Investigation of the Mechanical and Fracture Properties of Recycled Aggregate Concrete

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Abstract
This study investigates the effects of incorporating recycled coarse aggregates (RCAs) at different substitution rates on the mechanical and fracture properties of recycled aggregate concrete (RAC). Four concrete mixtures were prepared: a reference mixture using natural coarse aggregates (NCAs) and three RAC mixtures in which 30%, 60%, and 100% of the NCA mass was replaced with RCAs. The RAC mixtures were compared to natural aggregate concrete (NAC) in terms of compressive strength, splitting tensile strength, modulus of elasticity, hydration rate, water-accessible porosity, pore size distribution, post-peak behavior, and fracture energy. The results show that as the RCA substitution rate increases, the RAC porosity rises and its modulus of elasticity decreases. However, the compressive strength and splitting tensile strength remain comparable to, or even exceed, those of NAC, with optimal performance observed at a 60% substitution rate. This optimal behavior can be attributed to a more favorable pore distribution and an increased hydration rate. For an equivalent strength class, RAC with up to 60% RCA substitution exhibits post-peak behavior and fracture energy comparable to NAC. However, at a 100% substitution rate, the behavior becomes more brittle, and fracture energy decreases by 23.20%.

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