The chloride binding capacity and stability of gap-graded blended cement with calcined hydrotalcite and metakaolin

Enhancing chloride binding capacity and stability of cement paste is beneficial to blocking chloride ingress and preventing the release of bound chloride, and consequently to improve the chloride resistance of cement-based materials. Incorporating supplementary cementitious materials (SCMs) into blended cement cannot increase the chloride binding remarkably, due to the chloride binding threshold of normal hydration products, even though the SCMs with high activity are introduced. In this study, a gap-graded particle distribution model was used to achieve higher packing density and continuous hydration of clinker and SCMs, then more hydration products were generated to reduce chloride ingress and heighten chloride binding. On this basis, metakaolin and calcined hydrotalcite were introduced to enhancing chloride binding capacity and stability furtherly by generating monocarboaluminate and hydrotalcite. The results show that the chloride binding capacity of modified gap-graded blended cement paste is 22% higher than that of interground blended cement paste. Introducing metakaolin helped the generation of Friedel’s salt, and improving the chloride binding stability of modified gap-graded blended cement, which can be attributed to the more hydrogen bonds around the interlayer chloride in Friedel’s salt compared with that in hydrotalcite. The provided method for design of blended cement with high binding capacity and the mechanism related to binding stability also lay solid foundation for the improvement of durability of cement-based materials.