PERFORMANCE EVALUATION OF SUSTAINABLE MATERIALS IN BRIDGE CONSTRUCTION WITH M50 GRADE

Bridge construction is a highly resource-intensive branch of civil engineering, heavily relying on cement, natural aggregates, and steel, which have a significant impact on environmental sustainability. Cement production contributes nearly 8% of global human-caused CO₂ emissions, while aggregate extraction depletes resources and harms ecosystems. Traditional reinforced concrete is prone to durability issues, such as chloride ingress, sulfate attack, and freeze–thaw damage, which increase maintenance costs and shorten its service life. To address this, the current research explores sustainable alternatives by using Class F fly ash as a partial cement substitute and incorporating hybrid fibers (polypropylene and basalt) in M50 concrete. The process involved systematic testing, including material characterization, mix design, specimen preparation, curing, and testing. Fly ash was used at replacement levels ranging from 0% to 10%, and fibers at 0%, 0.05%, and 0.10% by volume. The mixes were evaluated for workability, compressive, flexural, and split tensile strengths, water absorption, and static modulus of elasticity at 7, 14, and 28 days. Comparison with conventional M50 concrete identified enhancements in mechanical properties and durability. Fly ash improved workability owing to spherical particles, while fibers reduced slump but increased crack resistance. Initially, fly ash decreased the compressive strength; however, the optimized mix (10% fly ash + 10% fibers) achieved a maximum strength of 53.1 MPa at 28 days, surpassing the strength of traditional M50 concrete. Flexural and split tensile strengths improved significantly due to the synergistic effect of hybrid fibers in crack bridging and ductility enhancement. Durability was notably improved, with water absorption dropping to 1.45%, indicating a denser and less permeable matrix. The modulus of elasticity also rose, indicating increased stiffness and load resistance. Overall, incorporating supplementary cementitious materials and hybrid fibers into M50 concrete meets structural demands while promoting sustainability by reducing cement use, reusing industrial byproducts, and enhancing durability. This approach helps lower the carbon footprint, conserve resources, and prolong service life, making hybrid fiber–reinforced fly ash concretes a cost-effective, durable, and eco-friendly option for modern bridges.