Q. We are planning a large pervious parking lot paving project. The contractor will need to be very productive, placing at a rate perhaps twice as fast he has done in the past.
The engineer is concerned about our ability to maintain consistent fresh quality concrete throughout the entire pour. On previous pours, we were able to demonstrate our material's quality using our testing protocol. Now, the design engineer is asking if our methods include any approved testing procedures. The engineer would like to include these procedures in his specifications. What do you suggest?
A. For about three years, a task group from ASTM has shared information with the goal of developing several test methods for pervious concrete. Due to the material's open-gaped nature, technicians can't use traditional concrete testing methods to assess quality in either its fresh or hardened states.
The task group, ASTM Subcommittee C09.49 on Pervious Concrete, has been reviewing a wide range of test methods developed all across the world. Members have been reviewing procedures for testing pervious concrete for compressive strength, flexural strength, in-place permeability, and in-place density/porosity.
To evaluate these proposed methods, members have been conducting round robin testing that seems to have universal applicability. When the task group members agree a certain procedure is valid, accurate, and repeatable, the procedure is presented for review by the ASTM International Committee C09 on Concrete and Concrete Aggregates.
The first of these proposed standards, ASTM C1688/C1688M, Test Method for Density and Void Content of Freshly Mixed Pervious Concrete, was approved by the C09 committee in late 2008.
Michael Davy, chairman of the pervious subcommittee, says producers can use the new standard to verify that the fresh pervious concrete delivered to a project corresponds to the producer's mix proportions. This test method provides a procedure for determining the density and void content of freshly mixed pervious concrete. By measuring fresh density, technicians can verify the mixture proportions. The method is applicable to pervious concrete mixtures containing coarse aggregate with a nominal maximum size of 1 inch or smaller.
Producers may also discover that the approved test method has another benefit. “It may also be used by producers investigating different mix proportions,” says Davy. This may allow producers to develop a wider range of pervious mix designs incorporating various aggregate types, sizes, and gradations.
Remember, this test method's scope is very limited. Do not use it to determine the quality of the material after it is placed. Test results indicate that the fresh density and void content calculated from this test may differ from the in-place density and void content. “This test should not be used to determine in-place yield,” says Davy.
To buy a copy of C1688/C1688M, Test Method for Density and Void Content of Freshly Mixed Pervious Concrete, telephone ASTM international customer service department at 610-832-9585, or visit www.astm.org.