Application of soil improvement material using recycled gypsum considering the environmental safety

Abstract

Currently, in Japan, recycling of various industrial waste is proceeding to create a recycling-oriented society. Waste gypsum boards generated at the time of constructing and dismantling buildings are industrial waste requiring recycling. Waste gypsum boards are separated into board paper and recycled gypsum in the intermediate processing facilities. The recycled gypsum powder is effectively used as a raw material for cement, raw material for neutral ground improvement materials, and ground improvement materials for agriculture. However, when used as a ground improvement material, it is pointed out that the fluorine contained in recycled gypsum powder may dissolve into the improved ground. Therefore, to use recycled gypsum powder effectively on the ground, it is important to ensure that the fluorine is insolubilized for the environmental safety. In this research, applicability of ground improvement solidification material using regenerated hemihydrate gypsum powder was investigated. Especially on improvement of soft ground, the results of investigation is reported focusing on the improved properties of regenerated hemihydrate gypsum improved soil, long term durability, and re-sludge characteristics.