Effect of seed emulsion on the early hydration behavior of basic magnesium sulfate cement

Abstract

Basic magnesium sulphate cement (BMSC) has been known as a lightweight and high strength magnesium-based cementitious material. However, the addition of admixtures (e.g. citric acid) significantly retards the early hydration process of cement, which is not conducive to its actual utilization in construction. In this work, BMSC and fly ash (FA, 50 wt%)-BMSC with extremely high early strength were prepared by addition of the seed emulsion (SE) of BMSC obtained by wet grinding. Meanwhile, the influence of SE on the early hydration behavior of BMSC was investigated and the corresponding hydration mechanism was proposed as well. The results demonstrated that wet grinding can effectively reduce the particle size of crystal seeds and increase their specific surface area. The crystal seeds were emulsified after 3 h of wet grinding, with a particle size of 2–6 μm and a specific surface area of 14.36 m2/g. The SE could provide crystal nuclei to directly induce the generation of 5·1·7 phase, which could significantly accelerate the early hydration process at low temperature (15 °C). The 12 h-strength of BMSC was reached to 33 MPa with a sharply shorten initial setting time of 48 min when adding 6% SE. Moreover, the mechanical properties of FA-BMSC with addition of SE were improved by 30% since FA particles can be tightly encapsulated in the reticulated whisker structures of 5⋅1⋅7 phase. This work provides a theoretical and technical support to better understand and properly use of SE in the production of BMSC.