The Effect of Varying Heat Temperatures on the Grading and the Swelling Behavior of Expansive Clay Soils

Because of their alternate swelling and shrinkage behavior during wet and dry seasons respectively, expansive soils are highly problematic, causing damage to structures and pavements built on them. There are many methods of improving such soils. This paper examines the effect of thermal stabilization on the grading and swelling characteristics of a naturally occurring black cotton spoil, an expansive clay. The thermal treatment involved heating the soil in temperatures ranging from 200 to 12000C for 2 hours in a closed kiln, and then carrying out tests on the neat and heated samples so as to obtain an optimal temperature. The tests included particle size distribution, atterberg limits and free swell. The soil grading altered progressively from one consisting of clay and silt to one consisting of sand and gravel. The swelling characteristics increased as the clay was up-to a temperature of 2500C then decreased steadily, diminishing at 7000C. Thus the optimal temperature was obtained as 7000C. This shows that heating expansive clays to 7000C can reduce their swelling characteristics, and make them suitable for use as fill materials.