Developing strain-hardening ultra-rapid-hardening mortar containing high-volume supplementary cementitious materials and polyethylene fibers

This study aims to develop a robust strain-hardening ultra-rapid-hardening mortar (URHM) with high-volume cementitious materials and polyethylene (PE) fibers. To achieve this, the combined effect of cement kiln dust (CKD) and silica fume (SF) on the initial hydration process of ultra-rapid-hardening cement and the tensile performance of URHM was analyzed. Optimum amounts of CKD and SF of 0.15 and 0.2, respectively, by weight ratios to cement, were determined to develop the strain-hardening URHM containing 2% PE fibers. As a result, the tensile strength of 7.3 MPa, strain capacity of 5.12%, and energy absorption capacity prior to tension softening of 297.5 kJ/m³, respectively, were achieved at a very early age (4 h) of air-drying curing. The tensile performance of URHM deteriorated when the CKD content was 0.4 or greater, regardless of the SF content. A lower SF content of 0.2 was effective in terms of the tensile performance enhancement compared with the higher content of 0.4 up to the CKD content of 0.2, but they became similarly lower at higher CKD contents due to insufficient initial hydration.