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Chemical, Morphological, and Fundamental Properties of Rejuvenated Asphalt Binders
Abstract
This study investigates the chemical characteristics of rejuvenators and the effect of different rejuvenators on the morphology and fundamental behavior of rejuvenated asphalt binders. Gas chromatography-mass spectroscopy (GC-MS) and atomic force microscopy (AFM) were conducted to determine the chemical composition of rejuvenators and asphalt surfaces' morphology. Also, surface free energy (SFE) measurements were performed to quantify the cohesive bond energy of rejuvenated binders. The thin film oven test (TFOT)-aged performance graded (PG) 58-28 binder was rejuvenated with waste cooking oil (UT), chemically modified waste cooking oil (TR), and Hydrolene H90T (HL) at concentrations of 3%, 6%, and 9% by weight of the total binder. To understand the compatibility, styrene-butadiene-styrene (SBS) was also blended with rejuvenated binders. The experimental study found the variability of free fatty acid compositions in rejuvenators, which is hypothesized to affect pavement performance. Results showed that rejuvenation alters the surface microstructure of binders, which provides insights into the overall performance of the binder. Also, rejuvenation improves the moisture damage resistance of binders significantly. This experimental study found a good correlation between the chemical, morphological, and fundamental behavior of the rejuvenated binders, which is expected to help quantify the performance of rejuvenated asphalt mixes.
... The rejuvenators are waste cooking oil (WCO), chemically modified WCO and Hydrolene, which are denoted throughout this paper as R1, R2, and R3 respectively. Detailed information on the physical properties of the rejuvenators can be found in [31]. R1 was collected from two different sources (NJs Kitchen and Eco Oil Limited). ...
... The transesterification process may reduce the capacity of R2 to rejuvenate the aged asphalt, by inhibiting the interaction between the rejuvenator and aged binder. This is fairly consistent with our concurrent study, which observed similar findings using Atomic Force Microscopy (AFM) when this rejuvenator was used [31]. ...
... The second is that excess rejuvenator oil has surrounded SBS particles and prevented them from absorbing aromatic oils in the binder. This problem is likely more prevalent in cases where high amounts of non-aromatic rejuvenator were used and has previously been observed in other studies where high dosages of rejuvenators were used [31]. In the case of the SBS modified R2, a higher phase angle and a higher stiffness are observed than that of the aged binder and R1 ? ...
Using reclaimed asphalt pavement (RAP) material in pavement construction is typically an environmentally friendly practice. However, the asphalt available in RAP is already oxidized and stiffened due to various environmental processes. To compensate these problems, rejuvenators can be mixed with aged binder with the aim of restoring its original properties. This study investigates the performance of aged binders blended with three different types of rejuvenators. Thin film oven test aged PG 58–28 binder was mixed with raw waste cooking oil (R1), modified waste cooking oil (R2), and Hydrolene H90T (R3) at the concentrations of 3%, 6% and 9% by the weight of the total binder. To enhance rutting resistance, styrene–butadiene–styrene was also blended with rejuvenated binders and tested. Frequency sweep testing at a wide range of temperatures and frequencies was conducted in the Dynamic Shear Rheometer, and time–temperature superposition was used to obtain parameters including Superpave, Glover-Rowe, Shenoy, Crossover frequency and Rheological index parameters. In addition, the Multi Stress Creep Recovery test was performed to gain an in-depth understanding of the rutting performance of the binders. Based on the comparative study of different rejuvenated binders, the binder rejuvenated using a chemically modified waste cooking oil seems to most be effective in improving the overall performance of the binder without compromising its rutting resistance. In addition, the relationship between different cracking parameters indicated that they are not all compatible with each other in terms of ranking binder performance. Finally, the MSCR parameter seems to more effectively capture the influence of rejuvenation and SBS addition to rejuvenated binders more than other parameters.
... When using Gas Chromatography-Mass Spectrometry (GC-MS) based on C16 and C18 standards, the compounds are expected to exhibit retention times of 18.39 and 20.21 minutes. However, in the case of Rej-A, lower molecular weight compounds were observed, as illustrated in Fig. 2. Conversely, the chromatograms for Rej- B revealed no fatty acids within these specified retention times, as depicted in Fig. 3. Previous studies reported that bio-rejuvenators with a high content of monounsaturated and stable and fatty acids exhibit better rejuvenation efficiency [46,47]. Therefore, quantifying fatty acid content can provide insight into performance changes exhibited by the rejuvenated binders. ...
... Notably, at a temperature of 150 • C, the mass loss was 13.16 %, while at 135 • C, the mass loss was only 9.96 %. Therefore, using dry treatments to remove moisture from Rej-A or implementing warm mix technology could maximise the rejuvenation efficiency of Rej-A [47]. ...
Ageing of bitumen leads to significant performance deterioration of asphalt pavements and leads to material properties that are not conducive to recycling. Aiming to maximise the reusability of bitumen, this study investigated the feasibility of rejuvenating aged bitumen using bio-based rejuvenators synthesised from municipal wastes. Two bio-rejuvenators were used in this study, namely Rej-A which was a crude polymer with bio-waste pyrolysis dense fractions and Rej-B which was a filtered pyrolysis wax further derived from Rej-A. The bio-rejuvenators, virgin, aged, and rejuvenated bitumen were characterised using a comprehensive testing programme of gas chromatography and mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), and frequency sweep tests. It was observed that both bio-rejuvenators produced in this study can effectively recover the rheological properties of aged bitumen, improving its fatigue performance, e.g. the fatigue lives (at 15 % strain level) of Rej-A and Rej-B rejuvenated bitumen were 5.4 times and 3.0 times of that for aged bitumen when the dosage was 14 %. The rejuvenated bitumen was more sensitive to strain while less sensitive to temperature compared with virgin bitumen. Overall, Rej-A outperformed Rej-B in recovering the properties of aged bitumen. However, Rej-A was thermally unstable, undergoing 15.6 % mass loss when heated to 160 • C.
... The rejuvenation effect diminishes as WO content increases, and similar conclusions are reached for Matolia et al. [76]. Different from virgin asphalt, the adhesive forces of SBS modified asphalt become higher after aging, and WO will decrease it, while 7% WO leads to an increase of adhesive force after ultraviolet (UV) aging [34,50,77]. Jiménez del Barco Carrión et al. [78] found the SFE of bio-oil is larger than 50/70 asphalt, combining the adhesion work and pull-off tensile strength (POTS), bio-oil can restore the adhesion work of aged asphalt. ...
