SIMULATING THE FIELD DISINTEGRATION BEHAVIOR OF CLAY-BEARING ROCKS

Clay-bearing rocks exhibit varying degrees of disintegration when subjected to atmoshperic conditions which results in numerous problems in engineering constructions. This study simulated the disintegration behavior of clay-bearing rocks under natural atmospheric conditions, and evaluated the degree of disintegration quantitatively. The simulation set up involved exposing 12 replicate samples each of 20 different clay-bearing rocks (5 claystones, 5 mudstones, 5 siltstones, and 5 shales), a total of 240 samples, to natural atmospheric conditions. To accomplish this, the samples were placed on the roof of McGilvrey Hall at Kent State University for a one-year period, from September 2009 to September 2010. All samples consisted of 10 pieces, with each piece weighing 40-60 g, and the total sample weight being 450 to 550 g. Each month, one sample from each of the 20 rock types was taken out, oven dried, and tested for grain size distribution using a series of standard sieves. The amount of disintegration was evaluated using “Disintegration Ratio” which is defined as the ratio of the area under the grain size distribution curve for a given clay-bearing rock to the total area encompassing grain size distribution curves of all 20 clay-bearing rocks. A disintegration ratio close to zero indicates a very low durability while a value close to 1 means high durability. The simulation experiment results show that the clay-bearing rocks exhibit a wide range of disintegration behavior. After 9 months of exposure, the disintegration ratio averages 0.029 for claystones, 0.226 for mudstones, 0.764 for siltstones, and 0.355 for shales. Claystones disintegrated the most and siltstones the least, with shales and mudstones exhibiting the intermediate amount of disintegration. The advantage of using the disintegration ratio approach is that it indicates not only the durability of the rock tested but also the nature of disintegrated material in terms of particle sizes.