Abstract: To optimize the mechanical properties of iron tailings sand and enhance its deviatoric stress and deformation modulus,the approach of external addition of fly ash along with curing was employed for improvement. Through conventional triaxial compression tests,the enhancement effects of different fly ash dosages and curing ages on the shear strength and deformation modulus of the specimens were investigated. The influences of fly ash dosage on the microstructure of the specimens and the effects of curing age on the composition variations of the specimens were explored via scanning electron microscopetests and X-ray diffraction tests. The intrinsic mechanisms of these changes on the mechanical properties were analyzed. The results indicate that as the fly ash dosage increases,the deviatoric stress and deformation modulus of the specimens initially increase and subsequently decrease,reaching the maximum when the fly ash dosage is 25%. As the fly ash dosage rises,the cohesion of the specimens significantly increases,while the internal friction angle gradually reduces. Through microscopic tests,it is evident that fly ash can effectively fill the pores between iron tailings sand particles,making the specimens more compact. Moreover,the fly ash within the specimens reacts with water to generate amorphous gels,hydrated calcium silicate gel and calcium carbonate after reacting with water. And after the sample is cured,the mechanical properties of the sample can be improved. Comprehensively considering the performance improvement effect of fly ash modified iron tailings sand,25% fly ash is used to improve and maintain the best effect. 

Key words: iron tailing sands,mechanical properties,fly ash,scanning electron microscope test,X-ray diffraction test