HARDENING PROPERTIES OF GRANULATED BLAST FURNACE SLAG ACTIVATED BY FINE SLAG POWDERS FROM DIFFERENT SOURCES

Abstract

Granulated blast furnace slag (GBFS), when activated by an alkaline stimulant, GBFS releases chemical components and forms hydrates such as calcium silicate hydrate (C-S-H), leading to strength development and imparting cohesive properties despite its granular nature. However, because GBFS hardens slowly and its cohesive properties also varies, making it difficult to predict, this behavior is not reflected in Japanese design standards. To incorporate its cohesive properties into geotechnical design, a better understanding of its hardening behavior is required. Approaches to accelerate GBFS hardening is not only the addition of cement but also the addition of blast furnace slag powder (BFS-P) as an alkaline stimulant. However, the effectiveness of BFS-P varies depending on its production source. This study examined the hardening properties of GBFS mixed with three types of BFS-P sourced from different steel plants. Two moisture conditions—unsaturated and saturated—were considered to simulate applications in land and port structures. The results revealed that the MnO, Fe₂O₃, and TiO₂ contents in BFS-P significantly influenced GBFS hardening. A strong correlation was observed between compressive strength and hydrate content measured by thermogravimetric (TG) analysis at 30–600°C. Furthermore, the degree of saturation had a notable effect on strength development. Specifically, the hydrate content required for strength development was 0.283% and 0.376% in the unsaturated and saturated conditions. Unsaturated conditions, hydrates formed bridges between GBFS particles via the meniscus, which also increased the density of the hydrates themselves, resulting in higher strength despite lower levels of hydration reaction.