Effect of nano-metakaolinite clay on hydration behavior of cement-based materials at early curing age

The aim of this study was to improve the physical and mechanical properties of cement-based materials by using the additive nano-metakaolinite clay (NKC). The results show the mechanism by which NKC modifies cement-based materials at the micro-scales. By considering the influence of the dispersion method and time on the dispersion of NKC in the cement slurry, a comparative test of micromorphology and pore structure of NKC-incorporated cement specimens prepared using different NKC dispersion methods was performed. NKC could be well dispersed in the cement slurry by ultrasonic dispersion and stirring for 15 min, and the improvement in the cement pore structure was most significant in this case. A large number of Ca(OH)₂ (CH) crystals in the early stage of hydration of cement are transformed into the closely packed calcium silicate hydrate gel, thereby increasing the compactness of the cement matrix. After 28 days of standard curing, the CH crystal content in the slurry containing 5% NKC by weight of cement is 12.72% lower than that of ordinary cement paste. The micro-level analysis of the cement slurry shows that NKC can effectively fill the internal pores of cement-based materials, optimize the pore structure, and significantly improve the microscale compactness.