# Effect of Human Hair Fibers on the Performance of Concrete Incorporating High Dosage of Silica Fume
## 1 Introduction  
Concrete, a material developed millennia ago, is used to construct the vast majority of modern constructions. However, after the discovery of Portland cement in the early 1800s, the term was widely employed. Nonetheless, in recent years, rigorous study and progressive work in academia and industry have given hope to a new, innovative, and eco-friendly material [1]. New cementitious binders, with optimal mix designs and enhanced casting methods, have reduced the carbon footprint of cement while also increasing its strength [2, 3]. Concrete cracks are unavoidable, and they should be repaired for long-term durability. The main reason for this is that only small cracks can heal completely [4]. A structure's service life mainly depends on the durability properties of the concrete. Concrete's long-term durability has always been a source of concern for researchers and structural engineers. The research community agrees that the durability of concrete is primarily affected by various cracks that form due to multiple types of loads during its service life. These flaws allow hazardous substances such as alkalis, sulfates, and chlorides to permeate the concrete structure, eventually causing concrete deterioration [4, 5, 6]. Different reinforcements are utilized to reduce cracks and minimize damages; fiber reinforced concrete (FRC) performsbetter than plain concrete. Because concrete is a weaker material when subjected to tensile stresses; various fibers such as synthetic, natural, and steel fibers are used to improve their flexural and tensile properties. [6; 7; 8; 9; 10] Microfibers (human hair fibers) are added to the concrete mixture because they control the formation of many small cracks. Macrofibers are used to bridge macro cracks, allowing for reducing crack widths from micro to macro [11; 12; 13]. Combining the two types of fibers could be a novel way to increase the durability of concrete constructions [14; 15; 16]. The current human population is almost 7.7 billion people, and it is estimated that \(6.9\times 10^{5}\) tonnes of hair are produced each year. Human hair fiber is composed of around 80% protein, which contains a high sulphur content generated by the amino acid cysteine, which distinguishes it from other keratin proteins. Keratin is a laminated complex that contributes to the hair's cylindrical structure, strength, durability, elasticity, and functioning. At the molecular level, hair strands have an incredibly stiff structure that provides mechanical resistance and flexibility [17; 18; 19]. In SF, having a dense structure helps reduce the voids in the concrete matrix. [PERSON] et al. showed that silica-enhanced concrete had 24-38% less voids than control mix. Test results further explained that SF-based concrete's performance was better in compressive strength, pore structure, water sorptivity, and surface radon exhalations [20]. [PERSON] and [PERSON] et al., [21] studied SF enriched concrete using mercury intrusion porosimetry (MIP) and isothermal calorimetry experiments, respectively, to examine the microstructure and hydration kinetics. Field emission scanning electron microscopy (FE-SEM) was also used to analyze the influence of SF addition on the concrete matrix's microstructure. The results showed that porosity decreased, and compressive strength, flexural strength, and split tensile strength improved. Concrete's dense matrix promotes excellent durability capabilities, possibly the material's most significant advantage. This durable concrete allows structures to survive longer, reduces repair costs, and contributes to more sustainable infrastructure. Sustainable resources such as SF, fly ash, and carbon black, among others, can be used to densify concrete matrix [22]. To corroborate this, the performance of M20-grade concrete was studied using human hair fiber (HHF) in various percentages ranging from 0% to 5%. Ref. [23] discovered that SF matrix has a considerable increase in chemical resistance to most salts and acids. In SF concrete, mechanical erosion resistance improved slightly.