Hydration Activation of Alite-Belite-Ye’elimite Cements by Doping with Boron
Jesus D. Zea-García, Susana G. Sanfélix, Oriol Vallcorba, Miguel Á. G. Aranda, Isabel Santacruz, Ángeles G. De la Torre
Abstract
The hydration behavior of two alite-belite-ye’elimite (ABY) cements has been studied. The production of these materials releases into atmosphere ∼17% less CO2 compared to Portland cement. The ABY cement contains alite, β-C2S, and ye’elimite as main phases, while dABY (activated by adding borax) contains not only these three phases but also α′H-C2S. The role of boron in these systems is 2-fold: (i) acting as a retarder at early hydration ages since the precipitation of AH3 gel has been delayed from over 4 h in ABY to over 24 h in dABY; and (ii) as an activator at late hydration ages by stabilizing highly reactive β- and α′H-belites. The degree of hydration of β-C2S in ABY is 42% at 28 days, while that of β-C2S and α′H-C2S in dABY at the same age is 80 and 88%, respectively. Moreover, the main hydration products in both systems are ettringite and C–S–H gel. The local structure of these hydrated products has been studied by 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS–NMR) and found to be similar in both cements. However, the amount of C–S–H gel is 63% of all silicon-bearing phases in ABY after 28 days while it is 76% (determined by 29Si MAS–NMR) in dABY, which justifies the higher mechanical strengths of dABY mortars.