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Title: Effects of Calcium Bromide on the Early Hydration of Portland Cement at Low Temperature (5°C)

Author(s): Feng Zhang, Yin Bai, and Yuebo Cai

Publication: Materials Journal

Volume: 119

Issue: 5

Appears on pages(s): 11-24

Keywords: calcium bromide; dissolution; early strength; hydration; low temperature

Date: 9/1/2022

Abstract:
At low temperatures, the development of concrete strength is slow and can seriously hinder construction progress. The traditional early-strength components cannot meet the requirements of green and high-performance concrete. In addition, research on the early-strength accelerators at low temperature is paltry, and the effect of early strength was limited, but the mechanism of early strength at low temperature remains unclear. Calcium bromide (CaBr2) was used as a new kind of early-strength component, and its effects on mortar strength, cement paste setting time, and early hydration characteristics were evaluated. The incorporation of CaBr2 shortened the setting time of cement pastes and accelerated the strength development of specimens of all ages (the 28-day strength continued to increase dramatically). The compressive strength of mixed mortars increased between 18 and 376%, and the mortar strengths after 3 days met or even exceeded that of the contrast sample, cured at 20°C (293.15 K). The presence of CaBr2 decreased the solubility of Ca(OH)2, so it reached saturation and precipitated more easily. CaBr2 also significantly increased the dissolution and hydration rates of C3S by shortening hydration induction and advancing acceleration. Furthermore, the maximum heat-release rate and cumulative heat release could be increased by CaBr2, which shortens the nucleation and crystal growth (NG) stage and the phase-boundary reaction (I) stage. Large amounts of Ca(OH)2 formed after only 12 hours, and new products, such as bromine-containing calcium-silicate-hydrate (C-S-H) gels and hydrated calcium bromoaluminate (Ca4Al2O6Br2∙10H2O), were also generated. These products piled up and bonded, resulting in a denser microstructure.


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