Waste oil (WO) is an important recyclable resource that can be used for asphalt rejuvenation and modification applications. This paper summarizes the current research on WO application in rejuvenating aged asphalt and modifying asphalt. First, the basic and chemical properties of WO and the preparation process of rejuvenated asphalt and modified asphalt were introduced. Then the various properties including basic physical, rheological, fatigue, adhesion, chemical, and mixture properties were summarized separately. Finally, the aging resistance and economic and environmental benefits were presented. The review work shows that WO may restore the properties of aged asphalt, except for the viscoelastic ratio. WO containing more asphaltenes and saturates or ash will promote the rapid aging of rejuvenated asphalt. Combined with chemical characteristics and molecular dynamics (MD) simulation, the interaction between WO and aged asphalt belongs to physical dissolution, and the rejuvenation process is achieved by restoring the colloid structure of asphalt and increasing molecular mobility. In the modification process, WO is mainly used to improve the intermediate fatigue resistance and low-temperature cracking resistance of asphalt in winter areas, and can also be used as an anti-aging agent, but will harm the high-temperature properties. The composite rejuvenation/modification of WO and crumb rubber (CR) makes the properties of asphalt more comprehensive. For asphalt mixture, the cracking resistance and the moisture susceptibility of WO recycled asphalt mixture are worse than hot mix asphalt (HMA). The future research focus is to evaluate the performance of WO recycled asphalt mixture and WO modified asphalt mixture after long-term aging and conduct field experiments combined with economic and environmental benefits analysis.
... Shortterm ageing is defined as the period between the production of hot mix asphalt and the opening of the pavement to traffic, whereas long-term ageing is defined as the period between the opening of the pavement to traffic and the production of hot mix asphalt. In the laboratory, ageing can be simulated using standard and non-standard methods such as the thin film oven test, the pressure ageing vessel test, and oxidative ageing for both short and long-term ageing situations [5]. On the whole, several studies were presented, including the utilization of waste oil [6][7][8][9][10][11]. ...
Waste cooking oil (WCO) and waste engine oil (WEO) have been generated in huge quantities in recent years as a result of the improvement of society's living standards and the advancement of automobiles and The molecular structure of WCO and WEO is similar to bitumen, indicating their potential for usage in highway construction to mitigate the hardening effect of recovered asphalt pavement materials. In this study, five different ratios of WCO and WEO were blended with VG40 grade bitumen under ageing conditions in accordance with the adaptability of the paving bitumen specification (IS 73: 2013). The waste oil treated samples were artificially short-aged by means of the thin film oven test. The penetration, softening point, viscosity, temperature sensitivity, penetration ageing ratio, and ductility tests were used to evaluate the physical performance parameters of the WCO and WEO modified bitumen.
The results of the tests reveal that the blending of WCO and WEO with neat bitumen softens the workability of aged bitumen. The physical properties of aged bitumen improved when treated with WEO as compared to when treated with WCO. Based on the results of the analyses and the overall ranking, it has been found that a blend of 3 percent WEO and 3 percent WCO resulted in the most significant improvement in bitumen modification. Significant differences were observed when waste oil was blended with a higher percentage, resulting in a change in the grade of bitumen.
... The acid values of bio-oils, CRM, and BMR are shown in Table 1 and Fig. 3. Table 1 shows that the initial acid value of bio-oils is 1.76 mg KOH/g, resulting from the abundant carboxylic acid components of biooils (Azahar et al., 2016). It should be noted that the introduction of bio-oil by grafting it to rubber resulted in a 68% increase in the initial acid value of BMR compared to CRM, which is significantly lower than that of bio-modified asphalt binders when bio-oil was directly added to asphalt (Ahmed et al., 2021;Lopa et al., 2018). This is attributed to the selective adsorption of bio-oil molecules to rubber during bio-grafting (Kabir et al., 2020). ...
This paper introduces a hybrid utilization of scrap tires and bio-oil made from biomass waste to create bio-modified rubberized asphalt for use in roadway construction. This in turn promotes clean and sustainable manufacturing while enhancing resource conservation and durability of pavements. The durability of pavements is impacted by the resistance of their asphalt binder to moisture damage and aging. This study examines the moisture resistance of bio-modified rubberized asphalt when exposed to thermal aging and ultraviolet aging. Study results show that thermal aging significantly weakens the cohesive properties of rubberized asphalt binder, while ultraviolet aging reduces its adhesive properties when exposed to water. Bio-modification of rubberized asphalt binder was found to be effective to improve resistance to cohesive damage by three times based on the rheological test, and resistance to adhesive damage by 70% as measured by the moisture-induced shear-thinning index. The observed improvement is attributed to the bio-oil's role as a sacrificial agent, delaying the reaction of free radicals and asphalt. Also, computational modeling shows that bio-oil molecules supersede asphalt molecules in adsorption to stones aggregates creating a stable bridge between stone and asphalt. The outcome of this study promotes clean and sustainable manufacturing while turning two waste streams (rubber and biomass waste) into a product (bio-modified rubber) in support of resource conservation and sustainability.
... Ja is a rejuvenator composed of maltene fractions normally found in asphalt binders, and therefore results in a change in maltene/asphaltene ratio to a value perhaps even greater than that of the original binder. While, Jb is a waste cooking oil based rejuvenator which contains free fatty acids that are thought to be less potent [47]. Further analysis of Fig. 5 shows that aging had less effect on the already PAV-aged or rejuvenated-PAV aged asphalt binders than on the unaged binders. ...
A procedure based on the linear amplitude sweep (LAS) test has been developed to determine the optimum rejuvenator content for restoring the properties of aged asphalt binders. The LAS test was employed to assess the damage tolerance, fatigue resistance, and fracture behavior of rejuvenated aged binders. In case of fracture analysis, a crack-based indicator to govern the stable crack propagation was defined to characterize fracture resistance of asphalt binders. While rejuvenators improved all of these properties, higher contents were required to restore the cracking behavior of the original binder. The linear relationship between the integrated damage-fatigue-fracture indicator and rejuvenator content was used to determine the optimum content. Unlike the similar permissible range based on restoration of the low and high-temperature performance, the LAS-based approach demonstrated superior performance of the aromatic extract rejuvenator over the waste cooking oil at higher contents.
