Influence of superfine ettringite on the properties of sulphoaluminate cement-based grouting materials

Superfine ettringite (S-ettringite) synthesized in this research presents same structure with the ettringite produced by the hydration of cement, which is expected to promote the hydration of sulphoaluminate cement-based materials. There are few literature reports on laboratory synthesis of superfine ettringite. In this paper, preparation of S-ettringite via separate nucleation and aging steps method by introduction of citric acid is presented. The effect of the S-ettringite on hydration, microstructure and properties of CSA cement-based grouting materials (CBGM) was experimentally investigated. Results show that specimens containing S-ettringite displayed a significant improved performance with regard to compressive strength at early and later ages and setting time. Compared to the control specimen, 4-h compressive strength increased by 380% and initial setting time shortened by 55.6% when 4 wt% S-ettringite was added, respectively. Due to the crystallization inducting effect and seed effect, the addition of S-ettringite changed the morphology of ettringite, and meanwhile promoted the hydration exothermic rate and increased the amount of hydration products, which thus generate higher compressive strength and shorter setting time.