Study On Mechanical Properties And Curing Mechanism Of Solidified/stabilized Of Zn-Contaminated Red Clay

Zinc mining,galvanizing,instrument,machinery manufacturing and other industrial activities make the soil contaminated by heavy metal zinc especially red clay which is more serious zinc pollution.The contaminated soil is cured by Solidification/Stabilization(S/S)in order to control the red clay stained by heavy metal zinc.The mechanical properties,engineering properties,chemical stability and curing mechanism of the cured soil were studied.It provides some basic data for solidified contaminated soil as the construction materials of non-sensitive areas such as shallow ground or bank revetment,which is expected to achieve the purpose of pollution control and secondary utilization.The main research results are as follows.(1)The zinc nitrate solution was mixed with air-dried red clay,and different concentrations of artificial polluted soil were arranged.It was cured with different curing age after adding cement,and then the unconfined compressive strength test was carried out.The effects of zinc concentration,cement content and curing age on the unconfined compressive strength,failure strain and deformation modulus of the cured materials were studied.The stress-strain curves of the cured materials were analyzed at different concentrations.The effect of the mechanical properties of the cured material on threshold value of zinc concentration was proposed.The method of unconfined strength prediction based on zinc concentration,cement content and curing age was discussed.(2)The effects of different zinc concentration,cement content and curing age on the stability of the cured product were studied by leaching test of solidified contaminated soil.The results show that when the cement content is 10%,the stability of the zinc-stained red clay is better.It is suggested that the adsorption of zinc on red clay plays a major role in the stability of the curing process and the hydration reaction of cement plays a synergistic role in the encapsulation and confinement of heavy metal zinc.(3)The effects of various factors on the moisture content,volume and quality of the cured product was studied by measuring the volume,water content and quality of the cured product.It was suggested that the high concentration of zinc could change the properties of the red clay and make the red clay appear hydrophilic,which resulted in the water swelling of the cured product under the standard curing condition.It is concluded that increasing the cement content can effectively reduce the expansion of the cured product,improve its unconfined compressive strength and improve the engineering applicability of the contaminated red clay.The method of analyzing the degree of hydraulicity of cured product according to the change of cured material dry mass is put forward.(4)The pore structure of the cured product was studied by mercury injection test.The curing mechanism of the cured product was discussed from meso level and micro level.(5)The chemical products of the cured product in different curing stages were studied by XRD.The chemical reaction mechanism of the cured product in different curing stages was analyzed.It was found that silica crystals were produced in the later stage of curing,and it was suggested that silica crystals which was aggregate were cemented with alcium silicate hydrate which was produced by hydration reaction in the later stage of curing,which was the main source of the later strength of the cured product.