Microscale and macroscale strength behaviors of blast furnace slag- cement based materials: Modeling and analysis

Abstract

Blast furnace slag (BFS) is used extensively as a cement replacement material, improving both the microstructure and the mechanical properties. How to optimize the content of BFS used without losing the mechanical properties of the composite is a very important theoretical problem. Essentially, the strength evolution of BFS-cement based materials is mainly dominated by the hydration reaction of the cementitious material. The formed hydration products bind the dispersed aggregate particles together, so that the material exhibits a certain strength and stiffness on the macroscopic scale. Exploring the microstructural evolution of BFS-cement based materials contributes to the understanding of the failure and instability process under external stress loading, and the optimization of proportion ratios to achieve optimum mechanical properties. Consequently, a better understanding of the microstructure evolution of BFS-cement based material is required. In this study, the microstructure of the BFS-cement based material was modeled using the discrete element method in combination with techniques such as thermogravimetric (TG) analysis and X-ray diffraction (XRD). In addition, mercury intrusion porosimetry and uniaxial compressive strength tests were performed to verify the reliability of the model. Finally, a series of mechanical simulations were carried out using the model. The simulated porosity and compressive strength were compared with the relevant experimental data with an error rate of less than 10%, showing the strong simulation capability of the proposed model. Through representative elementary volume simulation analysis, it is shown that the 30 wt% addition of BFS had a more positive effect on long-term strength, with an increase of approximately 5% compared to that of pure cement sample. The proposed model exhibited that the slag hydration reaction consumes portlandite (CH) and produces more cementitious calcium silicate hydrate (CSH) particles, resulting in the simulated 28d strength starting to be larger than that of pure cement. The established microstructure model of BFS-cement based materials provides a basis for predicting the strength structural.