Influence of UV-treated polypropylene fibres on residual compressive strength of cement paste

Abstract. Concrete can experience high temperatures in various situations, including accidental fire. It is known that high temperature degrades the material, disintegrates calcium silicate hydrate (C-S-H), and decreases compressive strength. Polypropylene fibres (PPF) are often added to concrete to reduce its likelihood of spalling when exposed to fire. However, it is also known that the addition of PPF tends to reduce the compressive strength, probably because the PPF doesn’t bond well to the cement due to the hydrophobic nature of PPF. So, this research investigates the efficacy of ultraviolet treatment of polypropylene fibers (UV-TPPF) in enhancing the residual compressive strength of cement paste. Results indicate that UV-TPPF significantly increases the compressive strength of cement paste at ambient temperature, achieving improvements of 24%, 16%, and 10% for PPF additions of 2%, 3%, and 4%, respectively. At elevated temperatures, UV-TPPF samples maintained higher residual compressive strength than non-treated polypropylene fibre (NON-TPPF), showing peak strength increases of 32%, 25%, and 6% at 200°C for respective PPF contents. These enhancements are attributed to the improved bond between the UV-TPPF and cement paste due to changing the surface chemistry of PPF from hydrophobic to hydrophilic. This study demonstrates that UV-TPPF offers a promising approach to mitigating the adverse effects of high temperatures on concrete strength.