Tailored rheological development in OPC systems by controlled ettringite precipitation and its effect on compressive strength

The control of rheological properties is gaining in importance to meet the special requirements for cementitious materials in novel technologies such as 3D‐printing. A deeper understanding of the underlying mechanisms of cement hydration is necessary to customize the mix design to the specific application.

The hydration of OPC is mainly characterized by the silicate and aluminate reaction. The aluminate reaction is especially relevant for the early rheological development, whereas the formation of C‐S‐H (silicate reaction) is responsible for the later hardening of the hydrating paste.

A hydration control agent is used to delay the initial aluminate reaction to a defined point in time. When no additional mixing occurs during this period of rapid ettringite precipitation, the cement paste stiffens to a solid cement stone. However, when the sample is mixed during this period, the workability of the paste is retained. The rheological changes can be correlated directly to the magnitude of ettringite formation. Additionally, the compressive strength and pore size distribution of all systems (reference, HCA, HCA with additional mixing) are investigated to analyze the long‐term properties. These results predict future customized mix designs in various application fields.