Performance Assessment of Repair Mortar of Concrete Structures Exposed to Sulfate Physical Attack, Dry–Wet Cycles, and Freeze–Thaw Cycles

The environmental exposure conditions for concrete structures could be very severe in some areas, which makes the application of repair mortar to restore their performance particularly challenging. This study investigated the durability of an optimized repair mortar that was exposed to multienvironmental conditions, which included sulfate physical attack, dry–wet, and freeze–thaw cycles. The repair mortar was first optimized by employing an orthogonal mix design method and an efficiency coefficient method that incorporates silica fume (SF), sodium silicate (SS), basalt fiber (BF), and a united expansive agent (UEA). Its properties, which include workability, compressive strength, and length change at different curing ages, were evaluated. The top three optimized mixes were then selected for durability tests (which include visual inspection, mass change, and compressive strength after being exposed to the combined environmental conditions). The experimental results showed that the optimized mortar exhibited strong erosion resistance under combined sulfate attack, dry–wet, and freeze–thaw cycles. In addition, interfacial bonding tests were performed between the optimized mortar and the existing substrates with different concrete strength grades. In most cases, failure initiates primarily in the existing substrate. Finally, prediction models for the compressive strength of the optimized mortar were developed. These models could be used to predict the mechanical behavior of the optimized mortar after exposure to severe conditions, which could provide valuable guidance for designing repair mortars and evaluating their performance in harsh environments.