The effect of sewage sludge ash as a mineral admixture on concrete strength

The recycling of sewage sludge plays a crucial role in sustainable environmental management. The Isparta Municipality wastewater treatment plant generates approximately 3000 tons of dried waste annually. This study investigates the potential of utilizing sewage sludge ash (SSA) as a mineral admixture in concrete. The dried waste was subjected to incineration at 800 degrees C, followed by grinding, and its physical-chemical properties were subsequently analyzed. The specific gravity of SSA was determined to be 2.62 g/cm3 , while its specific surface area was found to be 6600 cm2/g. The pozzolanic content was measured at 70 %, and the pozzolanic activity index was established as 80 %. Sewage sludge ash (SSA) was used as a partial replacement for cement at 5 %, 10 %, and 15 % in concrete mixes. Concrete specimens of C25, C35, and C45 grades were prepared and cured for 7, 28, and 90 days. The water content, superplasticizer ratio, and slump value were maintained constant throughout the experiments. Various tests, including density, compressive strength, splitting tensile strength, and ultrasonic velocity, were conducted on the specimens. According to the 28-day test results, the strength development of the C35 series specimens containing 5 % SSA was measured at 96 %, while for the C45 series, it was measured at 101 %. According to the 90-day results, the C45 series concretes containing 5 % and 10 % SSA exhibited higher strength than the control specimens. However, the modulus of elasticity and tensile strength at splitting decreased as the SSA content increased. Based on these data, the 28-day efficiency factors of specimens containing 5 % and 10 % SSA were calculated to be 0.44 and 0.27, respectively. The incorporation of SSA resulted in a cost reduction of 4-12 % and a decrease in carbon emissions by 5-14 %, depending on the concrete grade and admixture ratio. The use of SSA as a mineral admixture in concrete can lead to significant environmental and economic benefits.