Experimental Study On The Engineering Performance Of Calcium Carbide Slag-fly Ash Solidified Sulfate Saline Soil

Influenced by the geographical environment and regional climatic conditions,there are more sulfate saline soils in the soils of the central arid zone of Ningxia region.Due to the sulfate saline soil itself in the external environment of the temperature,humidity and other changes are prone to salt freeze swelling,solution trap and other engineering diseases,causing the internal structure of the soil damage,reduce the soil bearing capacity,and then affect the stability of the foundation.In order to eliminate or reduce the engineering damage caused by sulfate saline soils and to improve the structural stability of the soil,it is necessary to use curing agents to solidify them.Among them,cement and lime are two saline soil curing agents frequently used by domestic and foreign scholars,but the high energy consumption and high carbon dioxide emission make them contrary to the current national policy of environmental protection,energy conservation and emission reduction.Thus,it is necessary to explore the use of solid waste materials to realize the solidification of sulfate saline soils in Ningxia area and provide new ideas for the treatment of sulfate saline soils in local engineering construction.On the basis of extensive literature research,the paper took a typical sulfate saline soil in Hongsibu district of Ningxia as the research object,made sulfate saline soil specimens by washing salt and removing impurities,and then uniformly controlled the dry density and water content of the specimen soil,added sodium sulfate salt,calcium carbide slag and fly ash into the soil according to a certain mixing ratio,and carried out the unconfined compressive strength test,salt-freeze swelling test and microscopic characteristics test of calcium carbide slag fly ash solidified sulfate saline soil.The main results obtained in this paper are as follows:(1)The overall results of salt-freeze swelling test of solidified soil show that the salt-freeze swelling rate of solidified saline soil increases with the increase of salt content,and decreases significantly with the increase of calcium carbide slag and fly ash admixture.(2)The test results of the compressive strength characteristics of solidified soil show that under the condition of single blending 0～6%calcium carbide slag,the strength of solidified soil with the increase of salt content showed a trend of decreasing and then increasing,and the minimum strength at 1%salt content;and when compounded with fly ash calcium carbide slag,the strength of solidified soil with the increase of salt content showed a trend of increasing and then decreasing,and was at the peak strength at 1%salt content.In 0～1%salt content,the strength of solidified soil increases with the increase of single dose of calcium carbide slag,and in 3～5%salt content,the strength of solidified soil increases with the increase of single dose of calcium carbide slag and then decreases.And when compounded with fly ash calcium carbide slag,the strength of solidified soil increases with the increase of calcium carbide slag admixture.Whether it is single blended fly ash,or the solidified soil after compounding fly ash and calcium carbide slag,its strength increases with the increase of fly ash blending,and the strength of compounding is much higher than that of single blending.(3)Frost resistance test results show that the 0%salt content curing soil strength with the increase in the number of freeze-thaw cycles shows a trend of increasing first and then decreasing.The strength of the solidified soil with different salt content decreased significantly after one freeze-thaw,in which the strength of the 5%salt content solidified soil continued to decrease with the increase in the number of freeze-thaw.3%salt content solidified soil increased its strength after three freeze-thaws,after which the strength gradually decreased with the increase in the number of freeze-thaws.1%salt content solidified soil gradually increased its strength after three freeze-thaws,and the peak strength appeared after seven freeze-thaws,after which it decreased.(4)Water stability test results show that the strength of 1%,3%and 5%salt content solidified soil all decreased after 1d of water immersion,and then increased,reaching a peak after 3d,and then continued to decrease,and gradually stabilized after 7d.While 0%salt content solidified soil,the strength continued to decrease after 1～5d of water immersion,then slightly rebounded and gradually stabilized after 7d.(5)Diffraction analysis(XRD)tests showed that the number of low dwarf peaks in the diffraction pattern of the solidified soil samples was higher compared to that of the non-solidified soil,indicating that the curing agent reacted with water and salt in the soil to produce more gelling substances.Meanwhile,scanning electron microscopy(SEM)tests showed that the hydrated substances generated inside the solidified soil filled the soil pores and agglomerated the soil particles,resulting in stronger connections between particle groups and enhanced soil structure.