Essay: Asphalt binder

Chapter One: Introduction
1.1 Overview
Asphalt binder is the basic building material in road pavement construction; it is mixed with mineral aggregate to produce the asphalt concrete. Due to the big differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play a major role in determining the asphalt’s concrete performance. However, bonding failure between the asphalt and aggregate surface is one of the principal causes of distresses that could exist in asphalt pavements. The bonding failure is caused by a combination of two types of failure: cohesive and adhesive failure. Cohesive failure occurs when there is a bonds rupture between molecules in the asphalt film. While the adhesive failure happens when bonds between molecules of different phases rupture.
The most common types of pavement distress include: rutting, fatigue cracking, and thermal cracking. Pavements distress can accumulate and compound to each other as the pavement age and being subjected to repeated traffic loading; for instance, a crack can permit the entrance of water to the pavement and lead to the formation of a pothole or stripping.
Scientists and pavement engineers are regularly trying to develop the performance of
pavements through several programs such as the Strategic Highway Research Program (SHRP), the aim of SHRP research was to develop a system that relates the material properties of hot mix asphalt to pavement performance. The final product of this program was a new system for specifying, testing and designing unmodified or neat asphalt materials, aggregate, and mix design methods; known as Superpave, which stands for Superior Performing Pavements, so that a well performing, long lasting asphalt pavements can be constructed.
The Asphalt grading system in Superpave is known as the performance grading (PG) system, it takes in to account the impact of traffic, aging, and climatic conditions at both cold and hot temperatures on asphalt characteristics. In order to simulate the traffic conditions, an average loading rate for normal highway speeds was assumed. The binder aging can be simulated by using the rolling thin film oven procedure which allows for rapid oxidation/aging of asphalt. To simulate for climatic circumstances, asphalt binders are tested at three different pavement temperatures: cold, intermediate and hot.
1.2 How Asphalt Binder Behaves
Asphalt is a viscoelastic; thermoplastic material so it has the properties of both an elastic solid, and a viscous liquid. As any viscoelastic material, the asphalt’s response to an imposed stress or strain is highly dependent on both loading time and temperature. The superposition concept for asphalt binder implies that the behavior at low temperatures over long time periods is equivalent to the behavior at higher temperatures and shorter times.
In hot climates or under the conditions of slow- moving traffic loading, asphalt binder acts like a viscous fluid and flows. Viscous fluids are often called plastic because they cannot return to their original condition as they start flowing. In cold conditions or in the case of fast- moving traffic loading asphalt binder acts like an elastic solid; it deforms when loaded and returns to it’s original condition upon the removal of the load. Although asphalt binder behaves like an elastic solid under low temperatures, it becomes very brittle and breaks down when it is extremely loaded, and this is why asphalt pavements in cold regions suffer from thermal cracking. Generally, the climatic conditions are between extreme cold and hot situations, under these conditions asphalt behaves like a viscoelastic material, because of this property it is considered as an excellent adhesive material for road pavements construction.
1.3 Asphalt Modification
In order to construct a durable pavement that has high resistance against rutting and low temperature cracking, Arabani et al. (2010) suggested two principal ways for that: firstly, increasing the thickness of asphalt pavement layers which will result in higher construction costs. Secondly, utilization of different types of additives to improve the performance of asphaltic materials, and this option is adopted as one of the best strategies for meeting the requirements for constructing a well performing asphaltic structure [1].
Additives such as polymers and fibers can significantly improve the engineering properties of asphalt mixtures by providing a three-dimensional network structure that favors the formation of a thick mastic coating without draining down of asphalt [2, 3]. Polymers increase the useful temperature range of the asphalts [4]. The added polymers can considerably enhance the binder properties and allow the building of safer roads and reduce the maintenance costs by increasing the stiffness of the bitumen and improving its temperature susceptibility [5-7].
Many researchers have reported the advantages of fiber’s utilization in the asphalt matrix. Fibers increase the asphalt mixtures performance against fatigue cracking and permanent deformation by improving the tensile strength and cohesive of the mix [8,9].Fibers also change the viscoelasticity of the modified asphalt by increasing the dynamic modulus; rutting resistance, creep compliance and freeze-thaw resistance while reducing the reflective cracking of the pavement [10], these benefits can obviously prolong the service life of pavement.
Nowadays there has been an eager among pavement technologists to study and analyze the performance of highway properties using nanomaterials. The nanomaterial can be defined as the material with at least one external dimension that measures 100 nanometers or less. Nonoparticles are differing from other conventional materials in the physical and chemical characteristics owing to the higher surface area to volume ratio which can increase the number and frequency of collisions. Therefore, the rate of reaction and the chemical reactivity will be enhanced. According to some studies, nanomaterials can considerably improve the properties of asphalt mixtures such as increasing the rutting and fatigue resistance and decreasing the aging, moisture susceptibility, and maintenance costs [11].
1.5 Electrospinning
Electrospinning is a simple and economical method to produce nanofibers from a polymer melts or solutions. It’s based mainly on applying high voltage to a polymer solution to produce sufficient electrostatic force that overcomes the surface tension of a droplet of polymer solution. The increase in the electrostatic force causes the droplet to stretch in to a conical shape known as Taylor cone. When the surface tension is overcome, a solution jet is ejected from the con’s tip, and then the jet will move towards a region of lower potential which is mostly a grounded collector.
The morphology of the resultant electrospun fibers are greatly affected by many parameters which can be divided in to: polymer solution parameters and processing parameters .If these parameters are well controlled, electrospun fibers with the desired diameters and morphologies can be fabricated.
