Study on the Compressive Mechanical Properties of Recycled Aggregate Expansive Concrete

Abstract

Recycled aggregate concrete (RAC) is a promising low-carbon alternative to conventional concrete, yet its higher porosity and weaker interfacial transition zones (ITZs) often lead to reduced stiffness and increased deformation, which may amplify shrinkage-related serviceability risks. This study investigates the 28-day uniaxial compressive response of RAC incorporating a magnesium-oxide expansive agent (MEA) using a full factorial matrix. Twelve mixtures were prepared at a fixed water-to-binder ratio of 0.40 by crossing recycled coarse aggregate (RCA) replacement levels (0%, 30%, and 50%) with MEA dosages (0%, 6%, 8%, and 10% by binder mass). Cube specimens (100 mm) were tested under displacement control, and peak stress, peak strain, and static elastic modulus were obtained from the recorded load–deformation data; the modulus was evaluated by linear regression on the ascending branch within 0.2–0.5 of the peak stress. At 0% MEA, increasing RCA replacement decreased peak stress from 38.0 MPa to 33.4 MPa and reduced modulus from 32.0 GPa to 26.4 GPa, while peak strain increased from 1.75*10?3 to 2.30*10?3. Across all RCA levels, MEA exhibited a non-monotonic effect: a modest improvement at 6% was followed by strength and stiffness reductions and higher peak strain at 8–10%, indicating a limited beneficial dosage window. The coupled trends suggest that deformation-related performance of MgO expansive RAC should be assessed using measured pairs of stiffness and strain capacity rather than peak stress alone. Given n = 1 per mixture at 28 days, the findings are interpreted as trend-based observations and motivate further replicated testing and microstructural verification.