Comparison of Hydration of Thermally Activated Water-Washed Kaolins in Cement Mortar

This article investigated the hydration process, mechanical properties, and pore distribution of two kinds of thermally activated water-washed kaolin in cement-based materials. The metakaolin was obtained through the calcination process at 600°C–700°C for 3 h, and its pozzolanic activity was evaluated using the X-ray diffraction analysis of metakaolin-lime blends. The results indicated that the well-crystallized kaolinite in Maoming, China, had a higher pozzolanic activity than the poorly crystallized kaolinite from Beihai, China, when calcined at the same temperature. The highest pozzolanic activity was observed during the calcination at 650°C, which also indicated a turning point for the specific surface area and the particle size distribution of both kaolins. Furthermore, when mixed at a replacement level of 10 wt%, the metakaolin in Maoming showed the promotion of the hydration of cement to a greater extent, an effective reduction in harmful voids (>20 nm), and a higher compressive strength (i.e., an increase by 120–140 %).