Leaching of Hexavalent Chromium from cement treated soil

摘要

The following conclusions have been reached based on the results of the experiments and the investigation: 1) Some cement treated soil leaches Cr(Ⅳ) in spite of the fact that soil itself does not leach Cr(Ⅵ). This means that the Cr(Ⅵ) originates in stabilizing agents; 2) JLT46 values (leaching values of Cr(Ⅳ) from cement treated soil) of some soil types and stabilizing agent types, such as volcanic soil and Portland cement, are more likely to exceed JES (0.05mg/l): the Japanese environmental standard. Furthermore, JLT46 values are not affected by unconfined compressive strengths and curing periods of cement treated soil. Soil types and stabilizing agent types are the most important factors determining JLT46 values. 3) 6% of treated soil in construction sites showed JLT46 values higher than JES. In such cases, the type and dosage of the stabilizing agent are changed to satisfy JES. Applying Japanese environmental standards that are targeted at soil to cement treated soil is under consideration. But, we think it is essential to check cement treated soil to protect the health of people in Japan, because not all cement treated soil can be distinguished from ordinal soil, especially when performing shallow improvement. At the same time, Japanese cement manufacturers have prepared a guideline prohibiting the water-soluble Cr(Ⅵ) content of cement products to be under 20mg/kg. Further studies must be carried out in the future to clarify the environmental effects of Cr(Ⅵ) leached from cement treated soil.