Highly ductile ultra-rapid-hardening mortar containing oxidized polyethylene fibers

This study aims to develop a strain-hardening ultra-rapid-hardening mortar (URHM). A mixture of calcium sulfoaluminate (CSA) cement, ordinary Portland cement (OPC), and gypsum was used to prepare the ultra-rapid hardening cement along with 2% (by volume) polyethylene (PE) fibers. The PE fibers were oxidized by plasma and chromic acid treatments to achieve a robust strain-hardening characteristic. Test results indicated that the tensile strain-hardening behavior of the URHM was achieved in only 4 h of air-drying curing and further improved through surface treatments. The compressive strength of the URHM with untreated PE fibers at 4 h and 28 d of air-drying curing was found to be 37.9 and 60.0 MPa, respectively, and it was slightly enhanced by using the treated PE fibers. Tensile strength and energy absorption capacity of about 5.1 MPa and 124.8 kJ/m³, respectively, were achieved for the URHM at an early age (4 h) using the plasma-treated PE fibers. The tensile performance of the URHM improved with the increase in the air-drying curing age and by using oxidized PE fibers. It was identified that the plasma treatments were more effective than the chromic acid treatment. Finally, the highest tensile strength and energy absorption capacity of approximately 9.95 MPa and 381.1 kJ/m³ were observed in the URHM containing oxygen-gas-treated PE fibers after 28 d of curing.