2 - Calcium aluminate cements

Abstract

This chapter provides an understanding of the properties and behavior of calcium aluminate cements as relevant to their present-day applications in order to support appropriate and intelligent use of these materials. Calcium aluminate cements (CACs) are extensively used in combination with other mineral binders (e.g. Portland cement, calcium sulfate, lime) and admixtures to produce a range of specialist mortars. Properties that can be achieved through the use of CACs are— rapid hardening, resistance to high temperatures and temperature changes, and resistance to chemical attack, particularly acids. The setting times of calcium aluminate cements are similar to those of Portland cement, namely around 3-5 hours. The setting time of calcium aluminate phases becomes progressively longer with decreasing lime-to-alumina ratio. C3A, the lime rich phase present in Portland cements, reacts rapidly with water, necessitating the addition of gypsum to Portland cement clinker to prevent flash setting. In the absence of admixtures the intrinsic ease of placing CAC concretes is similar to that of Portland concretes at the same water-to-cement ratio. CAC concretes appear dryer, but the temptation to add water must be avoided as they flow well under vibration. An increasingly important use of calcium aluminate cements today is as a component of mixed binder systems for specialist applications. The ingredients are usually blended dry and sold as mortars ready to mix with water. The applications are typically non-structural finishing operations in buildings, such as floor levellers, tile adhesives or fixing mortars. Another application is rapid-hardening repair mortars.