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Benefits
Design
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Inspection and Maintenance
► Construction Inspection and Testing
Normal
construction inspection practices that base acceptance on
slump and cylinder strengths are not meaningful for pervious
concrete. Strength is a function of the degree of
compaction, and compaction of pervious concrete is difficult
to reproduce in cylinders. Instead, a unit weight test is
usually used for quality assurance, with acceptable values
dependent on the mix design, but generally
► Post-Construction Inspection and Testing
After
seven days, core samples can be taken (per ASTM C 42) and
measured for thickness and unit weight as quality assurance
and acceptance tests. A typical testing rate is three cores
for each 100 yd³
(75 m³).
Compression testing for strength is not recommended, because
of the dependence of compressive strength on compaction.
Unit weights, in accordance with ASTM C 140, provide an
acceptance measurement; typical requirements
Questions have been raised about the freeze-thaw durability of pervious concrete. Even though most experience with pervious concrete has been in warmer climates, recently there have been several pervious concrete projects in colder climates. Pervious concrete in freeze-thaw environments must not become fully saturated. Saturation of installed pervious concrete pavement can be prevented by placing the concrete on a thick layer of 8-24 inches (200 to 600 mm) of open-graded stone base. Limited laboratory testing has shown that entrained air may improve the freeze-thaw durability even when the pervious concrete is in a fully saturated condition. However, the entrained air content cannot be verified by any standard ASTM test procedure.
► Maintenance
The majority of pervious concrete pavements function well with little or no maintenance. Maintenance of pervious concrete pavement consists primarily of prevention of clogging of the void structure. In preparing the site prior to construction, drainage of surrounding landscaping should be designed to prevent flow of materials onto pavement surfaces. Soil, rocks, leaves, and other debris may infiltrate the voids and hinder the flow of water, decreasing the utility of the pavement. Landscaping materials such as mulch, sand, and topsoil should not be concrete, even temporarily.
Vacuuming annually or more often may be necessary to remove debris from the surface of the pavements. Other cleaning options may include power blowing and pressure washing. Pressure washing of a clogged pervious concrete pavement has restored 80% to 90% of the permeability in some cases. It also should be noted that maintenance practices for pervious concrete pavements are still being developed.
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ConcreteAnswers for Architects, Engineers and Developers:
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About NRMCA
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between 100 lb/ft³
and 125 lb/ft³
(1600 kg/m³
and 2000
kg/m³).
ASTM C 29 generally is preferred over ASTM C 138 because of
the consistency of pervious concrete, although ASTM C 138 is
used in some areas. Testing frequencies of once per day, or
when visual inspection indicates a change in the concrete,
are common. Acceptance criteria typically are plus or minus
5 lb/ft³
(80 kg/m³)
of the target value for the mix design.
dictate that
average unit weights be within 5 lb/ft³
(80 kg/m³)
of the design unit weight. The common criterion for
acceptance of thickness is that no core shall be under the
design thickness by more than
½
in. (13 mm). It should be noted that pervious concrete
pavements may have a higher
variability in pavement
thicknesses when placed on an open-graded subgrade, compared
with conventional concrete pavements.
