Aggregatesgrading used in porous concrete are normally either single size coarseaggregate or grading between 19-9.5 mm. rounded and crushed aggregates, bothnormal and lightweight, have been used to make porous concrete.
The aggregateused should meet requirements of ASTM D448 and C33/C33/M. fine aggregatecontent is limited in porous concrete mixtures because it tends to compromisethe connectedness of the pore system. The addition of fine aggregate mayincrease compressive strength and density but correspondingly reduce the flowrate of water through the porous concrete mass.Aggregatequality in porous concrete is equally important as in conventional concrete.Flaky or elongated particles should be avoided. The narrow-grade coarseaggregate should be hard and clean, and free of coatings such as dust or clay,or other absorbed chemicals that might detrimentally affect the paste/aggregatebond or cement hydration. Aggregate sources with a service record of acceptableperformance are preferable. In the absence of a source with an acceptableservice record, a combination of tests could be conducted to provide a basisfor assessing the suitability of a candidate aggregate for incorporation into aporous concrete mixture.
Unit weights of aggregates should be determined inaccordance with ASTM C29/C29M.(Neptuneand Putman2010)In general, as the Cu of the aggregateincreased that is, the gradation became less uniform or single sized and morewell-graded the strength also increased,whereas the porosity and permeability decreased.Thecompressive, split-tensile, and flexural strengths are inversely related topermeability. As the permeability increased, the strength properties of porousconcrete mixtures decreased. The compressive, split-tensile, and flexuralstrengths increased with the Cu to points, after which a decrease instrength was observedThisis consistent with the literature; as the aggregate size decreases, the bindingarea increases and results in an improvement of the strength (Yang and Jiang2003).Nguyenet al. 2013 studied the use of sea shell by products in partial replacement ofaggregates in porous concrete both as an environment friendly building materialand a potential component.
(W.T. Kuo et al 2013) demonstrated Washed municipalsolid waste incinerator bottom ash (MSWIBA) of maximum size 12.5 mm was used asa substitute for natural aggregate and results shows that there is nosignificant difference in connected porosities, compressive strength andpermeability coefficient.Gaedickeet al.
2014 studied three different types of coarse aggregate namely pea gravel,limestone and ablend of RCAB of max. Size 9.5mm.Theuse of waste material such as recycle aggregate in porous concrete furtherincreases its environmental benefits by reducing the amount of materialsextracted from quarries and riverbeds. Li and Rizvi et al.(F.Tittarelli et al.
/2014) no-fines concretes with compressive strength ranging from 7 to 30MPa were obtained by changing the w/cfrom0.41 to 0.34 and the a/c ratio from 8 to 4.