Research On Mechanical Properties And Durability Of Composite Modified Porous Steel Slag Asphalt Mixture In Seasonal Frozen Region

The permeable pavement made of porous asphalt mixture has many advantages,such as rapid drainage in rainy weather,improved driving safety,better sound absorption and noise reduction,and alleviation of the"heat island effect"in the city,etc.However,the strength of porous asphalt mixture is less than that of traditional dense-graded mixture due to its unique large void structure.It is a feasible method to improve the mechanical properties of porous asphalt mixture by adding appropriate modified materials,which can improve its applicability.In addition,pavement is facing increasing traffic load and changing natural environment during the service process,which may cause insufficient durability and cause early damage.Especially for the seasonally frozen areas in northern China,where the climate is diverse,the summer is hot and rainy,and urban waterlogging is prone to occur.The use of permeable pavements in appropriate areas can greatly alleviate the waterlogging problem.At the same time,the winter is cold,and the spring is prone to freezing and thawing.Therefore,it is of great significance to conduct a comprehensive research on the mechanical properties and durability of porous asphalt mixtures in seasonal freezing areas.This paper relies on the Jilin Province Science and Technology Development Plan Project"Research and Application of Ecological Green Permeable Pavement Materials in Severe Cold Areas".First,a systematic study was carried out on steel slag,and its applicability as aggregate in porous asphalt mixture was studied.Then,based on the response surface design method and Marshall compaction molding method,the crumb rubber and basalt fiber composite modified porous asphalt mixture specimen was prepared,and the performance of the composite modified porous asphalt mixture was optimized,Then the optimized porous asphalt mixture was comprehensively evaluated through mechanical properties,viscoelastic properties and fatigue resistance.Finally,the effect of water-medium high temperature coupling and freeze-thaw cycles on mechanical properties and viscoelastic properties and durability of the composite modified porous asphalt mixture are studied through low temperature splitting experiment,normal temperature compression experiment,static creep experiment and indirect tensile fatigue experiment.The specific research work carried out in this paper is as follows:1.Through high-definition cameras and SEM scanning electron microscopes,the surface morphology of steel slag has been studied on the macro and micro scales.The shape characteristics of crude steel slag were studied through needle flake content test,and the adhesion between the surface of steel slag and asphalt was evaluated.In addition,the physicochemical properties of steel slag have been tested and studied,including density,water absorption,chemical composition and high temperature stability.In addition,the engineering mechanical properties of steel slag were studied,including volume expansion,compression and wear resistance,and adhesion to asphalt and the applicability of steel slag as an aggregate was comprehensively judged.2.Based on the response surface design method,the optimum dosage of the crumb rubber and basalt fiber composite modified porous asphalt mixture was optimized,and the independent variables（the amount of crumb rubber,basalt fiber,asphalt aggregate ratio）and the response values（Marshall parameters,Cantabro particle loss）were established.Statistical methods such as analysis of variance and F-test were used to analyze the significance of the numerical model and parameters,and finally the optimal dosage of the independent variables was determined.The accuracy of the model was further verified by experiments.3.The optimized composite modified porous asphalt mixture was evaluated for the pavement performance of high and low temperature and water stability.Evaluate the water permeability of porous asphalt mixture with the help of a self-made constant head permeability coefficient tester,the static viscoelastic mechanical response of the composite modified porous asphalt mixture is studied based on the basic viscoelastic theory and uniaxial compression creep test,the Burgers model is used to parametrically explain the creep behavior of the mixture,the anti-fatigue properties of the composite modified porous asphalt mixture were studied based on the indirect tensile fatigue experiment and the fatigue theory.The above experiments revealed the reinforcement mechanism of rubber powder and basalt fiber.4.The durability of the composite modified porous asphalt mixture under the coupling action of water-medium-high temperature is studied by using the low-temperature splitting test,the normal-temperature compression test,and the acoustic emission technology.The influence of the coupling effect of water-medium-high temperature on the mechanical properties of the mixture is evaluated by the changes of mechanical indicators such as strength,modulus,strain,etc.With the aid of acoustic emission parameters,the stress process of the mixture is divided into stages,and the influence of the coupling effect of water-medium-high temperature on the durability of the composite modified porous asphalt mixture is evaluated according to the changes of the divided stages.With the help of Burgers model parameters,the changes in the deformation resistance of the composite modified porous asphalt mixture under the coupled action of water-medium-high temperature are discussed.The changes in the anti-fatigue performance of the porous asphalt mixture under the coupled action of water and medium and high temperature were discussed through the indirect tensile fatigue test and the fatigue equation parameters.5.In view of the unique climatic characteristics of the seasonal freezing region,the frost resistance of the composite modified porous asphalt mixture has been systematically studied.First,the porous asphalt mixture samples were treated with different times and different saturation heights of freeze-thaw cycles.The effect of freeze-thaw cycle on the mechanical properties of composite modified porous asphalt mixture was studied using low-temperature splitting test,normal temperature compression test,combined with acoustic emission technology.The Burgers parameters E₁,E₂,η₁,andη₂ are used to explore the changes in the high temperature resistance of the porous asphalt mixture under the action of freeze-thaw cycles.The changes in fatigue resistance of porous asphalt mixture under freeze-thaw cycles were discussed through indirect tensile fatigue test and fatigue equation parameters.