Zhonghe Shui

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 heat treated the kaolin at 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 the compressive strength of mortar which contains metakaolin is higher than that of mortar without metakaolin, but that the clay with 50% content where the particle size is below 2 μm 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 rate of strength increase is high. The relative rate of strength increase can be more than 20% at 7 days and 28 days.

Influence of MK-Based Admixtures on the Early Hydration, Pore Structure and Compressive Strength of Steam Curing Mortars

Prestressed high-strength concrete (PHC) pipe piles are one of the most widely used concrete elements in building foundation construction. In this study, the effects of material composition on the compressive strength development, early hydration and pore structure of PHC were investigated by a series of analytical techniques. Supplementary cementitious materials, namely metakaolin (MK), granulated ground blast-furnace slag (GGBFS) and limestone powder (L.S) were used to prepare cement pastes and mortars under steam curing condition to improve early compressive strength. Finally the mortar containing 10 % MK and 10 % L.S was prepared, with the compressive strength up to 89 MPa at 1 day and 93 MPa at 7 days. The effects of the blended mineral admixtures on the early hydration and microstructure of steam cured pastes and mortars were investigated by XRD, TG-DTC and MIP. The results showed that the mineral admixtures could consume Ca(OH)2 owing to pozzolanic reaction and promote concrete hydration, which led to the improvement of the properties of hydration products and optimization of pore structure and pore size distribution.