Impact of triethanolamine on the sulfate balance of Portland cements with mixed sulfate carriers

Abstract

The differences between the hydration of Portland cements with single and with mixed sulfate carriers in the presence of triethanolamine (TEA) were investigated, and possible mechanisms were proposed. Without TEA, cements with different types of sulfate carriers (gypsum, hemihydrate, anhydrite, and mixture of these) have a comparable hydration process at the same molar amount of calcium sulfate. At a TEA dosage of 0.5 wt.%, the sample with a mixture of three sulfate carriers shows substantially stronger retardation of the C3S (This publication uses the cement chemist notation: C3S = Ca3SiO5, C2S = Ca2SiO4, C3A = Ca3Al2O6, C4AF = Ca2(Al, Fe)2O5.) hydration than the cements with only one of these sulfate carriers, which is likely caused by the rapid formation of ettringite and the fast depletion of all sulfate carriers. These effects indicate that TEA influences the balance of sulfate carriers with aluminate-containing clinker phases. On the one hand, TEA can disturb the original sulfate balance due to the accelerated dissolution of aluminate-containing clinker phases, especially C4AF. On the other hand, these effects are closely related to the types and amounts of the sulfate carriers in the cement. A higher amount of sulfate carriers can minimize the TEA-related retardation of the C3S hydration, and hemihydrate shows the strongest impact at the same calcium sulfate quantity.