Physical and Mechanical Properties of High Performance Concrete with Alum Sludge as Partial Cement Replacement

Alum sludge (AS) is a by-product of water treatment plants that use aluminum salts as a primary coagulant, and is the most widely generated water treatment residual/sludge worldwide. It usually contains colloidal alum hydroxides that are often amorphous species. The present paper examines the influence of AS powder as partial Portland cement type I replacement on the mechanical properties of high-performance concrete (HPC). AS with 90% fineness was passed through a 45 μm sieve (No. 325).The present study used a concrete mix with a fixed water/binder ratio of 0.33 and a constant total binder content of 483 kg/m³.The percentages of the alum sludge by weight of cement were: 0%, 6%, 9%, 12%, and 15%. Slump tests were performed on fresh concrete to measure workability. The mechanical properties, dry densities, compressive strengths, and splitting tensile strengths of the concrete samples were investigated at 3, 7, and 28 days, whereas flexural strength was monitored at the age 28 days. Specimens without AS were compared with those that contained AS. The results revealed that the workability of the concrete consistently increased as the amount of cement replaced with AS increased. It was found that the concrete with 6% AS cement replacement demonstrated improved compressive strength and splitting tensile strength at all ages, compared with the control concrete.