Effects of alkanolamines on calcium sulfoaluminate belite cement hydration and fresh properties

Calcium sulfoaluminate belite cements have found widespread use in specialised applications but have not been applied broadly due to rapid setting times. Conventional set retarders such as citric and tartaric acids modify hydration kinetics, introducing ancillary effects that alkanolamines may avoid. This study examined the effects of three alkanolamines, triisopropanolamine (TIPA), triethanolamine (TEA) and diisopropanolamine (DIPA), on early hydration at 0.02% dosage; TIPA was also tested across a broader dosage range. Reaction kinetics and phase evolution were examined in pastes by calorimetry, thermogravimetric analysis (TGA) and in situ quantitative X-ray diffraction (QXRD) for 72 h of hydration, along with setting time and amplitude-sweep rheometry. Calorimetry showed that TEA and DIPA delayed and reduced the main cement hydration peak, while all alkanolamines delayed and enhanced the shoulder and secondary hydration peaks. In situ QXRD and TGA suggested that alkanolamines decrease ettringite and alumina gel formation by 24 h and may lead to poorly crystallised ettringite that cannot be quantified by QXRD. Alkanolamine-containing samples demonstrated increased storage and loss moduli and extended linear viscoelastic ranges. A consistent grouping of similar behaviour emerged: control/TIPA versus TEA/DIPA, suggesting distinct mechanisms. Finally, among the alkanolamines, TEA was the most effective, increasing the setting time by 18 min.