1.5.1 Polymer Solution Parameters
1.5.1.1 Molecular Weight and Viscosity
The molecular weight of a polymer has a great effect on the viscosity of the solution and it represents the amount of entanglements of polymer chains in the solvent that are important to maintain the continuity of the electrically driven jet during electrospinning process. In general a polymer with higher molecular weight has a higher viscosity than the same polymer with lower molecular weight when they are dissolved in a solvent, so that one of the essential conditions for electrospinning process to occur is the polymer must has a sufficient molecular weight and the solution must be of sufficient viscosity.
The viscosity of the solution can be increased by increasing the polymer concentration which will result in larger polymer chains entanglements that prevents the driven jet from breaking up in to small droplets.
It is important to note that too high viscosity will result in a difficulty in pumping the solution through the needle [1]; furthermore the solution may be dry at the tip of the needle before the electrospinning process is initiated [2].
Several experiments have indicated that in order to obtain fibers without beads a minimum viscosity for the polymer solution is needed. At low viscosity, it is natural to find beads along the fibers since less chain entanglements are present which means that the surface tension has a principal influence along the jet so beads are formed. As the viscosity increases there will be a larger amount of polymer chains entanglements and the charges on the jet become enough to completely stretch the solution , so that there will be a gradual change in the shape of beads from spherical to spindle like till smooth fibers are obtained.
1.5.1.2 Surface Tension
Surface tension is a function of solvent compositions of a solution, it plays an important role in electrospinning process since it is required that the charged solution overcomes it is surface tension, also it has the influence of reducing the surface area per unit mass of a solution. When there is a high concentration of solvent molecules, they tend to assemble to each other and form a spherical shape under the influence of surface tension.
At high viscosities there will be a great interaction between the polymer molecules and solvent, so as the solution is elongated under the effect of charges, solvent molecules tend to spread over the polymer molecules, thus the tendency of solvent molecules to congregate to each other is reduced.
1.5.1.3 Solution Conductivity
The stretching of the solution during electrospinning process is caused by charges repulsion at it is surface. As the conductivity of a solution is increased more charges can be hold on it is surface. Solution conductivity can be improved by the addition of ionic salts like NaCl and KH2PO4 and so on [3], which increase the stretching of the solution and prevent beads formation.
The fiber morphology is greatly affected by the size of the added ions; it was found that the electrospun fibers from a solution with dissolved NaCl have smaller diameters than the fibers from solution with dissolved KH2PO4, because the sodium and chloride ions have smaller atomic radius than the potassium and phosphate ions so that they have higher mobility under the influence of electrostatic field.
1.5.2 Processing Conditions
There are various external factors that affect the electrospinning process and have an influence on the morphologies of the fabricated fibers although they are less important than the solution parameters. These factors include the supplied voltage, solution’s temperature, flow rate, collector’s type, needle’s diameter, and the distance between the tip of the needle and the collector.
1.5.2.1 Voltage
An essential element in the electrospinning process is the application of high voltage to the polymer solution such that the charges are induced within the solution. Together with the external electric field and as the electrostatic force in the polymer solution overcomes the surface tension the process is initiated.
In general, both high positive or negative voltage higher than 6 KV cause the polymer solution to drop at the needle’s tip and form a Taylor Cone. A high voltage will lead to a greater stretching of the solution due to the stronger external electric field as well as the greater repulsive columbic forces. These have the effect of decreasing the fiber diameters and increasing the evaporation rate of the solvent to yield drier fibers. It was also found that the morphology of the electrospun fibers change from smooth fibers to beaded fibers and the density of the beads increases with increasing the supplied voltage [4] , this can be explained by the fact that at higher applied voltage a greater amount of charges causes the electrospinning jet to accelerate faster and more volume of the solution will be drawn from the needle’s tip , so a less stable Taylor Con will result , and when the rate of drawing of the solution is higher than the feed rate from the source the Taylor Cone recedes in to the needle.
1.5.2.2 Temperature
The solution’s temperature has the effect of decreasing the viscosity and increasing the evaporation rate of the polymer solution, this is due to the higher solubility of the polymer molecules in the solvent. At lower viscosity, the columbic repulsive forces have the ability to more stretch the solution and result in fibers of smaller diameters [5]. The increased temperature also increases the mobility of the polymer molecules and that allows the columbic forces to stretch the solution further.
1.5.2.3 Effect of the collector
In order to initiate the electrospinning process there must be an electrical field between the source and the collector. The collector plate is made out of conductive material like Aluminum foil which must be electrically grounded to get a stable potential difference between the source and the collector. When a non-conductive material is used as a collector, charges on the jet will accumulate on the collector so that fewer fibers will be deposited. Fibers that are collected on a conducting surface have a higher packing density compared to those collected on a non-conducting one, and this is due to the repulsive forces of the charges that accumulate on the collector as fibers are deposited on it. In the case of a conducting collector, charges are quickly dissipated thus more fibers are attracted to the collector.
1.5.2.4 Diameter of the needle
It was found that the amount of beads as well as the clogging of the fabricated fibers reduces as the internal diameter of the needle gets smaller [6].
1.5.2.5 Flow rate
The flow rate of the polymer solution greatly affects the morphology of the electrospun fibers. In general a lower flow rate is recommended since it gives enough time for the solution for polarization. When the flow rate is very high fibers with beads will form owing to the short drying time before the fibers reach the collector.
