Hydration of C 3 S in presence of CA : Mineral‐pore solution interaction

C 3 S and CA are the main phases of OPC and Fe‐rich CAC , respectively. The objective of this research was to investigate the influence of CA on C 3 S hydration, representing an under sulfated OPC ‐rich binder, and to shed light on the underlying hydration mechanisms. To this end, C 3 S was blended with 1‐30 wt‐% CA and the pastes (w/c 0.5) were investigated by heat flow calorimetry, in situ X‐ray diffraction and analysis of the pore solution chemistry. CA additions ≥5 wt‐% reveal a separation into three distinct heat flow maxima, whereas additions ≤3 wt‐% just retard the start of the main reaction. The silicate reaction (dissolution of C 3 S and precipitation of C–S–H with or without CH ) can be retarded for 4 to ≥22 hours in comparison to pure C 3 S depending on the admixed CA content. The start of the silicate reaction seems to be related to a decrease in Al‐ and increase in Ca‐concentration in the pore solution. However, it can be shown in this study that C 3 S is able to dissolve even at high Al concentrations in the pore solution.