Basic Principles of Hybrid Alkaline Cements

Abstract

A line of research of particular interest being pursued at this time is the development of new cements known as blended or hybrid alkaline cements. These cements form when blends containing low proportions of cement and high proportions (60-70 %) of mineral additions (such as blast furnace slag, fly ash or  metakaolin) are alkali activated. The reaction products precipitating in these systems are very complex and actually comprise a mix of gels: C?(A)?S?H type gels (similar to the gels obtained during cement hydration, but with aluminium in their composition) and (C,N)?A?S?H gels (similar to the N?A?S?H gels obtained during the alkaline activation of aluminosilicates, but with calcium in their composition). The prevalence of one or the other gel depends on a number of factors, including the concentration of the initial species in the solution, type of activator used, pH values and reaction time. The paper reviews the fundamental chemistry governing these new systems and the activation mechanisms involved.  It also analyses the nature of the reaction products formed and their compatibility under different reaction conditions.