Pervious concrete has been used in the United State for over 30 years. Because of its high porosity, the most common usages have been in the area of stormwater management, but have been limited to use in pavements with low volume traffic because of its low compressive strength compared to conventional concrete. Fly ash has been shown in numerous post studies to increase the strength and durability of conventional concrete. In this study, six batches of pervious concrete with different amounts of aggregate, cement, and fly ash were prepared to find the mix that generated high compressive strength and study the effect of fly ash on the compressive strength and permeability of pervious concrete.
Materials used in this study were selected based on literature reviews and recommendations from local sources. Unconfined compressive strength tests were carried out on pervious concrete specimens with fly ash contents of 0%, 2%, 9%, 30%, 32% by weight of the total cementitious materials. Falling head permeability tests were carried out on specimens having 2% and 32% fly ash.
The results indicated the pervious concrete containing 2% fly ash can achieve compressive strength greater than 3,000 psi at void content of 12%, and a compressive strength 2,300 psi with a permeability of 0.13 cm/s at a void content of 15%. The pervious concrete with 32% fly ash had a compressive strength of 2,000 psi and the permeability of 0.21 cm/s at a void content of 15.8%. The failure surfaces of specimens with 2% fly ash developed through the coarse aggregates, indicating the high strength of cement bonds. The failure of specimens containing 32% fly ash was observed to be along the coarse aggregates surfaces, indicating a lower strength of the paste. Although it was expected for pervious concrete with 32% fly ash to reach a higher compressive strength at lower void content, the failure mode indicated that it may not reach the value as high as that of pervious concrete with 2% fly ash at the same void content.