Effect of nano‐silica on the mechanical performance and porosity evolution of concrete under freezing and thawing cycles

Abstract The enhancement of freeze–thaw resistance in concrete is crucial for improving the durability and longevity of infrastructure in cold regions. Although the benefits of nano‐silica (NS) on concrete's freeze–thaw resistance have been demonstrated, there is still controversy surrounding the optimal concentration of admixture and underlying mechanisms. In this study, the mechanical performance (mass weight, elastic modulus, compressive and splitting strength) and porosity evolution (total porosity, porosity distribution and micro‐surface morphologies) of control concrete and concrete modified with five different NS admixture concentration (1%–5%) were tested under freezing and thawing (F–T) cycles, and damage models were established to assess the correlations between macroscopic and microscopic damages. The results indicate that F–T cycles lead to both damage in mechanic properties and porosity in concrete specimens. The effects of NS particles on macroscopic and microscopic damage under F–T conditions depend on their admixture concentration. A 2% concentration mitigates while a 5% dosage promotes both macroscopic and microscopic damages during F–T cycles. These differences can primarily be attributed to different dispersion status of NS particles in concrete, leading to variations in porosity evolution during F–T cycles. The macroscopic damage exhibit stronger correlation with microscopic damage factor modified by proportion of large pores compared to that only based on total porosity, suggest that the microscopic damage, especially large pores' proportion, contribute to macroscopic damage of concrete specimens under F–T cycles. These findings provide valuable references for field concrete engineering applications in cold areas.