The Material And Performance Research Of Steel Slag Asphalt Mixtures

China is currently the largest steel producer in the world,and the rising steel production causes a large discharge of steel slag.The comprehensive utilization ratio of steel slag in China is only about 20%.As of 2016,the amount of steel slag accumulated in China had reached 1 billion tons.The accumulation of steel slag not only occupies the land resources,but also causes serious environmental pollution to the surrounding environment.The mechanical properties of steel slag are similar to rolling crushed stone.Moreover,steel slag has good abrasive resistance,good particle shape and excellent adhesivity with asphalt,so it has great potential to be applied in asphalt mixture as aggregate.The research on applying steel slag in asphalt pavement is necessary in the present situation where the steel slag accumulation is too large and the high quality road aggregate is scarce.In this paper,the steel slag from Meishan iron & steel Co.LTD which has been weathered for 6 months is taken as the research object.At first,the tests of SEM,XRF and XRD are used to analyze the surface micro texture,chemical composition and mineral composition of steel slag.Secondly,the aggregate performances of steel slag are evaluated by testing the natural gradation,density,water absorption,volume expansion ratio,the adhesivity with asphalt,crushed value and weared value.The feasibility of using steel slag as aggregate of asphalt mixture is verified.Considering the high water absorption of steel slag,the effective specific gravity of steel slag aggregate is measured by asphalt immersion test.Then,the Marshall test method is used to design and prepare two types of asphalt mixture—AC-13 and AC-25,and the optimal asphalt-aggregate ratio is determined.The test results show that the optimal asphalt-aggregate ratio of steel slag based asphalt mixture is 0.5%~0.7% higher than that of basalt based asphalt mixture.And then,the pavement performances of steel slag based asphalt mixture are evaluated,including high temperature property,resistance to low temperature cracking,water sensitivity,volume stability and skid resistance.After analysing the pavement performances of steel slag based asphalt mixture,it can be found that the steel slag based asphalt mixture has qualified skid resistance,high and low temperature property.But the expansion caused by f-CaO hydration inside the steel slag aggregate results in the disqualification of water stability and immersion expansion ratio.The volume instability is the decisive factor to limit the practical application of steel slag.In order to solve this problem,the surface modification treatment is used to form a hermetic film on the surface of steel slag,which can prevent the intrusion of water and control the expansion of steel slag,meanwhile,the mechanical properties is strengthened and the oil absorption is reduced.The surface modifications of steel slag are carried out by using cement paste,silicone water repellent and the solution of silane coupling agent.The result shows that the comprehensive modification effect of silicone water repellent is the best,the water absorption and crushed value of steel slag which has been treated with 4% silicone water repellent decrease from 2.02% and 17.6% to 0.56% and 10.1% respectively,and immersion expansion ratio decreases from 1.78% to 1.18%.The modified steel slag based asphalt mixture with AC-13 gradation is prepared by using the steel slag which has been treated with silicone water repellent as coarse aggregate,and its basic pavement performances are evaluated.The results show that the optimal asphaltaggregate ratio of modified steel slag based asphalt mixture is reduced by 0.7%,the water stability is greatly improved,which is even better than that of basalt based asphalt mixture.Meanwhile,the dynamic stability increased by about 20%,the immersion expansion ratio of asphalt mixture is also well controlled.The method of surface modification treatment can loosen up the limit of f-CaO content of steel slag in engineering application,increase the amount of steel slag in pavement,and expand the applied range of steel slag in road field,which contributes to promote the large-scale utilization of steel slag.