Surface modification of UHMWPE fibers from hydrophobic to hydrophilic and hydrophilic-roughened for enhanced fiber/matrix interfacial bonding in strain-hardening cementitious composites (SHCC)

This study investigates the fiber/matrix interfacial bonding mechanism considering hydrophobic, hydrophilic, and hydrophilic-roughened fibers in Strain-Hardening Cementitious Composites (SHCC). Ultrahigh molecular weight polyethylene (UHMWPE) fibers (P-fibers) were modified using an amphiphilic modifier entrapment technique to enhance their hydrophilicity (I-fibers) and further coated with nanoclay to increase their surface roughness (I-NC-fibers). Surface characterizations including wetting behavior, FTIR, and SEM–EDX analysis were used to confirm the effectiveness of the modification techniques. The mechanical performance of SHCC reinforced with the three types of fibers was evaluated using uniaxial tensile tests. Compared to P-fibers, incorporating I-fibers and I-NC-fibers into SHCC increased the first-cracking tensile strength by 43.3% and 62.2%, ultimate tensile strength by 19.1% and 50.4%, and strain capacity by 21% and 45.7%, respectively. Single-fiber pull-out tests further validated the findings, showing that I-fibers and I-NC-fibers exhibited enhanced interfacial frictional stress of 17.4% and 50.4%, and pull-out energy of 20.5% and 65.2%, respectively. The superior mechanical performance of SHCC can be attributed to the improved chemical bond fracture energy, frictional bonding stress, and pull-out energy at the fiber/matrix interface. Through micromechanical analysis, high pseudo strain hardening indicators, \({PSH}_{strength}\) and \({PSH}_{energy}\) , also ensured the saturated cracking and stable strain hardening behavior of SHCC reinforced with I-fibers and I-NC-fibers under tensile loading.