Evolution of kinetics and pore water composition during hydration of a CAC‐Calcite system by addition of Na₅P₃O₁₀

It was analysed how a low Na₅P₃O₁₀ (STPP) concentration influences the hydration of a calcium aluminate cement. It is known that the hydration of a CAC‐Calcite system precipitates C₂AH_X as a precursor phase at 23°C during hydration before the formation of hemi‐ or monocarbonate and the additional formation of CAH₁₀ and AH₃. In our study the addition of 0.2 and 1.0 wt.% STPP (bwoc) to a CAC‐Calcite system at 23 °C and with a w/b of 0.33 was investigated and is compared with mixes without STPP addition. Heat flow calorimetry data showed that STPP accelerates the main reaction. Moreover, an additional heat flow event within the first 30 minutes was detected by STPP addition. However, from the results of QXRD analysis, crystalline hydrate phases are formed only during the main reaction. These are CAH₁₀, C₂AH_X, AH₃, hemicarbonate and monocarbonate. STPP shows an influence on the amount of crystalline C₂AH_X, otherwise, no difference in the qualitative phase content is observed. Gillmore‐Needle‐Testing (IMETER device) could observe an accelerated hardness development during the early heat flow event despite initially reduced viscosity. Pore water studies and thermodynamic modelling (PhreeqC) indicate the formation of an amorphous C‐P‐H phase during this early heat flow event.