Hydration mechanism of anhydrite and calcium sulfoaluminate co-activated slag cement: insights into the role of composition

Abstract

Utilization of Portland cement to initiate the dissolution of blast furnace slag (BFS) in super-sulfated cement is limited by low slag substitution level and poor early strength. In this study, a new activator composed of anhydrite and calcium sulfoaluminate cement clinker was proposed to enhance the utilization of BFS in super-sulfated cement. Tests were conducted on the compressive strength, autogenous shrinkage, hydration heat, pH and conductivity of the composites. XRD, ²⁹Si NMR, BSE and MIP were employed. Results reveal that ettringite, gypsum and C-S-H are the primary hydration products. The composites with 20% activator display the highest compressive strength and shrinkage accompanied by the highest hydration heat and degree, as well as the highest quantity of monomer silica tetrahedrons and the largest volume of fine pores. Thermodynamic modeling confirms the critical value for the activator-substitution level. Additionally, the activator-BFS composite exhibited significantly lower carbon emissions compared to Portland cement.

Keywords:

• super sulfated cement
• calcium sulfoaluminate cement
• hydration mechanism
• reaction degree
• thermodynamic modelling

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the National Key Research and Development Program of China (2022YFE0135100), National Natural Science Fund of China (52278270, 52378255 and 52008151), Shanghai Rising Star Program. Additionally, thanks are extended to Professor Barbara Lothenbach for her helpful suggestions on the modelling, as well as the anonymous reviewers whose suggestions improved this manuscript.