Optimizing characteristics of high-performance concrete incorporating hybrid polypropylene fibers

Abstract The purpose of this investigation is to assess and optimize the impact of hybrid polypropylene fibers (coarse monofilament and staple fibers) on the mechanical characteristics and resistance to elevated temperature of high-performance concrete. Concrete mixtures were designed using central composite design under response surface methodology. Slump test, compressive strength, flexural strength, impact test, elevated temperature resistance and microstructure of concrete were the tests performed. The slump values were slightly decreased with the addition of polypropylene fibers. Concrete mixtures reinforced with hybrid polypropylene fibers have significantly improved in terms of compressive strength and flexural strength ranged from 1.96% to 12% and 14.28% to 41.9%, respectively, at age 56 days compared to control mixture without fibers. The hybridization of 5 kg monofilament and 0.75 kg staple fibers achieved the highest compressive strength (84.6 MPa), flexural strength (14.9 MPa), and the optimum impact resistance at age 56 days. The increase of coarse monofilament fibers significantly improved the spalling resistance performance. The residual compressive strength of mixture containing 5 kg monofilament and 0.75 kg staple fibers up to 63.8% of the initial strength after exposure to 800 C0. Strong relationships were obtained for predicting and optimizing compressive and flexural strength of concrete incorporating hybrid polypropylene fibers.