| Additives are defined as the materials which would usually be added to/or mixed with the asphalt before mix production,or during mix production,to improve the properties or performance of the resulting binder or mix.Asphalt binders,with or without additives,were tested in the laboratory to determine physical properties and rheological characteristics.The results were analyzed to determine the preferable modifier because of its improvement on the pavement performance by reducing the pavement distress and prolong pavement service life.The appropriate additive was specified mainly by enhancing the physical proprieties and mechanical characteristics of asphalt binders and mixtures.The primary objective of this study was to evaluate the performance of materials added to asphalt binders or asphalt concrete mixtures to reduce the pavement rutting and crack potential.The overall objectives of this research study were to evaluate the asphalt additives to determine the most appropriate modifier.To improve the pavement performance and reduce permanent deformations(rutting)in hot-mixes asphalt pavements by enhancing the physical properties and mechanical performance of the asphalt binders and mixtures in medium and high-temperature range.This research also aims to assess and compare the high-temperature performance of asphalt binders utilizing tafpack super(TPS),crumb rubber modifier(CRM),styrene-butadienestyrene(SBS),ethylene-vinyl-acetate(EVA),and Polypropylene(PP)modifiers in medium and high-temperature range.The widespread usage of polymer modified binders is due to the growing perception that they offer better resistance to pavement distresses.The availability of inherently different modifiers has expanded the range of the polymer-modified bitumen binders to select from when designing asphalt pavements.A proper blending of the polymer in bitumen remains an essential requirement for optimal performance of polymer modified binders.Hence,the benefits of modified asphalt binders and mixtures can only be realized by an accurate selection of the modifier(s);also,not all the modifiers are appropriate for all applications.So,the purpose of the chosen of these modifiers are: these additives were selected as the most abundant,high quality in improving the asphalt materials,economy(cheapness)and an environmentally friendly procedure,flexibility,toughness,adhesion characteristics and longer service life with less maintenance.The physical and rheological properties of these modifiers were assessed by applying various tests.These tests included ductility,rotational viscosity,toughness,tenacity,and the dynamic shear rheometer(DSR).Dynamic shear rheometer experiment was performed to measure the linear viscoelasticity areas of the modified bitumen at medium and high-temperature ranged from 58 to 88 ℃.Additionally,the modified asphalt mixtures’ rut depth is measured in millimeters using the wheel tracking test(WTT).The laboratory test program was designed to examine Marshall stability,indirect tensile strength,indirect tensile strength ratio,moisture susceptibility,permanent deformation(rutting)of the asphalt mixtures as functions of temperature,toughness and tenacity of the asphalt binders and rheological characteristics of the modified bitumen binders at medium and high-temperatures ranged from 58 to 88 ℃.This study also aims to propose the new methodology for mixing crumb rubber modifier with asphalt and aggregate based on the binder mix design.To achieve this goal crumb rubber modified asphalt mixtures were prepared and tested by applying various tests such as Marshall stability test,indirect tensile strength test,and wheel tracking test.Three crumb rubber modifier(CRM)mixing methods(dry,wet,and the new method called complex process)were studied via evaluating their stability,rutting,and moisture susceptibility.The new mixing method for mixing crumb rubber modifier with asphalt and aggregate was suggested for the first time,and compared with the dry and wet methods.Through the results analysis,the new method showed a good mechanical property and a good pavement performance.As mentioned above,this study focuses on determining the most preferred additive to improve the physical and rheological properties and mechanical performance of CRM-,TPS-,PP-,EVA-,and SBS-modified bitumen binders and mixtures.Five different types of modified bitumen binders and mixtures were prepared by utilizing the additives mentioned above with ratios of2%,3%,3.5%,and 4% respectively by weight of the virgin asphalt binder for each modifier.The results indicated that the resistance of asphalt mixtures to medium and high temperature cracking and rutting at high-temperature is significant.This significance will ensure the service performance of asphalt pavement under seasonal changes in temperature and loading.The experimental results also showed that the dynamic stability of modified asphalt mixtures is significantly increased due to the addition of the modifiers.Still,the increase is observed considerably in the CRM-modified mixtures.The results of indirect tensile strength and indirect tensile strength ratio indicated that the CRM-modified binders were more flexible.Likewise,the results of the rheological properties evaluation demonstrated that the asphalt binder properties significantly improved by utilizing CRM followed by EVA,SBS,PP,and TPS modifiers.The rutting parameter(G*/sin(δ))increases after the asphalt modification,which indicates excellent performance at medium-and high-temperatures.Finally,rheological features of improved asphalt binders were contrasted together with each other as well as with the virgin bitumen.It isn’t straightforward to determine the modifier morphology by just measuring the physical properties of the modified binders.This study also uses a microscopic technique that enables the use of high energy light(e.g.ultraviolet light or high-energy visible light).This energy light excites and consequently cause the modifier-rich phase to fluoresce at a wavelength that can be detected by the eye.Epi-fluorescence microscopy can be used to differentiate between the bitumen phase(which does not fluoresce)and the modifier phase to show the modifier distribution/dispersion in the base bitumen.The Epi-fluorescence microscopy is a valuable tool to characterize the in situ structural and chemistry effect of modifiers within asphalt to determine their influence on the modified binder performance.The outcomes of this study show that a sufficient degree of compatibility between modifier and bitumen is necessary to avoid separation during handling for the modified binders to achieve the expected pavement performance.The consequences of the statistical analysis of the asphalt mixtures indicated that CRM and PP have a significant effect on dynamic stability(DS)when the value is less than 0.05.Meanwhile,TPS and SBS have an insignificant impact on the DS when the value is higher than 0.05.The results also indicated that CRM and SBS have a statistically significant effect on the rut depth(RD)when the value is less than 0.05.Meantime,TPS and PP have an insignificant impact on the RD when the value is higher than 0.05.The results of the statistical analysis of the modified bitumen binders indicated that all utilized additives have a significant effect on the rheological characteristics(e.g.,phase angle)when the value is less than 0.05.Meanwhile,CRM has a more substantial impact on rheological characteristics.This study conclusively proved that incorporating CRM in asphalt binders and mixtures can improve pavement performance at both medium and high-temperatures better than those of SBS,EVA,PP,and TPS modifiers.Thus,CRM has a more excellent additive in the highest resistance to medium and high-temperatures deformation and fatigue,less rutting depth,fewer agglomerates,excellent compatibility with an asphalt binder phase,and a good dispersion than those of utilized modifiers.Lastly,crumb rubber modifier(CRM)determined as the most appropriate additive for improving asphalt binders and mixtures because of its positive effect on physical properties,rheological features,and mechanical characteristics.On conversely,the TPS-modified asphalt exhibits the worst performance in practically every respect compared to the other utilized modifiers.Thus,the better enhancing in pavement performance achieved by using CRM,as well as it was deemed as an environmentally friendly procedure of scrap tires.The innovative points of this thesis are representing the main contributions of the dissertation. |
