Study On Characteristics Of Waterproof Material In Underground Engineering Based On Micro Scanning Technology

At present,waterproof layer is an important structure for impervious building in tunnel and underground engineering.Normal performance of material is a prerequisite for guaranteeing its service life.Therefore,it is of great significance to study on performance index changes of waterproof material in groundwater environment at a micro level.Based on the background,considering corrosive groundwater environment around Ethylene Propylene Diene Monomer?EPDM?waterproof material,macro-mechanical indexes were tested,synchronously with micro-CT and Scanning Electron Microscope?SEM?,macro-mechanical behavior of material was given a count of from microstructure and chemical composition.Finally permeation based on reconstructed model was simulated.The main research contents and achievements of this dissertation include the following aspects:?1?The samples were tested after they were soaked in the solution with different concentration or different corrosion medium for some time.The testing indexes included tensile strength,elongation at break and tear strength.Through the tests,change laws of mechanical performance index to the material in corrosive groundwater environment were obtained.The medium and concentration of corrosive solution have a significant impact on the change of mechanical properties.In the solution with the same medium,the higher the concentration is,the greater the influence is not.In these corrosive solutions,NaOH solution with pH=14 has the greatest influence on the mechanical properties of waterproof material.During the whole process of soaking,the mechanical properties of the material have been decreasing,and tensile strength and elongation at break have a linear relationship with the soaking time.Water molecules filling open pores or fractures and the corrosion changing molecular structure or chemical composition of waterproof material,can lead to the variation of the mechanical properties of the material.?2?The corroded samples were scanned by using micro-CT,three-dimension reconstruction of digital images was carried out,and finally clear reconstruction images were obtained.Different composition such as pores can be separated from reconstructed images,and the separated images can directly reflect the spatial distribution of the pores.?3?According to the early test results,the characterization parameters were optimized.They included pore number,pore volume,porosity,pore connectivity and the parameters relevant to pore diameter.It was difficult to characterize the connectivity with the indexes relevant to permeability before connecting path formed.The ratio of maximum pore volume to total pore volume was regarded as pore connectivity,which was used to measure the degree of the connectivity.The connectivity of big pores plays a leading role in water permeation under the certain conditions.?4?The data of the pore parameters were extracted,the changing trend of the pore parameters with the soaking time was obtained,and the corresponding relationship between the changing trend and the macro-mechanical behavior was constructed.If pore microstructure parameter has the same?or opposite?trend with macro-mechanical index,the changing trend of the index is macroscopic expression of the change in pore microstructure parameter.?5?By using SEM the sections of the corroded samples were scanned,and the morphology images of the sections were obtained.The four soaking solutions have certain corrosive effects on the samples,and NaOH solution with pH=14 has the greatest influence.In the process of soaking some crystals similar to chrysanthemums appeared.When the soaking continued,there was massive expansion on sample sections?6?Based on energy spectrum of element,the changing trend of main element content with the soaking time was summed up.The corresponding relationship between the changing trend and the macro-mechanical behavior was constructed.If element content has the same?or opposite?trend with macro-mechanical index,the changing trend of the index is macroscopic expression of the change in the element content.?7?Through the simulation of the reconstructed models,pore connectivity in three orthogonal directions was distinguished,permeability and permeability coefficient were calculated.A new method for calculating permeability coefficient was formed.In the sixteen corroded samples,there are connecting paths in three orthogonal directions of the four ones.The permeability coefficient in the direction that the connecting path exits is 10^-4 cm/s magnitude,and the coefficient in the other direction is 10^-5 cm/s magnitude.