Effect of metakaolin dispersion on the fresh and hardened state properties of concrete

The use of pozzolanic materials such as metakaolin in mortars and concretes is growing. Their use is usually related to the promotion of hydraulic binder reactions or to the mitigation of expansive reactions that can occur in concrete. Introduction of fine particles such as metakaolins, can have a strong effect on fresh and hardened state properties. This paper aims to study the effect of metakaolin in concrete formulations with a preset workability and to assess the system rheology but also its hardened state properties such as mechanical strength. The effect that the dispersion of metakaolin particles induces on concrete microstructure, particularly in porosity, is discussed. Formulations were prepared with several metakaolin amounts and workability was controlled either with water or a high range water reducer admixture (HRWRA). The use of HRWRA can cause deflocculation of metakaolin particles, allowing workability control in concrete and leading to better efficiency and improved performance.