1.5.2.6 Distance between the collector and the tip of the needle
It was found that the distance between the collector and the needle tip also affects the diameter of the fabricated fibers. If the distance is too short the electrical field strength increases so that the acceleration of the electrospinning jet toward the collector increases, hence the fibers may not have enough time for solidification and beads will form. As the distance increases, the fibers diameters increase and that is due to the decrease in the strength of the electrical field which results in less stretching of the fibers.
1.6 Aluminum Oxide (Alumina)
Aluminum oxide is one of the most commonly used materials in the engineering ceramics family. It is a chemical compound of oxygen and aluminum with a chemical formula of Al2O3.It occurs naturally in the crystalline polymorphic phase (”-Al2O3) as the mineral corundum which is the most thermodynamically stable form. The oxygen ions form a hexagonal close-packed structure with aluminum ions filling two-thirds of the octahedral interstices. Owing to it is excellent properties and reasonable price, the fine grain Alumina can be used in a wide range of applications.
1.7 New Parameters
The current SUPERPAVE PG system specification for asphalt cement was mainly based on unmodified binders, and as it is known one of the most effective and common approaches for improving the asphalt performance is by the incorporating different types of polymers and chemical additives to meet the specific requirements for different loading and environmental conditions. There are some drawbacks of the current SUPERPAVE PG system; first, it is based on unmodified binders. Second, the rutting and fatigue cracking occur at high levels of strain and stress whereas the SHRP specifications are based on the measured properties at low strain levels and this shortcoming indicates that there is a poor correlation between the field performance and the PG specifications, this drawback has been minimized by introducing a new and well established creep and recovery test concept to evaluate the asphalt’s potential for permanent deformation at service temperatures known as multiple stress creep recovery (MSCR) test. An alternate use of tests in the dynamic shear rheometer has resulted in a new parameter that is better characterize the fracture and fatigue cracking especially in the case of non-load related cracking, namely the Glover Rowe parameter.
1.8 Research Objectives
The main goal of this research is to assess the impact of using Micro and Nano ceramic fibers as modifiers on rejuvenating physical and rheological properties of asphalt binders. Besides, another objective of this study would be to try to determine the optimum content of these additives considering modification and cost aspects. In addition, the study is set to investigate the impact of size of modifiers on asphalt material performance. To this end, the modified asphalt binder will be tested to determine characteristics such as penetration, ductility, softening point, flash and fire points. Additionally, the performance properties are checked using the SUPERPAVE tests; namely: the Rotational Viscometer (RV) is used to measure the response at storage and pumping temperatures, the Dynamic Shear Rheometer (DSR) is used to investigate the response at intermediate and maximum temperatures, and the Bending Beam Rheometer (BBR) is used to measure the response at low pavement temperatures. Applying new and improved approaches to better characterize the fatigue cracking and rutting resistance for modified binders such as frequency sweep test and multiple stress creep recovery test, was also one of the important goals for this study. Scanning Electron Microscopy (SEM) will be used to evaluate and characterize the distribution of additive particles in asphalt binder. It is well-known in the paving industry that uniform distribution of additives is a must to ensure homogenous mixtures prior to testing.
1.9 Thesis Plan
After the completion
Chapter Two: Literature Review
Many researches have shown that the fibers either synthetic or natural can improve the cohesion and tensile strength of asphalt mixtures as well as permitting higher binder content without significant effect on the draindown [13].Nowadays, nanotechnology has been widely used in the asphalt modification field owing to the great effects of nanomaterials in improving the characteristics of asphalt binders and hence mixtures such as increasing rutting and cracking resistance in addition to decreasing aging, and therefore maintenance costs. Nonoparticles are differing from other conventional materials in the physical and chemical characteristics due to the higher surface area to volume ratio which can increase the number and frequency of collisions. Therefore, the rate of reaction and the chemical reactivity will be enhanced and that is why the nanotechnology superior to other methods of asphalt binder modifications. In the following review, various additives used in asphalt binder modification and their effects on the performance of base asphalt will be presented and discussed.
2.1 Naturally Modified Asphalt Binder
The utilization of natural fibers to modify asphalt mixtures is a very popular phenomenon since they have a good potential to improve the tensile strength of bituminous mixes. The advantages of natural fibers over other modifiers are: low cost, good thermal properties and low density. Based on their origin, natural fibres can be classified in to three classes: bast (jute, banana, flax, hemp, kenaf, mesta), seed or fruit fibres (coir, cotton, palm), and leaf (pineapple, sisal, henequen, screw pine).
It was reported by Abiola et al. (2013) that the utilization of natural fibers such as coir, sisal, hemp, juite, and palm as modifiers in asphalt concrete mixtures helps in improving the mechanical properties of them and that the natural fibers can replace synthetic fibers in SMA mixtures due the good adhesion of fibers with asphalt. The natural fibers provide an extended fatigue life, increase the stability and the structural resistance of flexible pavements to distresses.
Satyavathi et al. (2016) investigated the suitability of using coir fiber and pineapple fiber as stabilizing agents in SMA by analyzing the flow and stability values using Marshall Stability test. Different percentages of bitumen were selected then the draindown test was performed to determine both the optimum asphalt and fiber contents, results indicated that the fibers reduce the draindown and increase the stability of the mixes. The optimum fiber content was 0.3% for coir fiber and 0.1% for pineapple fiber. The coir fiber showed better stability when compared to pineapple fiber.
Mohan et al. (2016) studied the effect of coir fiber and marble waste on the indirect tensile strength of asphalt mixtures. It was found that the tensile strength of mixtures modified with coir fiber and marble increased by 199 % compared to the original mix, this improvement was due to the good adhesion between the aggregate and bitumen. BC mix with 0.5% coir fiber and 8% marble showed maximum strength.
