Mechanisms underlying the carbonation of Portland cement incorporating triethanolamine to enhance CO2 curing effectiveness

Abstract

This study comprehensively investigated the effects of triethanolamine (TEA) on cement carbonation, with a focus on carbonation kinetics, microstructure development, and underlying mechanisms. The results demonstrated that TEA retarded cement carbonation, with this effect intensifying as TEA concentration increased. This retardation primarily occurred because TEA promoted initial Ca²⁺ precipitation and accelerated pH reduction, converting absorbed CO₂ into HCO₃^-, which retarded subsequent CaCO₃ formation. Notably, higher TEA concentrations facilitated the carbonation of the aluminate phase, contributing to a two-stage carbonation mechanism, characterized by a distinctive double-peak feature in the heat evolution curve. TEA exhibited a CO₂ absorption capacity of 31.56 g/mol and was negligibly consumed during carbonation, suggesting that TEA behaved similarly to a catalyst, exerting a significant impact even in small quantities. Consequently, a more homogeneous and denser microstructure, along with enhanced strength development were achieved at a low TEA concentration. In contrast, high TEA concentrations significantly exacerbated the retardation and caused an uneven distribution of products within the matrix. These findings reveal the mechanisms through which TEA influences cement carbonation and underscore its potential to enhance CO₂ curing effectiveness.