Study On Mechanical Properties And Anti-freezing Performance Of Silica Fume-carbide Slag Stabilized Soft Soi

Calcium carbide slag and silica fume are industrial solid wastes with huge waste volumes.How to reasonably treat and utilize them is an urgent problem to be solved.Using calcium carbide slag and silica fume to modify coastal soft soil can not only improve the comprehensive utilization rate of calcium carbide slag and silica fume,but also improve the mechanical properties of coastal soft soil.Considering the change of ambient temperature,the influence of freeze-thaw cycle on the mechanical properties of silica fume-calcium carbide slag solidified soft soil（CF）can be discussed.This paper considered six groups of silica fume admixtures（0,3%,5%,7%,9%,and11%）for studying coastal soft soils in the Shaoxing area with 8%of calcium carbide slag.The compressive strength,shear strength,and compression characteristics of CF at different silica fume admixtures.Maintenance ages were investigated using an unconfined compressive strength test,unconsolidated undrained triaxial test,and consolidation compression test to obtain the optimal dosage of silica fume.In order to investigate the effect of freeze-thaw cycles on cured soft soils,unconfined compressive strength tests,unconsolidated undrained triaxial tests,and consolidation compression tests were conducted on the specimens with optimal fit ratio after 1,3,5,and 7 freeze-thaw cycles to investigate the mechanical properties of CF specimens under freeze-thaw cycles.At the same time,combined with scanning electron microscopy（SEM）,X-ray diffraction（XRD）and Fourier transform infrared spectroscopy（FTIR）,the microscopic mechanism of the influence of different silica fume content and freeze-thaw cycles on the mechanical properties of CF samples was analyzed.The main research conclusions are as follows:（1）The unconfined compressive strength tests show that adding silica fume can improve the compressive strength of CF sample.Under the same curing age,the compressive strength of CF sample increases with the increase of silica fume content,and the increase range is between 10%and 60%.When the silica fume content is 5%,the compressive strength,failure strain,deformation modulus and residual stress of the sample are the most obvious.Although the freeze-thaw cycle can reduce the compressive strength of CF samples,the addition of silica fume can weaken this deterioration.（2）The unconsolidated undrained triaxial tests show that the failure deviator stress of CF sample increases with the increase of silica fume content,and the increase is the largest when the silica fume content reaches 5%.The internal friction angle of CF sample with silica fume is basically stable at 24°～26°,and the maximum growth rate is 17%.The cohesion fluctuates between 200 and 336k Pa,and the maximum growth rate is 56%,indicating that the improvement of shear strength mainly depends on the improvement of cohesion.When the silica fume content is 5%,the increase in the cohesive force of CF reaches the maximum.With the increase in the number of freeze-thaw cycles,the damage bias stress of CF0 and CF5kept decreasing.The decrease in the cohesive force of CF0 and CF5 after freeze-thaw cycles is large,which indicates that the decrease in shear strength is mainly due to the decay of the cohesive.（3）The consolidation compression test shows that the incorporation of silica fume can improve the compression resistance of CF samples,and the compression resistance of soil is further improved with the growth of curing ages.According to the relationship between compression deformation and silica fume dosing,an empirical formula between silica fume dosing and compression deformation can be established,providing a theoretical reference for applying CF in practical engineering.The pore ratio of CF5 after freeze-thaw cycles is low compared with CF0,which indicates that the specimens are more resistant to freezing after silica fume incorporation.（4）The microcosmic tests show that by adding silica fume,the active Si O₂reacts with Ca（OH）₂to form a large amount of C-S-H gel,which has strong cementation.After freeze-thaw cycle,the free water in the soil is transformed between solid and liquid,and the large aggregates are gradually frozen and damaged into small particles.The cementation ability between particles is weakened,which leads to the deterioration of compressive,shear and compressive properties of CF samples.In summary,the incorporation of silica fume into CF samples can effectively improve the compressive strength,shear strength and compressive properties,and reduce the deterioration effect of freeze-thaw cycles on CF samples.Considering the growth rate,the optimal content of silica fume is 5%.The research conclusions can provide references for the effective utilization of silica fume,carbide slag and coastal soft soil.