Avaliação do concreto autoadensável com areia de RCD reforçados com fibras de aço e de polietileno submetidos ao ataque acelerado por cloretos

Abstract

The generation of Construction and Demolition Waste (CDW) has been growing every year. Properly disposing of this material is an obligation of society. One solution is its reuse as recycled aggregate (RA) in concrete. However, its use in replacement of natural aggregates in concrete shows that there is a reduction in mechanical and durability properties. To alleviate this problem, the addition of fibers to concrete and the use of self-compacting concrete (SCC) can be alternatives to improve the mechanical behavior and durability, since the SCC uses low water/cement ratios. Recent researches have intensified the study of CDW in structural concrete in order to understand its behavior. The objective of this research is to evaluate the resistance to penetration of chloride ions in self-compacting concrete with the addition of steel fibers and commercial polyethylene, combined with the replacement of natural sand by fine recycled aggregate of CDW, submitted to accelerated action in wetting and drying cycles in saline solution, as well as the mechanical behavior to compression, flexural strength, and toughness. The definition of fiber content and superplasticizer additive was carried out through a study of mortars to then verify the behavior of SCC in the fresh state. In the hardened state, the compressive behavior was evaluated before and after the wetting and drying cycles in saline solution, and flexural strength and tenacity only after the wetting and drying cycles in saline solution. The quality of the SCC was evaluated by determining the diffusion coefficient of chloride ions, chloride penetration, electrical resistivity, water absorption by immersion, open porosity in wet cure, in addition to the SEM to verify the state of the fibers after aggression cycles. and disruption of the SCC. The study of mortars showed that it was possible to obtain SCC with SF2 and SF3 classification according to NBR 15823 (ABNT, 2017) from mortars with a spread between 280 mm ± 20 mm. The replacement of fine natural aggregate by RA reduced the compressive strength in all mixes. The addition of steel fibers increased the compressive strength, flexural strength and toughness of the composite compared to the reference concrete with RA. The addition of commercial polyethylene fibers did not show significant increases in compressive strength and flexural strength compared to the reference concrete with RA, however the toughness showed a significant increase. Fiber composites showed greater porosity and water absorption by immersion, caused by the incorporation of fibers in concrete. The penetration of chloride ions was greater in concretes with fibers, as well as the diffusion coefficients. Finally, the steel fibers in the SEM showed no evidence of corrosion, and the polyethylene fibers showed surface wear caused by mechanical stress.