Optimization of Steel-Polypropylene Fiber Ratio in Graphene Oxide-Modified Ultra-High Performance Concrete for Enhanced Compressive Strength

Abstract

Ultra-High Performance Concrete (UHPC) has attracted increasing attention for advanced structural applications due to its high compressive strength and dense matrix. However, its brittle behavior and susceptibility to crack propagation remain important limitations. This study investigates the optimization of hybrid steel fiber (SF) and polypropylene fiber (PPF) ratios in graphene oxide (GO)-modified UHPC, with emphasis on compressive strength performance. UHPC and/or High Strength Concrete (HSC) specimens were prepared using Ordinary Portland Cement, Class F fly ash, river sand, GO solution, hooked steel fibers, polypropylene fibers and superplasticizer. Cube specimens were tested at curing ages of 7, 14 and 28 days using the compression testing procedure described in the methodology. The results showed that the hybrid combination of 2.0% SF and 0.15% PPF produced the highest 28-day compressive strength of approximately 121.8 MPa for UHPC. The strength enhancement is attributed to the complementary function of steel fibers in crack bridging and stress transfer, and polypropylene fibers in microcrack control. However, excessive fiber content reduced compressive strength due to lower workability, fiber agglomeration and possible void formation. The findings indicate that an optimized hybrid fiber system can improve the compressive strength performance of UHPC. Further microstructural, flexural and durability investigations are recommended to validate the proposed mechanisms.