Evaluating salt-freeze damage in concrete and mortar: Interfacial transition zone vulnerability and non-destructive estimation of mechanical degradation

Abstract

This study investigated the degradation mechanisms of concrete and mortar exposed to sodium chloride attack and freeze-thaw cycles. A comprehensive experimental program has been conducted, including mechanical testing (flexural, splitting, and compressive strength), chloride penetration analysis, and mercury intrusion porosimetry (MIP) tests to examine pore structure changes. The results demonstrated that concrete suffered significant reductions in mechanical strength after repeated salt-freeze cycles, with flexural and splitting tensile strengths decreasing by 35.33 % and 37.95 %, respectively, after 75 cycles. Chloride ions penetrated deeper into the concrete matrix compared to mortar. The interfacial transition zone ITZ was found to be susceptible to chloride ion ingress, leading to accelerated degradation. A novel salt frost damage index was introduced that enhanced the accuracy of damage quantification by incorporating corrections for unsaturated conditions. A predictive model was developed based on salt frost damage index. This model enables the non-destructive assessment of concrete's mechanical performance and provides a reliable tool for evaluating the mechanical degradation under after-freeze damage.