Research On Influence Of Shape And Surface Characteristics Of Steel Slag Aggregate On Asphalt Concrete Performance

The construction and maintenance of roads in my country require amounts of aggregates every year.The strengthening of environmental protection and the shortage of aggregate resources have led to a prominent contradiction between the supply and demand of aggregates for asphalt pavement construction.At the same time,the annual output of steel slag in my country is nearly 100 million tons.The effective utilization rate of steel slag is less than 30%.Steel slag is anti-skid and wear-resistant.Steel slag has great advantages to replace natural aggregates in preparation of asphalt concrete.However,the physical and chemical properties of steel slag are different from those of natural aggregates.It has great significance to study the influence of steel slag aggregate particle shape and surface characteristics on the performance of asphalt concrete.This article first studied the characteristics of different BOF slag aggregates and their corresponding characterization methods.The influence of the natural aging of aggregates on particle shape and surface characteristics of BOF slag.Secondly,the influence of particle shape and surface characteristics of BOF slag aggregate on asphalt concrete gradation and asphalt content is discussed.The design optimization method of BOF slag aggregate asphalt concrete with different grading types is proposed.Thirdly,the characteristics of BOF slag-asphalt interface are analyzed from the perspectives of selective adsorption and surface adhesion.The influence of the surface properties of BOF slag on the interface mechanics of BOF slag and asphalt are studied.Finally,the influence of BOF slag particle shape and surface characteristics on the performance of different grading types of concrete is discussed.The optimal BOF slag aggregate particle shape characteristic index is proposed.The main conclusions are as follows.1)Compared with natural aggregates,the sphericity index and angularity index of BOF slag aggregates are about 10%-20% higher.There are a large number of pore structures in the size of 1-50μm on the surface of BOF slag.This results in rough micro-texture on the surface of BOF slag,which increases its ability to absorb asphalt.The sphericity index and angularity index of BOF slag with different cooling treatment processes are different by about 5%.The size of the microscopic pore structure of ordinary BOF slag is larger than that of pyrolytic BOF slag.Natural aging not only reduces the free calcium oxide,but also changes the particle shape of BOF slag.As the aging time increases,its angularity index gradually decreases,while the sphericity index first decreases and then increases.2)Coarse BOF slag aggregate with a larger sphericity index is conducive to the formation of a better stable framework structure.When the angularity index is around3200,the compactness of the aggregate is relatively highest.The higher sphericity of BOF slag aggregate is beneficial to reduce the amount of asphalt.However,the excessively high angularity of BOF slag will increase the clearance ratio of the asphalt concrete skeleton,which will increase the amount of asphalt.The rich open pore structure on the surface of BOF slag will also increase the amount of asphalt,and the asphalt absorption of different types of BOF slag aggregates is different.The volume ratio of asphalt concrete with ordinary BOF slag aggregate increases by about10%-20%.Among the three grading types,the volume ratio of the skeleton-void type has the largest increase.3)BOF slag aggregate mainly adsorbs the saturated components in the light components of the asphalt.The selective adsorption of asphalt by BOF slag aggregate is a continuous behavior.After about 2 months,the change in the content of the four components caused by the selective adsorption behavior tends to slow down.The main adsorption behavior between BOF slag aggregate and asphalt is a physical reaction.The rough micro-texture on the surface of BOF slag aggregate makes the interface with asphalt higher tensile strength.The selective adsorption of BOF slag aggregate to asphalt will reduce the tensile strength of its interface with asphalt,but the effect is small.The mechanical properties of BOF slag-asphalt interface are higher than natural aggregates.4)The high-temperature rutting resistance,water stability and fatigue resistance of the suspension-dense,skeleton-dense,and skeleton-void BOF slag aggregate asphalt concrete are increased by 5%-10%.The difference in the degree of improvement is related with type of BOF slag and type of gradation.The dynamic stability of OGFC13 and SMA13 improved by BOF slag aggregate is higher than that of AC13.The improvement effect of OGFC13 anti-low temperature cracking and anti-fatigue performance is better than the other two gradation types.Ordinary BOF slag aggregate has better fatigue life improvement effect than pyrolytic BOF slag.The richer surface micro-textures and more edges are beneficial to improve its fatigue life.Higher sphericity and proper angularity of BOF slag aggregate(angularity index is about 3250)are the main reasons for the improvement of mechanical properties of asphalt concrete.The surface characteristics of BOF slag coarse aggregate are the main influencing factors for the improvement of the water damage resistance of SMA13 asphalt concrete.