Influence of set retarding admixtures on calcium sulfoaluminate cement hydration and property development

Little published data is available to guide specification calcium sulfoaluminate cement (CSA) mixtures with citric acid retarder dosage rates capable of achieving adequate field working times, nor to understand the effect of retarder dosage on hydration and property development, representing a significant barrier to widespread CSA concrete use. Thus, this study investigated the use of citric acid with two commercially-available CSA cements, tracking the effects of dosage on phase development, hydration, setting, and compressive strengths. Key findings were that: citric acid successfully retarded initial set past 120 min for both cements despite significantly different chemistries; increasing cement anhydrite content reduced retarder effectiveness and altered hardened binder microstructure, reducing compressive strengths; greater retarder dosages did not negatively affect cumulative hydration, nor strengths; and the time at which the maximum rate of heat evolution occurred correlated with final setting, a relationship useful for predicting field mixture behavior based on laboratory testing.