Effects Of Steel Slag Powder On The Performance Of Asphalt And Asphalt Mixture And Their Interaction Mechanism

One of the by-products from the converter steelmaking process in a steelmaking plant is converter slag(hereinafter referred to as “steel slag”).Every year,a large amount of steel slag waste is produced in China’s steelmaking.Failure to properly handle it will do great harm to the natural environment.In this paper,attempts were made to replace the conventional mineral fillers in the asphalt mixture containing steel slag powder.The mechanism of the changes in and influence on the material properties of asphalt containing steel slag powder was studied by the test characterization method based on properties for asphalt binder,asphalt mortar and asphalt mixture.The main contents and results of this paper are as follows:(1)The rheological properties of asphalt mortar containing steel slag powder were studied by rotational viscosity test,multi-stress creep recovery test(MSCR)and linear amplitude sweep test(LAS).The results showed that: 1)For unmodified asphalt binder,the order of the viscosity of the three kinds of filler asphalt mortar from high to low is: asphalt mortar containing steel slag powder > Portland cement asphalt mortar > limestone asphalt mortar.2)The viscosity predicted by the viscosity-temperature equation of asphalt mortar containing steel slag powder established based on the four-parameter linear function model is in good agreement with the test results.According to this model,the mixing and compaction temperature width of the asphalt mortar containing steel slag powder was the maximum.In other words,compared with other conventional fillers,it is easier to control the temperature of the asphalt concrete containing steel slag powder during construction.3)Steel slag powder is more suitable than matrix asphalt to be added to SBS modified asphalt;and the high temperature performance of asphalt mortar containing steel slag powder is optimal when the ratio of powder to binder is around 0.6.4)During asphalt pavement design,steel slag powder should be used in pavement systems with small strain instead of pavement systems with great strain,so as to extend the fatigue life of the corresponding asphalt pavement.(2)The mechanism of the physical hardening properties of modified asphalt binder containing steel slag powder was studied.Besides,the ductile fracture performance of asphalt binder containing steel slag powder was studied by the rheological test method and characterization method.The results showed that: 1)With the addition of steel slag powder filler,the stiffness and m value of DBSA modified asphalt and SBS modified asphalt mortar are improved;with the extension of constant temperature curing time,the stiffness of various asphalt binder is improved,while the m value is reduced.2)The m value of the asphalt mortar cured for1 h and 72 h added with 5% steel slag powder is about 42% higher than that of the modified asphalt added with 5% limestone.Meanwhile,the difference in the m value of the asphalt mortar containing steel slag powder is smaller than that of the asphalt mortar containing limestone filler.That is,adding steel slag powder can alleviate the severity of the physical aging of asphalt binder.3)Since the content of CaO in steel slag powder is high,at high temperatures and low loading rates,the critical crack tip opening displacement of the asphalt mortar containing steel slag powder is much higher than that of asphalt mortar system containing limestone filler.It can be seen that,compared with conventional limestone filler,steel slag powder and asphalt binder have better adhesion.4)According to the main curves of critical crack tip opening displacement(CTOD),specific basic fracture work and specific plastic fracture work of asphalt mortar,the ductile fracture resistance of bituminous mortar can be better improved by using steel slag powder with small particle size than using steel slag powder with large particle size;and it is better than the mortar system containing limestone.(3)The microscopic properties of the interface between steel slag powder and asphalt were studied by molecular dynamics to explore its mechanism of adhesion enhancement and explain the intermolecular adhesion mechanism.The results showed that: the order of the interaction between the oxide in the steel slag powder and the asphaltene in the asphalt binder from great to small is: CaO > MgO > Al2O3 > SiO2.Since more than 50% of the chemical composition of steel slag powder,this can better explain why steel slag powder has better adhesion than another fine aggregate.Considering the content of oxides,the ordering results of the interfacial energy of oxides and the interfacial energy at different temperatures: the interfacial energy between steel slag powder and asphalt at 25℃ is the maximum and the adhesion is the best;the interfacial energy at 40℃ is the minimum and the adhesion is the poorest.(4)The low temperature toughening mechanism of asphalt mixture containing steel slag powder was studied.The influence of various environmental change parameters on the anticracking ability of the asphalt mixture containing steel slag powder was analyzed and studied.The results showed that: 1)The anti-cracking index of the asphalt mixture containing steel slag powder after short-term oven aging(STOA)is higher than that of the asphalt mixture containing limestone filler.The asphalt mixture containing steel slag powder after STOA has better anticracking ability than that after long-term oven aging.2)The cracking index of the asphalt mixture compacted at a constant temperature of 25℃ for 30 min to 3 days shows no significant change.When it is stored at a constant temperature for more than 3 days,the low temperature cracking resistance of the asphalt concrete containing steel slag powder will be reduced significantly.3)When the amount replaced by steel slag powder exceeds 40%,the cracking index CTIndex shows an obvious increasing trend.However,when the conventional limestone filler is completely replaced by steel slag powder,the IDEAL-CT cracking index is almost twice as much as the original.Therefore,the amount replaced by steel slag powder in the SBS AC-16 asphalt mixture should not exceed 40%.(5)The influence of tree parameters,the amount replaced by steel slag powder,stress level and temperature,on the resistance to permanent deformation of the asphalt mixture containing steel slag powder was studied with the indirect tensile stiffness modulus as the characterization parameters of the asphalt mixture containing steel slag powder against permanent deformation.The results showed that: With the increase in the content of steel slag powder,stress level and temperature,the stiffness of the asphalt mixture decreases.However,the slope of stiffness changes over the changes in temperature is the greatest,indicating that the changes in temperature have the greatest influence on the stiffness of the asphalt mixture.At the parameter levels studied,the amount of conventional filler replaced by steel slag powder should be around39%,so that the asphalt mixture containing steel slag powder has optimal resistance to permanent deformation.In combination with the conclusions above,under the two conditions of low temperature crack resistance and permanent deformation of a mixture,the optimal amount replaced by steel slag powder in SBS AC-16 asphalt mixture should be around 39%,and should not exceed 40%.