Hydration of C₃S in presence of CA: Mineral‐pore solution interaction

Abstract

C3S 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 C3S hydration, representing an under sulfated OPC‐rich binder, and to shed light on the underlying hydration mechanisms. To this end, C3S 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 C3S and precipitation of C–S–H with or without CH) can be retarded for 4 to ≥22 hours in comparison to pure C3S 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 C3S is able to dissolve even at high Al concentrations in the pore solution.

Early-Age Hydration Mechanism of Ternary Binders: Quantitative Relation between Microstructure Evolution and Strength Build-Up

“…Such calcium aluminate-based systems are commonly used as accelerators for various applications such as selflevelling mortar and tile adhesive. There are some studies in literature which talk about the hydration mechanisms of such systems [14][15][16], however, those studies do not focus in the first hour of acceleration. Nehring et al reported that ettringite is the major hydration product that forms in the first few hours.…”

“…In another study by Nehring et al, where they studied the hydration of C 3 S in presence of CA, it was concluded that C 3 S can dissolve even at high Al concentrations in the pore solution. The reason mentioned was that the additional Ca ions needed for precipitation of calcium aluminate hydrates comes from C 3 S [16].…”