Experiment and Analytical Model for Pore Structure of Early-Age Composite Cement Pastes by LF-NMR

This study investigated mineral admixtures that are often utilized as replacements for cement in high-performance concrete with a view to enhancing their durability and workability. The properties of concrete are closely related to the structure of its pores. This research employed low-field nuclear magnetic resonance technology to explore the influence of water-to-cement ratio, curing time, and mineral admixture content on the pore structure of early-age cement pastes. The findings indicated that the pore size distribution curves of all composite cement pastes display a distinct bimodal nature. The size of gel pores increases with a higher water-to-cement ratio, but decreases as the curing period extends. Fly ash, slag, and silica fume improve the pore structure at 14 days, 7 days, and 3 days, respectively. The addition of admixtures has little effect on the most probable pore diameter, but raises the proportion of gel pores with increasing content. In order to better fit the experimental data, a bimodal model integrating Shimomura and Maekawa’s model with the Weibull distribution function was introduced to describe the pore structure of cement pastes with or without fly ash, slag, and silica fume.