Effects of curing temperature on mechanical properties and pore size distribution of cement clay modified by metakaolin and basalt fiber

Owing to the increase in human activities, a large number of construction and maintenance projects in cold regions are facing problems associated with cement soil materials. Undoubtedly, the cement soil structures are inevitably cured at negative temperature conditions. In the present study, the effects of curing temperature and curing age on the unconfined compressive strength (UCS), splitting tensile strength, E50, and failure mode of cement clay modified by metakaolin (CCM) and cement clay modified by metakaolin and basalt fiber (CCMB) were systematically studied. Moreover, the nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) tests were performed to investigate the characteristics of pore size distribution and microstructure of CCM and CCMB specimens at different curing temperatures. Test results indicate that negative curing temperature leads to the increase of peak strain, as well as the decrease in the decline rate of the post-peak stage of stress-strain curves. In addition, the curing age and positive curing temperature contribute to the increase of cement clay strengths, while the incorporation of basalt fiber shows opposite effects on the UCS and splitting tensile strength of CCMB specimens at two curing temperatures. The meso-pores and large-pores will transform into small-pores and micro-pores with the increase of curing age, and the values of total porosity and the proportion of meso-pores and large-pores of specimens at −10 °C curing temperature are higher compared with that at positive curing environment. Furthermore, negative curing temperature inhibits the cement hydration and destroys the bonding effect between basalt fiber and matrix.