Effects of fiber type and content on the mechanical and water transport properties of ultra-high performance concrete

Incorporating short fibers into ultra-high-performance concrete (UHPC) enhances mechanical properties but may negatively impact durability by altering fluid transport characteristics. However, the combined effects of fiber type and dosage on both mechanical and transport performance remain underexplored. This study experimentally investigates the influence of fiber type (steel, polyethylene, and basalt) and volume fraction (0.5% and 1.0%) on UHPC properties. Seven mixes were prepared, including six fiber-reinforced and one plain UHPC. Mechanical performance was evaluated through compressive and tensile tests, while transport properties were assessed using capillary water absorption and permeability measurements. Results showed that steel fibers provided the greatest strength enhancement but slightly reduced resistance to fluid ingress due to increased maximum pore size. PE fibers achieved a more balanced performance, offering moderate strength improvement while maintaining low sorptivity and permeability. Basalt fibers effectively preserved resistance to fluid ingress but yielded only limited mechanical gains. These findings highlight the importance of selecting appropriate fiber types and contents to optimize the performance of UHPC in structural applications where both strength and controlled fluid ingress are critical. ● Steel fibers maximize strength but slightly reduce water resistance. ● PE fibers balance strength gain and transport performance. ● Basalt fibers best control permeability with limited strength gain. ● Fiber type and dosage must balance strength and durability.