Experimental study and predictive modeling of compressive strength size effect on recycled aggregate concrete

This paper is about the size effect on the compressive strength of recycled aggregate concrete (RAC), an important consideration for its structural design applications. Although RAC is becoming increasingly prevalent, its size effect has not been sufficiently studied, with current test specimen sizes ranging only from 70 to 200 mm. This range fails to fully capture the size effect seen in actual structural components. Existing formulas for calculating the size effect of RAC are primarily based on experiments conducted by individual researchers, with the coarse recycled aggregate (CRA) replacement ratio as the sole parameter considered. The available experimental data are limited, and the CRAs are typically sourced from a single origin, which fails to consider the impact of varying physical properties of recycled aggregates on the size effect of RAC. To address these research gaps, this study conducted 12 sets of size effect tests on RAC, a total of 36 specimens, using CRA replacement ratios (0 %, 50 %, and 100 %) and specimen diameters (150 mm, 225 mm, 300 mm, and 400 mm) as parameters. A mathematical relationship between residual mortar content and crack propagation range was derived theoretically. Building on crack band theory, a size effect model for the compressive strength of RAC was developed, accounting for the physical properties and replacement ratios of CRAs. The reliability of the proposed model was validated with 156 sets of RAC size effect test data, registering a coefficient of determination ( R ²) of 0.97.