Quantification and characterization of the microstructural damage of recycled aggregate self-compacting concrete under cyclic temperature changes

Recycled Aggregate (RA) usually increases porosity and weakens Interfacial Transition Zones (ITZs) of concrete, which favors the appearance of internal thermal damage. Four Self-Compacting Concrete (SCC) mixes with coarse and fine RA were subjected to positive and negative cyclic temperature variations to characterize their thermal damage and quantify its effects. Two damage mechanisms were found. On the one hand, micro-cracks appeared in the ITZs. On the other hand, micro-cracks arose from the micro-pores and propagated through the cementitious matrix. Both damage mechanisms were promoted by the use of coarse and fine RA, respectively. The damage was most notable at sub-zero temperatures and when adding coarse RA. Furthermore, it primarily affected compressive strength, although ultrasonic pulse velocity and hardened density also decreased, which served as non-destructive indicators to indirectly quantify the level of thermal internal damage of SCC.