Characteristics And Mechanism Of MgO-based Binders Stabilized/solidified Contaminated Soil:Curing Under Different Temperatures

China has large area and complex climatic conditions,the temperature of soil of these area changes a lot under different seasons.It has been reported that temperature put great impact on the physical,chemical and mechanical properties of soils.However,the effects of temperature on stabilized/solidified contaminated soil is seldom studied.This thesis is supported by the National Natural Science Foundation(No.51608113,41330641).In this study,a MgO-based binder was used to treat lead-zinc contaminated soil.The characteristics of strength,leaching property,durability and microscopic mechanism are discussed by the unconfined compressive strength test,the toxic characteristic leaching procedure(TCLP),the freeze-thaw cycle test,the wet-dry cycle test and micro-tests.The main findings are listed below:(1)The strength : The unconfined compressive strength of GMC treated contaminated soil increases with the increase of curing temperature.The strength of GMC soil cured under 45? is 58% higher than that cured under 21?.Compared with PC treated soil,the strength of GMC cured soil was affected more significantly by curing temperature.The strength of the GMC treated soil increases linearly with the addition of binder dosage(5%-15%).The strength of GMC solidified soil decreases with the increases of the concentration of lead.(2)The leaching property: The TCLP test shows that the leaching concentrations of zinc and lead decrease with the increase of binder dosage and curing temperature.Compared with PC treated soil,the leaching concentrations of Pb and Zn in the GMC stabilized/solidified soil was affected more significantly by their curing temperature.For example,when the curing temperature of GMC treated soil increases from21°C to 45?,the leaching concentration of Zn decreased by 44%,while the lead leaching concentration decreased by 62%.With the increase of Pb concentration,the Pb and Zn leaching concentrations of GMC and PC treated soil both increased.Compared with PC,GMC showed a better performance on the treatment of high-concentration Pb-contaminated soil as well as complex heavy metal contaminated soil.(3)The durability: After the freeze-thaw cycle test,the mass loss rate,strength loss rate and the Pb and Zn leaching concentrations change rate of GMC treated soil are found lower than PC treated soil.However,after the drying and wetting cycle test,the mass loss rate and strength loss of GMC treated soil are found higher than that of PC cured soil.The Pb and Zn leaching concentrations of GMC treated soil are found higher than that of PC solidified soil.The durability of both PC and GMC treated soil increases with the raise of curing temperature.(4)The microscopic mechanism: The X-ray diffraction results show that the main hydration products of GMC treated soil are hydrated calcium silicate(C-S-H)and hydrotalcite(Ht).The results of scanning electron microscopy show that when GMC treated soil cured under high temperature,the Ht-gels make the treated sample more dense,and compact network structures are also identified.