Development of composite geomaterials with immobilization effect of harmful substance and evaluation of recycle efficiency of wastes

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Geomaterials using waste materials have been developed in the geotechnical engineering field. It is important to clarify immobilisation effect of harmful substances and the extent of environmental load of these geomate-rials. In this study, laboratory tests for investigating the leachate and mechanical properties are carried out on four types of geomaterials with immobilisation treatments for heavy metals : cement-treated soil, baking solidification material, plastic melting solidification material and mixture with charcoal A parameter for representing recycling efficiency is proposed in consideration of the utilisation of waste and CO2 emission in the manufacturing process of the geomaterials. The recycling efficiency of composite geomaterials is calculated using MSW(Municipal Solid Waste) incineration bottom ash, and its environmental impact is evaluated.Geomaterials with various immobilisation treat-ments for heavy metals are produced and several laboratory tests have been carried out. The environ-mental impact of the geomaterials using wastes is also discussed. The following conclusions are ob-tained from this study :1)The immobilisation effects of heavy metals on the cement-treated soil, baking solidification mate-rial, plastic melting solidification material and mix-ture with charcoal are clarified by the results of the leaching test.2)Cement-treated soil and baking solidification material are effective for the immobilisation treat-ment of polluted sandy soil with heavy metals and their effect becomes much greater by mixing clay. Plastic melting solidification material and mixture with charcoal are also effective as new treatment methods.3)CO_2 emission of the geomaterials using MSW incineration bottom ash is calculated based on the concept of LCA.4)A parameter for representing recycling effi-ciency is proposed. It is confirmed that the recycling efficiency of various geomaterials can be evaluated from this calculation method.