A cement-based composite curing agent was developed for solidifying chromium-contaminated shield muck to overcome the problems of high emissions and unsatisfactory curing performance of single curing materials,and to realize resource utilization.A five-factor and four-level orthogonal test was designed to determine the optimum ratio of the composite curing agent,using the unconfined compression strength and leaching toxicity of the cured soil at 14 d of age as the evaluation index.The main effect analysis of each influencing factor was carried out by using the method of extreme deviations analysis,and the mechanism of the compound organic-inorganic curing agent was investigated by combining XRD and SEM tests.The results show that the optimum solution of the two evaluation indexes of unconfined compression strength and leaching toxicity is that the mass fractions of cement,quicklime,polyacrylamide,sodium silicate and sodium alginate are 11% ,5.50% ,0.25% ,1.10% and 0.05% ,respectively.The unconfined compressive strength of the cured soil in No.13 test reaches 1 217.58 kPa and the leaching mass concentration of heavy metal chromium is 2.4 mg/L at the age of 14 d,which meets the requirements of the relevant specifications.Cement,sodium alginate and sodium silicate are the main influencing factors for the evaluation index of unconfined compressive strength of cured soil,and cement,sodium alginate and quicklime are the main influencing factors for the evaluation index of leaching toxicity.The unconfined compressive strength of cured soil is closely related to the leaching mass concentration of chromium heavy metal,which shows that the greater the unconfined compressive strength of cured soil,the more obvious the stabilization effect of chromium heavy metal.A large amount of free water is consumed,and the increase of pH,the formation of new minerals and the microstructural changes of the soil are the main factors for the improved performance of the shield muck.The increase in strength of the cured soil is accompanied by the increase of the physical confinement of the heavy chromium metal.In addition,the higher pH at which the hydration reaction occurs also promotes the formation of water-insoluble hydroxide precipitates of trivalent chromium,thus reducing the toxicity of the leaching of heavy chromium metal from the cured soil.
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