Enhancement of clay-concrete interface strength through applying cycles of heating and cooling

Abstract

This research studied the effect of heating and cooling cycles on the interface strength of saturated low plasticity clay soil (with a plasticity index of 12) in contact with concrete and the potential for using heating to increase pile capacity. A modified direct shear test device with clay specimen dimensions of 300 × 300 × 200 mm, featuring a concrete block at the bottom, was used for the tests. The heating system used heating rods to warm circulating water, which in turn heated the specimens. Four tests were conducted without heating-cooling cycles at ∼ 20 °C at effective normal stress of 30, 69, 110, and 150 kPa. Specimens subjected to effective normal stresses of 69, 110, and 150 kPa were tested under one heating cooling cycle up to 40, 55, and 70 °C, while the specimen under 30 kPa underwent only one heating-cooling cycle up to 70 °C. Additional tests were performed on specimens under 110 kPa with 4 heating-cooling cycles up to 40 °C, 4 heating-cooling cycles up to 55 °C, and 4 heating-cooling cycles up to 70 °C, as well as 9 heating-cooling cycles up to 55 °C. The results showed a significant increase in peak and post-peak interface friction angles by a range of 5.4% to 43.2%. The thermally induced volumetric strain due to contraction (TIVS) increased with increasing target temperature, but remained constant regardless of changes in applied effective normal stress.