Hydration and Durability of Ternary Binders Based on Metakaolin and Limestone Filler

Abstract

The combination of Portland cement and mineral additions allows reducing the carbon footprint of cement-based materials and improving their resistance to several environmental actions. The development of binary binders is limited by the reactivity of pozzolanic materials at high substitution levels and the availability of industrial by-products such as slags and fly ash. Thus, it is necessary to develop new cements from natural raw materials such as clay and limestone and to combine them to design ternary binders with higher hydraulic activity. The study is focused on mortar based on binary and ternary binders (Portland cement, metakaolin, limestone filler) with a maximum substitution level of 45%. Two sets of mortar mixtures with different water-to-cement ratios were designed. The experimental program includes the determination of strength, porosity, hydration heat, portlandite content, shrinkage and natural carbonation. The analysis of data aimed at correlating the evolution of mechanical properties with hydration degree and reactivity of calcined clays. The results actually showed that the performances of ternary binders closely depend on the properties of the three studied metakaolins, especially their production process and physical properties. For a given substitution level, the studied ternary binders clearly showed better performances than other mineral additions. The reduction of water-to-cement ratio resulted in an acceleration of pozzolanic reaction. This allowed an improvement of short-term strength as well as potential durability.