Waste cooking oil (WCO) as a rejuvenator is gaining attention in the pavement industry to incorporate higher reclaimed asphalt (RA) in asphalt mixture. This review article provides a comprehensive review on the current state and the feasibility of turning WCO and RA into cleaner and sustainable asphalt pavement material. Considering the advancements in research related to the utilization of WCO in RA mixture, it was necessary to critically review the past and recent studies to provide a methodological scope for future research. The review discusses a plethora of characteristics focusing on chemical, rheological, simulation, environmental, and economical findings related to the utilization of WCO in RA mixtures. Based on the review, WCO can be adjudged as a potential material to rejuvenate asphalt mixtures with higher recycled asphalt content. Furthermore, although WCO enhances low-to-intermediate temperature performance, studies indicated that moisture damage and higher temperature properties are compromised. Future research scope exists in understanding the rejuvenation capabilities of different WCOs and blends of different types of WCO, optimizing the transesterification process of WCO to improve its quality, molecular dynamic simulations focusing on transesterified WCO, quantification of environmental and economic benefits of recycled asphalt mixtures with WCO, and field performance studies.
Worldwide, flexible pavements are the paramount type of pavements. These national assets can be recycled to serve the next design life without the need to dispose of them in landfill. The old/distressed, flexible pavement material is called, reclaimed asphalt pavement (RAP) material. In view of the sustainable development practice, 100% RAP should be recycled. However, the practical range of RAP incorporation in a drum mix plant ranges from 10% to 50% whereas in a batch mix plant, it is 10% to 35%. In a batch mix plant, incorporation of the hot dried RAP (instead of cold RAP feeding) can increase the RAP incorporation level by 20%. Studies recommended that the rejuvenator should be added over the RAP material instead adding with the base binder. The addition of rejuvenator on the RAP conveyor belt (to the pug mill), provided sufficient time for rejuvenating the aged binder coating over RAP aggregates. Further, a thorough knowledge of the mix design process of recycled hot mix asphalt (RAP-HMA) is essential to produce a durable mix. For high RAP content (>20%), the RAP binder properties are important for the mix design process. However, very limited studies discussed (in detail) the recovery process of the RAP binder. The review article through light on the binder recovery process, method of RAP gradation, specific gravity determination for RAP material, minimum desirable properties of the RAP material etc. This review paper also provides a narrative review of the historical development of RAP-HMA technology, technical aspects related to the procurement of RAP material, mix design and production of the recycled mix. Moreover, the international & national policies/laws for construction and demolition waste are discussed.
Waste cooking oil (WCO) has received more and more attention as an asphalt rejuvenator. The properties of WCO itself will change with the use of time, affecting its rejuvenation effect on aged asphalt. This paper explored the property changes of WCO with the cooking process and the rejuvenation effect on aged asphalt through molecular dynamics (MD) simulations and density functional theory (DFT) calculations. First, the representative molecules of WCO at different stages were determined. The polarity, basic properties, and solubility parameters of WCO at different stages were discussed. Finally, the thermodynamics properties, binding energy, free volume, and diffusion characteristics of WCO rejuvenated asphalt at different stages were compared. With the cooking process, the triglyceride (TG) is converted into fatty acid (FA), positive maximum electrostatic potential and electrostatic interaction increase, FA has stronger adsorption capacity leads to the reduction of model energy. After chemical treatment, the dipole moment and cohesive energy density of treated fatty acid (TFA) decrease. WCO at different stages can restore asphalt properties, and the surface free energy of asphalt can be better restored by FA. WCO at different stages mainly affects non-bond energy. Compared with FA, the incorporation of TFA has a better rejuvenation effect on the free volume fraction and diffusion coefficient of aged asphalt. The diffusion coefficients in asphalt are respectively: TFA > TG > FA.
Since 2008, the number of roads in Canada has been going up due to rapid urbanization and economic growth, and by 2020, there is more than 1.08 million kilometres of roads across the country. Around 90% of roads managed in Canada are paved with asphalt materials. During the service life, asphalt pavement experiences various surface distresses due to aging, the effect of environmental factors, and traffic loading. A way to mitigate the early deterioration of asphalt pavement is to blend suitable modifiers and additives with asphalt binders during asphalt mixture production. The current study aims to understand the relative effect of different liquid anti-stripping additives on the rheological and fundamental properties of styrene butadiene styrene (SBS)- and Gilsonite-modified binders (4 and10% by the weight of base binder, respectively) containing various percentages of anti-stripping additives in short-term aging conditions. Four different anti-stripping additives: ZycoTherm SP2 (0.05%, 0.075%, and 0.1%), Kling Beta 2914 (0.5%, 0.75%, and 1%), Pave Bond Lite (0.5%, 0.75%, and 1%), and AD-Here (0.5%, 0.75%, and 1%) were selected for this study. To attain our research goal, anti-stripping additives were blended to SBS and Gilsonite modified PG 58-28 binder. Later, all binders were aged using Rolling Thin Film Oven (RTFO) protocol. This thesis summarizes the results of rheological behaviour by considering the rutting and cracking parameters, such as the Superpave rutting parameter, Shenoy’s rutting parameter, non-recoverable creep compliance, and Glover-Rowe parameter. Additionally, this study considered using the Surface Free Energy (SFE) as a fundamental material property to evaluate the cohesive bond strength of the SBS and Gilsonite-modified asphalt binders. The results show that anti-stripping additives significantly affect the binders’ rheological behavior and fundamental properties, which can influence the overall performance of the asphalt binder. Furthermore, the comparative analysis showed that modified binders containing liquid anti-stripping additives enhance the moisture damage, rutting and cracking resistance of asphalt binders.
Prompting high content of reclaimed asphalt pavement (RAP) to be used in road building and maintenance has drawn great attention. The application of rejuvenators is an efficient way to ensure the performance of recycled asphalt mixtures. However, as various types of rejuvenators emerging, limited understanding about rejuvenation poses challenges to put effective ones into use. For precisely evaluating the performance of rejuvenators, plenty of studies were conducted to ascertain the fundamental mechanism of rejuvenating from the microscopic view. This paper provides an overview of studies focusing on the change inside asphalt after adding rejuvenators. Chemical compositions of rejuvenators were collected as basic information. Both laboratorial experiments and molecular dynamic simulations were investigated to not only compare the effectiveness of several rejuvenators but also explain the rejuvenating mechanism. Finally, functional groups of rejuvenator structures were comprehensively examined to provide global understanding about how chemical compositions influence the efficacy of rejuvenators. This review highlights that the essential capacity of a true rejuvenator is to disturb asphaltene agglomerations. Besides, the molecular structures of rejuvenators will not only affect their deagglomerating abilities but also the performances of diffusion and durability. It has been found that gel-permeation chromatography (GPC) analysis is effective in evaluating the performance of rejuvenators, while Fourier transform infrared spectroscopy (FT-IR) and SARA (saturates, aromatics, resins and asphaltenes) analysis are only suitable for assessing asphalt oxidization. In addition, comparing some tests can only detect changes, molecular dynamic simulation can reveal the mechanism both of data and vision. The results of this work can provide comprehensive knowledge for the evaluation and development of rejuvenators.
