Insight into the role of early C3A hydration in structural build-up of cement paste

This research sheds light on the two origins of C3A hydration in structural build-up of cement paste. The largest critical strain is associated with colloidal interaction, whereas the smallest critical strain originates from the cohesion between calcium sulfoaluminate hydrate (CA$H) particles. Interestingly, we have found that the structural build-up primarily relies on the total colloidal interaction within 2 h of hydration rather than the cohesion between CA$H particles. In C3A-gypsum-CaCO3 pastes, a two-stage structural build-up was observed. The swift progression within the first tens of minutes can be traced back to the augmentation in the number of bonds (solid volume fraction), which then proceeds to the bond strength (colloidal interaction between two flocculated particles). The subsequent slow, linear development is attributed to the strengthening of bonds. As a result of this analysis, a time-dependent model for structural build-up was established. Two rates, namely Acol and ACA$H, were employed to illustrate the impact of the strength and number of bonds. This model is proven to be well-suited for analyzing cement paste within the initial tens of minutes.