APPENDIX 6PERVIOUS CONCRETE MIXTURE PROPORTIONING
A6.1General
This guide provides a method for proportioning no-slump pervious concrete that is used for
pavements and other applications where drainage and percolation are needed. Pervious
concrete is an open-graded material that is bound by cement paste. The structure of the
material allows the passage of water, yet provides moderate structural strength. Because of
the high percentage of voids, pervious concrete has been used also as an insulating
material.
A6.2Materials
Pervious concrete is composed of cement or a combination of cement and pozzolan,
coarse aggregate, and water. Occasionally, a small amount of fine aggregate has been
incorporated to increase compressive strength and to reduce percolation through the
concrete. The most common gradings of coarse aggregate used in pervious concrete meet
the requirements of ASTM C 33 sieve sizes 9.5 to 2.36 mm (size number 8), 12.5 to 4.75
mm (size number 7), and 19.0 to 4.75 mm (size number 67). Portland cement should
conform to ASTM C 150 or a combination of cementitious materials can be used that
conform to the appropriate ASTM specifications.
A6.3Water-cementitious materials ratio
The w/cm is an important consideration for maintaining strength and the void structure of
the concrete. A high w/cm reduces the adhesion of the paste to the aggregate and causes
the paste to flow and fill the voids even when lightly compacted. A low w/cm will tend to
cause balling in the mixer and prevent an even distribution of materials. Experience has
shown a range of 0.35 to 0.45 will provide the best aggregate coating and paste stability.
Higher values of w/cm should only be used if the concrete is lightly tamped or compacted.
The w/cm versus compressive strength relationship, which is normally used with
conventional concrete, does not apply to pervious concrete.
A6.4Durability
Freezing-and-thawing tests of pervious concrete indicate poor durability if the void system
is filled with water. Tests have indicated that durability is improved when the void structure
is permitted to drain and the cement paste is air-entrained. No research has been
conducted on resistance of pervious concrete to the aggressive attack by sulfate-bearing or
acidic water that can percolate through the concrete. Therefore, caution should be used in
applications where aggressive water may exist.
A6.5Percent voids
Compressive strength versus percolation-To ensure that water will percolate through
pervious concrete, the percent voids, calculated as percent air by the gravimetric method
(ASTM C 138), should be 15% or greater as shown on Fig. A6.1.6 At this void content, the
compressive strength of the concrete as shown in Fig. A6.2 would be approximately 24 MPa
(3500 psi) at 28 days. The higher the percent voids, the higher the percolation rate and the
lower the compressive strength. The lower the percent voids, the lower the percolation rate
and the higher the compressive strength. Also, the compressive strength increases as the
nominal maximum size aggregate decreases.
A6.6Amount of coarse aggregate
Coarse aggregate, b/bo, dry-rodded density tests made by the National Aggregates
Association-National Ready Mixed Concrete Association (NAA-NRMCA) 6 show that the
dry-rodded density of coarse aggregate, as determined by ASTM C 29/C 29M, can be
effectively used in proportioning pervious concrete, where:
b/ b o=dryrodded volume of coarse aggregateaunit Volume of concrete
b=solid volume of coarse aggregatea unit volume of concrete ;
b0 =solid volume of coarse aggregatea unit volume of coarse aggregate
The b/bo value automatically compensates for the effects of different coarse aggregate
particle shape, grading, and specific gravity. Furthermore, the b/bo values for a range of
nominal maximum-size aggregates normally used in pervious concrete, 10 to 20 mm (3/8
to 3/4 in.), are very similar. Table A6.1 gives the b/bo values for coarse aggregate sizes
No. 8 and No. 67 for fine aggregate contents of 0, 10, and 20% of the total aggregate.
