Experiment And Numerical Analysis Of The Dissolution-scour Wear Process Of Cement-based Materials

The concrete infrastructure projects in water environment for a long time such as the sea,rivers and lakes suffer from the environment water erosion and cause calcium leaching damage of cement paste in concrete,which resulting in concrete resistance to water flow scour wear action decline and the degradation of concrete durability,then affecting the service safety and service life of these infrastructure projects.According to the problem,this paper replaces cement-based materials such as concrete with hardened cement paste,carries out the calcium leaching experiment of cylindrical specimens in 3M ammonium chloride solution and the scour and wear experiment of cylindrical specimens with different leaching time.Through the related experiment and model study,the scour and wear process and its influencing factors of cylindrical specimens with different leaching times are studied.The main research contents and conclusions are listed as follows:(1)The calcium leaching experiment of cylindrical specimens in 3M ammonium chloride solution was carried out,and the concentration of calcium ions in ammonium chloride solution,the leaching depth,porosity,composition of the object phaes,the calcium silica ratio and the microscopic morphology of cylindrical specimens with different leaching time are obtained by EDTA titration method,phenolphthalein indicator method,saturated drying weighing method,XRD and scanning electron microscope(SEM).Results show that calcium leaching causes the microstructure deterioration of cylindrical specimens such as calcium hydroxide dissolution,CSH gel decalcification and the porosity increase,and the longer the dissolution time,the more serious the microstructure deterioration of cylindrical specimens.(2)A test device for the scour and wear experiment is designed and made,and it was used to get the scour and wear resistance of cylindrical specimens with different leaching time.Results show that the longer the leaching time when the scour and wear conditions are the same,the greater the mass loss rate in the unit time of the cylindrical specimen,that is,the decrease of the scour and wear resistance of cylindrical specimens due to the calcium leaching.The critical content of surface failure of cylindrical specimens with the same degree of leaching under the action of water flow scour is studied experimentally,and the boundary movement equation of cylindrical specimens is established.(3)The wear rate model of cylindrical specimens with different leaching time under the action of water flow scour is established,which takes into account the influence of the deterioration of the surface microstructure of cylindrical specimens caused by calcium leaching on the scour and wear resistance.The corresponding computer program is developed by using MATLAB language,which is used to analyze numerically the variation of the parameters such as the porosity,the calcium silica ratio and the wear rate with the leaching time.Compared with the experimental data,the rationality of the model is verified,and on this basis,the influence of the parameters variation such as the time step,the position step,the water ash ratio and the leaching rate on the calculation of the model results is analyzed.Results show that the model has high convergence and accuracy under different time step and position step;the larger the water ash ratio,the faster the leaching process of the cylinder,the greater the wear rate;the faster the leaching rate at the same time,the lower the solid phase calcium content of the cylindrical surface,the greater the wear rate.