Waste Rice Husk Ash and Waste Rubber Chips Added Light Weight Concrete Paving Blocks: Mechanical Behaviour and Forecasting Strength Properties

This paper investigates the potential application of waste Rice Husk Ash (RHA) and waste crumbed rubber (CR) as substitutes for cement and fine aggregates, respectively, and the potential of forecasting the mechanical properties of concrete paving blocks. Mechanical properties were experimentally investigated, and predictive formulas were derived, enabling forecasting of strength properties.  Paving blocks of Grade 20 were cast by replacing fine aggregate with 5% CR (by weight) and replacing cement with waste RHA at four percentages: 0%, 5%, 10%, and 15% (by weight). Specific gravity, bulk density, compressive strength, flexural strength, and splitting tensile strength were experimentally tested. The bulk density of blocks decreases by 12% when the CR content increases from 0% to 5%, resulting in lightweight blocks. The 5%CR10%RHA paving blocks satisfied the minimum 28 day compressive strength requirement. Compared to the control block, 28 day compressive strength, flexural strength and splitting tensile strengths were decreased by 58%, 40% and 43%, respectively, with the addition of 5% CR. By replacing 10% of cement with RHA, the reductions were recovered by 32% in compressive strength and 40% in flexural strength. Flexural failure modes confirmed that adding CR contributed to overcoming the quasi-brittle behaviour of the blocks. It was found that the strength properties were proportionately varied with the density, leading to a potential for forecasting the mechanical properties of the blocks.