Run-off water qualities and engineering properties of sustainable paving blocks with combined waste: waste rice husk ash and coal bottom ash

Substitute material for concrete mixtures is a prominent approach in upholding the sustainability in the construction industry. However, to convince the sustainability, the direct impact of the substitute materials on the environment is an imperative need. This paper investigates the effect of coal bottom ash on the water quality of run-off and engineering properties of waste rice husk ash added paving block. Cement was substituted with Waste rice husk ash (RHA) a constant percentage (i.e., 10%, by wt) while sand was substituted with coal bottom ash (BA) with varying percentages: of 0%, 5%, 10%, 15%, 20% and 25% (by wt). The run-off water quality was assessed by determining the pH value, total suspended solids, turbidity and conductivity of run-off water of waste added paving blocks. The engineering properties were evaluated by conducting tests for compressive strength, splitting tensile strength, water absorption and skid resistance. SEM analysis was conducted to investigate microstructure of waste added paving blocks. The pH, turbidity and conductivity of the run-off water were reduced from 7.93 to 7.82, from 2.95 to 2.30 NTU and from 240 to 205 µs/cm, respectively, with the increase of coal BA from 0 to 25% as a sand replacement, indicating that the water quality of run-off can be improved by modifying the cement matrix of the RHA-based paving blocks by using coal BA. Findings have further affirmed that paving blocks with 10% waste RHA and 25% coal BA, as cement and sand substitutes, respectively, can be used as construction materials without comprising engineering properties, yet, with enhanced utilization of waste and enhanced water quality of run-off, which are sustainable for development of infrastructure.