Effects of combination of retarders on calcium sulfoaluminate (CSA) cement systems

Abstract

One method of increasing the sustainability of concrete construction through reductions in emissions and energy requirements is through the use of alternative binders. Calcium Sulfoaluminate (CSA) cement has been developed as a low energy cement, as it has up to 40% less embodied carbon dioxide emissions due to its lower calcium content and reduced clinkering temperature relative to Portland cement. However, despite the advantages of CSA cement, its rapid setting time limits the use of this material to applications when short working time is required. To facilitate better control of the timing of CSA hardening and strength gain, several approaches to retarder usage and dosing have been studied. In this paper, use of chemical retardants, including citric acid, tartaric acid, and borax with CSA cement used alone and in combination with each other, and their effects on phase development and hardened binder properties were evaluated and discussed in relation to their retardation mechanisms. Because of differing working mechanisms of the retarders, combinations of citric acid and borax showed relationships that averaged the properties of each retarder, while combinations of citric acid and tartaric acid showed relationships that added the effects of the two retarders together. Setting time of CSA cement was delayed successfully, using retarders both alone and in combination, however combination mixes generally decreased compressive strength compared to the strengths of equivalent total singular retarder dosage. Relationships between heat release and setting time were developed and may prove useful for prediction of largescale application field performance.