Abstract
Resistance to sulfate degradation is an important index used to measure concrete’s durability. In this study, recycled aggregate concrete (RAC) with a 0%, 30%, and 50% recycled coarse aggregate substitution rate and a 0% and 15% recycled fine aggregate replacement rate was used as the research object, and its degradation resistance was evaluated by the mass loss rate and the relative dynamic modulus of elasticity. The degradation products were studied and analyzed with SEM scanning electron microscopy and XRD phase analysis. The relative dynamic modulus of elasticity was selected as the degradation index, the RAC concrete’s degradation resistance was modeled by Wiener, and the reliability curve was obtained. The results showed that expansion products, such as gypsum and Ettringite, were produced in RAC concrete in a dry‐wet sulfate cycling environment, and such defects as pores and voids were filled in the initial stage. The stress the expansion products exerted in the later stage caused the concrete to crack and peel, which demonstrated that the fluctuation law of mass and the dynamic elastic modulus increased first and then decreased. The recycled coarse aggregate substitution ratio’s effect on RAC concrete is higher than that of recycled fine aggregate. The reliability curve established by the Wiener model can reflect the reliability of RAC concrete under different cycles well and can obtain RAC concrete’s sulfate degradation resistance life with different aggregate substitution rates.
Highlights
Because of China’s rapid urbanization in recent decades, urban construction is increasing with each passing day, which at the same time leads to a series of problems, such as environmental degradation and resource depletion. e “China Resources Comprehensive Utilization Annual Report” (2014) the China Development and Reform Commission issued pointed out in detail that in 2013 alone, China produced approximately 1 billion tons of construction waste, while only approximately 50 million tons of the waste were used, which equates to a utilization rate of only 5%
recycled aggregate concrete (RAC) with a 0%, 30%, and 50% recycled coarse aggregate replacement rate and 0% and 15% recycled fine aggregate replacement rate was taken as the research object
It was observed that the RAC concrete contained calcium carbonate. e primary reason for this is that the surface of regenerated aggregate was attached with old mortar, and its CaCO3 content was more, during the dry-wet cycle, part of the CO2 in the air enters the concrete through the pores on the test pieces’ surface, and the coarseness in the RAC concrete. e fine aggregate showed a considerable degree of carbonization, so calcium carbonate formed in the phase analysis
Summary
Because of China’s rapid urbanization in recent decades, urban construction is increasing with each passing day, which at the same time leads to a series of problems, such as environmental degradation and resource depletion. e “China Resources Comprehensive Utilization Annual Report” (2014) the China Development and Reform Commission issued pointed out in detail that in 2013 alone, China produced approximately 1 billion tons of construction waste, while only approximately 50 million tons of the waste were used, which equates to a utilization rate of only 5%. RAC is a concrete prepared by recycling or processing waste concrete to replace natural aggregate completely or in part [5], and its promotion can reduce the exploitation of natural sand and gravel greatly. It can realize the recycling of waste concrete and meet the requirements of “green sustainable development.”. Luisa et al [6] studied recycled coarse aggregate’s (RA) effect on concrete’s mechanical properties when different replacement ratios of natural aggregates were used and indicated that the concrete’s compressive and tensile strength and elasticity were prepared regardless of the amount of natural aggregate RA. In the case of sulfate attack, the RAC’s quality loss rate and relative dynamic elastic modulus were studied macroscopically. e degradation law and microscopic analysis of RAC’s microstructure and chemical elements were evaluated with XRD and SEM, and the data were processed by the Wiener probability distribution method to predict RAC’s life
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