Influence of temperature and importance of sulfate content on the triethanolamine-enhanced aluminate reaction during Portland cement hydration

The enhancement and acceleration of the aluminate reaction of a commercial cement (CEM I 52.5R) with the addition of 7.4% anhydrite, 2.2% triethanolamine and 0.25% tartaric acid (TA) was studied at temperatures of 10, 23 and 40°C up to 28 days. Heat flow calorimetry, quantitative X-ray diffraction and thermodynamic modelling were used to follow the hydration process. The samples at 10°C were strongly retarded and the degree of hydration (DoH) of tricalcium aluminate (C3A) was low. At 40°C, the samples were accelerated and showed at least the same DoH of C3A compared with the 23°C samples but the ettringite content decreased with an increase in storage time. Therefore, the TA dosage was adjusted for the 10°C and 40°C samples. Thermodynamic modelling showed the possibility of thaumasite formation when the sulfate addition did not perfectly match the content of aluminate phases. This imbalance could even be caused by an unexpected low DoH of C3A, as was found at 10°C.