UHPFRC with Steel-Fiber Surface Functionalized with TEOS

Ultrahigh performance fiber-reinforced concrete (UHPFRC) is a promising composite material, exhibiting compressive strength of around 150 MPa and flexural strength of up to 45 MPa. Despite its impressive properties, the characteristics of the interfacial transition zone (ITZ) between the fiber and the cementitious matrix, which are similar to those in conventional fiber reinforced concrete, significantly influence the behavior of the composite. Since the fiber surface is in direct contact with the ITZ, modifying this interface presents a promising technique to enhance the performance of the composite. In this context, silanes can be used as coupling agents to improve fiber–matrix interactions. This study investigates UHPFRC with the fibers’ surface functionalized using tetraethoxysilane (TEOS) at different proportions: 0.1, 0.5, and 1.0% silane in surface treatments. The analysis was conducted on both fresh and hardened states, evaluating workability and hydration through calorimetry, and flexural and compressive strength through mechanical testing. The results demonstrated that the addition of 0.5% of TEOS improved workability and hydration, showing 7% more heat released in the acceleration period in comparison to the reference (REF) series. The bending results indicated that the sample with 0.5% TEOS in the treatment resulted in an improvement in strength indices up 15% on maximum load, and a 28-day equivalent compressive strength was achieved.