Pore-scale drying kinetics of white cement mortars through the LF-NMR relaxation technique

Many engineering properties of cement-based materials (CBMs) are intimately linked with their moisture contents and pore structure. The drying kinetics of CBMs is essential for elucidating their mass transport, shrinkage cracking, and durability performance. To clarify the pore-scale drying kinetics of CBMs and compare them with those of other rigid porous media, the low-field nuclear magnetic resonance relaxation technique is employed to non-destructively monitor the dynamic water allocation in white cement mortar and sandstone specimens during drying. Experimental results show that at the pore scale, the drying of sandstone is found to be a water removal process from coarse to fine pores sequentially. However, regarding cement mortars, not only does capillary pore water evaporate and lose upon drying, but the water confined in interlayer and gel pores is also progressively drained out at the same time. This pore-scale water removal kinetics indicates the contraction of [Figure presented] gel, collapse of interlayer and gel pores, and remarkable coarsening of overall pore structure. This moisture-dependent pore structure of CBMs is rooted in the featured nanoscale pore structure of [Figure presented] gel and its high sensitivity to moisture, which is critical for modeling moisture transport and other moisture-regulated performances of CBMs.