The role of boron during the early hydration of belite ye’elimite ferrite cements: Fid-Bau Portal

The role of boron during the early hydration of belite ye’elimite ferrite cements

Bullerjahn, F. / Zajac, M. / Skocek, J. / Ben Haha, M.

Highlights • Effectiveness of boron-bearing phases for the retardation of BYF cements. • Impact of boron on hydration kinetics. • Improvement of fresh and hardened mortar properties by retarder dosage optimisation. • Depletion of boron from solution. • Boron binding in hydrated cement matrix.

Abstract This study investigates the effects of soluble boron-bearing compounds such as borax on the hydration and performance of belite ye’elimite ferrite cements (BYF). Boron effectively retards the hydration of BYF, independently of the type of borate used. The addition results in the higher initial spread, the slower decrease of the workability and increase of the compressive strength of mortar, when compared to the non-retarded systems. Tested boron-bearing phases dissolves fast, providing high initial concentration of boron in solution, depending on the initial boron content in mix. The concentration of boron decreases rapidly during the first 5 min of hydration, e.g. during the mortar mixing, independently whether the boron source was dissolved in the mixing water or added during the cement grinding. The boron concentration continues to steadily decrease afterwards. The dissolution of hydraulic reactive aluminate phases such as ye’elimite is slowed down or fully inhibited as long as boron concentration is relatively high. The initial rapid depletion of boron occurs simultaneously with the precipitation of an amorphous phase. Hence, we assume that boron is mainly adsorbed onto the surface of the amorphous phase. Contrary, the slower second period of the depletion of boron from solution can be more clearly linked to the formation of ettringite and monosulfate.