Research On Performance And Fatigue Damage Of Steel Slag Fine Aggregates In Asphalt Mixture

Road construction and maintenance require large amounts of natural aggregates,and aggregate shortages will inevitably occur.As a solid waste,steel slag has a low utilization rate in China,and most of it is abandoned in piles or landfills.The mechanical properties of steel slag are better than those of natural aggregates,and its use in asphalt pavements can realize the reuse of solid waste resources and alleviate the shortage of aggregates,which has good social and economic benefits.In asphalt pavements,fatigue damage has been one of the most important problems in asphalt pavement damage.Due to the viscoelasticity of asphalt mixture,the traditional research method is difficult to reflect its fatigue performance effectively,and a suitable fatigue damage model needs to be selected for analysis.In this paper,the physical and chemical properties of steel slag fine aggregates are first tested,and the gradation design of steel slag asphalt mixture is carried out by using fractal theory,so as to test the road performance of asphalt mixture with different steel slag fine material content(0%,25%,50%,75%and 100%),including high temperature rutting,low temperature trabecular bending,water stability(freeze-thaw splitting test,water-immersion Marshall test,slag asphalt mixture immersion expansion test),anti-slip performance and water permeability performance,etc.,to analyze the reasons for the change of road performance.Then,the dynamic characteristics of steel slag asphalt mixture were analyzed by dynamic modulus test.Based on the simplified viscoelastic continuous damage model,a uniaxial direct tensile fatigue test was carried out,and the damage characteristic curve(C-S curve)was established to study the fatigue damage characteristics of asphalt mixture,and the fatigue performance was evaluated by using the average reduction value of pseudo secant modulus D~Rduring fatigue.The following conclusions were obtained:(1)Steel slag fine aggregate has better angularity and cleanliness;it has a certain alkalinity,which can adhere better to asphalt and has better resistance to water stripping.In addition,its free calcium oxide content and water immersion swelling rate are low,which can be used in asphalt mixture.(2)Fractal theory can be well used in the gradation design of asphalt mixture.As the fractal number D increases,the void volume and void in mineral aggregate of the steel slag asphalt mixture decreases,and voids filled with asphalt is increasing.The volume index of the asphalt mixture can be predicted by the fractal dimension number D of the gradation.(3)With the increase of steel slag fine aggregate,the high temperature stability of the asphalt mixture is increasing,and the low temperature crack resistance of the asphalt mixture is also enhanced;in water stability,the incorporation of steel slag makes the residual stability of the asphalt mixture and freeze-thaw splitting strength ratio is reduced,and the immersion swelling rate is increased,which means that the steel slag is more suitable for the surface layer not in contact with water;the incorporation of steel slag fine aggregate on the slip resistance of the asphalt mixture The incorporation of steel slag fine aggregate has a certain improvement on the anti-slip performance of asphalt mixture,but has no significant effect on the water penetration performance.Combined with the road performance and economic benefits,the recommended amount of steel slag fine aggregate for AC-20 asphalt mixture is75%.(4)In the case of an increase in test temperature or a decrease in loading frequency,the dynamic characteristics of steel slag asphalt mixture and limestone asphalt mixture change trend is the same.The main dynamic modulus curve of steel slag asphalt mixture is higher,and its deformation resistance is better than that of limestone asphalt mixture.(5)The position of damage characteristic curve(C-S curve)of steel slag asphalt mixture is higher than that of limestone asphalt mixture,and its damage resistance is better.the D~Rvalue is independent of the strain level,and all the D~Rvalues of steel slag asphalt mix are lower than that of limestone asphalt mix,and the adoption of steel slag fine aggregate to replace limestone fine aggregate in the asphalt mixture helps to improve the fatigue resistance performance.