Environmental effects on durability of soil stabilized with recycled gypsum

The use of recycled gypsum, which is derived from gypsum waste plasterboard, for ground improvement has recently been initiated in Japan and is not widespread around the world. As such, it is essential to explore the effect of environmental conditions on the performance and durability of soil stabilized with recycled gypsum. This is especially important in cold and rainfall regions such as in Japan, due to the solubility of gypsum. This paper presents an integrated experimental study to investigate the effect of environmental factors, in terms of freeze–thaw and wet–dry cycles, on the durability of soil stabilized with recycled gypsum. For this purpose, four different contents of recycled gypsum ranging from 0 to 20% were used. Four different cement contents ranging from 0 to 5% were used as solidification agent to optimize the cement content which is adequate to prevent the solubility and improve the durability. To study the effect of environmental factors on the durability, cylindrical specimens of stabilized soil were compacted at maximum dry unit weight and cured for 7 days under constant temperature and humidity. Subsequently, specimens were subjected to different numbers of freeze–thaw and wet–dry cycles. They were then tested for compressive strength, loss soil weight, and volume change. Results showed that compressive strength of stabilized specimens decreased while accumulated soil losses weight increased with the increase of both numbers of freeze–thaw and wet–dry cycles. Freeze–thaw cycles have a significant effect on the durability reduction of stabilized soil compared with the effect of wet–dry cycles. The durability of stabilized soil improved with the increase of both contents of recycled gypsum and cement. The 2.5% cement content is adequate to improve the durability of soil stabilized with recycled gypsum based on ground mechanical and economic functions. Both freeze–thaw and wet–dry cycles have insignificant effect on the volume change of soil stabilized with recycled gypsum. After using 2.5% of cement content, the strength of stabilized soil specimens increased slightly with the increase of wet–dry cycles; subsequent to that, the strength declined with increasing wet–dry cycles. Soil stabilized with only recycled gypsum and without any solidification agents, such as cement, is not durable against environmental conditions.