Experimental Study On The Effect Of Water Content And Particle Size On The Electrochemical And Mechanical Properties Of Kaolin

In this paper,the physical,mechanical and electrical properties of Kaolin with different water content(15%,20%,25%)and different particle size(400 #,800 #,1000 #)were tested,including shear strength,compressive properties,complex permittivity,conductance,conductivity the electrochemical impedance spectroscopy(EIS).Moreover,the influence of particle size and water content on the properties and the relationship between mechanical and electrical parameters were also analyzed.Dry density test for Kaolin samples with variables of water content and particle size shows that the dry density of Kaolin increases with the water content and particle size,and the porosity ratio and plasticity index of Kaolin decreased with the increase of particle size.The shear strength curves and the compression curves respectively were analyzed by the calculation of the cohesion,the internal friction angle and the porosity ratio in the compression process.The results show that the increase of water content and the decrease of particle size increase the cohesion of kaolin,while the change of friction angledoes not show regularity.It indicates that water content and particle size significantly affect the cohesion of Kaolin,but the effect on friction angle is relatively small.The porosity ratio of Kaolin decreases with the increasing water content at the same particle size,and it also decreases with the increasing particle size at the same water content.The influence of water content and particle size on porosity ratio of Kaolin is mainly caused by the change of contact surface between particles and pore volume.The complex permittivity and conductivity diagram of Kaolin under two variables of water content and particle size show that the real and imaginary parts of the complex permittivity decrease with the frequency,and the dispersion characteristics also occurs.The real and imaginary parts of complex permittivity for Kaolin increase with the increase of water content and particle size due to the effect of the amount of water and charged ions in soil.The mechanism is mainly as follows: water is a strong polar molecule,and Kaolin is a weakly polar molecule.The dielectric constant of water is much larger than that of Kaolin,so the real part of complex permittivity for Kaolin increase with the increasing water content in soil.Besides,with the increase of water content,the imaginary part of complex permittivity for Kaolin also increase,which indicates that the polarization loss caused by water is also larger.While the effect of particle size on complex permittivity mainly include two aspects of dry density and the form of water(free water and bound water).The equivalent circuit analysis of electrochemical impedance spectroscopyfor Kaolin indicates that electrochemical impedance spectroscopies of Kaolin with different variables all present the Quasi-Randles circuit model.With the increase of water content,the solution resistance Rs and the diffusion resistance Rt decrease,while the internal double layer CPE-T increases when the particle size is the same.When the water content is constant,the solution resistance Rs and the internal double layer CPE-T increase with the decrease of particle size,while the diffusion resistance Rt decreases.The water content changes the connectivity and conductivity of the pore environment in Kaolin,while the particle size affects the pore ratio and specific surface area of Kaolin.Therefore,charge on the surface of soil particles and electrochemical properties of Kaolin are both different under various of water content and particle size.Analysis for relationship between the mechanical parameters and the electrical parameters of kaolin make it clear that double electric layer capacitor in Kaolin determine the cohesive force of Kaolin to a large extent under the same particle size.And then the shear strength of it also is affected.There is a good linear correlation between the electric double layer capacitance and the cohesive force.In addition,there are also good linear correlations between the solution resistance and the complex permittivity in the equivalent circuit,and the dielectric constant and the electric double layer capacitance are also linearly related at the fixed frequency.