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Ettringite-accelerated binders composed of CAC-PC-C$ (calcium aluminate cement-Portland cement-calcium sulfate) and CSA-PC-C$ (calcium sulfoaluminate cement-Portland cement-calcium sulfate) have been used widely for indoor applications, such as self-leveling floor screeds, underlayment, and tile adhesives owing to their rapid setting, early strength gain, and shrinkage compensation properties. These properties also make these binders appealing candidates for outdoor rapid repair (e.g., highways, bridge decks, and airfield pavements). However, a central question remains: Does ettringite remain stable in outdoor exposure conditions? If so, which factors will contribute positively/negatively to the long-term stability of ettringite in these systems? To address these questions, this critical review presents the current state of knowledge regarding the hydration of ternary binders composed of CAC-PC-C$ and CSA-PC-C$ with respect to ettringite formation and the factors affecting the stability of ettringite thereafter. The purpose of this review paper is to synthesize and analyze current research regarding conditions that promote or deter ettringite stability, establish what information is missing, unclear, or contradictory, and identify remaining research needs to address the identified knowledge gaps.

Ettringite binders are increasingly being used as rapid-repair materials to extend the service-life of reinforced concrete where rebar corrosion has caused deterioration and spalling. The transport properties of these ettringite binders are important in assessing the longevity of such repairs. This study demonstrates how the electrical properties of such binders can be interpreted to obtain meaningful results related to the transport properties. In addition to the pore solution chemistry, the degree of saturation in calcium sulfoaluminate (CSA) cement was found to be an important factor in the electrical properties since ettringite binders can have greater self-desiccation at earlier ages than ordinary portland cement (OPC). After one day of hydration, the electrical properties suggested that the CSA containing mixtures had greater pore network connectivity than the OPC mixture and this can be attributed to the varying phase compositions. Thermodynamic modelling confirmed a high amount of ettringite formation in the CSA system and a lower capillary water and capillary porosity associated with this. The lower internal relative humidity of ettringite binders should be considered when using electrical measurements to evaluate their transport properties since it increases the total electrical resistivity.