Influence of DEIPA and TIPA on the hydration and microstructure of model cements

This study investigates the impact of diethanol-isopropanolamine (DEIPA) and triisopropanolamine (TIPA) on hydration kinetics, phase assemblage and microstructure of C3S and a model cement (which clinker only contains C3S and C3A) pastes. Results showed that DEIPA initially delayed C3S reaction, probably due to the formation of DEIPA-Ca2+ complexes that slow down the supersaturation required for the nucleation of hydrates and/or by adsorbing onto the hydrates. In contrast, TIPA did not significantly modify the hydration kinetics of both studied cementitious materials. Furthermore, DEIPA adsorbs onto Ca(OH)2 and has a relevant impact on the amount of portlandite and morphology and stoichiometry of C–S–H. In particular, DEIPA decreased the amount of portlandite and favored the formation of a C–S–H with a higher Ca/Si than the one formed in plain C3S pastes. DEIPA also favored the intermixing of portlandite and AFm phase with C–S–H in C3S pastes and model cement pastes, as well as the formation of greater plates of portlandite in the latter. In contrast, TIPA did not impact the C–S–H stoichoimetry and the amount of portlandite, but a higher intermixing of C–S–H with portlandite and AFm has been observed in both model cementitious systems. The observed low impact of DEIPA and TIPA on the reactivity of the C3A and the amount of early aluminate hydrates in model cements in comparison to previous studies done on Portland cement, highlights the relevance of the presence of Fe on the working mechanims of both alkanolamines and in particular on the enhancement of C4AF reactivity by the formation of Fe-amino complexes.