Comparing the Slaking of Clay-Bearing Rocks Under Laboratory Conditions to Slaking Under Natural Climatic Conditions

The objective of this study was to compare the laboratory slaking behavior of common clay-bearing rocks to their slaking behavior under natural climatic conditions observed during a 1-year experimental study. Five-cycle slake durability tests were performed in the laboratory on five claystones, five mudstones, five siltstones, and five shales. Twelve replicate specimens of each of these 20 rocks were also exposed to natural climatic conditions for 12 months. After each month of exposure, one replicate specimen of each rock was removed from natural exposure and its grain size distribution was determined. The results of laboratory tests and field experiment were compared in terms of 1st, 2nd, 3rd, 4th, and 5th cycle slake durability indices (Id(1), Id(2), Id(3), Id(4), Id(5)), grain size distribution of slaked material, and disintegration ratio (D (R)), where D (R) is the ratio of the area under the grain size distribution curve of slaked material for a given specimen to the total area encompassing all grain size distribution curves of the specimens tested. Correlations of Id(1), Id(2), Id(3), Id(4), and Id(5) with D (R) values for laboratory specimens exhibit R (2) values of 0.87, 0.88, 0.83, 0.75, and 0.70, respectively. However, the relationship between Id(2) and D (R), determined after 1, 3, 6, and 12 months of natural exposure, becomes weaker with increasing time of exposure, with R (2) values of 0.65, 0.63, 0.63, and 0.25, respectively. The fifth-cycle slake durability index (Id(5)) for laboratory tested specimens shows a better correlation with D (R) values for naturally exposed specimens (R (2) up to 0.80). A comparison of grain size distribution curves of slaked material for laboratory specimens, after the 2nd cycle slake durability test, with those of specimens exposed to natural climatic conditions shows that the laboratory test underestimates the field durability for claystones, and overestimates it for siltstones.