Experimental investigations on the durability and degradation mechanism of cast-in-situ recycled aggregate concrete under chemical sulfate attack

With the increase of construction solid waste (CSW) in China's urbanization construction, many ecological and environmental problems have been raised. Recycling and reusing of construction waste is conductive to reducing pollution, carbon emissions and conserving resources. Cast-in-situ concrete structures have been widely used in foundation engineering, application of cast-in-situ recycled aggregate concrete (CRAC) has broad application prospect. This paper investigated the mechanical properties and durability of cast-in-situ recycled aggregate concrete under chemical sulfate attack. Cylinder specimens were casted with four recycled concrete aggregate (RCA) replacements of 0%, 30%, 50% and 100%, and immersed into the exposures of tap water, single sulfate solution and chloride-sulfate mixed solution, respectively. Visual inspection and indicators of sulfate concentration, mass and diameter variation, compressive strength were monitored in the exposure of 52 weeks. The results exhibited that RCA replacement has a significant impact on the mechanical properties and sulfate resistance of CRAC, and the existence of chloride can significantly hinder the sulfate diffusion and delays the deterioration of CRAC. Microscopic evidence also indicated that the dissolving of calcium hydroxide and formation of ettringite resulted in the CRAC degradation. Most importantly, RCA and ITZ can avoid serious chemical attack due to less residual calcium hydroxide existed, while ITZ with a higher porosity can further provide the diffusion path for the sulfate. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The recycling and reuse of construction waste can help reduce pollution and resource waste. Cast-in-situ recycled aggregate concrete shows promising application prospects. Research results indicate that the replacement rate of recycled concrete aggregate has a significant impact on the performance and durability of CRAC, and the presence of chlorides can delay its deterioration.