Study On Fatigue Performance Of Asphalt Mixture Based On Oyster Shell Solid Waste Utilization

In recent years,the production of oysters in coastal areas has continued to maintain a high level.The waste oyster shells were prepared into clean fine powder below 0.075mm,instead of ordinary dolomite mineral powder（DL）mixed with asphalt mixture and applied to asphalt pavement has certain engineering feasibility for saving natural mineral resources and waste scale.At present,most of the highways in China are under heavy traffic conditions,and the pavement structure is prone to fatigue damage.Therefore,anti-fatigue cracking is the key factor to determine whether the asphalt pavement can be used for a long time.In this thesis,the variation of fatigue performance of oyster shell powder（OS）asphalt mixture is studied to provide a theoretical reference for the large-scale application of oyster shell powder in asphalt pavement.The physical and mechanical properties,appearance,chemical composition and microscopic pores of oyster shell powder and dolomite mineral powder were compared and analyzed by X-ray diffraction,scanning electron microscopy and low temperature nitrogen adsorption test.The specific surface area of oyster shell powder was 5.9%higher than that of dolomite mineral powder,and the hydrophilic coefficient was only 57%of dolomite ore powder.Oyster shell powder has richer pore structure and can adsorb more free asphalt,which preliminarily verifies the feasibility of oyster shell powder as asphalt mixture filler.The orthogonal test is used to optimize the gradation range of the surface layer（AC-13C）oyster shell powder asphalt mixture,and the gradation optimization range is obtained by combining the specification limit value and the actual project.The mixture ratio design of oyster shell powder asphalt mixture and dolomite asphalt mixture is carried out,and the best oil-stone ratio is 4.9%and 5%respectively.The fatigue loading test of oyster shell powder asphalt mixture was carried out by four-point trabecular bending fatigue test method.The fatigue life was verified by two-parameter Weibull distribution function.The fatigue performance was evaluated by fatigue life,stiffness modulus,stiffness modulus damage rate,energy dissipation rate and cumulative dissipation energy under different strain and temperature conditions.Based on the phenomenological method,the fatigue equation of oyster shell powder asphalt mixture and dolomite mineral powder asphalt mixture was established.Compared with dolomite mineral powder,oyster shell powder increased the fatigue life of asphalt mixture by 64%under different strain conditions at 15°C.In the 40%damage stage,the stiffness modulus damage rate of oyster shell powder asphalt mixture is lower than that of dolomite powder by%.Based on the analysis of energy dissipation theory,oyster shell powder has increased the cumulative dissipation of asphalt mixture by 31%,34%,37%,34%and33%respectively compared with dolomite powder under five strain levels,indicating that oyster shell powder asphalt mixture has better stability,and there is a good correlation between cumulative dissipation energy and fatigue life.It is verified that oyster shell powder has a positive effect on the fatigue performance of asphalt mixture.Through the asphalt mixture healing recovery test,the intermittent time was introduced,and 9 kinds of self-healing conditions were designed on the basis of three curing temperatures for simple testing.The fatigue damage rate ratio is selected as the self-healing index to study the factors affecting its recovery performance.The results show that when the high temperature causes healing,the self-healing recovery ability of oyster shell powder asphalt mixture is 7.3%higher than that of dolomite mineral powder asphalt mixture.With the increase of intermittent time,the healing index growth rates of oyster shell powder asphalt mixture and dolomite mineral powder asphalt mixture cured for 6h are 5.1%and 4.7%respectively.Oyster shell powder keeps the healing ability of the mixture more vigorous.Propose a multi factor index based fatigue life prediction equation for asphalt mixtures based on strain control mode.Using indicators such as strain,initial stiffness modulus,and asphalt saturation as parameters,an indoor fatigue prediction model was obtained.In the equation,k_1（OS）>k_1（DL）indicates that the fatigue prediction life of oyster shell powder asphalt mixture is generally higher than that of dolomite asphalt mixture.And verify and evaluate its prediction effect,with fitted straight line slopes of 0.9087 and1.0217,and correlation coefficients of 0.9901 and 0.9905.The overall estimated fatigue life of oyster shell powder asphalt mixture is relatively small,while the overall estimated fatigue life of dolomite asphalt mixture is relatively large.In fact,both fatigue prediction models have high prediction accuracy and can be used to predict the fatigue life of indoor asphalt mixture.