Influence of geologic and index properties on disintegration behavior of clay-bearing rocks

Clay-bearing rocks exhibit a broad range of disintegration behaviors with 2nd-cycle slake durability index values from 0% for some claystones to nearly 100% for some siltstones. This variability comes from their geologic make up, especially clay content, clay mineral composition, and related index properties. To investigate the influence of geologic and index properties on disintegration behavior under natural climatic conditions, 12 replicate samples of each of 20 clay-bearing rocks (5 claystones, 5 mudstones, 5 siltstones, and 5 shales) were exposed to natural conditions for 12 months. After each month, one replicate sample of each rock was tested for grain size distribution. Disintegration ratio (DR), the ratio of the area under the grain size distribution curve of slaked material for a given rock to the total area encompassing all grain size distribution curves of the tested samples, was used to quantify the amount of disintegration. Additionally, clay mineralogy, natural water content, dry density, void ratio, absorption, adsorption, Atterberg limits, and slake durability index were determined. Clay mineralogy and index properties were correlated with DR values after 1, 6, and 12 months of exposure. Results show that clay content, percentage of expandable clay minerals, plasticity index, adsorption, and slake durability index are better indicators of short-term disintegration behavior, whereas expandable clay mineral content and absorption influence long-term behavior. Regression models suggest that short term disintegration behavior can be predicted more accurately than long term behavior, as indicated by decreasing R2 values for samples exposed for 1, 6, and 12 months, respectively.