Behbahani et.al. (2009) evaluated the effect of fiber type and content on rutting performance of SMA using two types: cellulose fiber and mineral fiber at different percentages 0.1-0.5% of the total weight of SMA mixture. Laboratory tests results demonstrated that the variation of fiber type and content considerably change the rutting performance of SMA and that the specimens made with 3% cellulose have the highest tensile strength and least permanent deformation.
The properties of coir fiber and kenaf fiber modified asphalt mixes were examined by Sani et al. (2011).The obtained laboratory results indicated that the Marshall Stability of HMA increases by 3.2% and 9.7% with the addition of coir fiber and kenaf fiber respectively, so that that the damages of pavement can be controlled and an extended service life is also expected. The optimum weight of coir fiber and kenaf fiber was determined to be 4 g, 4.4 g respectively.
The utilization of coconut fiber and coconut shell in pavement construction was reported by Tinga et.al. (2015). It was found that the coconut fiber increases the skid resistance; resilient modulus and stability while the shell improves the static creep behavior and tensile strength of the modified asphalt mixtures.
Silva et al. (2013) studied the behavior of asphalt mixtures reinforced with coconut fibers .It was concluded that the coconut fibers have a little porous microstructure which prevents the runoff of the binder and increases the hardening of the mix. The obtained results showed that the modified mixtures have a volume of voids below the established limit which results in higher stiffness, resilient modulus and tensile strength.
Hadiwardoyo (2013) evaluated the addition of different sizes of coconut fibers on the engineering properties of asphalt mixtures at different percentages, it was found that the use of 5 -12.5mm fibers in the range of 0-1.5% by weight of virgin asphalt reduces the bitumen penetration grade but increases the softening point. The 0.75% of coconut fiber content gave the best properties and performance among all the content studied.
Xiong, R. et al. (2015) conducted a laboratory investigation on the brucite fiber reinforced asphalt binder and asphalt concrete. For comparative studies other types of fibers were used such as: lignin fiber, basalt fiber and polyester fiber. Tests of water absorption, oven heating and mesh-basket draindown, were performed on fibers, to investigate their wettability, asphalt absorption, thermostability, and stabilization respectively. The cone sink and the standard dynamic shear rheometer tests were done to study the rutting resistance and rheological properties of the modified asphalt.It was found that the brucite fiber poses a better state of preservation in humid environments and thermostability than do lignin fiber, and it has a more significant effect on asphalt absorption and stabilization than other fibers. The brucite fibers can effectively improve the rutting resistance, low temperature cracking resistance and moisture susceptibility of modified asphalt.
2.2 Polymer modified Asphalt Binder
Another approach that can be used to enhance and improve the asphalt binder quality is utilization of polymers. A ‘polymer’ is a large molecule made of many repeated subunits, the properties of a given polymer are dependent on it’s molecular weight, and the arrangement and chemical structure of the monomers. When polymers are introduced to the binder, the characteristics of the modified binder depend on: asphalt characteristic, polymer properties, and mixing conditions. The gained improvements in fatigue resistance, thermal cracking, rutting, and stripping have led to use polymer modified asphalts to build economical pavements that will perform better for extended periods of time
A study by Chen (2009) on the dynamic and volumetric properties of fiber reinforced mixtures using four different fiber types: polyester, polyacrylonitrile, asbestos, and lignin showed that the bulk specific gravity decreases, while the air voids, VMA, and the optimum asphalt content increase after the adding of fibers into the mixtures. Marshall Stability increases initially and then decreases with increasing fiber content. It was also found that the mixtures with polyester and polyacrylonitrile fibers pose higher stability, and the mixtures with lignin and asbestos fibers have higher optimum asphalt content and VFA due to their higher absorption of asphalt. A fiber content of 0.35% by mass of mixture is recommended for the polyester fiber
The effect of using fibers on the mechanical properties of bituminous mixes was studied by Supriya et al. (2013) by performing mix design, Marshall Stability and the indirect tensile strength tests. The overall results showed that the addition of polyster fibers improves the performance when compared with the reference mix. The optimum asphalt content for the mixture increases with the increasing in fiber content and fiber length. The Marshall stability and the indirect tensile strength increased by 30% and 20% for fibers of 12 mm with optimum content of 0.4 % respectively. So stiffer bitumen can be obtained and higher rutting resistance is expected, but the unit weight, phase angle, and flow tend to decrease.
A.Zare-Shahabadi et al. (2010) have used Bentonitecaly (BT) and organically modified Bentonite (OBT) to modify asphalt. They have investigated the physical properties, high temperature rheological behavior, and low temperature cracking of modified asphalts. They showed that the modified asphalts have higher rutting resistance and improved low-temperature cracking resistance. Moreover, the OBT modified asphalts have better properties than the BT modified asphalts which may be due to the exfoliated structure of the OBT modified asphalts which results in a better dispersion of clay platelets in the matrix, and the better surface compatibility of OBT nanoparticles with the organic molecules of the asphalt matrix
Xu, Q et al. (2010) have studied the performance of fiber reinforced asphalt concrete under environmental temperature and water effects. They have used four different fiber types: polyester, polyacrylonitrile, lignin and asbestos to modify asphalt. Laboratory tests were conducted on the modified asphalts to measure their strength, strain and fatigue behavior. Results indicated that the fibers have improved asphalt’s rutting resistance, toughness and fatigue life. Additionally, the flexural strength, ultimate flexural strain, and the split indirect tensile strength (SITS) at low temperature have improved. The polymer fibers (polyacrylonitrile and polyester) have significantly improved rutting resistance, fatigue life, and SITS more than lignin and asbestos fibers; while asbestos and lignin fibers result in higher flexural strength and ultimate flexural strain. However, fiber’s effect under water freezing’thaw action does not seem promising, and the SITS of modified asphalts with lignin and asbestos fibers reduces to some extent under this action.
