Research on mix design of fully recycled concrete based on the pore characteristics and rheological principles of recycled aggregates

To address the issues of significant performance variability and insufficient theoretical support in the mix design of fully recycled aggregate concrete (FRAC) caused by the high porosity and strong water absorption of recycled aggregates, this study starts from the microscopic characteristics of recycled aggregates by introducing the open porosity influence coefficients γ and δ. Based on the particle shape features of the aggregates and integrating the theoretical framework of ''pore adsorption–Mortar filling–skeleton expansion'' with rheological principles, the study introduces surplus coefficients for Mortar, Neat Paste, and Net Water (λs,m, λs,b, λb,w), as well as the minimum Mortar-to-coarse aggregate volume ratio (ω), minimum Neat Paste-to-fine aggregate volume ratio (ε), and minimum Net Water-to-Binder volume ratio (τ). By deriving the calculation formulas and their interrelated models for these parameters based on the physical properties of each component, the study reveals the objective relationship between the macroscopic performance of FRAC and the microscopic characteristics of materials. Through normalization processing, air content adjustment, and coordinated optimization of strength and workability, a universal mix design method suitable for high-fluidity FRAC is established. The research findings provide a theoretical foundation and technical solution for the commercial application of FRAC.