2011 Volume 51 Issue 6 Pages 975-990
Approximately 1.6 million tons of gypsum waste plasterboard are produced annually in Japan. As such, it is essential to find an alternative way to reduce the quantities of this waste material to avoid environmental problems and the high cost of disposal in landfill. This paper describes a case study focused on the use of recycled gypsum, which is derived from gypsum waste plasterboard, to improve the strength of soft clay soil for embankment construction projects taken in consideration environmental impacts. Four different recycled gypsum contents ranging from 0 to 10% was investigated. Two different types of cements—Portland and Furnace slag type B—with a content ranging from 0 to 3% was used to develop solidification for recycled gypsum and improve environmental properties. For this purpose, a series of unconfined compression tests were conducted to evaluate strength performance of treated clay. While a series of environmental tests were conducted to explore the solubility concentration of fluorine, boron, and hexavalent chromium in the untreated and treated soil specimens. Furthermore, hydrogen sulfide and pH were investigated. Results showed that compressive strength and unit weight of treated clay soil increased with the increase of recycled gypsum content. The strength obtained in the field for treated soil with recycled gypsum was found to be greater than that obtained in the laboratory. The early curing days for soil-gypsum mixture had a significant effect on strength performance compared to the later days. The additives of recycled gypsum for tested soil swiftly increased the strength. This is a vital property for improvement embankment trafficability that helps to reduce the construction time and cost. The use of recycled gypsum within the investigated limits had no adverse effect on pH value and hydrogen sulfide gas was found to be less than the standard permitted limits. As well, the solubility concentrations for fluorine, boron, and hexavalent chromium were found within the permitted standard limits in Japan. The curing time had a significant effect on the reduction the release of harmful substance elements investigated. Furnace cement type B had the potential to improve the mechanical and environmental functions for soil-gypsum mixture. It is recommended that Furnace cement type B be used as a solidification agent for soil treated with recycled gypsum because it has low cost and it is more environmentally friendly than Portland cement.
