Durability and Microstructural Performance of Self-Compacting Concrete Made with Recycled Aggregates

Abstract

The present study investigates the durability and microstructural behavior of self-compacting concrete (SCC) made with recycled aggregates (RA) under aggressive environmental conditions, including sulfate, acid, and chloride attacks. Three RA replacement ratios (0%, 50%, and 100%) were examined. The study evaluates the influence of RA on the chemical resistance of SCC, supported by microstructural analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results reveal that RA content influences the performance of SCC in aggressive environments. Under sulfate exposure, the mix with 100% RA showed higher expansion rates (96% in magnesium sulfate and 53% in sodium sulfate) compared with the control mix (64% and 24%, respectively). Similarly, in acid environments, the 100% RA mix exhibited greater mass loss (12.6% in sulfuric acid and 9.2% in hydrochloric acid) than the control mix (7% and 5.7%, respectively). Furthermore, chloride penetrability increased with RA content, as evidenced by a higher charge passed, from 3,378 coulombs for the control mix to 4,586 coulombs for the 100% RA mix at 28 days. Microstructural analysis identified the formation of expansive products such as ettringite and gypsum in sulfate-exposed samples, while acid exposure led to the formation of calcium chloride and non-expansive salts, contributing to material changes. The study highlights that attached mortar play a significant role in the behavior of SCC under aggressive conditions. These findings demonstrate that RA can be effective when used in SCC, though careful consideration of its properties is essential to ensure performance in challenging environments.