Environmental Evaluation for Clayey Soil Stabilized with Gypsum Waste Plasterboard in Japan

This paper presents results of a preliminary investigation of utilizing recycled gypsum derived from gypsum waste plasterboard to improve the strength of clayey soil for embankment construction, while considering environmental impacts. A case study was conducted to investigate different recycled gypsum content percentages, cement types, and cement content percentages. Four different recycled gypsum content percentages range from 0 to 10% were investigated. In this case study, cement was added to develop solidification for recycled gypsum and to improve environmental properties. Two different types of cements, the Portland and Furnace slag type B with a content range from 0 to 3% were used. A series of unconfined compression tests were conducted to evaluate the strength of treated clay. In addition, a series of environmental tests were conducted to explore the solubility concentration of Fluorine, Boron, and Chromium in the untreated and treated clay specimens. Furthermore, hydrogen sulfide and pH were investigated. Results showed that compressive strength of treated clay increased with the increase of recycled gypsum content. The use of recycled gypsum within the investigated limits has no adverse effect on pH value. The hydrogen sulfide gas is less than the standard permitted limits. The solubility of Fluorine, Boron, and Chromium leached from soil-gypsum mixture within the investigated limits were found less than the approved standard values.