Chen, H., &Xu, Q. (2010) have examined the mechanism of different fiber types for stabilizing and reinforcing asphalt binder. Laboratory tests of water absorption, oven heating and mesh-basket draindown, were performed on five fiber types: two polyesters, one polyacrylonitrile, one asbestos and one lignin, to investigate their wettability, asphalt absorption, thermostability, and stabilization respectively. The cone sink experiment was done to study the modified asphalt’s resistance to flow, and the standard dynamic shear rheometer test was performed to evaluate the modified asphalt’s rheological properties and rutting resistance. Results indicated that fibers can improve asphalt binder’s resistance to flow and rutting, and that the lignin fiber has the highest water absorption but the lowest thermostability. The lignin and asbestos fibers pose greater effects of asphalt absorption and stabilization than do polymer fibers.
Wang, D. et al. (2013) investigated the effect of basalt fiber on asphalt binder and mastic at low temperatures.The modified specimens were tested using the direct tension test and a newly developed procedure for fatigue test, which directly applies cyclic tensile loading to asphalt binder and mastic specimens. The direct tension test results showed that the tensile strength of the asphalt binder was improved with the use of basalt fiber. The basalt fiber also increases the stiffness and the fatigue life of both the asphalt binder and mastic specimens.
Liu, X. et al. (2008) reported that the graphite powder can transform free asphalt to structure asphalt, so that the softening temperature of asphalt binders was increased from 45 to 82 ”C with graphite addition of 9.0 vol. %. The rutting parameter G * /sin” increased from 1 .555 to 3.745 when the graphite content was raised from 0 to 9.0 vol. %. Furthermore, the electrical conductivity of asphalt-based composites increased from 8.7x 10 -11 S/cm to 8.9 x10-2 S/cm, which indicates that the three- dimension electrical conductive networks had formed in the composites system and the graphite particles connected together. The increase in the electrical conductivity would make asphalt-based composites transform from insulator to conductor, which made self-monitoring of asphalt pavement become feasible.
H”n”sl”o”lu, S., &A”ar, E. (2004). Studied the suitability of using waste high density polyethylene as bitumen modifier in asphalt concrete mixes. The modified asphalts used in Hot Mix Asphalt (HMA) were prepared by the mixing of HDPE fiber at different percentages 4 ‘ 6% and 8% by the weight of optimum bitumen content at temperatures of 145 ‘ 155 and 165 ”C and 5 ‘ 15 and 30 min of mixing time. Results demonstrated that the HDPE-modified asphalt concrete obtains a better permanent deformation resistance due to their high Marshall Stability and high Marshall Quotient value (Stability to flow ratio).
Lu, X., &Isacsson, U. (2000) studied the fundamental properties of modified asphalts with different thermoplastic polymers (SBS, SEBS, EVA and EBA).The morphology, rheology and ageing properties of the modified asphalts were examined using fluorescence microscopy, dynamic mechanical analysis, and creep test. Results showed that the morphology, rheological properties and aging properties of the modified asphalts were affected by the type and content of the polymer. The rheological properties could be improved significantly at higher polymer contents (about 6%).In addition, the modified asphalts containing EVA and EBA differ widely in their rheological behavior from those containing SBS and SEBS at the same polymer content.
2.3 Nano Modified asphalt binder
Nowadays there has been an eager among pavement technologists to study and analyze the performance of highway properties using nanomaterials. The nanomaterial can be defined as the material with at least one external dimension that measures 100 nanometers or less. Nonoparticles are differing from other conventional materials in the physical and chemical characteristics owing to the higher surface area to volume ratio which can increase the number and frequency of collisions. Therefore, the rate of reaction and the chemical reactivity will be enhanced. According to some studies, nanomaterials can considerably improve the properties of asphalt mixtures such as increasing the rutting and fatigue resistance and decreasing the aging, moisture susceptibility, and maintenance costs [11].
Goh, S. W.et al. (2011) studied the effect of deicing solutions on the tensile strength of macro- or nano-modified asphalt mixtures. Asphalt mixtures were prepared by using various percentages of nanoclay and/or carbon microfiber, and compacted using the Superpave gyratory compactor. In order to assess the moisture susceptibility and deicer impacts, the samples were exposed to water or deicing chemicals (NaCl, MgCl2 and CaCl2), and seven freeze’thaw cycles. Based on the obtained results of indirect tensile strength tests, it was clear that the microfibers and nanoclays have great potential in improving the asphalt mixtures performance. The addition of nanoclay and carbon microfiber would decrease the moisture damage in most cases.
Yao, H. et al. (2016) evaluated the utilization of graphite nanoplatelets to modify the asphalt due to their unique characteristics such as: the high optical absorption, self-lubrication, high thermal stability and conductivity. Various amounts of graphite nanoplatelets without further treatment were added to the asphalt and different properties of the modified asphalt binder were tested, including viscosity, the complex shear modulus, and the thermal cracking temperature. Through these tests, it was found that the addition of graphite nanoplatelets enhances the high- and low-temperature performance of the modified asphalt binder; therefore, the resistance to rutting and cracking is improved.
