Effect of nano-TiO 2 and polypropylene fiber on the performance of alkali-activated slag-fly ash geopolymer mortar under −10 °C curing

This paper aims to evaluate the effects of pre-curing time (2 h and 4 h), single-doped nano-TiO2, and polypropylene fiber (PPF) on the properties of alkali-activated slag-fly ash geopolymer mortar (AASFM) cured at −10 °C. The physical and mechanical properties such as setting time, ultrasonic pulse velocity, compressive strength, and flexural strength of AASFM were tested, and the microscopic mechanism was analyzed using a scanning electron microscope and mercury intrusion porosimetry (MIP). The results revealed that a pre-curing time of 2 h and 4 h can significantly improve the mechanical properties of AASFM. Compared with the control group, the compressive strength of AASFM at −7 + 28 days could be increased by 65% under the synergistic effect of pre-curing for 2 h and adding 1.5% nano-TiO2. Likewise, the compressive strength of AASFM could be increased by 73% after pre-curing for 2 h and adding 1.5 kg/m3 PPF. With pre-curing for 2 h and curing for 7 days, the flexural strength of AASFM could be increased by 232% and 236% by adding 1% nano-TiO2 and 0.5 kg/m3 PPF, respectively. Therefore, the application of alkali-activated slag-fly ash geopolymer mortar in winter construction has a bright prospect.