Study On Mechanical Properties Of Carbon Nanotube Composite Cement-based Grouting Materials Under Impact Loading

Cement-based grouting material is a key means to strengthen broken surrounding rock and block fracture water passage in underground engineering.a large number of studies have shown that carbon nanotubes can reasonably modify cement-based grouting materials and optimize pore structure.improve strength and durability.However,there are few research results on the strengthening mechanism of carbon nanotubes on cement-based materials under dynamic impact loading.For this reason,this thesis first experimentally studies the optimal ratio of carbon nanotube composite cementbased grouting material,then studies the dynamic mechanical properties of carbon nanotube cementbased grouting material by using split Hopkinson pressure bar,and reveals the strengthening mechanism of carbon nanotube to cement-based grouting material from the point of view of energy.finally,combined with molecular dynamics simulation,the effect of impact load on C-S-H structure is studied.The impact response of C-S-H structure along layered structure under different impact velocities is analyzed.The main conclusions are as follows:(1)through the analysis of the fluidity and mechanical properties of different amount of fly ash and carbon nanotube experimental group,considering the workability,pore structure,mechanical properties and cost effect of slurry,it is found that 0.08wt% carbon nanotube mixed with 20wt% fly ash can well replace the cement with moderate proportion of grouting material.Compared with ordinary cement slurry,the mechanical properties and workability are improved.(2)carbon nanotube composite cement-based grouting material was prepared by magnetic stirring process,and its coating effect was verified by microscopic test.It is found that the dispersion of carbon nanotube by amino functionalization method can be used to replace the medium proportion cement of composite grouting material by combining 0.023wt% carbon nanotube with 14.3wt% fly ash,and its fluidity can be improved by about 21.6%.The 7-day consolidation strength is enhanced by about 7.9%,and the feasibility of industrial preparation is explored,which provides a scientific basis for promoting the application of carbon nanotubes and fly ash in the process of underground grouting.(3)compared with ordinary cement-based grouting materials,the dynamic compressive strength of composite cement-based materials mixed with carbon nanotubes and fly ash is increased by10.25%-31.86%.The results of strain cloud diagram and fractal dimension further show that the carbon nanotubes in the dispersed cement-based grouting materials have good impact resistance.On this basis,the mathematical and physical model of carbon nanotube reinforced cement-based material is established,the strengthening mechanism of carbon nanotube on cement-based material is revealed from the point of view of energy,and the index to measure its strengthening performance is given.(4)the microscopic molecular model of cement-based grouting materials containing carbon nanosheets is established,and the effect of impact load on the structure of C-S-H is studied on the atomic scale.The simulation results show that the nanowires can slow down the strain of the C-S-H structure,absorb the shock wave energy and increase the structural stress of the system under dynamic impact.There are 48 pictures,24 tables and 129 references.