The Research On The Carbonation Of Solidified Pb-contaminated Expansive Soil

The research on solidified/stabilized heavy metal-contaminated soil has been a focus in Geoenvironmental engineering field,and tremendous achievements have been achieved.However,the investigating subject was limited in ordinary clay and fewer reports concerning the special clay like expansive soil are in press.Besides,the excessive attention on type of binders,type of heavy metal ions or some other factors will impose restrictions on the development of solidification/stabilization theory.The investigations,focusing on the long-term behavior of solidified/stabilized heavy metal-contaminated soil under the ambient environmental attack,such as drying and watering cycling,freezing and thawing cycle,chemical leaching and attack,carbonation and so on,are a significant constituent part of solidification/stabilization theory.The effects and mechanism of these attacks still remain unclear.With the financial support of National Natural Science Foundation of China?NO.4167020957?,this study investigated the effects on basic physical and mechanics properties,chemical leaching behaviors and micro structure characters of solidified/stabilized lead contaminated-expansive soil imposed by accelerated carbonation.With the combination of qualitative analysis and quantitative analysis,the mechanism of carbonation has been revealed from the perspective of microcosm.The major findings are summarized as following:?1?The research states of the carbonation on concrete and cement mortar are reviewed systematically.The methods of carbonation depth measuring and effects of carbonation on concrete,cement and solidified matrix are summarized.?2?With the subject of lime solidified soil and the way of single axis carbonation,the carbonation depth and rate have been investigated and the results indicate that the carbonation depth and square of time?d?exhibits a good linear relationship.And the power function can depict the relationship between carbonation rate and time?h?.?3?Based on the complete carbonated specimen of lime and alkaline residue-solidified soil,the basic physical properties like water content,clay particle content,plastic and liquid limit,pH,free expansive ratio,specific gravity and unconfined compression strength were investigated.And the comparison between lime and alkaline residue-solidified soil has been made.?4?Based on the semi-dynamic leaching test,the leaching behavior of lead(Pb²⁺)and calcium(Ca²⁺)were investigated under the carbonation curing and standard curing condition.With the quantitative analysis,the effective diffusion coefficient?D_e?,leachability index?Lx?,and the leaching mechanism of ions were used to evaluate the efficient of solidification and the adverse effect of carbonation.?5?A series of micro experimental methods,such as X-ray Diffraction?XRD?,Thermo-gravimetric Analysis?TGA?,Mercury Intrusion Porosimetry?MIP?,and Scanning Electron Microscope?SEM?,have been adopted to study the pore structure and minerals.With the combination of qualitative analysis and quantitative analysis,the micro mechanisms which can explain the macro evolution heave been proposed.The mechanism of degradation caused by carbonation can be revealed clearly from both micro and macro perspective.