Análise das propriedades de concreto produzido com resíduo sólido da lavagem de caminhões betoneiras

Abstract

Just like de the various sectors that incorporate the civil construction industry, concrete batching amounts are responsible for the generation of numerous types of waste, including waste concrete sludge, which is generated in the washing of concrete mixer trucks responsible for transporting concrete. After washing the truck, the generated waste remains in decantation tanks to separate the water from the solid residual that accumulates at the bottom of the tanks, then the surface water is drained, the solid residual is stored and later disposed in an appropriate place. Thus, this paper objective was to analyze the mechanical properties of the concrete produced with the partial replacement of the cement by the solid residual generated in the washing of the concrete mixer trucks. The collected waste underwent physical and chemical characterization, through granulometry, specific gravity, unit weigh, BET surface, X-ray fluorescence, and X-ray diffraction tests, as well as the test for experimental performance index of the waste concrete sludge. Three concrete mixes were set, with 10%, 20% and 30% replacement of cement by waste sludge and a reference mixture without the use of waste. For the analysis of the concrete, slump and specific mass tests were carried out in the concrete in the fresh state, and compressive and traction strength, absorption, voids index and specific gravity in the hardened concrete. The waste concrete sludge characterization showed similarity between the granulometric curve of the cement, just like the BET surface of 14,92 m²/g indicating the high-water absorption capacity of the waste. The sludge waste presented a 61% performance with Portland cement, that is, it does not have pozzolanic activity, indicating that it behaves as a filler in the mixture. The ability of the waste concrete sludge to fill the voids in the concrete, reducing porosity and balancing the replacement of the cement by the residual was confirmed with a reduction of 83% in water absorption, and of 82% in the void index when replacing 30% of the cement with the waste. The compressive strength results of the concrete were 54,40 MPa, 51,28 MPa, 54 MPa and 38,37 MPa for the replacement contents of 0%, 10%, 20% and 30% respectively. The values obtained for the contents of 10% and 20% did not present a significant difference when compared to the result obtained in the reference concrete without using the waste concrete sludge, however the concrete with 30% of substitution presented a reduction of 30% in the compressive strength values. The reduction in mechanical strength for concrete with higher waste content is due to the lack of pozzolanic activity in the waste not being fully compensated by the filler effect promoted by it. Based on the results, it was concluded that the use of the waste concrete sludge in substitution of the cement in contents of up to 30% is feasible comparing to the mechanical properties and meets the criteria of resistance of concrete for structural purposes in class C35.