Hydration of a two-component CSA–OPC mix: timing of component blending and setting on demand

With the ongoing development of new technologies like three-dimensional printing, the requirements for the performance of cementitious materials are becoming more complex. Setting on demand, while the workability of the material is retained until placement, is an important aspect. A ternary system comprising CSA (calcium sulfoaluminate cement), OPC (ordinary Portland cement) and C$ (anhydrite) was developed to achieve setting on demand in a two-component setup, where two retarded cementitious components were mixed after specific times of storage. The kinetics of the individual systems and the blend were examined by heat flow calorimetry, quantitative X-ray diffraction and pore water analysis. The rheological development was monitored by a penetration test method. The results showed that the performance of the blend was independent of the storage time of the individual components and could be tailored by changes in the retarder dosage in the individual components. The initial reaction in the blend was characterised by the simultaneous dissolution of ye'elimite and C₃S, resulting in the formation of ettringite as the sole detectable hydrate phase. The fate of silicon remains unclear as, with the methodology at hand, no silicon-bearing hydrate phase could be identified.