Effect Of Salt Content On Strength Characteristics Of Solidified Sulphate Saline Soil

The salt content has a great influence on the type and content of the curing agent in the solidified saline soil,but the research on the curing of the sulphate saline soil is carried out for certain salt content and its general law is less.The purpose of this paper is to study the change law of mechanical properties of the solidified sulphate saline soil caused by the change of sulfate salt content,the lime-fly ash,sodium silicate,lime-fly ash and sodium silicate are selected to solidify sulphate saline soil.The unconfined compressive strength test was conducted to research the variation law of the compressive strength of the solidified sulphate saline soil with the change of salt content.Also,limit moisture content,X-ray diffraction(XRD),Fourier Transform infrared spectroscopy(FTIR)and physical adsorption tests were carried out to reaearch the consistency characteristics,phase characteristics,chemical composition and microstructure of the solidified soil with different salt content and discuss the mechanism of the effect of salt content on compressive strength.(1)The results of unconfined compressive strength test of sulphate saline soil with different salt content solidified by lime-fly ash are shown as:? Under the same salt content,the unconfined compressive strength of the solidified soil increases firstly and then decreases with the increase of lime content when the salt content is lower than 2.8%,and peak strength corresponds to a lime content of 9%.but the strength of solidified soil increases with the increase of lime content when the salt content is higher than 2.8%.?Under the same lime content,the unconfined compressive strength of solidified soil increases firstly and then decreases with the increase of salt content,and peak strength corresponds to the salt content of 1.8%.A certain amount of SO42-in the soil is benefit to improve the compressive strength of the soil solidified by lime-fly ash,the strength growth mechanism:on the one hand,under the action of Ca2+,high strength and dense ettringite is produced by the reaction of SO42-and activated alumina in the fly ash,on the other hand,sulphate stimulates the activity of fly ash as a base activator and the pozzolanic reaction of active SiO2 and Al2O3 with Ca(OH)2 produces more hydrated calcium silicate gel and hydrated calcium aluminate gel,so it improves the strength of the solidified soil.(2)The results of unconfined compressive strength test of sulphate saline soil with different salt content solidified by sodium silicate are shown as:The unconfined compressive strength of the solidified soil shows a decreasing trend with the increase of salt content.When the salt content increases to 2.3%,on the one hand,the mirabilite crystal will be formed in the solidified soil samples,as the mirabilite crystal volume is 4.18 times the sodium sulphate anhydrous,the formation of a large number of mirabilite crystal will extrude solidified sulphate saline soil samples so that the volume of samples swell intensely resulting in micro-cracks,so the destruction of structure will appear;on the other hand,Na+ is dissociated from Na2SO4 so that the Na+concentration increases around colloidal silicate.It accelerates the polymerization of colloidal silicate to promote its gelation so that the bond strength of the soil solidified by sodium silicate is reduced,resulting in the decrease in unconfined compressive strength of the saline soil solidified by sodium silicate.(3)The results of unconfined compressive strength test of sulphate saline soil with different salt content solidified by lime-fly ash and sodium silicate are shown as:the unconfined compressive strength of solidified soil increases firstly and then decreases with the increase of salt content,and peak strength corresponds to the salt content of 1.8%.The change law of compressive strength of lime-fly ash and sodium silicate solidified soil with salt content is approximately the same as that of lime-fly as hsolidified soil.