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.

Automated summary

Recycled Aggregate (RA) increases porosity and weakens Interfacial Transition Zones (ITZs) of concrete, leading to internal thermal damage. Four Self-Compacting Concrete (SCC) mixes with coarse and fine RA underwent cyclic temperature variations to characterize and quantify thermal damage. Two damage mechanisms were identified: micro-cracks in ITZs and micro-cracks from micro-pores propagating through the cementitious matrix. Coarse and fine RA enhanced these damage mechanisms respectively, with the most significant damage occurring at sub-zero temperatures and with the addition of coarse RA. Compressive strength was primarily affected, while ultrasonic pulse velocity and hardened density served as non-destructive indicators to indirectly quantify the level of thermal internal damage of SCC.