Slaking mechanisms of a mudstone and prediction of its number-size distribution considering shape evolution

The wide distribution of mudstone poses challenges to efficient construction and safe long-term maintenance of infrastructure, primarily due to its susceptibility to slaking. To explore the slaking mechanisms, cyclic wetting–drying slaking tests under both atmospheric and vacuum conditions were conducted on natural mudstone collected from Akita Prefecture, Japan. A multi-view approach was employed to capture the evolution of three-dimensional particle shape, enabling quantitative analysis of slaking mechanisms and the development of number-size and surface area-size distribution models that account for shape effects. The results indicate that the atmospheric slaking proceeds more rapidly than vacuum slaking tests, attributed to the elimination of the air-breakage phenomenon. Shape evolution analysis reveals that the shell-like medium-sized particles possess higher specific surface areas, resulting from the typical layered slaking phenomenon observed during slaking. These layered fragments are attributed to differential swelling, driven by non-uniform moisture distribution in the specimens. The contribution of this mechanism is validated and quantitatively assessed through a comparative analysis of particle shape compositions across different slaking conditions. Finally, particle shape evolution is integrated into predictive models for number-size and surface area-size distributions. The performance of these models is verified against experimental measurements.