| The macadam foundation of alluvial fan in front of the high-speed railway bridge and culvert in western China is treated by dynamic compaction.After dynamic compaction,a certain thickness of cement stabilized macadam layer is set.However,the characteristics of cement stabilized macadam are easily affected by sulfate,so the arch phenomenon of subgrade appears in some lines in this area.Compared with cement-based materials,geopolymer cementitious materials have better sulfate resistance,but there is little research on the sulfate resistance of geopolymer stabilized macadam.In this paper,cement stabilized macadam and low calcium fly ash-based geopolymer stabilized macadam are taken as the research objects,and the dry-wet cycle and freeze-thaw cycle are taken as the environmental factors.By means of mass loss,unconfined compressive strength,elastic wave velocity,volume expansion,X-ray diffraction（XRD）,scanning electron microscope（SEM）and energy disperse spectroscopy（EDS）,the sulfate corrosion resistance of stabilized macadam samples with different stabilizer contents was studied,and the sulfate corrosion deterioration mechanism under different environmental conditions was discussed.The main conclusions are as follows:（1）Under the condition of dry-wet cycle,the higher the cement content,the better the sulfate corrosion resistance of the sample.The physical crystallization erosion of sulfate mainly results in the particle spalling on the surface of the sample.The chemical erosion of sulfate mainly produced gypsum,and leads to the gradual decrease of p H value in the system.In addition,the C-S-H gel decalcified and decomposed.Consequently,the strength and wave velocity of the 3% cement content decreased.However,the strength of 5% and 7% cement addition increased,this is because the formation of gypsum and calcium carbonate crystals promoted the transition of cementation structure to mosaic-cementation structure in the system,which improves the bond strength of the samples.The sulfate attack resistance of geopolymer stabilized macadam samples is poor.Under the action of sulfate physical attack,the mass,strength and wave velocity decrease gradually.（2）Under the condition of freeze-thaw cycle,the sample stabilized by 7%cement still shows good resistance to sulfate corrosion,while the cracks continue to expand and the volume expansion increases in the samples stabilized by 5% cement under the action of freeze-thaw.The surface of sample stabilized by 3% cement peels off seriously and the strength decreases rapidly in 6 freeze-thaw cycles.The chemical erosion reaction produces gypsum and ettringite,the ettringite content generated in the 7% cement stabilized sample is higher than that of the other two admixtures,but there is no obvious correlation between the ettringite content and the damage degree of the sample.Under the condition of freeze-thaw cycles,the sulfate resistance of geopolymer stabilized sample is inferior to that of high cement content sample.Under the action of freeze-corrosion,cracks appear in the sample,the number of pores increases,the structure gradually loosens,and the mass,strength and wave velocity of the sample decrease rapidly.（3）The process of sulfate corrosion expansion of stabilized macadam is closely related to temperature,which is basically characterized by salt expansion when cooling and thawing when heating,which is consistent with the mechanism of sulfate physical crystallization erosion.The salt frost heaving of uncured samples increases or decreases sharply near 0℃.The deformation is no longer mutagenic,but increases gradually in the cooling range of 5～-15℃.The maximum expansion deformation is negatively correlated with cement content,and positively correlated with the concentration of corrosion solution.The deformation of geopolymer stabilized sample is larger than that of cement stabilized sample,and the deformation of geopolymer sample with 10% fly ash content is smaller than that of geopolymer sample with 15%and 5% fly ash. |
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