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.
Concretes that contain binary-blended binders (BBB) and ternary-blended binders (TBB) incorporating thermally activated alum sludge ash (AASA), silica fume (SF), ground-granulated blast-furnace slag (GGBS) and palm oil fuel ash (POFA) are exposed to temperatures as high as 800 °C. The water-binder ratio of the multiple-blended binder (MBB) concretes was 0.30, and the total binder and polypropylene (PP) fibre contents were 493 and 1.8 kg/m 3 , respectively. The elevated temperature performance of the MBB concretes is evaluated in terms of the mass loss, compressive strength, ultrasonic pulse velocity (UPV) and surface cracks. The concrete strength deteriorated significantly due to elevated temperature up to 800 °C, but the residual strength of the BBB containing 15 % AASA was higher than that of the control and 20 % AASA concretes. Hightemperature exposure decreased measured UPV values. The concrete weight loss was more pronounced for TBB concretes. The elevated temperature performance of all of the TBB concretes was better than that of the BBB concretes with the same AASA replacement levels. It was observed that PP fibres help reduce spalling. BBB concrete containing 15 % AASA combined with either SF or GGBS or POFA exhibits superior performance at elevated temperature than Portland cement concrete at the same mix design proportion.
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