Enhancing the Sulfate Resistance of Composite Concrete Systems: Influence of Steel Fiber Reinforcement on Mechanical Performance

Including ultra-high performance fiber reinforced concrete (UHPFRC) layer in tension with normal strength concrete (NSC) significantly enhances the structural properties of concrete infrastructures. However, the durability of the interfacial bond between the two materials under aggressive chemical exposure remains uncertain. This study investigates the impact of severe magnesium sulfate exposure in conjunction with drying-wetting cycles, a common environmental challenge for infrastructures, on the mechanical properties of composite concrete systems (CCS) consisting of a UHPFRC tension layer and an NSC compression layer. In addition, the effect of varying steel fiber concentrations (0%, 1%, 1.5%, and 2%) in the UHPFRC layer was examined. The results show that the reduction in compressive strength was approximately 40% regardless of the fiber content. However, the use of fibers highly enhanced the mechanical interaction between the NSC and UHPFRC layers, resulting in superior mechanical resistance against the effect of the magnesium sulfate exposure. Adding 1% steel fibers slightly increased toughness, further increasing the fiber content to 2% resulted in a negligible effect on the energy absorption capacity under the severe magnesium sulfate environment.