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.Aggregate quality in porous concrete is equally important asin conventional concrete. Flaky or elongated particles should be avoided.
The narrow-gradecoarse aggregate should be hard and clean, and free of coatings such as dust orclay, or other absorbed chemicals that might detrimentally affect thepaste/aggregate bond or cement hydration. Aggregate sources with a servicerecord of acceptable performance are preferable. In the absence of a sourcewith an acceptable service record, a combination of tests could be conducted toprovide a basis for assessing the suitability of a candidate aggregate forincorporation into a porous concrete mixture.
Unit weights of aggregates shouldbe determined in accordance with ASTM C29/C29M (Neptuneand Putman 2010). In general, as the Cu ofthe aggregate increased that is, the gradation became less uniform or singlesized and well-graded, the strength increases, whereas the porosity andpermeability decreases.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 observed. This is consistent with the literature; as the aggregatesize decreases, the binding area increases and results in an improvement of thestrength (Yang and Jiang 2003). 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 peagravel, limestone and a blend of RCAB of maximum 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). Evaluated no-fines concretes withcompressive strength ranging from 7 to 30 MPa by changing the w/cfrom0.41 to 0.34 and the a/c ratio from 8 to 4.
