PERVIOUS CONCRETE - STANDARDS FOR TESTING AND MAINTENANCE

An ASTM subcommittee on pervious concrete, ASTM C09.49, was formed in 2008.  ASTM  C1688,  Standard  Test  Method  for  Density  and  Void  Content  of  Pervious  Concrete,  has  been  standardized  to  measure  the  density  and  void  content  of  freshly  mixed pervious concrete. Efforts continue to determine the density and void content of  hardened pervious concrete for core samples that might be obtained from a pavement.  It  should  be  realized  that  the  values  obtained  on  a  freshly  mixed  pervious  concrete  sample using standardized consolidation procedures can be significantly different from  those measured on a pavement core. Various methods are used to place and consolidate  pervious concrete in pavements. One should not expect equivalence of the measured  densities by ASTM C1688 and that in hardened concrete cylinders or cores.

ASTM  C1701  is  a  standard  test  method  to  calculate  the  infiltration  rate  of  in- place pervious concrete (Figure 1). An infiltration ring is temporarily sealed to the  surface of a pervious pavement. After prewetting the test location, a given mass of  water is introduced into the ring and the time for the water to infiltrate the pavement  is  recorded.  The  infiltration  rate  is  calculated  using  the  equations  provided  in  the  standard. Tests performed at the same location across a span of years may be used to  detect a reduction of infiltration rate of the pervious concrete, possibly by clogging,  thereby  identifying  the  need  for  remediation.  A  low  infiltration-rate  reading  on  a  new pervious concrete pavement suggests paste sealing during construction due to  either improper mixture proportions or construction practices. This test should be  conducted at several locations and the average infiltration rate calculated.

ACI Committee 522.1 is a pervious concrete specification that requires the following test methods. Job site acceptance must be based on the density (unit weight)  of fresh concrete measured according to ASTM C1688. An acceptable tolerance is  ±5 lb/ft3 (80 kg/m3) of the design density. This ensures that the concrete that is sup- plied to the job site is the same as the concrete that was ordered for the project. Once  the pavement has been constructed, cores are taken and tested for thickness and density. Density is determined according to ASTM C 140. Slump and air content tests  are  not  applicable  to  pervious  concrete.  ACI  522.1  also  requires  that  each  project  include at least three pervious concrete installers or one craftsman which are levels  of the pervious concrete contractor certification conducted by the NRMCA.

If the pervious concrete pavement is an element of the storm-water management  plan, the designer should ensure that it is functioning properly through visual observation of its drainage characteristics prior to opening of the facility.

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   ow  of  materials  onto  pavement surfaces. The two commonly accepted maintenance methods are pressure  washing  and  power  vacuuming.  Pressure  washing  forces  the  contaminants  down  through the pavement surface. This is effective, but care should be taken not to use  too much pressure because this will damage the pervious concrete. Power vacuum- ing  removes  contaminants  by  extracting  them  from  the  pavement  voids.  The  most  effective scheme, however, is to combine the two techniques and power vacuum after  pressure washing.