Reclaimed Asphalt Pavement (RAP) continues to be the most recycled product in America. In 2018, the National Asphalt Pavement Association (NAPA) determined that 82.2 million tons of RAP was reused in new Hot Mix Asphalt (HMA). The average RAP content was 21 percent, which is similar to estimates in Canada where 15 to 20 percent of RAP is typically reused.
However, the same survey highlighted that in 2018 approximately 110 million tons of RAP was left unused in stockpiles, which is problematic from a sustainability perspective. Properly engineered asphalt mixtures incorporating RAP have been shown to perform as well as virgin HMA. Rejuvenating agents such as organic compounds generated from petroleum processing have been utilized to achieve the desired quality while ongoing evaluation of newer recycling agents such as waste or vegetable oil derivatives shows considerable promise.
The focus of this paper is to provide a better understanding of how to engineer and produce mixtures containing various proportions of RAP (and potentially Reclaimed Asphalt Shingles, RAS) while improving cracking performance. The development of a potential framework for the use of rejuvenating agents is presented along with a discussion on the proper design and production of durable quality mixtures using RAP.
Recently, the interest in converting waste cooking oils (WCOs) to raw materials has grown exponentially. The driving force of such a trend is mainly represented by the increasing number of WCO applications, combined with the definition, in many countries, of new regulations on waste management. From an industrial perspective, the simple chemical composition of WCOs make them suitable as valuable chemical building blocks, in fuel, materials, and lubricant productions. The sustainability of such applications is sprightly related to proper recycling procedures. In this context, the development of new recycling processes, as well as the optimization of the existing ones, represents a priority for applied chemistry, chemical engineering, and material science. With the aim of providing useful updates to the scientific community involved in vegetable oil processing, the current available technologies for WCO recycling are herein reported, described, and discussed. In detail, two main types of WCO treatments will be considered: chemical transformations, to exploit the chemical functional groups present in the waste for the synthesis of added value products, and physical treatments as extraction, filtration, and distillation procedures. The first part, regarding chemical synthesis, will be connected mostly to the production of fuels. The second part, concerning physical treatments, will focus on bio-lubricant production. Moreover, during the description of filtering procedures, a special focus will be given to the development and applicability of new materials and technologies for WCO treatments.
This research is based on the possibility of using waste cooking oil as a rejuvenator in the construction of asphalt pavement
Conventional methods for evaluating the effects of additives on moisture damage resistance of asphalt mixtures are either empirical or unable to quantify the contributions of material component properties to the overall mixture performance. To overcome these drawbacks, this study proposes a surface free energy (SFE) method to investigate the effects of various additives on moisture susceptibility of asphalt mixtures. One neat asphalt and one acidic gravel aggregate are selected as the test materials along with 6 commonly-used additives: a warm mix asphalt additive, two nano-materials, a hydrated lime, a Portland cement and a non-amine liquid asphalt anti-stripping agent. All the additives are blended with the neat asphalt to fabricate modified asphalt binders. The SFE components of these modified asphalt binders and the gravel aggregates are measured with the Wilhelmy plate method and the vapor adsorption method, respectively. An energy ratio, defined as the ratio of adhesion of asphalt-aggregate to that of asphalt-aggregate-water, is calculated and used to rank the asphalt mixtures that consist of gravel and asphalt binders modified with different additives in terms of their moisture susceptibility performance. In order to validate the proposed SFE method, two mixture moisture susceptibility tests, the modified boiling water test and the indirect tensile strength test, are conducted on loose and compacted asphalt mixtures, respectively. A consistent moisture susceptibility ranking is obtained from the SFE method and the mixture moisture susceptibility tests, which validates the SFE method proposed in this paper can be used to accurately quantify the effects of additives on the moisture susceptibility of asphalt mixtures.
Alternative binders not derived from fossil fuels, known as biobinders, are opening new paths for multiple applications in road infrastructure. Biobinders, usually produced from bio-oils obtained from the processing of biomass and industry by-products, are tuneable materials whose properties can be adjusted to meet specific targets. For this reason, an interesting approach is to couple biobinders with Reclaimed Asphalt (RA) by taking advantage of their rejuvenating properties to design bio-asphalt mixtures with high-content RA and no additional virgin bitumen. Recent research has proven the feasibility of this approach through validation at full-scale (BioRePavation project). However certain aspects related to the durability of bio-asphalt mixtures still require further research, one of these being their resistance to moisture damage. This study aims at filling some of these current gaps by conducting an initial investigation of the moisture sensitivity of selected biobinders and bio-rejuvenated asphalt binders. In order to do this, the intrinsic adhesion and cohesion properties of an extracted RA binder, two biobinders, their blends and two types of aggregates were characterised by means of Surface Free Energy (SFE), individually and as a system. The binders/blends-aggregate systems were further tested by means of the Pneumatic Adhesion Tensile Test Instrument (PATTI) to determine their pull-off tensile strength (POTS). The results show that the bio-rejuvenated asphalt binders present equivalent cohesive and adhesive properties to a conventional bitumen and superior performance when compared to the RA binder. Hence, the combination of biobinders and RA has great potential to guarantee resistance to moisture damage of bio-recycled asphalt mixtures with high-content RA and no additional bitumen.
Asphalt binder is a very complex chemical compound. Much work has been done to understand and model its chemical, morphological, rheological, and mechanical features. This paper synthesizes and presents findings from pertinent studies available in the public domain. Understanding of asphalt characteristics at the very finite level is the first critical step to develop a better macroscopic- or pavement-level performance model. This paper showcases a summary of current knowledge gained on (a) how chemical elemental compositions and molecular groups play critical roles in asphalt binder’s performance in pavement composites; (b) morphological properties and their relationships with the asphalt’s structural performance; and (c) mechanistic characteristics of asphalt binder’s at nanoscopic, mesoscopic, and microscopic levels, and how they are related to macroscopic- or pavement-level performance.
