Influence of surface treated metakaolin with coupling agent on the properties of concrete.

The utilization of metakaolin as concrete admixture is limited because of its higher water-consumption, which has an adverse effect on the workability and homogeneity of concrete. The work presented in this paper has been focused on the evaluation of the influence of the addition of surface treated metakaolin with coupling agent (MMK) on physical and mechanical properties of fresh and hardened concrete. Meanwhile, the effects of MMK are evaluated by drying shrinkage and electric flux test, and the properties of MMK paste are characterized by XRD and TG. It is shown that the concrete with MMK has excellent workability and compressive strength, compared to the mix with metakaolin. In addition, MMK modified concrete mixtures show better drying shrinkage and resistance to chloride penetrability. It is concluded that MMK can improve the rheological properties and reactivity of metakaolin effectively. In fresh concrete, the self-assembled membranes of coupling agent form on the surface of the particles through a condensation reaction. In hardened concrete, the introduction of silane provides the network of covalent coupling among the particles. Meanwhile, the hydrophilic nature of the silane improves the wettability of metakaolin, which increase the chance to react with Ca(OH). [ABSTRACT FROM AUTHOR]