The Effect of Ultraviolet Modification on the Performance of Polyamide Fiber-Reinforced Cement Mortars: Optimization and Characterization Using Response Surface Methodology

In this study, a UV surface modification method was applied to polyamide (PA) fibers, and its effect on certain fresh and hardened properties of fiber-reinforced cementitious systems was investigated. Within the scope of the study, the individual and interactive effects of fiber volume fraction and UV surface modification time were optimized using the Response Surface Methodology (RSM) based on Central Composite Design (CCD). The optimal performance parameters with CCD were identified at 0.50% fiber content and 18 min of UV exposure. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were utilized to analyze the fibers and examine the impacts of surface modification. Three different sample groups were prepared to test the effect of UV treatment after optimization: a control cement mortar without fibers, a polyamide fiber-reinforced mortar without UV treatment, and a polyamide fiber-reinforced mortar with UV surface modification. The tensile, flexural, and compressive strength values of the specimens were determined. The results indicated that UV surface modification led to changes in fiber roughness and an increase in oxygen-containing functional groups on the fiber surface. The data revealed that the mechanical performance of fiber-reinforced composites subjected to surface modification improved (with a 27.4% increase in flexural strength and an 11.3% increase in compressive strength compared to the control samples). The findings indicate that UV surface modification improves the fiber–matrix bond in cement-based systems reinforced with polyamide fibers. UV surface modification emerges as an effective and environmentally friendly method for enhancing the performance properties of fiber-reinforced cement-based systems.