This study evaluated the effects of the commercial product, AR 5, and two alternative products, waste cooking oil and castor oil, in the rejuvenation process of two asphalt binders. The analyses were carried out on microscopic and macroscopic scales on virgin, aged, and rejuvenated binders. Tests in a dynamic shear rheometer were performed to characterize rheological properties of the binders. Then, an atomic force microscope was used to identify microstructural changes in the materials. A digital image analysis technique enabled the quantification of key variables such as area fraction and spatial and size distributions of the binder constituents. Finally, the following chemical tests were performed to identify changes in the chemical composition of the binders resulting from the aging and rejuvenation processes: SARA (which measures saturates, asphaltenes, resins, and aromatics), gel permeation chromatography, and nuclear magnetic resonance. The results obtained from the tests were further compared to identify correlations between the properties evaluated in different scales. The results demonstrated the efficiency and potential of the rejuvenators evaluated in this study. The results also highlighted the importance of the use of advanced techniques to characterize and understand the material aging and rejuvenation processes.
The interaction between asphalt binder and aggregate is fundamental to ensure adequate performance of asphalt mixtures, mainly in the presence of water. The work of adhesion generated between both materials directly affects the resistance of asphalt mixture to moisture damage, because it measures the ease with which water can displace asphalt binder from the aggregate surface. The objective of this study was to characterize the bond strength between asphalt and several aggregate sources. A PG 64-22 neat binder was modified with several additives to determine the effect on adhesion: polymers, nanomaterials, and adhesion promoters. To measure the strength of adhesion, the bitumen bond strength (BBS) test and contact angle measurements between asphalt binder and the aggregate surface by means of goniometry were used. The surface energy of the asphalt and the aggregate, with and without the presence of water, was estimated also. Testing was performed on all binders and on each binder-aggregate combination after (a) rolling thin-film oven (RTFO) aging and (b) RTFO and pressure aging vessel aging. The BBS results identified differences in bond strength as a result of moisture conditioning and aging. The differences depended on the aggregate source and binder type. Different failure modes were also observed (i.e., cohesive, adhesive). The results also indicated an increase in strength of adhesion associated with the aging process: the main resistance gain was observed after RTFO aging. Finally, changes in bond strength were compared with functional composition changes associated with the aging process and related to changes in performance.
Moisture susceptibility is one of the key issues of warm mix asphalt (WMA). In this research, the moisture susceptibility of asphalt mixtures and binders containing Sasobit warm mix additive was investigated in comparison to that of hot mixture asphalt (HMA) through laboratory aging experiments. The WMA asphalt mixtures were aged in the laboratory at three aging temperatures and times. The moisture susceptibility of the asphalt mixtures was measured through the laboratory immersed Marshall test and freeze-thaw splitting test. The surface free energy (SFE) of asphalt binders extracted from WMA asphalt mixtures was determined by the sessile drop method. The results show that the aging time and temperature have a significant effect on the improvement in moisture susceptibility in terms of both the freeze-thaw splitting strength ratios and the residual Marshall stability of asphalt mixtures containing Sasobit warm mix additive. The SFE of asphalt binders extracted from Sasobit warm mix increased with the aging time and temperature. The moisture susceptibility of the asphalt mixtures and binders containing Sasobit warm mixes was similar to or even greater than that of HMA aging under certain conditions.
The objective of this study was to examine if asphalt rejuvenators can offset the stiffness attributed by the hardened binder from reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in mixtures that incorporate high RAP and RAS content without adverse impact on the performance of the mixtures. Also, to assess, if rejuvenators can help the hardened binder from the RAP/RAS comingle with the virgin binder. Overall, the results showed that asphalt rejuvenators can mitigate the stiffness of the resultant binder. The cracking characteristics of the mixture improved by the addition of the rejuvenators, however, the rutting and moisture susceptibility were adversely impacted at the dosage and the testing conditions used. Also, the tests results at 4°C generally showed that there was blending of the rejuvenated and virgin binder, however, no conclusion could be made at the higher temperatures.
Because of aged binder, high reclaimed asphalt pavement (RAP) content mixes are susceptible to cracking failures and are less workable than virgin mixtures. The potential of six differently originated recycling agents was evaluated in this study to restore the desired binder properties using conventional binder test methods and the results were compared with performance-related test results of 100 % RAP mixture. Binder test results showed that application of organic products require much lower dose to provide the same softening effect as petroleum products. The workability of binder and mixture was improved compared to RAP, but remained lower than that of reference virgin mixture. All rejuvenated mixtures proved to be very rut resistant. Low temperature performance of RAP, measured by creep compliance at -10 °C, was improved with the application of all recycling agents and RAP mixes rejuvenated with waste vegetable products even performed equal or better than virgin mixture. Organic oil and both waste vegetable products provided the best performance in binder and mixture fatigue resistance tests as measured by linear amplitude sweep and fracture work density respectively. Overall, the organic products outperformed the petroleum based additives in most tests, which partly can be attributed to un-optimized recycling agent dose. It was observed that penetration test may be a good indicator for initial selection of optimum dose since the results provide indication of rut resistance as well as fatigue performance of mixture and can be easily predicted using an exponential relationship that was developed in the research.
We investigated the short and long term aging of asphalt cement (AC) with different AFM techniques (topography, phase and friction imaging and nano-indentation experiments). The aging process induces a growth and nucleation of the asphaltene micelles with a concomitant reduction of the maltene phase, whereas the short term aging induces the formation of fractal-like micellar structures. The friction investigation shows that the aging processes reduce the binder friction coefficient by 50%, and this reduction occur predominantly during the short term aging, while the growth of the micelles occur predominantly during the long term aging. The micro-indentation experiments revealed that the aging processes cause a stiffening of the AC film (half-order of magnitude for short term aging, and one order of magnitude for long term aging). The aging process also increased the apparent viscosity of the AC films by half-order of magnitude.
Conventional methods to quantify the moisture sensitivity of asphalt mixtures are based on the comparison of mechanical properties of the mix before and after a moisture-conditioning process. Although this approach consolidates the effect of material and mixture properties on moisture sensitivity, it does not identify the causes responsible for the poor or good performance of the mixture. In this study, surface free energy of asphalt binders and aggregates was used to derive energy parameters that quantify the moisture sensitivity of various combinations of materials. The moisture sensitivity of 12 asphalt mixtures carefully designed to represent a wide range of asphalt-aggregate interactions was measured in the laboratory under controlled conditions. Test results indicate that the moisture sensitivity of these mixtures correlates well with the energy parameters, which are based on the surface energy properties of the constituent materials. Incorporating the specific surface area of the aggregate into the energy parameters improved this correlation. The proposed energy parameters have the potential to serve as an effective tool by which to select material combinations that result in asphalt mixtures that are more resistant to moisture-induced damage.
