Study On Mechanical And Durability Damage Mechanism Of Fly Ash Pisha-sandstone Cement Composite Soil Activated By Water Glass

In the present study,as the weathering geotechnical body of Pisha-sandstone was highly susceptible to gravitational,hydraulic and wind erosion,and due to the influence of human factors such as engineering development.It caused a large amount of loose Pisha-sandstone to be exposed on the surface,resulting in a large amount of soil erosion and ecological environment damage.If loose Pisha-sandstone can be used as available resources,it can be combined with local abundant fly ash and water glass to develop economical and environmentally friendly green construction materials,which can be applied in the engineering fields of road pavement base,roadbed enclosure and farmland lining,etc.It has important economic and environmental benefits and engineering practical significance for soil consolidation and sand retention,reducing local soil erosion and realizing effective use of resources.In this thesis,mechanical properties and durability tests were carried out on fly ash Pisha-sandstone cement composite soil and fly ash Pisha-sandstone cement composite soil activated by water glass,taking Pisha-sandstone cement composite soil as the research object.Meanwhile,the analysis was also performed by combining technical means such as ultra-deep field 3D microscopy,nuclear magnetic resonance(NMR),scanning electron microscopy(SEM),thermogravimetry(TG),and X-ray diffractometer(XRD),which revealed the strength enhancement of fly ash Pisha-sandstone cement composite soil activated by water glass and the damage mechanism of chloride salt erosion-freeze-thaw in terms of microstructure and apparent pore structure evolution.The results of the study are as follows.1.The larger the replacement rate of fly ash,the more obvious the decrease of static and dynamic compressive strength of Pisha-sandstone cement composite soil.Meanwhile,the internal porosity and apparent pore percentage of 4%fly ash replacement rate Pisha-sandstone cement composite soil are closest to 0%fly ash replacement rate Pisha-sandstone cement composite soil,and the internal micro-density is also basically the same.Thus,the best effect of 4%fly ash replacement in this test range.2.With the increase of water glass content,the unconfined compressive strength of fly ash Pisha-sandstone cement composite soil activated by water glass shows a trend of rising and then falling,and the unconfined compressive strength shows a rising trend with the increase of age.At the elastic stress,peak stress and damage stress,with the increase of water glass content,the total strain energy,elastic strain energy,dissipation energy and damage variables all show a trend of rising and then falling.Consequently,the energy change and damage variables are positively correlated with the strength growth.Moreover,the degree of damage to the specimen is mainly influenced by the dissipation energy U~d.3.With the increase of the number of freeze-thaw cycles of clear water and magnesium chloride cycles,the strength of Pisha-sandstone cement composite soil under each water glass content showed a decreasing trend.Meanwhile,the mass loss rate under freezing and thawing of clear water gradually decreases,while the mass loss rate under magnesium chloride-freezing and thawing shows a trend of first small increase and then decrease.Moreover,the internal porosity and apparent pore content of Pisha-sandstone cement composite soil keeps increasing,and the internal micro and small pores and apparent small area pores deteriorate rapidly into medium and large pores as well as large area pores and high depth pores.At the same time,the greater the concentration of magnesium chloride the more significant the microstructure and apparent damage destruction of the specimen.Also,the Pisha-sandstone cement composite soil with 15%water glass admixture has better frost resistance and chloride salt erosion resistance.