCAPE
ratios
exceed
3:1,
the
aggregate
bases can be
stiffened
by adding
asphalt or portland cement.
Consider the base thickness. The proper base
thickness is determined by local soils and drain-
age conditions, expected traffic, freeze-thaw
conditions and availability of adequate base
materials. A civil engineer familiar with local
soils and construction materials can provide
essential guidance in pavement-thickness
design, as well as drainage and construction
specifications.
ARCHITECTURE
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......... ШЯ ......... . ........
Use proven pavement design methods
for
flexand lubricate the
bedding
sand, causing it to
ible pavements. In most situations,
design
standeform under
traffic and pump
up through the
<
dards for the base should follow those used for
joints. Experience has shown that so-called
flexible asphalt pavement. For example, 3v8inch-thick pavers on 1 to 1V2 inches of bedding
sand can be used in place of an equivalent thickness of asphalt in most municipalities.
The Concrete Paver Institute, a division of
the National Concrete Masonry Association that
represents member manufacturers, suppliers
and contractors throughout North America, has
technical resources to help landscape architects
build better interlocking concrete pavements.
One such resource is PAVE CHE K, an inexpen-
"concrete sand," conforming to the requirements
Q-
of ASTM C33, performs adequately.
In pavements undergoing vehicular traffic,
Û
sand particle shape, hardness and durability
are important. The sand particles should be
<
cubical so that they will compact tightly, yet
still offer movement of moisture through the
sand. Such sands, having a high silica content,
resist abrasion and degradation under vehicular traffic. The modest extra expense will be
more than offset by preventing costly repairs
Z
о
<
X
sive ($50) pavement-design software package
that determines base thickness, incorporating
concepts and terminology developed by the
American Association of State Highway and
Transportation Officials (AASHTO) familiar to
in the future.
Test compaction. After the soil sub-grade is
compacted and aggregate base materials are
placed, the degree of compaction, as measured
moist most of the time, these types of limestone
Limestone screenings or stone dust should
not be used in place of sand. Limestone particles
are often flat and elongated, making them difficult to compact. Moreover, some limestones are
soluble in water, and, since bedding sand is
many civil engineers.
will degrade.
Do not compact the bedding sand. Some specifications call for compacting the sand prior to
installing and vibrating the pavers. Such compaction, however, can decrease the necessary
by density and moisture in the materials, should
be monitored and corrected. This will minimize
deformations of the paving surface. Compaction testing is one of the most neglected as-
movement of sand into the bottom of the joints
worth investing in both soil and base compaction tests to avoid more costly problems in the
between each paver. After pavers are placed,
they are compacted into the bedding sand with
a plate compactor, forcing the sand into the
final elevation of the base should be plus or
joints from the bottom as well as from the top as
sand is spread and the pavers are vibrated to fill
the joints. It is critical that this sand be loose so
pects of quality control; even on small jobs, it is
future.
Insist on a base with consistent elevations. The
minus V2 inch (15 mm) over a 10-foot (3-meter)
Thebe
seven most commonly
straightedge. Any low or high areas should
smoothed. A common construction error is to
specified paver shapes are
available
compensate for a sloppy base installation
by in modules for
mechanical
filling surface depressions with sand. The sand
depth should be 1 to 1 V2 inches (25 to 40 mm); if
dips in the base are filled with sand exceeding
these depths, the filled areas will result in a
"washboard" pavement surface.
Specify the right bedding sand. Those who
specify bedding sand sometimes err by specifying too fine a gradation or none at all. As in the
aggregate base, sand particles that will pass
through the Number 200 sieve will hold water
installation.
that it can infiltrate the joints and cause the
pavers to interlock. Sand between the pavers
also enables the units to spread loads by shear
transfer.
Some contractors will compact the sand to
compensate for an uneven surface in the base.
Such unevenness should be corrected in the
base, not with bedding sand.
Drain the sand layer when installing pavers
over existing pavements. Existing asphalt or
concrete pavements can be rehabilitated with a
concrete-paver-and-sand overlay. When this is
done, moisture in the sand layer must be drained
into a catch basin or small pea-gravel-filled
AUGUST
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1991
TECHNIQUE
PRACTICE
MATERIALS
Э
z
>
<
и
z
interlock and load distribution
as well as resisdrain
under
the
p
Left:
A specialized machine
tion.
Geotextiles
a
grips the edges of one layer
tance to the lateral forces of stopping and turnthe
existing
of pavers as the operator
ing tires. Although the pavem
patterns possible with
uses the machine's boom
sand
and
concrete
the
20 available paver shapes offer practically
the
migration
s
and clamp device to
endless design possibilities, parking of
and street
maneuver the module into pavement
existing
pavements should conform to herringbone
For
crosswalks
,
co
place on the smoothed
patterns.
о
u
X
walks
are
bedding sand. Right: One of
often
Maintain consistent joint widths. Each unitcon
by
removing
exist
the 50 drawings from the
should be placed with a 2- to 3-mm-wide
joint
Paver Institute's
grade Concrete
beams
e
that enables the sand in the for
joints to spread
an
aggregate
Vertex CADalog software.
loads without chipping the edges of the base
pavers.
Traffic
loads
may
d
Some manufacturers place
2-mm-thick spacer
bars on the sides of each unit to ensure this
walks
differently
order
to
make
the
minimum joint.
pavements,
they
m
Design Resources for
the Landscape Architect
poured-concrete
Concrete Paver Institute members have pro- b
will
yieldduced the
software that generates 50 leas
drawings with
vertical deformation from vehicular traffic.
specifications for use in producing construction
Excess moisture in the bedding sand should be
documents. Paver applications represented in
removed as described above.
the drawings include residential pavements,
Installation
Consider mechanical installation. Although
concrete pavers may be installed by hand,
mechanical installation can sometimes triple
installation efficiencies, saving both time and
money. When pavers are installed mechani-
cally, they are delivered to the job site in the
laying pattern. Machines can pave areas as
narrow as a sidewalk or as large as a parking lot.
Work with the contractor to increase efficiencies. The designer can save the client money by
working closely with an experienced contractor
during the design phase to sequence the areas
to be paved. For better efficiency in mechanical
installation, the pavement should be designed
according to the width of the paver module,
with a view to reducing cutting any modules or
removing excess pavers. In other words, design
with the module rather than to specific
dimensions - for example, by adjusting tree
collars by a few inches to avoid having to cut
crosswalks, interiors, fountains, plazas, parking
lots, roof decks, gas stations, streets, ports,
airports, and curb and utility structure details.
The program, the Vertex CADalog, operates on
IBM PCs and compatibles in MS/DOS without
the use of CAD. Detailed drawings are export-
able as .DXF files to popular CAD systems.
Custom specifications can be transferred as
ASCII files to common word-processing programs for changes. The software can reduce
drawing production time while giving the landscape architect technical guidance on the appropriate application at hand.
The Vertex CADalog is available through
members of the Concrete Paver Institute, as is
technical literature on design, installation, clean-
ing and sealing. For more information, write
CPI, 2302 Horse Pen Road, Herndon, VA 22071,
or call (703) 435-4900; fax (703) 435-9480. In
Canada, write P.O. Box 362, Milton, Ontario,
L9T 4Y9 Canada. ■
the module.
Use herringbone patterns in parking lots and
streets. An uninterrupted 45-degree or 90-de-
gree herringbone pattern allows continuous
LANDSCAPE
David R. Smith , Affiliate , ASLA , is director of pav-
ing products at the Concrete Paver Institute in
Herndon , Virginia.
ARCHITECTURE
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