Experimental Investigation on the Mechanical Performance of Sustainable Hybrid Fiber-Reinforced Concrete Incorporating Silica Fume and GGBS

Abstract

The construction industry's reliance on ordinary Portland cement (OPC) is a major contributor to global anthropogenic CO₂ emissions, while plain concrete's inherent brittleness and low tensile capacity remain persistent structural limitations. This study presents an experimental investigation into a sustainable hybrid fiber-reinforced concrete (HFRC) of M30 grade, formulated by partially replacing cement with Ground Granulated Blast Furnace Slag (GGBS, 20–50% by weight) and silica fume (5–25% by weight), together with a fixed 2% (by volume of coarse aggregate) hybrid dosage of steel and polypropylene fibers. Six mix combinations were cast and evaluated for compressive, flexural, and split tensile strength at 7, 14, 28, and 60 days of water curing. Compressive strength increased consistently with binder replacement up to 50% GGBS and 20% silica fume, after which higher silica fume content (25%) reduced strength due to workability loss and particle agglomeration. The mix containing 50% GGBS, 20% silica fume, and 2% hybrid fiber (designated M5) produced the best overall performance, reaching 36 MPa compressive strength, 5.3 MPa flexural strength, and 4.1 MPa split tensile strength at 28 days, rising further to 40 MPa, 5.7 MPa, and 4.5 MPa respectively at 60 days. Relative to the mix with the lowest replacement level (M1: 20% GGBS, 5% silica fume), mix M5 showed gains of approximately 24% in compressive strength, 29% in flexural strength, and 41% in split tensile strength at 28 days. The results confirm that the combined pozzolanic action of silica fume and GGBS densifies the cementitious matrix, while the hybrid steel–polypropylene fiber system restrains crack propagation and improves post-cracking ductility. The study establishes 50% GGBS with 20% silica fume and 2% hybrid fiber as the optimum replacement level for producing high-performance, low-carbon M30 structural concrete. Keywords: Sustainable concrete; Hybrid fiber reinforcement; Ground Granulated Blast Furnace Slag (GGBS); Silica fume; Compressive strength; Flexural strength; Split tensile strength.