Experimental Study On Mechanics And Durability Of Alkali-excited Fly Ash Concrete Under Freeze-thaw-wind Erosion Environment

In this thesis,aiming at the special service environment of concrete in Hetao irrigation area of Inner Mongolia,alkali excitation technology is used to prepare alkali-excited fly ash concrete at room temperature,the influence of alkali equivalent on concrete strength is explored by compressive strength test,the pore structure and chemical composition changes are analyzed by nuclear magnetic resonance technology and FTIR technology,the concrete rapid freeze-thaw testing machine and aeolian sand blowing testing machine are used to simulate the field service environment of concrete,and the 3D microscope with ultra-depth field is used to observe the erosion damage morphology of concrete surface.The freeze-thaw damage model of concrete and the Weibull distribution model are introduced to predict the service life of alkali-excited fly ash concrete,which provides a theoretical basis for the development of low-carbon concrete materials with high fly ash substitution rate suitable for normal temperature construction conditions,and provides theoretical support for the promotion and application of low-carbon concrete in practical engineering.1.Adding an appropriate amount of alkali initiator at room temperature is beneficial to improve the internal pore structure of concrete,optimize particle gradation,and make the microstructure more dense.When the fly ash content is 40%,the addition of 4%alkali initiator helps N-A-S-H gel and C?S?H gel to form,improve the paste bonding strength,improve the compressive strength of concrete,and the compressive strength reaches46.45MPa at the age of 28d,which is equivalent to the strength of the unalkalid 20%fly ash content group,so that the fly ash replacement cement rate increases from 20%to 40%.2.Based on fractal theory,the relationship between nuclear magnetic resonance and infrared spectroscopy and fractal dimension was established,and the microscopic characteristics of alkali-excited fly ash concrete were quantitatively characterized.NMR fractal dimension D_min is positively correlated with the internal porosity and free fluid saturation of concrete,and negatively correlated with bound fluid saturation.FTIR tests showed that the alkali equivalent of 4%was beneficial to generate N?A?S?H gel and C?S?H gel,and improve the compressive strength of concrete.The FTIT fractal dimension D_s value is related to the compressive strength of concrete,and the larger the value,the greater the compressive strength of concrete.3.The addition of alkali initiator at room temperature can effectively improve the durability of fly ash concrete.The wind erosion resistance of concrete decreases with the increase of fly ash content,and the addition of alkaline initiator is beneficial to improve the wind erosion resistance of fly ash concrete.Under the freeze-thaw environment,the internal pore structure of concrete changes,the T₂ spectrum shifts to the right to different degrees,the relaxation time range becomes larger,the signal amplitude increases,the small pores evolve to large pores,and the complexity of the pore structure gradually decreases,resulting in the gradual failure or failure of the concrete structure under the action of freeze-thaw cycle.In the freeze-thaw-wind erosion coupling environment,the surface slurry is peeled off due to the erosion of wind and sand flow,resulting in microcracks,and when coupled with the freeze-thaw cycle,the internal micro-cracks of concrete develop rapidly,forming internal and external penetrating cracks,accelerating the freeze-thaw failure of concrete,but the main factor is freeze-thaw.The addition of 4%alkali initiator can slow down the failure rate of concrete,improve the frost resistance of alkali-excited fly ash concrete and the resistance to freeze-thaw-wind erosion.4.Based on the freeze-thaw damage model of concrete and the Weibull distribution model,the service life prediction model of alkali-excited fly ash concrete was established,and the single-stage freeze-thaw damage model had a high degree of fitting with the experimental values,which reflected the damage law of alkali-excited fly ash concrete in service in complex environment,and was suitable for the life prediction of alkali-excited fly ash concrete.