Characterization and modeling of hydration and microstructure formation for blast furnace slag cement

Abstract

Degree of hydration of cement minerals and BFS, amount of hydration products of pastes were determined by XRD/Rietveld method. The hydration mechanism of slag was also investigated, considering the role of calcium hydroxide as activator and the Ca/Si ratio of C-S-H. Assumed that for low Ca/Si ratio, the C-S-H inner product resists strongly against ion diffusion and thus the hydration of BSF retards, an enhanced model for slag hydration was proposed. The validity of enhanced model is verified by both hydration degree and heat generation tests. The capillary porosity of BFS blended cement pastes is larger at lower hydration degree, and remarkably decreases as its hydration progresses. Gel water in BFS paste increase nonlinearly with the hydration degree of BSF. This implies that C-S-H produced from BFS hydration at later age has larger amount of gel water and becomes lower density, can fills in large pores more efficiently. Enhanced modeling of pore structure taking into account of these new findings could reproduce the experimental results of porosity and higher long-term strength development of BSF paste even though the hydration degree of BSF was lower than OPC.