Damage to recycled concrete with different aggregate substitution rates from the coupled action of freeze-thaw cycles and sulfate attack

Abstract

To study the frost resistance of recycled concrete in a sulfate-rich environment, we prepared recycled concrete with 0%, 30%, 50%, and 100% recycled aggregate replacement rate. The physical and mechanical properties of the recycled concrete in the coupled action of freeze-thaw cycles and a sulfate environment for different replacement rates of aggregate was then studied. We analyzed the micro-structure and the reaction products of the recycled concrete. We used a two-factor Weibull distribution model to establish the damage equation, then predict the service life of the recycled concrete. The results show that when the replacement rate of recycled aggregate increases, the physical and mechanical properties of the recycled concrete gradually deteriorate in the later stages of the freeze-thaw test. When the number of freeze-thaw cycles increases, ettringite and gypsum are gradually formed due to the reaction with sulfate. The Weibull model accurately describes the damage variation in the recycled concrete. Through the prediction of the service life of the recycled concrete, we found that the durability was reduced. Given our analysis, we found that the proportion of recycled aggregate should not exceed 30% to meet the requirements for durability design of a concrete structure in China (GB/T 50746-2008).