Hamedi, G. H. (2017) investigated the effects of using nano-materials on the moisture damage of hot mix asphalt. The asphalt binder was modified using nano Al2O3 and Fe2O3 at 2% and 4% percentages, respectively. The mechanical tests results showed that using the nanomaterials significantly improves the moisture damage of the samples and that the cohesion free energy of asphalt binder increases so that the probability of cohesion failure occurrence will decrease.
Hamedi. et al. (2016) evaluated the effect of nanoparticles as an antistrip agent on the moisture damage of HMA. Two types of aggregate were used in the study (limestone and granite aggregate), and asphalt binder with 60-70 penetration grade and nano zinc oxide (ZnO) at 2% and 4% by weight of asphalt binder. The modified specimens were tested by applying the surface free energy and AASHTO T283 tests. The results showed that the ratio of wet/dry values of indirect tensile strength for the modified mixtures for both types of aggregate were higher than the control mixtures. In addition, it was noted that the nano ZnO particles increased the total SFE of the asphalt binder, which led to better coating of the aggregate with asphalt binder.
Azarhoosh. et al. (2016) studied the effects of nano-TiO2 on the adhesion between the asphalt binder and aggregate using the surface free energy (SFE) method. The SFE components of asphalt were calculated using Wilhelmy plate test, while the SFE components of the aggregates were determined by universal sorption device test. The results of the SFE method showed that the nano-TiO2 increases the wettability of asphalt binder on the aggregate and so the adhesion between the asphalt binder and the aggregate improved.
Azarhoosh. et al. (2016) evaluated the effects of using nano-TiO2 on the fatigue life of asphalt mixtures using the surface free surface energy method and the indirect tensile fatigue test. Two types of aggregate were used in the study (limestone and granite aggregate), and asphalt binder with 85-100 penetration grade and nano-TiO2 at 3% and 6% by weight of asphalt binder. It was obvious that the fatigue lives of modified mixtures containing nano-TiO2 were higher than the control mixtures, and this is due to the fact that nano-TiO2 leads to decrease the acid component of SFE and increase the basic component in SFE of the asphalt binder which enhances the adhesion between asphalt binder and aggregate.
Chapter Three: Materials and Testing Procedure
This chapter gives more detailed descriptions and insights on the materials and testing methods used throughout this study. The information presented contains full details on asphalt binder, Alumina, and experimental procedures that were employed in the research work
3.1. Asphalt binder
Asphalt is a dark brown to black, viscoelastic, highly viscous, and sticky material, it can be obtained by the distillation process from crude petroleum or occurred naturally. It has excellent adhesive and waterproofing properties, and can be mixed with mineral aggregates to produce the asphalt concrete.
Asphalt binders were previously graded according to their viscosity or penetration; these systems of grading are considered limited in their abilities to characterize the asphalt binders that will be used in HMA pavements construction. The current asphalt grading system is known as the performance grading (PG) system, which takes in to account the impact of traffic, aging, and climatic conditions at both cold and hot temperatures on asphalt characteristics.
Asphalt binder’s physical properties are measured at different temperatures both prior to and after conducting the laboratory aging. The laboratory aging is used to simulate the aging during the production and service life of HMA pavements
One penetration grade of asphalt cement (60’70) was used in this study; it was obtained from the Jordan Petroleum Refinery Company in Zarqa, Jordan. The following table 3.1 shows the physical properties of used asphalt binder.
Table 3.1: The physical properties of used asphalt binder
Properties of asphalt binder Value Technical Criterion
Penetration (25”C,100g,5s) 64 60-70
Softening point(”C) 50 30-80
Flash point 291 ‘230
Fire point 296 ‘230
Ductility (25”C, 5 cm/min) 103 ‘100
Specific gravity(25”C) 1.015 0.97-1.02
3.2 Alumina
Aluminum oxide is one of the most commonly used materials in the engineering ceramics family. It is a chemical compound of oxygen and aluminum with a chemical formula of Al2O3.It occurs naturally in the crystalline polymorphic phase (”-Al2O3) as the mineral corundum which is the most thermodynamically stable form. The oxygen ions form a hexagonal close-packed structure with aluminum ions filling two-thirds of the octahedral interstices. Owing to it is excellent properties and reasonable price, the fine grain Alumina can be used in a wide range of applications.
3.2.1 Bayer Process
The Bayer process is the most economical mean for refining Bauxite to produce alumina .Bauxite is considered as the most important ore of aluminum since it contains 30’60% aluminum oxide and the rest being a mixture of silica, titanium dioxide, and various iron oxides.
The Bayer process is conducted in four stages. Firstly, after the bauxite is washed and ground in mills, it is dissolved with sodium hydroxide in a pressure vessel at elevated temperature of 150-200 ”C, and then the mixture is filtered to get rid of impurities which are called ‘red mud’. The remaining alumina solution is pumped to the precipitators where the hot solution is cooled and the aluminum hydroxide starts to seed. The aluminum hydroxide seeds promote the solid aluminum hydroxide crystals precipitation. The aluminum hydroxide deposited at the bottom of the precipitator tanks and is removed. At the end, the aluminum hydroxide is washed of any remaining caustic soda and heated to remove the excess water. The final product from this process is a dry white (”-Al2O3) powder with a size range of 0.5-10 ”m.
3.2.2 Alumina physical and mechanical properties
The following tables 3.2 and 3.3 contain the mechanical and physical properties of alumina that will be used in this research.
