Improvement of the durability of concrete with recycled aggregates in chloride exposed environment

Abstract

Recycled aggregates concrete (RAC) becomes an important participant in recycled materials, although there are still questionable issues about some of its properties. Durability of RAC and its relationship with recycled concrete aggregate (RCA) is often discussed, especially in relation with chloride penetration and diffusion properties. An extensive experimental campaign was performed in order to evaluate the effect of RCA content in the retention and diffusion of chlorides in RAC. The influence of composition and mix design of the concrete was first studied using only a 20% replacement of natural aggregate by recycled aggregate. The 20% replacement was chosen in order to comply with Spanish recommendations for structural concrete. The 20% replacement was chosen in order to comply with Spanish recommendations for structural concrete. In the second part of the study concrete mixes ranging from 0.45 to 0.65 w/c ratios, with 0%, 20%, 50% and 100% coarse aggregates replacement were tested. Cement pastes, recycled aggregates and concretes were submitted to saline attack and the total chloride contents were determined. Chloride penetration profiles were determined by means of the NT BUILD 443 specifications. XRD and SEM aided the chlorides binding determination. A chlorides retention phenomenon is detected by the average diffusion coefficient decrease in RAC, thus compensating the RCA higher permeability. According to chloride binding and diffusion results, high RCA content lead to an improvement of durability in RAC with sufficiently low w/c ratio, in terms of chlorides attack.