On the Differences in Chemistry and Performance Between Types of Rapid Strength Concretes (RSCs)

Abstract

Rapid-setting cements are used in concrete under a variety of acronyms (HES for High Early Strength concrete, or RSC for Rapid Strength Concrete, etc.). Their use is becoming increasingly important because our ageing highway and airport concrete infrastructure requires fast construction in order to minimize downtime. A simple but broad nomenclature for RSC concretes hides several important differences between materials. In some respects, there is no such thing as single RSC; there are several different types of RSCs with different mineralogies and characteristics. Specifications, appropriately so, focus on performance instead of chemical composition. One key RSC specification is early-age strength, for example 2.76 MPa (400 psi) flexural strength at 4 hours in order to re-open pavement to service. Yet, differences in materials usually result in differences in durability. For example, if only early strength is specified, what is the impact of mineralogical differences on other characteristics like freeze-thaw resistance or shrinkage? Protocols are also important: if pavement enters service at 4 hours, shouldn't a shrinkage measurement also start at 4 hours? Standard shrinkage testing protocols do not. This paper reviews the chemistry and hydration of three commercially available RSC materials (accelerated portland cement, belitic calcium sulfoaluminate cement and calcium sulfoaluminate blended with portland cement and calcium sulfates).