Study On Mechanical Properties Of Interfacial Transition Zone Of Concrete Reinforced By Carbon Nanotubes

The interface transition zone of concrete is the transition zone between aggregate and cement stone.Due to the high water-cement and low compactness,the morphology,composition,structure and distribution of the hydration products in the zone are much different from those in the matrix of ordinary cement stone.Therefore,combining with the key project of national natural science funds(51734009)and the national natural science fund project(52074259)finance,mainly study the carbon nanotube enhanced interfacial transition zone characteristics and mechanisms of the influence of the microstructure,and mechanical properties of concrete and the relationship between the characteristics of interface transition zone on the fitting and integrated many kinds of nanometer characterization technique and numerical simulation method,reveals the carbon nanotubes reinforced concrete microscopic mechanism of interface transition zone,the main research conclusions are as follows(1)The dispersibility and particle size of carbon nanotube suspension were analyzed by ultraviolet spectrophotometer and particle size analyzer,and the optimal energy range for ultrasonic dispersion of carbon nanotubes was obtained,which could enhance the properties of interfacial transition zone and mechanical properties of carbon nanotubes in concrete materials to the greatest extent.It was found that when the ultrasonic energy was between 225 J/m L and 338 J/m L,the dispersion ratio of carbon nanotubes in the suspension reached more than 93%,and the interfacial transition zone properties and mechanical properties increased the most.(2)By adjusting the water-cement ratio of concrete,combining with field emission electron probe microanalyzer and high resolution field emission scanning electron microscope and the test of mechanical properties,the optimal water-cement ratio of interfacial transition zone and mechanical properties of concrete reinforced by carbon nanotubes was determined.The results show that under different water-cement ratios,the enhancement effect of carbon nanotubes on the characteristics of concrete interfacial transition zone is highly consistent with the Gaussian fitting,and the mechanical properties are also different.The comprehensive conclusion is that the optimization effect is the best when the water-cement ratio is 0.4.(3)By adjusting the gradation index of concrete,based on the field emission electron probe microanalyzer,high resolution field emission scanning electron microscope and the test of mechanical properties,the most effective gradation index for the interfacial transition zone and mechanical properties of concrete reinforced by carbon nanotubes was obtained.It is found that when the gradation index is 0.8,the enhancement effect of carbon nanotubes is the best,the width of interfacial transition zone and the width of wear crack are increased by 30% and 22.8%,respectively,and the corresponding mechanical properties are improved by about 20.7%-35.6%.(4)Using ABAQUS finite element software,uniaxial tensile and compression numerical simulation experiments were carried out on a two-dimensional concrete model with different interfacial transition zone widths,and the internal enhancement mechanism of the interfacial transition zone widths enhanced by carbon nanotubes on its mechanical properties was revealed.The simulation results show that under the condition of uniaxial tension and compression,the failure first occurs in the interface transition zone,and finally the crack interconnects,resulting in the overall failure of the concrete specimen.The paper has 54 pairs of figures,11 tables and 121 references.