Quantifying the distribution of paste-void spacing of hardened cement paste using X-ray computed tomography

The distribution of paste-void spacing in cement-based materials is an important feature related to the freeze–thaw durability of these materials, but its reliable estimation remains an unresolved problem. Herein, we evaluate the capability of X-ray computed tomography (CT) for reliable quantification of the distribution of paste-void spacing. Using X-ray CT images of three mortar specimens having different air-entrainment characteristics, we calculate the distributions of paste-void spacing of the specimens by applying previously suggested methods for deriving the exact spacing of air-void systems. This methodology is assessed by comparing the 95th percentile of the cumulative distribution function of the paste-void spacing with spacing factors computed by applying the linear-traverse method to 3D air-void system and reconstructing equivalent air-void distribution in 3D. Results show that the distributions of equivalent void diameter and paste-void spacing follow lognormal and normal distributions, respectively, and the ratios between the 95th percentile paste-void spacing value and the spacing factors reside within the ranges reported by previous numerical studies. This experimental finding indicates that the distribution of paste-void spacing quantified using X-ray CT has the potential to be the basis for a statistical assessment of the freeze–thaw durability of cement-based materials.

► The paste-void spacing in 3D can be quantified by X-ray CT.
► The distribution of the paste-void spacing follows normal distribution.
► The spacing factor and 95th percentile of CDF of paste-void spacing are correlated.