Impact of carboxylated styrene–butadiene copolymer on the hydration kinetics of OPC and OPC/CAC/AH: The effect of Ca2 + sequestration from pore solution

It was found that carboxylated styrene–butadiene latex copolymer retards OPC and accelerates a ternary binder system based on OPC/CAC/anhydrite. The reason behind both effects is the sequestration of Ca2 + ions from the pore solution. In the case of OPC, the depletion of Ca2 + hinders the formation of cement hydrates and thus retards hydration of OPC, whereas for the ternary binder system, the depletion of Ca2 + shifts the solubility equilibrium of CaSO4 in favor of sulfate. As a result, the dissolution of anhydrite is accelerated and ettringite formation is enhanced. The consequence of these processes is earlier strength development, which is highly desirable in drymix mortar applications. The results explain why anionic SB latex performs particularly well in ternary binder systems.