Abstract
The current environmental issues of the cement industry lead to the partial substitution of clinker by different supplementary cementitious materials in Portland cement, such as slag and fly ash. However, these blended cements are less reactive than Portland cement. Activators are needed to accelerate their setting or their hardening. Many accelerator systems (molecules or ions) are known for their accelerating effect and studied in the literature, such as triethanolamine (TEA) and diethanol-isopropanolamine (DEIPA). However, a few studies have examined their impacts on blended cements and their effects on the physico-chemical properties of cement pastes.The aim of this work is to have a better understanding of the mode of action and the influence of these two molecules (TEA and DEIPA) on the dispersion state and the chemical reactivity of fresh cement paste. Granular characteristics of the nano/micro-structural to the meso-structural scale of the cementitious formulations at young age were studied in connection with their reactivity and the consequences on the macroscopic behavior of mortar. The analysis of pore solution, until 2h30, allowed highlighting the chemical contributions of mineral additions on reactivity with also the evaluation of the consumption of the two amines during hydration. The reaction kinetics were followed by isothermal microcalorimetry, X-ray diffractometry and thermogravimetric analysis, to determine the impact of the amines on the dissolution of anhydrous phases and on the precipitation of hydrated phases. Physicochemical stability was evaluated by Turbiscan measurement following the sedimentation behavior of lightly diluted pastes for the first 30 minutes of hydration. Finally, consequences of the observed effects were evaluated on the compressive strengths of mortar until 90 days.This methodology highlighted the chemical impact of mineral additions from the first minutes of hydration and the importance of their minor phases. The main mode of action of the two amines have been identified on blended cements with specific effects on slag and fly ash.