Using CT scanning to quantify the microstructure change due to freezing at various temperatures in highly-cemented clay

Deep soil mixing (DSM) has been adopted in cold regions with growing frequency over the past decade. Although there have been studies on the engineering properties of soilcrete (a product of DSM) subject to freezing/thawing (F/T) cycles, the change in microstructure, including pore size and its distribution, crack propagation, cavity volume, and cavity ratio, of the soilcrete after F/T cycles has not been sufficiently quantified. The objective of the present study was to develop and evaluate methods of assessing the microstructure of soilcrete using X-ray computed tomography (CT) scanning images. Cylindrical samples were formed by blending Edmonton clay with general Portland cement at 22% by weight. After curing for 274 days, samples underwent one F/T cycle at varying freezing temperatures from −2 to −20 °C. Samples with and without F/T cycles were scanned with a CT apparatus and the images were analyzed to quantify the microstructure of soilcrete. Results showed that the volumetric cavity ratio of the soilcrete changed significantly after the F/T cycle and increased with the declining temperature. The cavity was divided into planar cracks and bulky holes based on the difference in their geometry. The volumetric distribution of planar cracks was illustrated and the equivalent diameter distribution of bulky holes varied with temperatures. Unconfined compressive tests were carried out on dry samples to identify factors on the detrimental effect owing to F/T cycles. The ultimate strength of dry soilcrete samples slightly oscillated despite an exposure to severe F/T cycles. Therefore, one may infer that the pore water phase played a more significant role in the microstructure change caused by F/T cycles than the solids phase.