Effect of the addition of dolomite on the stability of the hydrate phase assemblage in Portland composite cement pastes

Due to the need to reduce the CO2 emissions during cement production, the demand for SCMs increased considerably in the last years and is predicted to keep doing so in the future. Alternative SCMs that are available in sufficient quality and quantity need therefore to be found, which provide, among others a similar or even improved durability compared to today’s commercial cements. The use of SCMs may significantly change the phase assemblage and phase composition of cementitious systems and therefore also their durability. It was shown that the addition of dolomite to Portland cement pastes may lead to the formation of hydrotalcite. As a first step in investigating the durability of such new composite cements, we investigated the stability of the hydrate phase assemblage in a new type of Portland composite cement containing dolomite and metakaolin. Typical deterioration mechanisms for reinforced concrete include carbonation-induced corrosion of the reinforcement and leaching of the cement paste. We therefore exposed well-cured cement paste samples to large amounts of deionized water or increased CO2 levels, and compared them to unexposed reference samples. While leaching and carbonation caused severe decalcification of the C-S-H and the decomposition of the portlandite and ettringite, hydrotalcite seemed to resist both deterioration mechanisms without changes in its Mg/Al ratio. The experimentally obtained results agree well with the thermodynamic modelling performed for leaching and carbonation. We consequently concluded that the hydrotalcite formed by the reaction of dolomite, is a stable hydration product.      «

Due to the need to reduce the CO2 emissions during cement production, the demand for SCMs increased considerably in the last years and is predicted to keep doing so in the future. Alternative SCMs that are available in sufficient quality and quantity need therefore to be found, which provide, among others a similar or even improved durability compared to today’s commercial cements. The use of SCMs may significantly change the phase assemblage and phase composition of cementitious systems and the...     »