Investigation of recycled gypsum in conjunction with waste plastic trays for ground improvement

During the three stages of production, construction and demolition, approximately 15 million tons of gypsum waste plasterboard is generated annually in the world. It is considered a serious problem due to scarcity of land-filling space, increasing the cost of disposal and increasing environmental regulations. Investigations of using recycled gypsum “bassanite” which is derived from gypsum waste plasterboard and waste plastic trays for ground improvement were studied. Recycled gypsum was used as a stabilizing agent to improve the compressive strength while the waste plastic trays were used to improve the tensile strength. Recycled gypsum content, curing time and frost heave property throughout capillary rise test were investigated to determine the behavior of treated soil with recycled gypsum. In addition, size, content and aspect ratio of strips of waste plastic trays were investigated. Test results showed that increasing recycled gypsum content has a more significant effect on compressive strength compared to the tensile strength. The effect of curing time on the strength of treated soil samples with recycled gypsum is much pronounced in the early curing days compared to later ages. Adding strips of waste plastic trays to samples treated with recycled gypsum enhanced both splitting tensile and compressive strengths as well increased the value of secant modulus. Capillary rise rate was reduced with the increase of recycled gypsum content, which helps to reduce the formation of ice lenses; hence the susceptibility of treated soil against frost heave is increased. The size and content of strips of waste plastic trays have significant effect on the potential of capillary rise and the enhancement of strength and stiffness of tested soil.