Thermo-mechanical behavior of mass concrete with promising ultra-fine SCMs: A multi-scale experimental and numerical study

Mass concrete structures face critical challenges regarding thermal cracking and durability, yet conventional evaluation methods based on standard curing fail to predict material performance under realistic thermal histories. This study systematically investigates the thermo-mechanical behavior of mass concrete containing four ultra-fine supplementary cementitious materials (SCMs): ultra-fine steel slag (USS), ultra-fine limestone powder (ULS), ultra-fine phosphorus slag (UPS), and ground fly ash (GFA). A multi-scale framework was established, integrating hydration kinetics testing, finite element analysis (FEA) for temperature field simulation, and mechanical/durability testing under temperature-matching curing conditions. Numerical and experimental results indicate that USS effectively reduced the early-age hydration heat peak while maintaining long-term strength comparable to fly ash. Conversely, GFA and ULS exacerbated early heat release due to high reactivity and nucleation effects, respectively. Notably, a high replacement level (45 %) of UPS successfully suppressed the initial heat peak through the dilution effect, while the subsequent temperature rise activated its latent reactivity, significantly enhancing late-age compressive strength and chloride resistance. The study confirms that an integrated approach combining numerical simulation and temperature-matching curing offers a more reliable method than conventional screening for selecting SCMs in mass concrete, effectively balancing the competing demands of low early-age heat and high long-term performance.