On the mechanical properties of recycled aggregate concretes and their correlations with the hydration processes

This study addresses the mechanical behaviour of structural concretes made with recycled concrete aggregates (RCA). Particularly, it is intended at investigating the influence of some critical parameters on the actual development of the cement hydration reactions and, then, on the time evolution of the concrete compressive strength. To this end, a wide research was carried out at the Laboratory of Materials testing and Structures (LMS) of the University of Salerno. Since the results of that comprehensive campaign are reported within a companion paper, only the key information about the composition of the ten tested mixtures and the relevant experimental observations in terms of both temperature monitoring and cubic compressive strength development in curing concrete samples are outlined herein. Then, the temperature measurements are considered to calibrate the parameters of a theoretical model already presented by the authors to simulate the cement hydration process in curing concrete: the fundamental assumptions of this model are briefly outlined herein. The numerical results obtained for such parameters, which characterise the ten concrete mixtures under consideration, are finally related to the corresponding mixture compositions. The resulting correlations unveil the fundamental influence of aggregate replacement ratio, nominal water/cement ratio and initial moisture conditions of coarse aggregates, on the mechanical properties of concrete made with recycled aggregates.