Study On Mechanical Properties And Numerical Simulation Of Alkali-Activated Fly Ash/Slag Mortar

China is in a period of rapid economic and social development,the construction of highway,railway,marine,water conservancy and other infrastructure is booming.Portland cement has become one of the most widely used and largest consumption building materials in the world.However,there are some problems in the production and application of cement,such as high energy consumption,high pollution and so forth.At the same time,alkali-activated materials have become one of the most potent green cementitious materials in the world with the advantages of rapid setting,early strength,low hydration heat and good durability.In the process of engineering application of alkali-activated materials,its mechanical properties are one of the key points.With the development of computer technology,the research on the mechanical properties of concrete and mortar has gradually developed to numerical simulation.However,at the meso level,whether the numerical simulation method can be applied to the mechanical properties of alkali-activated materials is worthy of further study.Based on the research on alkali-activated materials and numerical simulation,this paper uses fly ash and slag as matrix materials,fine aggregate river sand as aggregate to prepare alkali-activated fly ash/slag paste/mortar cementitious materials;Besides,two random particle models,Anm and Sphere,are used to compare the throwing stage with the uniaxial tension and compression stage,and the microfracture model of alkali-activated fly ash/slag mortar is established.This paper discusses the influence of slag content and fine aggregate content on the mechanical properties(compressive strength,elastic modulus and stress-strain curve)of alkali-activated fly ash/slag paste/mortar;Based on the Anm model,the paper discusses the throwing stage of different aggregate volume proportion,different aggregate gradation and fully graded aggregate,and discusses the uniaxial tension and compression simulation test in combination with lattice model;Based on Sphere model,the paper discusses the throwing stage of different aggregate volume proportion and different aggregate gradation,and combined with lattice model,the effects of different volume fraction,aggregate gradation,slurry properties and interfacial transition zone on uniaxial tensile and uniaxial compression tests were discussed.The main conclusions are as follows:(1)When the slag content is 100%,the compressive strength and elastic modulus of alkali activated paste / mortar at different ages(7 d and 28 d)are the largest,which is close to the mechanical properties when the slag content is 70%.The addition of slag can improve the compressive strength and elastic modulus,but with the increase of slag content,the effect of improving the mechanical properties gradually weakens.(2)With the increase of fine aggregate content,the compressive strength of alkali activated mortar decreases,and the elastic modulus slightly increases.(3)As for the stress-strain curve,the peak stress and peak strain decrease with the increase of fine aggregate content.However,when the volume fraction of fine aggregate increases to 40%,the stress-strain curve will appear obvious "mutation"-the decrease range of peak stress becomes larger and the peak strain becomes smaller.In this study,"40%" is the mutation point of interface phase.(4)In this study,the Anm model can describe the shape of irregular aggregate,but the throwing rate of aggregate is only about 20%,which leads to no difference in uniaxial tensile and uniaxial compression test results of different volume proportion and different aggregate grading,and the simulation results of full graded concrete are acceptable;Sphere model can only describe "spherical" aggregate,but the aggregate throwing rate reaches 60%.Based on this model,the uniaxial tensile and compression simulation tests with different slurry properties and different aggregate volume ratio can be realized by using Lattice model,and the simulation results show regularity,but the simulation results of different aggregate grading are not obvious.(5)Based on the meso fracture model of alkali activated fly ash / slag mortar established by Sphere and Lattice models,the uniaxial compression test was simulated,and the test results were compared with the simulation results.Different ages and specimens are suitable for different values of interfacial mechanical properties,which are mainly concentrated in the range of 30% ～ 60% of the slurry mechanical properties.The model can simulate the uniaxial compression of mortar specimens with 30%,40%,50% and 55% fine aggregate.In addition,the model can also obtain the unit failure diagram in the elastic stage,peak stress stage,crack propagation stage and complete failure stage,that is,the whole process of crack generation,development and penetration.