Balancing sustainability, workability, and hardened behavior in the mix design of self-compacting concrete

The specific physical properties of each byproduct added to a concrete mix significantly condition its in-fresh behavior. Its hardened performance, mainly a function of its compressive strength, is also affected by such aspects as porosity and interfacial transition zones (ITZs). A mix design that includes industrial residues must therefore be properly balanced, minimizing any negative effect of the byproduct, for optimal concrete performance in both states. Among the many industrial residues used in concrete, recycled concrete aggregate (RCA) differs from natural aggregate (NA), due to its notably different water absorption levels, an extremely relevant aggregate property in the mix design of concrete. In this chapter, these and other aspects of RCA are evaluated for achieving balanced designs of self-compacting concrete (SCC), a flowable concrete that is highly sensitive to changes in its composition. Therefore, proper estimation of a balanced amount of RCA added to the mix is necessary, which must simultaneously guarantee both good in-fresh and good hardened properties, while maximizing the sustainability of recycled SCC.