Micromechanical properties of the concrete interfacial transition zone under freeze–thaw cycling: From experimental characterization to mesoscale simulation

Abstract Freeze–thaw deterioration is a critical durability issue of concrete in cold‐region engineering. As the mechanical weak zone of concrete, the interfacial transition zone (ITZ) between aggregate and cement mortar determines the macroscopic concrete performance. However, existing studies have not clarified the quantitative correlations among nanoindentation hardness ( H IT ), Vickers hardness (HV), and elastic modulus of ITZ under freeze–thaw, and there is a lack of mathematical models directly applicable to numerical simulation. In addition, empirical values are mostly used for ITZ elastic modulus in traditional mesoscale simulation of freeze–thawed concrete, leading to low prediction accuracy. In this paper, a combined micromechanical testing method for ITZ by coupling nanoindentation and microhardness was proposed. The variations in ITZ thickness, H IT , HV, and elastic modulus were systematically measured by comparing specimens under 28‐day standard curing, rapid freeze–thaw in water, and deicing salt solution. The linear relationship between H IT and HV was established, and the mathematical models for the square of ITZ elastic modulus ( E 2 ) with H IT and HV were derived respectively. The E 2 –HV model was further applied to 3D mesoscale numerical simulation of concrete. The results show that freeze–thaw cycles can promote the further hydration of insufficiently hydrated parts in concrete; the ITZ elastic modulus calculated by the proposed model improves the simulation accuracy of freeze–thawed concrete compared with traditional empirical values. The testing method and mathematical models established in this study provide theoretical and technical support for the accurate prediction of freeze–thaw durability of concrete structures in cold regions.