HYDRATES AND MORPHOLOGY OF HYDRATED HIGH VOLUME BLAST FURNACE SLAG CEMENT

Abstract

The cement containing a large amount of blast furnace slag（BFS）is the promising material to reduce the CO₂ emission in cement industry. This paper describes the influence of Ca（NO₂）₂ on the hydrates, the hydrated layer of slag grains, and the composition of C-S-H in high-volume-slag cement. The composition of high-volume-slag cement in this paper was the following ratio, OPC（ordinary Portland cement）：BFS：Anhydrite＝30：65：5mass％. The chemical composition of C-S-H was measured by SEM-EDS method. By the addition of Ca（NO₂）₂, the reaction ratio of slag in the high-volume-slag cement was increased, and AFm（NO₂）was generated. In the hydrated high-volume-slag cement paste, a large amount of unreacted slag grains remained. The hydrated layers were observed in the surrounding of the unreacted slag grains. Inner and outer hydrated layers were observed in the hydrated layers. Thicknesses of the layers were approximately 0.5μm and independent of the grain size. The Ca/Si ratio of C-S-H in the high-volume-slag cement paste was 1.34, and the Al/Si ratio was 0.16. The addition of Ca（NO₂）₂ increased the Ca/Si ratio from 1.34 to approximately 1.5. This is because the hydration of cement, especially belite, is accelerated by the adding of Ca（NO₂）₂.