Behaviors of expansive soils mixed with polymeric stabilizing foams

Shrinkage cracking in pavement subbase layer is a major cause of distress in pavements, especially for pavements on expansive soils. Polymeric soil stabilizing agents can potentially mitigate such problems, because of its ability to improve soil mechanical properties, such as reducing shrinkage cracking and improving the soil strength. In this research, experiments have been conducted to investigate two types of polymeric stabilizing agents, i.e. one hydrophilic polyurethane foam and one hydrophobic polyurethane foam, for mitigating soil shrinkage. Bentonite clay was used in the experiment due to its high shrinkage potential. Two types of polymeric foam were mixed with bentonite at different weight ratios, and the moisture behavior reflected by water content change were studied over time. The behaviors of each chemical foam agent were also quantified by the video camera. The results show when PU foams were added at a relatively low weight ratio (< 5%), the shrinkage property has been improved, because 3%~5% more moisture can be retained inside samples. Besides, comparing with hydrophobic PU foam, hydrophilic PU foam has a greater effect on alleviating shrinkage distress at the early stage. In the meanwhile, samples with PU foam show earlier cracking than the pure bentonite sample, possibly because the application of PU foam makes sample be stiffer and of higher stress. Nonetheless, it is notable that the de-polymerization of hydrophobic PU foam occur in the experiment. Therefore, it is worth being studied further before applying polymeric stabilizing agents in engineering.