Table 3.2: Mechanical Properties of Alumina
Density 3.89 gm/cc
Porosity 0
Color White
Flexural Strength 379 MPa
Elastic Modulus 375 GPa
Shear Modulus 152 GPa
Poisson’s Ratio 0.22
Compressive Strength 2600 MPa
Hardness 1440 Kg/mm2
Maximum Use Temperature 1750 ”C
Table 3.3: Physical Properties of Alumina
Thermal Conductivity 35 W/m”K
Coefficient of Thermal Expansion 8.4 x 10-6 /”C
Specific Heat 880 J/Kg.”K
Dielectric Strength 16.9 ac-kv/mm
Dielectric Constant 9.8 @ 1 MHz
Volume Resistivity >1014 ohm.cm
3.3 Sample preparation
The modified binders were prepared in the laboratory by applying three different percentages by volume (0.05%, 0.1%, and 0.2%) of micro Al2O3 on (60-70) asphalt binder grade. The samples of each percentage were prepared by mixing the corresponding weight of asphalt binder and Micro Al2O3. The Nano Al2O3 was added into asphalt binder at only one percentage () due to it’s limited amount. A mixer was used to ensure a homogenous distribution of Micro and Nano particles. The asphalt binder was mixed with Micro and Al2O3 at 180 ”C and 100 rpm for 3 hours. The following figures show the mixing procedure.
3.4 Binder Testing
The physical properties of Aluminum Oxide (AL2O3) modified and control asphalt binders were tested by the following test procedures including penetration, softening point, ductility, flash point, and rotational viscosity. On the other hand, the rheology of the bitumen was examined using the following tests: Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) and Direct Tension Tester (DTT) if needed. At the end, new and improved approaches using DSR were applied to better characterize the fatigue cracking and rutting resistance for modified binders such as the frequency sweep test and multiple stress creep recovery test.
3.4.1 Penetration Test
In order to determine the workability of asphalt binder and it’s suitability to use under different climatic conditions , a standard needle allowed to penetrate in to a bituminous material under specified conditions of load(100g), time (5sec),and temperature(25C) figure (1).Then, the vertical distance penetrated by the needle is converted into penetration number [38].
Figure 1: Required apparatus for penetration test
3.4.2 Softening Point Test
This test aims at measuring the consistency of asphalt cement by filling a brass ring with asphalt binder and suspended it in a beaker filled with water at a distance of 1′ from the bottom plate figure (2). Then, a steel ball is placed in the center of the sample. The bath is heated and controlled at a rate of 5’C/min; the temperature is recorded at the instant when the softened asphalt touches the bottom plate [39].
Figure 2: Ring and Ball apparatus
3.4.3 Ductility
To measure the tensile properties of asphalt binder, a standard briquette mold is filled with asphalt binder, and then the two ends of the specimen are pulled apart in a water bath at 25’C at a rate of 5cm/min until failure figure (3), [40].
Figure 3: Ductilometer
3.4.4 Flash and Fire Points Test
A sample of asphalt binder is heated at a specified rate of 14’C/min, when the temperature reaches approximately 28’C below the flash point, a test flame is passed across it at rate of 2’C/min, and then the flash point is recorded when a flash appears figure (4). Fire point is slightly higher than the flash point and it recorded when the specimen burns for 5 continuous seconds [41].
Figure 4: Cleveland Open Cup apparatus
3.4.5 Rotational Viscosity
In order to be sure that the binder is sufficiently workable, a cylindrical spindle is submerged in asphalt binder at constant temperature of 135’C figure (5), then the torque that is required to maintain a constant rotational speed (20RPM) of the spindle is measured and converted to viscosity [42].
Figure 5: Required apparatus for R.V test
3.4.6 Dynamic Shear Rheometer
The DSR test can be used to characterize the elastic and viscous behavior of bitumen. The basic DSR test uses a thin asphalt binder sample sandwiched between two plates. The lower plate is fixed while the upper one oscillates back and forth at 1.59 Hz to create a shearing action figure (6).DSR test is conducted on unaged, RTFO aged and PAV aged asphalt binder samples, it measures the specimen’s complex shear modulus (G*) and phase angle (”).The complex shear modulus (G*) gives an indication about the sample’s total resistance to deformation when repeatedly sheared. The phase angle (”), is the lag between the applied shear stress and the resulting shear strain [43].
Figure 6: Dynamic Shear Rheometer
3.4.7 Bending Beam Rheometer
The BBR test can be used to investigate the asphalt binder’s ability to resist low temperature cracking; it provides a measure of low temperature stiffness and relaxation properties of asphalt binders figure (7). A small beam of binder (125mmX 12.5 mm X 6.25 mm) is tested at low temperature under constant load of 100g for 240 sec, the deflection of the beam is recorded and the creep stiffness is measured after 60 sec. BBR test is conducted on PAV aged asphalt binder samples [44].
Figure 7: Bending Beam Rheometer
3.4.8 Direct Tension Test
The basic DTT test measures the stress and strain at failure of a specimen of asphalt binder pulled apart at a constant rate of elongation at temperatures ranging from 0”C to -36”C, within which asphalt exhibits brittle behavior. Furthermore, the test is performed on binders that have been aged in a rolling thin film oven and pressure aging vessel [45].
(After Completion)
3.4.9 Frequency Sweep Test
3.4.10 MSCR Test
3.4.11 Scanning Electron Microscopy
Scanning Electron Microscopy can be used to evaluate and characterize the distribution of additive particles in asphalt binder.
Chapter Four: Results, Data Analysis and Discussion
After conducting all physical and rheological tests for neat and modified binders, data and results were summarized in order to assess the impact of using Micro and Nano ceramic fibers on rejuvenating physical and rheological properties of asphalt binders and to make comparisons between the properties of control binders and modified binders at different levels, data and results for each test were as follows:
4.1 Penetration Test Results
The penetration value of bituminous materials reflects their consistency and describes their deformation and flow properties. Table 4.1 shows the effect of adding Micro Al2O3 fibers at different percentages on the physical properties of the neat binder.
