Uso de resíduo de construção e demolição (RCD), cinza volante e cal hidratada para produção de concretos aplicados na construção civil

Abstract

The research was developed in two stages: In stage 1, the objective was to evaluate the effect of mixed recycled aggregate (MRA) as coarse aggregate on the mechanical properties (compressive strength and elastic modulus), physical (water absorption, porosity, and bulk density), in the diffusion of CO2 and microstructural (SEM and X-ray microtomography) in concretes with MRA in the substitution levels of 25, 50, 75 and 100% in partial substitution to the natural aggregate and reference concrete. The w/c ratios were 0.40, 0.50 and 0.60. Mathematical models were generated to calculate the elastic modulus from an fc28 and desired w/c ratio and the required MRA content. Stage 2, the objective was to evaluate the efficiency of adding hydrated dolomitic lime in Portland cement concrete, fly ash (CV), and recycled aggregate (RA) as coarse aggregate, as a way of improving the mechanical properties at the lowest ages, as well as reducing the depth of carbonation. For this, concretes were produced with 20% of CV in partial replacement of the CP, the addition of hydrated lime in the proportions of 5, and 10% of the total binder in mass and w/b ratio of 0.55. The MRA and recycled concrete aggregate (RCA) was 50% replaced by natural coarse aggregate. For this, mechanical (compressive strength, elastic modulus), physical (water absorption, porosity and bulk density), CO2 diffusion and microstructural analysis (SEM and X-ray microtomography) tests were performed. The results of Stage 1 showed that concretes with MRA content of 50% and w/c ratio of 0.50 presented a decrease in fc28 and Ec28 of 18% and 54.9%, respectively, when compared to the reference concrete. The increase in the volume of voids was 33% when compared to the reference concrete. The results of Stage 2 showed that the addition of 10% hydrated lime in concretes with 80% CP, 20% CV, and 50% ARC presented compressive strength at 63 days 12.47% higher when compared to concrete without lime hydrated. Ec28 improved by 3.78% compared to concrete without hydrated lime. The average ITZ thickness of the concretes without and with 10% hydrated lime was 3.61 μm and 6.28 μm, respectively. The addition of hydrated lime in Portland cement concretes with CV and RA restores the remaining Ca(OH)2 content in the matrix, anticipating pozzolanic reactions at early ages