Action of the combined presence of C-S-Hs-PCE and triethanolamine on the performances of cement paste/mortar

This paper aimed at investigating the action of the combined presence of calcium silicate hydrate seeds - polycarboxylate (C-S-Hs-PCE) and triethanolamine (TEA) on the performances of cement paste/mortar. Simultaneously, the mechanisms behind this action were explored. The results demonstrate that the composite addition of C-S-Hs-PCE and TEA further promotes the setting behaviour of cement pastes, but this promotion depends mainly on the TEA content. The composite use of 0.02% TEA and 0.5–2% C-S-Hs-PCE increases the mortar compressive strengths at 1, 3, 7 and even 28 days. This increase is related to the promotion of tricalcium silicate (C3S) hydration at 1 and 3 days, the increment of the calcium hydroxide (CH) content over 1–28 days, and the decrement of the number of gel pores and the volumes of the pores with sizes of less than 100 nm in the pastes with 0.02% TEA and 0.5%–2% C-S-Hs-PCE. However, the composite addition of 0.5%–1% TEA and 0.5%–2C-S-Hs-PCE reduces the compressive strengths at 1 and 28 days: 0.5%–1% TEA and 0.5%–2% C-S-Hs-PCE enhance the monosulfate (AFm) content at 1 day, promote the reaction from ettringite (AFt) to AFm, decrease the CH content, retard the C3S hydration at 1 day and 3 days and increase the gel pore quantity and the volume of the pores that are distributed from several nm to 100 nm. As a result, the mortars with 0.5%–1% TEA and 0.5%–2% C-S-Hs-PCE exhibit lower compressive strengths at 1 day and 28 days. These findings provide theoretical guidance for the composite use of TEA and C-S-Hs-PCE in cement-based materials.