The synergistic effects of microdamage due to repeated loading in Asphalt-Aggregate system at a high temperature (40°C) and
moisture damage analysis based on surface free energy theory are presented in this paper. The introduction of moisture in
either a liquid or vapor state during cyclic loading may well be more damaging than simply moisture conditioning an asphalt
concrete sample prior to testing. This difference may be due to the presence of a dynamic “network” of adhesive fracture,
which potentially provides a channel for moisture movement within the sample. The percentage of the surface area of aggregate
that has been exposed to water was used as a significant index to quantify the level of adhesive fracture. This index is calculated
with the surface free energies of aggregate and asphalt which are measured by two methods, the universal gas adsorption and
the Wilhelmy plate, respectively. The relation between the percentage of the surface area of the aggregate exposed to water
and the number of cycles of loading assists in quantifying adhesive fracture in the asphalt-aggregate mixture.
We combined optical and atomic force microscopy to observe morphology and kinetics of microstructures (typically referred to as bees) that formed at free surfaces of unmodified Performance Graded (PG) 64-22 asphalt binders upon cooling from 150°C to room temperature (RT) at 5°C/min, and changes in these microstructures when the surface was terminated with a transparent solid (glass) or liquid (glycerol) over-layer. The main findings are: (1) At free binder surfaces, wrinkled microstructures started to form near the crystallization temperature (∼45°C) of saturates such as wax observed by differential scanning calorimetry, then grew to ∼5 µm diameter, ∼25 nm wrinkle amplitude and 10-30% surface area coverage upon cooling to RT, where they persisted indefinitely without observable change in shape or density. (2) Glycerol coverage of the binder surface during cooling reduced wrinkled area and wrinkle amplitude three-fold compared to free binder surfaces upon initial cooling to RT; continued glycerol coverage at RT eliminated most surface microstructures within ∼4 hours. (3) No surface microstructures were observed to form at binder surfaces covered with glass. (4) Sub-micron bulk microstructures were observed by near-infrared microscopy beneath the surfaces of all binder samples, with size, shape and density independent of surface coverage. No tendency of such structures to float to the top or sink to the bottom of mm-thick samples was observed. (5) We attribute the dependence of surface wrinkling on surface coverage to variation in interface tension, based on a thin-film continuum mechanics model. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
In Canada, over 90% of the paved roads are asphalt pavements. Most of these pavements were built decades ago, which are currently exhibiting a significant amount of surface distresses. These distresses includes potholes, rutting (deformation in the wheel path), and cracking. To repair these distressed pavements, the road agencies spend millions of dollars every year, of which a significant portion goes to acquiring new natural aggregates and asphalt. To reduce the rehabilitation cost, road agencies use up to 100% reclaimed asphalt pavements (RAP) in new construction. However, the asphalt available in recycled pavements is oxidized and stiffened due to various environmental processes which are susceptible to thermal and fatigue cracking. To soften and to decrease the viscosity of the RAP materials, various rejuvenators are being in practice. The rejuvenators are able to reactivate and restore the original properties of this long-term aged asphalt binder. Using Waste Cooking Oil (WCO) is one of the eco-friendly solutions which contains the similar lighter oil components of asphalt and can be used as an acceptable rejuvenator. Recent studies showed that WCO has an excellent potential to be used as a good rejuvenator in the hot mix asphalt (HMA) industry. This review article summarizes the performance and adverse effects of WCO as a rejuvenator.
Asphalt binders in bituminous mixtures with reclaimed asphalt pavement (RAP) comprise fractions of both aged and unaged binders, existing as a single entity. The degree of blending between the aged and virgin binders dictates the extent of homogeneity of the binder in the mix and consequently its mixture performance. However, their mechanism of interaction has not been well understood yet. In this study, a fundamental measure of compatibility between aged binders and unaged binders was evaluated exercising an extension of the Hansen Solubility Parameter (HSP) model of solubility. Nine binders consisting of unaged binder, field aged binders and artificially aged binders were tested using a method of turbidimetric titrations, to identify the internal stability of the binders and relative extents of different intermolecular interactions in terms of dispersive forces, hydrogen bonding and polar interactions. The results show that some aged and unaged binders noticeably differ in terms of polar interactions, which may lead to low dispersibility of molecules and increased molecular associations. These findings were further corroborated by chemical composition analysis based on saturates, aromatics, resins and asphaltene (SARA) fractionation which verified that the content of the highest polar fraction, i.e., asphaltene, was considerably higher in the aged binders. Overall, the study indicated that there are noteworthy differences in internal stability and composition between aged and unaged binders. Consequently, mixing of certain virgin-aged binder pairs could be more compatible than others depending on their solubility parameters. To attain a homogenous blend while incorporating RAP, a more careful and detail-oriented approach that considers che-mistries and inter-solubility of these components is recommended.
This paper presents the results of a study that was conducted to understand the impacts of aging and rejuvenation on fundamental properties of asphalt binders. A Performance Grade (PG) 64-22 binder was aged to simulate aging of asphalt mixes during construction and in-service conditions. The binder’s surface tension property, i.e., the contact angles between the binder and three probe liquids, were measured using a sessile drop device. This property was then used to estimate surface free energy components of the control binder, aged binders, and rejuvenated binders using the Good-van-Oss-Chaudhury’s postulation. Cohesive and adhesive bond energies of asphalt–aggregate systems under dry and wet condition were also analyzed. The aggregates considered in this study were limestone and granite; these aggregates have different moisture affinity. The data showed that as asphalt ages, the contact angle between a liquid (distilled water) and the asphalt surface increases; however, for the other two probe liquids (formamide and glycerol), no pattern was observed. For the surface free energy components of the control binder, the aged binders, and the binders with rejuvenators, the contribution from Lifshitz-van der Waals components were comparatively much higher than that from acidic and basic components. The rejuvenators seemed to be effective in improving the cohesive energy of asphalt binder, suggesting improvement in water damage resistance of the mix. In general, the limestone-based asphalt concrete mixture showed a higher moisture damage resistance than the asphalt concrete mixture with granite.
The use of RAP (Reclaimed Asphalt Pavement) in new asphalt pavements could potentially generate environmental footprint reduction especially in terms of raw-material consumption. This investigation aims to evaluate the effectiveness of the addition of rejuvenator and plastomeric polymer on the performance of high RAP content (40%) asphalt mixture. Six combinations, varying proportion of rejuvenator and polymer , were studied. Mechanical and long-term performance was evaluated through laboratory investigations analyzing the physical properties and rheology of the binder and measuring stiffness modulus and permanent deformations (rutting) of recycled asphalt mixes. Outcomes showed that a proper calibration of rejuvenation agent and polymer can enhance the overall durability of high RAP content mixes. Statistical analysis of results was also conducted to determine the significance of variables involved.
