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A quantitative characterization of spatial arrangement of air voids in mortars via X-ray CT and numerical calculations



Edward Garboczi, Kai Lyu, Yufeng Gao, Changwen Miao, Xiaoyan Liu


Compared with overall air void content and size distribution, the spatial arrangement of air voids is probably of more importance in the durability of cement-based materials subjected to repeated freeze-thaw cycles. In this paper, using X-ray computed tomography (X-ray CT), the spatial distribution of air voids was characterized by various spacing factor indices. The effect of fine aggregate (sand) size and blended proportions were combined into sand specific surface area (SSA) in order to understand the influence of sand size, via SSA, on the spacing distribution computed in various ways. Spacing factors were defined and evaluated based on the void – void proximity and the paste – void proximity methods. The varying distributions were compared with each other, as well as with analytical results, to understand their reliability and differences. Characteristic parameters were quantitatively derived from the various distribution curves for further comparison and the relationship between average spacing factor and specific surface area of sand grains was established. To further understand the effect of the presence of aggregates, the images were segmented into paste, void, and sand phases. Finally, the air void content was artificially doubled through a blend of simulation and XCT experiment and used to compare the effect of void size and void count on the overall spacing factor calculation.
Construction and Building Materials


air void, void – void proximity, paste – void proximity, growing spheres count dilation method, random points method, X-ray computed tomography


Garboczi, E. , Lyu, K. , Gao, Y. , Miao, C. and Liu, X. (2022), A quantitative characterization of spatial arrangement of air voids in mortars via X-ray CT and numerical calculations, Construction and Building Materials, [online],, (Accessed April 13, 2024)
Created November 4, 2022, Updated February 7, 2023