Contribution to the use of wet sludge water treatment plant fine aggregate in portland cement concretes: Evaluation of consistency, density, porosity, absorption, strength and tensile strength

Abstract

The treatment of drinking water generates a large amount of waste, the sludge from the water treatment plant (WTS). These tailings are usually deposited in rivers, which can generate environmental impacts. As a way of using this waste, the present study evaluates the influence of the use of WTS, in natura, as a substitute for natural sand in Portland cement concretes, at levels of 0%, 5%, 10% and 20%, by weight. In order to evaluate the influence of the incorporation of WTS on the properties of the cementitious material in the fresh state, the slump tests were performed. In the hardened state, porosity, density, water absorption, strength and tensile strength by diametrical compression There was an increasing reduction (up to 50%) in the flowability of the concrete as the substitution content increased. Also, constant increases in the porosity of the samples were noticed when the WTS was added. As a consequence, there was a reduction in the density of the concretes and an increase in water absorption. The strength at 7 days decreased from 31,45% when 5% sludge was used, 41,52% with 10% and 63,89% with 20%. At 28 days, the resistance decreased 28,52% to the lowest levels and 65,98% to the highest amounts of WTS. At 91 days, the load capacity was 28,52%, 40,33% and 57,01% lower, respectively. The tensile strength followed the same trend, with a reduction of 29,06% in concretes with 5% of WTS and 65,98% with replacement of 20% of waste. In general, it was possible to observe that the WTS has great potential for application in civil construction, presenting a limit content of 10% as a fine aggregate, without causing major losses in physical and mechanical properties.