Human hair waste in concrete: A sustainable material for civilian and military uses

Abstract

In a context of environment threatening factors, managing all waste types is an earnest need. The present study aims to explore the advantages of incorporating rising amounts of human hair fibers in concrete and to propose the optimal dosages. The focus was on performances relevant to both civilian and military applications. Concrete was elaborated by partially substituting aggregate volume by short hair fibers HF, with lengths ranging from 2 to 8 mm and dosages varying between 0 and 20 kg/m³. Compared with plain concrete, HF content rise resulted in reductions in both slump and density, with a maximum density decrease of 32%. Peak enhancements in compressive and tensile strengths of 12.56% and 8.73% respectively, were recorded at a dosage of 15 kg/m³, beyond which both resistances decreased. Scanning electron microscopy revealed that these trends arise from antagonist evolutions within the concrete matrix: higher HF contents increase total porosity but also provide a crack bridging action, elucidating the existence of an optimal HF dosage. Furthermore, elevating HF contents enhanced thermal, ballistic and blast load resistances. At a dosage of 20 kg/m³, thermal conductivity was reduced by 50% and concrete slabs exhibited the highest ballistic performance as evidenced by decreases in crater area, penetration depth and lost concrete mass by 65.27%, 11.54% and 70% respectively. A preliminary qualitative assessment of HF inclusive concrete under shock wave loading also demonstrated a significant reduction in crack number and widths. Based on the findings, the present work proposes a recycling procedure that imparts concrete additional protective efficiencies: thermal, anti-ballistic and anti-shock wave. It fosters circular economy practices across both civilian and military sectors.