Strength and Durability of Soft Clay Stabilized with Recycled Gypsum (Bassanite)

Every construction has a certain efficient lifetime after which it would need to be repaired or demolished for further reconstruction. This would cause a specific range of waste materials, called construction and demolition (C&D) wastes. Because of the large volume of these bulky waste materials, their utilization in construction and geotechnical projects would be an attractive option in order to recycle and mitigate their volume. Gypsum and its derivatives, as a considerable fraction of C&D wastes, are classified as a group of binding agents in soil stabilization and upgrading its durability against environmental conditions. Bassanite is one of the main gypsum derivatives that is produced through heating gypsum powder at certain conditions. The feasibility of using gypseous wastes as a binding agent was studied by adding different amount of bassanite (0, 5, 10, and 20%) and 5% cement and lime to the clayey soil at different curing conditions (0, 7, 14, and 21 days). Next, the samples were subjected to wetting/drying cycles (0, 1, 2, and 3 cycles), and the effect of these factors on unconfined compressive strength and soil durability were assessed. Results showed that by adding bassanite (along with cement and lime), the unconfined compressive strength of the stabilized soils was considerably increased from 37 kPa to 603 kPa. Another effective factor on the unconfined compressive strength was the soil specimens’ conditions. The wetting/drying cycles over the stabilized samples caused 15–70% decrease in the unconfined compressive strength (according to the soil specimen and number of wetting/drying cycles). It can be concluded that the utilization of gypseous wastes is a proper method to mitigate the amount of landfilled C&D wastes and reusing these materials not only lowers the landfill costs but also significantly decreases the production costs of the materials used in soil stabilization and improvement.