Research On Engineering Characters And Wet-dry Durability Of Zn-contaminated Soils Stabilized By Magnesium Phosphate Cement

Magnesium phosphate cement?MPC?is a new kind of clean and efficient cementing material,which can replace the ordinary cement to deal with the increasingly serious problem of heavy metal contaminated sites.MPC is used to stabilize/solidify Zn-contaminated soils in the paper.Systematic tests and all-round analysis are carried out to investigate the UCS properties,leaching characters and durability of wet-dry.The erosion mechanism of wet-dry circulation on stabilized Zn-contaminated soils is analyzed by X-ray diffraction?XRD?and scanning electron microscopy?SEM?tests.The main conclusions are shown as below:?1?The ultimate strength and stress-strain characters of stabilized soils are obtained by UCS tests.It is showed that ultimate strength of stabilized Zn-contaminated soil grows with curing age.The UCS of stabilized Zn-contaminated soil has close relationship with the contents of fly ash,UCS increases firstly and then decreases with the increase of fly ash.The unconfined compressive strength of the sample decreases with the increase of the concentration of Zn,and downward trend is distinct in the different range of Zn concentration.With the increase of curing age and the decrease of initial concentration of Zn,the maximum strain decreases and the stress-strain relationship transformes from plasticity to brittle.?2?By leaching toxicity test,the influence of curing age,initial heavy metal concentration and fly ash content on Zn²⁺ concentration and pH value of leaching solution was studied.The results show that the leachate of Zn²⁺ is gradually decreases with the increase of curing age.The initial heavy metal concentration has a significant impact on leaching characters.With the initial concentration of Zn increases from 0.1% to 1.0%,the concentration of Zn²⁺ in leachate sharply boost.Besides,the leachate of Zn²⁺ has negative correlation with leachate p H,so the leaching concentration of Zn²⁺ decreases with the increase of pH value.The stronger of the acid-neutralizing of curing agent,the better of the stabilization effect to heavy metals.?3?Based on XRD and SEM tests,the variation of mineral composition and microstructure of the samples during wet-dry circulation was revealed.Besides,the corrosion mechanism of wet-dry circulation on solidified soil was analyzed.On the one hand,stress concentration effect in the weak positions of soil structure,which causes forming micro cracks on the soil surface and internal,then leads to compactness of the soil structure;On the other hand,the water intrusion along cracks,causes solution of excess phosphate,which formats acidic environment in water.resulting in a large number of MKP dissolves.Thus the strength of solidified soil decreases under wet-dry circulation.It is fragmentation and decomposition of the hydration gel that absorbe Zn²⁺,thus the concentration of zinc increased.