Effect of coal ash and rice husk ash partial replacement in ordinary Portland cement on pervious concrete

Abstract

Pervious concrete is a common green infrastructure material with a low-impact development technology that provides a water-sustainable engineering solution for urban cities. This study investigates an effective way to reuse coal fly ash (CFA), coal bottom ash (CBA), and rice husk ash (RHA) as partial replacements of ordinary Portland cement in pervious concrete. In experiments, single and binary replacement by these ash materials was conducted via cement material substitution in pervious concrete. The pervious concrete specimens contained 30% ash by volume and had a water-to-cement ratio of 0.21. The ash materials and pervious concrete specimens were characterized by field emission-scanning electron microscopy, X-ray fluorescence spectroscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the pervious concrete quality. The compressive strength of pervious concrete with single-ash partial replacement by CFA and CBA was higher than that of the control group and two specimens that contain single-ash partial replacement by RHA (sintered to 550 and 900 °C). The five pervious concrete specimens with binary partial replacement of RHA (sintered to 550 and 900 °C), CFA, CBA and CBA (sintered to 1100 °C) showed a synergistic effect and had a higher compressive strength than the control group and single-ash partial replacement with RHA (sintered to 550 and 900 °C) at 90 days. The water permeability ranged between 0.101 and 0.313 cm/sec, and the TCLP-released metal concentrations from all specimens satisfied the regulatory standards of Taiwan. The result of the carbon footprint showed that the replacement of ash materials reduced the total carbon footprint by 9.9%–20.6% per m3 of pervious concrete compared to the control group. The results indicated that CFA, CBA, and RHA replacement in cement materials yielded an acceptable compressive strength and water permeability.