4 - Heat-resisting and refractory concretes

Abstract

This chapter provides an overview of heat-resisting and refractory concretes. Refractory concrete is defines as a concrete which is suitable for use at high temperatures composed of hydraulic cement (calcium aluminate cement) as the binding agent. The boundary between heat-resistant and refractory concrete is somewhat arbitrary, but is probably about 1000°C although some definitions of refractory concrete start at 1500°C. However, there is, in fact, a more or less continuous spectrum of high-temperature resistant concretes, extending from about 300-400°C (the limit of concretes bound with Portland cements) to 2000°C or more, using high range calcium aluminate cements (CAC) containing 80 per cent alumina. It is often said that the refractoriness (i.e. the softening point or service temperature limit) of CAC is governed by the alumina content. The higher is the alumina, the more refractory the cement. While this is true in the first instance, refractoriness is also dependent on the presence or not of compounds that form low melting point eutectics - CaO, SIO2, Fe203. As the alumina content increases, in the higher grades of CAC, then the relative amounts of compounds that form low melting point eutectics decrease, leading to higher refractoriness.