Research on the Reactivity of Metakaolin with Different Grade

The price of metakaolin is one of the constraining factors to large-scale applications in concrete. In this paper, 6 grade kaolins have been applied in the experiment to seek one that has high performance-cost ratio. All grade kaolins were treated by the same calcination system that heated treating of 750¢C for 4 hours to produce metakaolin. Techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) were further employed to identify the composition and microstructure of metakaolin. Then mortar was prepared by replacing 10% Portland cement with different grade metakaolin to study the relative strength. The results show that all the compressive strength of mortar which contain metakaolin are higher than that of mortar without metakaolin, but the clay that the content of the particle size below 2 μm is 50% can be the best choice to use in concrete comprehensively considered from the strength enhancing efficiency and economic efficiency. The price of the clay is low and the intension rising rate is also high. The relative strength rising rate can be more than 20% at 7 day and 28 day.