Investigation on the suitability of aluminium-based water treatment sludge as a sustainable soil replacement for road construction

Abstract

Water treatment sludge is a by-product of the drinking water treatment process, and it has been considered as a waste for water authorities around the world. This study aims to investigate the reuse of aluminium-based water treatment sludge (AS) as a soil replacement in road construction which can improve sustainable waste management practices for positive environmental outcomes. To evaluate the potential reuse of AS, a 50/50 mixture ratio of AS and clay (CL) was selected and tested for geotechnical engineering parameters through Odometer Tests, Unconfined Compression Strength Tests, Static triaxial, Cyclic triaxial and California Bearing Ratio. Detailed physical and chemical were also conducted with the water treatment sludge. Results suggest that combining AS with CL increases the optimal moisture content and decreases the dry density of the soil. Oedometer tests indicated that the CLAS mixture distributed stress better than CL and AS independently. In the UCS tests, CLAS enhanced the strength of the mixture from 74 kPa with only CL to 126 kPa with the introduction of AS. The shear strength of CLAS samples increased by 50% compared to CL. In the cyclic triaxial test, CLAS showed less cumulative strain than CL, and improved the CBR results of the mixture from 0.95% to 1.92%. Results indicate that AS can be beneficially reused as a low-cost soil replacement to contribute the Circular Economy and net-zero emission targets. Future research should examine the variability of AS, optimal ratios of AS to CL, and the levelized cost of AS in different environmental conditions.