Fractal Theory-based Study On Fly Ash Of Its Pore Structure And Permeability

Along with the speedy development of the economy, the annual emission of flyash and its accumulative amount are on an increase gradually. The effects fly ashbrings to the environment have greatly attracted people’s attention. Integratedutilization of fly ash is of great urgency. In recent years, during the construction ofhighway in our country, the comprehensive utilization of fly ash is increasing.Thecompaction degree and stability of fly ash-based subgrade are closely related to thepermeability of the fly ash itself. However, studies on permeability of fly ash aremostly limited to the experimental stages. Therefore, how to evaluate the permeabilityof fly ash reasonably and effectively is meaningful. This study is based on the fractaltheory and applies the digital image processing technology to conduct a systematicresearch on the permeability of fly ash and obtain the formula of the fractaltheory-based permeability of fly ash.This study firstly reviewed comprehensively methods on researching micro-polestructures of porous medium and relative experimental research methods onpermeability of fly ash. On this basis, this study, making use of the theory that poresand particles of fly ash differ in the gray values, applied the digital image processingtechnology to extract the pores of fly ash from the particle background through thethreshold segmentation method, as the research object and obtain the relativeparameters about the permeability of fly ash (such as the number of pores, porediameter of equivalent circle, pore roundness and pore areas etc.).Then by combingthe fractal theory, this study proposed the fractal model on the distribution of poreradius of fly ash to get the fractal dimension of pore radius distribution of fly ash andfinally analyzed the differences between fractal dimension of pore radius of fly ashwith different dry density.According to the revised Hagen-poiseulle equation, this study combined the linearseepage equation Darcy law and established a theoretical formula for fractaltheory-based permeability of fly ash tocalculate the permeability of fly ash withdifferent dry densities. At last, this work determined the relative parameters in theformula for fractal theory-based permeability of fly ash, such as the fractal dimensionof the pore radius distribution in section I and section, i.e., D1and D2, the fractaldimension of pore tortuosity DT, the maximum pore diameter λmaxand the inflection point of pore diameter λg, and studies influences every parameter has on thepermeability of fly ash.The permeability coefficients of fly ash with different dry densities are obtainedthrough in-lab falling head permeability test. The transforming relationship betweenthe permeability coefficient and permeability to obtain the experimental values ofpermeability of fly ash samples with different dry densities. The comparion of theseexperimental data to the theoretical fractal values of permeability of fly ash withdifferent dry densities verified the accuracy of the formula for fractal theory-basedpermeability of fly ash and illustrated the causing about the difference between thetheoretical fractal values and the experimental values for the permeability of fly ash.