Enhancing the Sustainability of Concrete by Adding Recycled Sand and Silica Fume Along with Human Hair Fibers

This experimental study produced recycled sand–silica fume–hair fiber concrete to enhance concrete sustainability. Recycled sand and silica fume can be used to address the environmental issues caused by excessive river sand mining and the carbon footprint of the concrete industry. In addition, waste hair fibers (0.5–2%) were introduced to enhance the properties of newly developed concrete mixes. The absolute volume method was employed for four newly developed sustainable concrete mixes. A 100 mm slump was set as a structural concrete requirement, which was maintained by adding 0.5%, 1%, 1.4%, 1.9%, and 2.6% of the admixture by weight of the cement to the proposed mixes. The compressive strength, splitting tensile strength, and density of the hardened concrete mixtures were estimated. The study results show that combining optimized 10% silica fume with 0.5–2% hair fibers enhanced the properties of the newly developed sustainable mixes. The slump threshold was met when 1.5% of hair fibers were mixed with 10% silica fume, 50% manufactured sand, and 50% recycled sand. However, the splitting tensile strengths of the mixes with 1.5% and 2.0% hair fibers were found to be almost the same at 5.62 MPa and 5.65 MPa, respectively. The bulk density of the mixes increased with increasing percentages of hair fibers. Furthermore, in the mixes with 1.5% and 2.0% hair fibers, the bulk density was very similar at 2.708 g/cm3 and 2.792 g/cm3, respectively. Thus, it can be concluded from the study results that concrete containing recycled sand, silica fume, and hair fibers in optimal percentages is acceptable as structural concrete.