Atomic force microscopy (AFM) has the capacity to distinguish among different phases at high resolution, and it is widely used in obtaining topography and mechanical property maps for asphalt binders. This study investigated the effects of long-term aging on both SBS-modified asphalt and base asphalt using AFM. In describing the study findings, this paper introduces two new indices used to quantify changes in the microstructures of asphalt, namely, the percentage of elliptical bee structures and surface roughness. In addition, the Derjaguin-Muller-Toporov modulus and adhesive force were measured to quantify the mechanical properties of the micro-phases. Finally, to evaluate the influence of aging on composite phase properties, a parallel model from the field of composite materials was introduced and applied. The results indicate that aging significantly affected the microstructures and mechanical behavior of micro-phases of asphalt binders. Aging also had a significant influence on the microstructures of the asphalt, especially in the bee structures. The percentage of bee structures increased or decreased after aging depending on the asphalt binder type, while surface roughness always decreased. Aging also increased the composite modulus of the micro-phases and decreased the composite adhesion of the micro-phases. These findings are in agreement with the macroscale aging behavior of asphalt binders.
The quality of the interfacial bonding between asphalt binder and aggregates plays a significant role in determining the durability of asphalt mixtures. Warm mix asphalt (WMA) modifiers have been used extensively in the last decade primarily to reduce production and compaction temperatures as well as to improve workability of asphalt mixtures. This study aimed to provide better understanding of the effects of these WMA modifiers on the interfacial bonding between asphalt binders and aggregates. The evaluation focused on measuring surface energy of binders in unaged and aged states and aggregates and then calculating energy parameters that describe the potential of a given asphalt-aggregate combination to resist fatigue cracking and moisture damage. Results show that the combination of asphalt-WMA additive, as well as the content applied of WMA additive has a significant impact on the fatigue cracking and moisture damage resistance. The results suggest that it is poor practice to use a given type and percentage of WMA modifier without regard for binder type. Instead, test methods are recommended to evaluate the compatibility of asphalt binder, WMA additive type/content, and aggregates for improved performance at different conditions.
The performance of asphalt binder modified with waste cooking oil (WCO) is affected by the quality of the WCO itself because of the degradation process during frying activity. The quality of WCO can be determined by conducting an acid value test, wherein an increased acid value has caused the decreasing of rheological performance. Therefore, untreated WCO with a high acid value is chemically modified and pre-treated with alkaline catalysts to undergo transesterification. The transesterification of WCO is performed as a pre-treatment to reduce high free fatty acid (FFA) content, which is equivalent to the acid value. The treated WCO sample undergoes a chemical test (acid value), physical test (penetration and softening test), and rheological test through a dynamic shear rheometer (DSR). The rheological performance of rutting, which is analyzed using DSR, is compared between the untreated and treated WCO to determine any improvement in rutting resistance after chemical modification. Results show that the acid value reduces from 1.65 mL/g to 0.54 mL/g after the chemical treatment of WCO. The decrease in acid value affects the improvement of penetration, softening point test, and rheological performance test, wherein increased failure temperature is achieved at 70 °C for treated WCO compared with the untreated WCO at 64 °C.
Porous asphalt (PA) has high drainage and noise-abrasion properties, however, its performance regarding rutting resistance, fatigue life, and moisture susceptibility is not as efficient as dens-graded mixes. This paper evaluates the influence of crumb rubber (CR) on performance enhancement of porous asphalt. PAs fabricated by asphalt cement incorporating 10%, 15%, and 20% of CR were compared with control and 5% SBS modified ones regarding rutting resistance, resistant to draindown, skid resistance, moisture susceptibility and permeability. Results indicate that, on one hand, CR and SBS reduce permeability of PA and, on the other hand, they improve rutting resistance significantly. In addition, despite initial improvement of resilient modulus, skid resistance, and moisture damage resistance, adding more CR has negative effect on these properties.
Extensive researches have been conducted on using reclaimed asphalt pavement (RAP) material in
production of recycled hot mix asphalt. According to literature, the aged binder is the main obstacle to
incorporate high amount of RAP into asphalt pavement which causes premature distresses such as
fatigue failure and low temperature cracking in pavement structure. To overcome this problem,
rejuvenating agent or rejuvenator is usually used to restore the RAP binder properties to a condition that
resembles that of fresh asphalt binder. Different types of rejuvenators have been used previously. This
study provides an overview on utilizing RAP, and the use of rejuvenators, type and dosage, in production
of asphalt pavement.
Preventive maintenance of asphalt concrete can often extend the pavement life for a number of years at relatively low costs. The types of preventive maintenance discussed in this report include rejuvenators, slurry seals, surface treatments, and crack sealing. the report's emphasis is directed toward the use of asphalt rejuvenators. The maintenance procedure should be selected for a specific project to be maintained, and the treatment should be designed for the project. Random selection of maintenance procedures may be ineffective, resulting in loss in performance and additional life-cycle costs. This report provides some guidance into the selection process for maintenance procedures, problem areas to consider, and expected performance of various procedures.
Atomic force microscopy (AFM) is a non-destructive imaging tool, which is capable of qualitative and quantitative surface analysis with sub-nanometer resolution. Simultaneously with the topology at the micro-scale, AFM is capable of acquiring micro-mechanical information such as relative stiffness/Young's modulus, stickiness/adhesion, hardness, energy loss and sample deformation quantitatively. This paper presents an extensive review on the applications of AFM to investigate different physiochemical properties and performances of asphalt binder. AFM techniques and principles, different sample preparation techniques and its effect on observed micro-structures, chemical origin, surface or bulk phenomenon and temperature sensitivity of these micro-structures are also discussed in this paper. All of the studies conducted on this topic clearly indicated that AFM can successfully be utilised as a tool to better understand how the surface morphology and its physicochemical properties are interlinked and related to the binder performances.
