Optimum mix design of fly ash geopolymer paste and its use in pervious concrete for removal of fecal coliforms and phosphorus in water

Mix ratios of liquid-to-binder (L/B), fly ash-to-binder (FA/B), nanoSiO(2)-to-binder (NS/B) and NaOH concentration (NH) of fly ash-nanoSiO(2)-cement geopolymer pastes were optimized for the flow of paste and the compressive strength simultaneously. Optimum mix design was found at 50% L/B, 60% FA/B, 0.04% NS/B and 1.71 M NH resulting in a maximum achievable compressive strength at 22.2 MPa after a 7-day curing under ambient temperature (25 +/- 5 degrees C) and the desired flow of paste at 110%. It was found that NH had the greatest effect on the flow of paste: the higher NH, the smaller the flow of paste was. On the other hand, NS/B showed the least effect on the compressive strength. Pervious geopolymer concrete made with the optimum mix was able to reduce fecal coliforms and phosphorus by 54-100 and 25-85%, respectively, depending on the contact time (0.5-8 h). A greater FC and P removal % was achieved at a higher pH caused by pervious geopolymer concrete. (C) 2015 Elsevier Ltd. All rights reserved.