Explanation and Evaluation of Environmental-Geotechnical Properties of Foaming/Hardening-treated Soil Neutralized by Carbon Dioxide

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The purpose of this study is to clarify the possibility of incinerated ashes as hardening additives which affect the cement treatment of cohesive soil. The three kinds of ashes, i.e. the fluidized bed combustion coal fly ash, the pulverized coal fly ash and paper sludge incinerated ash, are used as hardening additives. The elution characteristics of heavy metals from cement treated cohesive soil were investigated by the X-ray fluorescence spectrometer for practical application. Furthermore, The neutralization method of the treated cohesive soil stabilized by cement using carbon dioxide is discussed.The main conclusions are summarized as follows :(1) It is found that the strength of the treated cohesive soil mixed with cement stabilizer and coal fly ashes have been increasing during aging period.(2) The fluidized bed combustion coal fly ash including many SO_3 and CaO works effectively as a hardening additives. However, the pulverized coal fly ash did not have much effect on the strength appearance of treated cohesive soil.(3) The main reaction products which contribute to strength are ettringite and calcium silicate hydrate compound.(4) The result of elution test of treated cohesive soil, chromium is only measured to exceed the allowable level of the Japanese environmental standard.(5) The treated cohesive soil can be fully neutralized by ventilation of carbon dioxide within about four hours.(6) A large amount of carbon dioxide is necessary to fully neutralize the cement-treated cohesive soil during mixing process.(7) It was confirmed that the neutralization method is impossible to apply to the in-pipe mixing method because the cohesive soil is placed in a few minutes from the dredging.