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 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.

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 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.

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.