Investigation of the effects of aggregate properties and gradation on pervious concrete mixtures.

摘要

Pervious concrete is a concrete mixture prepared from cement, aggregates, water, little or no fines and in some cases admixtures. It has been considered a Best Management Practice by the EPA because of its ability to reduce storm water runoff and to initiate the filtering of pollutants. Because the hydrologic properties of pervious concrete has been the primary reason for its reappearance in construction, the focus of previous research has been on maximizing the drainage properties of the mix with single-sized aggregates. This research, however, investigates the effects of aggregate properties and gradation on the strength, as well as hydrologic properties of pervious concrete mixtures.;The aggregates were retrieved from two sources and Type I cement was used to prepare the eight (8) batches of pervious concrete mixes for each source. An additional seven (7) batches were prepared with aggregate gradations derived from new uniformity coefficients (Cu). Each batch consisted of fifteen 3 x 6 in. cylinders and five 3 x 3 x 12 in. prisms. The water/cement ratio was held constant at 0.29 before factoring in absorption and the cement/aggregate ratio was 0.22. The design unit weight of the fresh concrete mixtures was 125 lb/ft3. The specimens were stored in a wet curing room for 28 days. The compressive, split-tensile, and flexural strengths were tested on 5 specimens each, along with the maximum specific gravity test that was conducted on loose cured concrete mixtures. The bulk and apparent specific gravity, the air voids and porosity, and permeability were all tested. Gradations were categorized according to nominal maximum aggregate sizes of ⅜, ½, and ¾ in. and in order of their Cu values.;The results were analyzed to evaluate the effects of properties, gradation and size. Strengths decreased as air voids increased, porosity increased with air voids, and permeability increased as air voids increased. The highest compressive strength was generated from the blended gradations with higher Cu values. In general, the single-sized mixes were on the lower end of the strength scale but on the higher end for air voids, porosity and permeability. However, blended mixes produced a relatively suitable strength and permeability. It was observed that compressive strength increased with Cu to a point after which there was a decrease in strength. Permeability decreased with the increase in Cu to a point after which it increased.