High-activity modified metakaolin-based mineral admixture for concrete and preparation method for mineral admixture

The invention relates to a high-activity modified metakaolin-based mineral admixture for concrete and a preparation method for the mineral admixture. The high-activity modified metakaolin-based mineral admixture for the concrete is prepared by mixing metakaolin and a composite modifying agent according to the mass ratio of 200:1 to 20:1, wherein the composite modifying agent is prepared by mixing 50 to 85 mass percent of stearic acid, 8 to 25 mass percent of calcium stearate and 7 to 25 mass percent of dimethyl silicone oil based on 100 mass percent. The high-activity modified metakaolin-based mineral admixture for the concrete and the preparation method for the mineral admixture have the advantages that 1) the early strength of the concrete can be remarkably strengthened; 2) the working performance of the concrete can be remarkably improved; 3) the osmosis resistance of the concrete can be improved; and 4) the mineral admixture is highly adapted to various kinds of cement and concrete additives.