Autogenous-shrinkage model for concrete with coarse and fine recycled aggregate

Autogenous shrinkage of recycled-aggregate concrete (RAC) is important for design of concrete structures with recycled aggregate, however, there are few studies on this critical topic. To address this, an experimental research study was undertaken to investigate the autogenous shrinkage of RAC made with fine and coarse recycled aggregate (termed FRA and CRA, respectively) to support the modification of existing shrinkage models to account for the effects of these aggregates. The experimental study investigated replacement ratios of 0%, 50% and 100% of one type of CRA and two types of FRAs; 15 mix designs were considered in total. Measurement of autogenous shrinkage was conducted on 30 specimens (two specimens for each mix design) for 360 days. Test results showed: (1) both FRA and CRA significantly reduced the autogenous shrinkage of RAC and (2) the influence of FRA is more significant with increasing content of CRA, and vice versa. Based on these results, a modified autogenous-shrinkage model for RAC was proposed, which accounts for the reduced aggregate stiffness and the additional water induced by CRA and FRA. The model provides an accurate prediction of the autogenous shrinkage of RAC.