Tensile behavior of ultra-high-performance concrete (UHPC) strengthened with fiber reinforced polymer (FRP) grid

In order to enhance the tensile strength and toughness of Ultra-High Performance Concrete (UHPC) at the macro level, this study developed Fiber-Reinforced Polymer (FRP)-reinforced UHPC composite materials. The steel fibers and FRP grids in UHPC play a reinforcing and toughening effect on UHPC at two different levels. Therefore, this paper examined, evaluated 48 FRP grid-UHPC specimens. The study includes independent parameters such as grid type (Carbon-FRP, Basalt-FRP, stainless steel wire mesh), grid size (5×5 mm, 10×10 mm, 20×20 mm), steel fiber content (0%, 0.5%, 1.0%, 1.5%, 2.0%), grid layers (1 layer, 2 layers, 3 layers, 4 layers), and the fiber bundle impregnation status. Based on the test results, a simplified tensile stress-strain relationship for FRP grid-UHPC was proposed. The test results show that when the steel fiber content is less than 1%, the FRP grid does not exert its reinforcing effect. The FRP grid-UHPC composite material exhibits strain-softening behavior. However, when the steel fiber content is greater than 1%, the FRP grid-UHPC specimens all exhibit strain-hardening phenomena. Compared to other grids type, the enhancement and toughening effects on UHPC are more pronounced when using CFRP grids. Specifically, when using a 20×20 mm CFRP grid, the tensile stress can be increased by 30.36%. Regardless of whether dry grids or impregnated grids are used, increasing the grid layers greatly improves the peak strain and stress of UHPC. Compared to dry grids, impregnation with epoxy resin further improves the stress state between fiber filaments in FRP grids, resulting in a more significant improvement in the tensile performance of FRP grid-UHPC composite materials. Finally, based on experimental data, a tensile stress-strain model for FRP grid-UHPC considering different mesh ratios was proposed and validated against experimental results. These conclusions and findings are of great significance for understanding and optimizing the performance of FRP grid-UHPC composite materials, providing valuable references for the future research and application of FRP grid-UHPC composite materials.