Table 4.1):Penetration Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
45 43 41 52 53 54 62 58 60 63 64 65 Results(#)
43 53 60 64 Average
Figure 4.1 indicates that Micro Al2O3 decreases penetration value of the asphalt and the decrease in penetration increased with increase in Micro Al2O3. At 0.2% Micro Al2O3 content it was observed that penetration decreases by almost 33% compared with control binder. It was also observed that Micro Al2O3 has a significant effect on control binder as indicated through penetration values reduction and hardness increase , so that the binder resistance against high temperature effects will be enhanced and makes it more resistant to pavement failures such as deformations. This was due to strong network formation of dispersed Micro Al2O3 .Furthermore, the decrease in penetration is also related to diffusion of oil fraction within the bitumen (maltenes) in the polymeric phase which causes higher interactions and swelling between the Micro Al2O3modifier and polar molecules of the binder (asphaltenes). ( waiting SEM photos to describe the precise effect of Al2O3 on asphalt )
Figure 4.1: Penetration Number vs. % of Al2O3
4.2 Softening Point Test Results
The plastic flow of asphalt as well as it’s stability under the conditions of elevated service temperatures can be described based on it’s softening point. As the softening point temperature increases, the stability of asphalt binder under high service temperatures increases. Table 4.2 shows the effect of adding Micro Al2O3 fibers at different percentages on the softening point of the neat binder.
Table (3): Softening Point Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
60 59 58 55 56 57 52 53 51 49 50 51 Results(”C)
59 56 52 50 Average
Figure 4.2 shows the softening point values of base and Micro Al2O3 modified binders, it’s obvious that addition of Micro Al2O3 raises softening point values for all the modified binders. At 0.2% Micro Al2O3 content it was observed that the softening point temperature increases by almost 15% compared with control binder. This means that the asphalt becomes less susceptible to temperature and more resistant to permanent deformation.
Figure 4.2: Softening Point Temperature (”C) vs. % Al2O3
4.3 Ductility Test Results
Ductility of asphalt binder is a property that describes it’s ability to elongate under repeated traffic loading without being cracked, it also shows the amount of tensile strength and elasticity of asphalt .As the ductility value increases a better properties of bitumen will result, Table 4.3 shows the effect of adding Micro Al2O3 fibers at different percentages on the ductility of the neat binder:
Table (2): Ductility Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
35 33 37 55 53 54 74 76 78 103 102 104 Results(cm)
35 54 76 103 Average
Figure 4.3 shows the ductility values of base and Micro Al2O3 modified binders; it’s obvious that addition of Micro Al2O3 decreases the ductility values for all the modified binders. At 0.2% Micro Al2O3 content it was observed that the ductility decreases by almost 66% compared with control binder. This means that the asphalt becomes stiffer and harder.
Figure 4.3: Ductility vs. % Al2O3
4.4 Flash and Fire Points Test Results
The flash and fire points test aims at evaluating the bituminous material in terms of safety during storage and construction, the higher values of flash and fire points, the higher the potential for using asphalt in hot regions. Tables 4.4 and 4.5 show the effect of adding Micro Al2O3 fibers at different percentages on the flash and fire points values of the neat binder:
Table 4.4: Flash Point Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
334 330 332 314 318 316 305 303 298 291 290 292 Results(”C)
332 316 302 291 Average
Table 4.5 :Fire Point Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
338 334 336 319 323 321 310 308 303 296 295 297 Results(”C)
336 316 307 296 Average
Figures 4.4 and 4.5 show that the flash and fire points increase as the % of Micro Al2O3 increases .The increment in both flash and fire points values of the modified bitumen with the addition 0f 0.2 % of Micro Al2O3 is from 291”C and 296”C to 332”C to 336 ”C respectively , compared with the control asphalt . The increment in both flash and fire points is around 4% with the addition 0.05 % of Micro Al2O3.
Figure 4.4: Flash Point vs. % Micro Al2O3
Figure 4.5: Fire Point vs. % Micro Al2O3
4.5 Rotational Viscosity Test Results
The rotational viscosity test can be used as an indicator of the stiffness of bituminous material, it also an important property to decide on working temperatures since it represents asphalt’s ability to be pumped, thoroughly coat the aggregate in an asphalt concrete mix. As the viscosity increases, the resistance to deformation increases .However, if the viscosity is too high it would be too hard to blend or compact the asphalt. Table 4.6 shows the effect of adding Micro Al2O3 fibers at different percentages on the rotational viscosity of the neat binder; it is obvious that the viscosity of all binders meets the Superpave specification since it requires that the maximum viscosity of asphalt binder at 135”C should be less than 3000 cp.
Table 4.6: Rotational Viscosity Test Results
0.2% 0.1% 0.05% 0% % of micro Al2O3
3 2 1 3 2 1 3 2 1 3 2 1 Samples
837.5 825 812.5 475 487.5 500 405 412.5 387 385 390 370 Results(mp.s)
825 487.5 401.5 381.67 Average
Figure 4.6 shows that the rotational viscosity value increases as the % of Micro Al2O3 increases .The increment in the viscosity of the modified asphalt is caused by the heating during the mixing and the stiffing effect of the Micro Al2O3 fibers, the increment in the rotational viscosity value of the modified bitumen with the addition 0f 0.2 % of Micro Al2O3 is almost two times of the control binder.
Figure 4.6: Rotational Viscosity vs. % Micro Al2O3
REFERENCES
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