Evaluating the Influential Factors on Cr(VI) Leaching from Compacted Cement-Stabilized Soil through Tank Leaching Tests

In Japan, one commonly uses soil improvement techniques, involving the application of cement-based stabilizer, which is readily available locally and can achieve sufficient compressive strength within a short period.However, previous research has indicated potential environmental concerns associated with the use of cement stabilized soil, since cement materials contain certain amounts of hexavalent chromium (Cr(VI)).In addition, in 2022, the environmental criterion for Cr(VI) concentration in groundwater was lowered to 0.02 mg/L in Japan.Considering these conditions, a comprehensive understanding of the leaching behavior of Cr(VI) released from the cement-stabilized soil is essential for evaluating their environmental consequences.This research investigates Cr(VI) leaching from the cement-stabilized soil by conducting the tank leaching tests (TLTs), focusing on influential factors such as mixing methods (dry (DM) and wet (WM) methods), curing periods, specific surface areas of the specimens, and liquid-to-solid ratios.The results indicate that the Cr(VI) leaching concentrations of the WM specimens are much lower than those of the DM specimens of equivalent unconfined compression strength, In WM, Cr(VI) is undetectable due to specimen homogeneity and enhanced hydration of the cement.Currently, the leaching concentration after immersing specimens for 28 days is measured according to the Japanese regulation.However, this may lead to underestimation of the leaching rate of Cr(VI) concentration, as the highest leaching concentrations are observed before 28 days.Moreover, the effect of curing periods suggests that the specimens cured for 7 days exhibit higher Cr(VI) leaching concentrations than those cured for 28 days, attributed to the enhanced precipitation of Cr(VI) by hydration products such as Ca(OH)2.A quicker leaching rate is achieved by a higher specific surface area.It is apparent that considering these effects is important to determine the appropriate regulations for the TLT.