Preparation of nano-kaolin by wet-grinding process and its application as accelerator in Portland cement

Abstract

Achieving the high early strength of cement-based materials is a necessary condition for the rapid demolding of prefabricated buildings. In this study, kaolin treated by wet-grinding process was utilized as an accelerator in Portland cement. Wet-grinded kaolin-Portland cement system was designed, and 1–4% wet-grinded kaolin was added. Compressive strength and setting time were measured. The related mechanism was researched by hydration heat, X-ray diffractometer, thermogravimetric, nuclear magnetic resonance and mercury intrusion porosimetry in details. Results showed that wet-grinded kaolin enhanced the early strength of Portland cement significantly and shortened the setting time; 4% wet-grinded kaolin increased the 16 h compressive strength by 44.1%; and 1 d, 7 d and 28 d strength were also improved. One reason was that the nucleation effect of wet-grinded kaolin induced the hydration of Portland cement and formation of hydrates. The other reason was that nano particles in wet-grinded kaolin were conducive to refine the pore structure. Such results testified that nano-kaolin treated by wet-grinding process was able to be used as an accelerator for Portland cement, providing a novel way in precast concrete for the fast demoulding process.