Asphalt mixtures are engineered and designed by treating the mixture as a two-component composite of the binder and mineral aggregate. Typically, asphalt binder is regarded as a homogeneous ‘glue’ that binds the mineral aggregates. However, there is a strong body of evidence in the literature spanning over five decades that indicates that the asphalt binder can be modelled as a colloid with a distinct microstructure. The introduction of advanced microscopic techniques such as Atomic Force Microscopy has generated a renewed interest in being able to better understand the relationship between the chemical makeup of the asphalt binder, its microstructure and engineering properties. The objective of this paper is to present a preliminary phase field model that was used to model the evolution of microstructure of a mixture comprising four fractions with different polarities, analogous to that of the asphalt binder. This work extends the concepts developed in previous research studies to explain the evolution of damage and self-healing at a micrometre length scale in asphalt binders. Although the model and parameters presented in this paper are not a definitive description of the microstructure evolution in asphalt binders, results show that with additional work on rigorous parameter estimation this methodology can be used as a reasonable approach to better understand the relationship between binder composition and microstructure evolution.
The recycling of reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA) is an important opportunity in regard to transportation infrastructure construction and maintenance because it helps to achieve more sustainable road transport systems (reduction of waste production and reduction of resource consumption). In particular, totally recycled HMAs can be a good alternative for road paving even if performance can be an issue. As is well known, the type of low-volume road pavement (gravel, coarse rocky soil, crushed aggregate, cobblestone, concrete block, or some type of bituminous seal coat or asphalt pavement) depends on traffic volume, native in-place soils, and the need to control surface and depth erosion. The objectives and scope of this research were confined to the formalization of strategies and technical procedures for recycling RAP from porous asphalt concretes to obtain permeable wearing courses for low-volume roads. Different solutions were investigated. High percentages of RAP were used in the recycling process, and traditional and advanced tests on RAP and recycled mixes were carried out. RAP variability was examined, and a method for facing its consequences was proposed. Mechanical performance was adequate. Recycling porous European mixes could be a proper way to achieve environmental sustainability in pavement construction, as the functional performance results are very promising and encouraging. Practical applications and perspectives in rehabilitation, maintenance, and research are outlined.
A quick routine analysis has been established for quantitative determination of thirteen individual C18 trans fatty acids in both pressed and solvent extracted non-hydrogenated edible vegetable oils, using gas chromatography-mass spectrometer (GC-MS) equipped with HP-88 capillary column following potassium hydroxide/methanol (KOH/MeOH) methylation. Based on optimization and appraisal of the characteristics of GC-MS, thirteen C18 trans fatty acid methyl ester (FAME) standards were separated and verified in 23 min, validation experiments were also conducted. The correlation coefficient was R2≥0.99 in the linear range of each FAME. At the low, medium and high fortification levels, recoveries fell within 90-119%. The relative standard deviations were below 9% for all 13 FAMEs. Low limits of detection (0.001-0.002 g/100g) and quantification (0.002-0.007 g/100g) were readily achieved. The content of C18 trans fatty acid isomers in pressed and solvent extracted oils were analyzed using this method.
Viscoelastic materials exhibit rate- and temperature-dependant behavior in terms of stress-strain response and fracture. As a representative of this class of materials, rate-dependant fracture should be expected for the bituminous asphalt binders used in the construction of pavement. Preliminary results are reported regarding studies using atomic force microscopy (AFM) to determine rate- and temperaturedependent adhesive fracture in bitumen thin films. This AFM technique involves creating then fracturing a microadhesive contact joint between a bitumen thin film and a glass microbead tip affixed to a cantilever by application of a direct tensile force to the contact. The mechanical work required to fracture this contact is measured as a function of temperature and separation rate. Results of this study suggest that adherence fracture energy of bitumen films is rate and temperature dependant based on measures of energy dissipation at and below the temperature of 25°C. These materials also exhibit a viscoelastic to viscous transition in adhesive behavior above 25°C attributed to observed loss of energy dissipation.
In this study atomic force microscopy (AFM) creep indentations were performed to extract viscoelastic properties of the different domains (defined as microrheology) observed in bitumen samples from two different sources. The microrheology and geometry obtained using the AFM were used to perform finite element (FE) simulations to study the effect of bitumen microstructure on internal stress distribution. FE analyses suggest that microstructures with varying mechanical properties cause localised stress amplification that can lead to cracking/phase separation. A custom-made loading frame in conjunction with an AFM was used to examine the effects of tensile strain on bitumen microstructure. FE simulation and experimental results show that applying strain resulted in damage/phase separation concentrated in the interstitial zone between neighbouring bee structures, defined as load-induced phase separation. This study suggests that evaluating the bitumen microstructure and microrheology is critical to understanding the mechanisms of damage evolution in bitumen and engineering binders with higher inherent durability.
The surface free energy (SFE) measurement of asphalt binder and aggregate is considered a reliable mechanistic framework for evaluating the moisture-induced damage potential of asphalt mixes. In the present study, the SFE method was used to evaluate the effects of asphalt binder type, Reclaimed Asphalt Pavement (RAP) and its amount, and aggregate type on the moisture-induced damage potential of asphalt mixes. The SFE components (non-polar, acid and base) of a PG 64-22 and a PG 76-28 (polymer-modified) asphalt binders, blended with different amounts of RAP binder (0%, 10%, 25% and 40%) were measured in the laboratory using a Dynamic Contact Angle (DCA) analyzer. Also, the SFE components of six types of aggregates, namely limestone, rhyolite, sandstone, granite, gravel, and basalt were used in this study. The SFE components of limestone and rhyolite aggregates were measured using a Universal Sorption Device (USD), while those of the sandstone, granite, gravel, and basalt aggregates were obtained from the literature. The energy ratio parameters estimated based on the spreading coefficient, the work of adhesion, and the work of debonding were used to assess the moisture-induced damage potential of different combinations of asphalt binders and different RAP binder contents and aggregates. The SFE test results indicated that the acid SFE component of PG 64-22 and PG 76-28 asphalt binders increase with the addition of RAP binder, while the base SFE component remains almost unchanged. Also, the wettability and the work of adhesion of both PG 64-22 and PG 76-28 asphalt binders over different types of aggregates increased with an increase in RAP content (by 25% and more). Based on the energy ratio parameters, it was found that the resistance to moisture-induced damage increased with an increase in RAP content for both PG 64-22 and PG 76-28 asphalt binders and all types of aggregates, specifically when higher RAP contents were used. Moreover, it was found that the higher the total SFE of the aggregates, the lower the energy ratio parameter values. Therefore, a high total SFE component of aggregate may result in a high moisture-induced damage potential of the mix. The results presented herein are expected to be helpful in mechanistically assessing the moisture-induced damage potential of asphalt mixes, produced with polymer-modified and non-polymer-modified asphalt binders, containing RAP.
The objective of this work is to study the common features and the evolution of microstructures of bituminous binders regardless of their grade (PEN 10/20 to 160/220) and source/origin using the atomic force microscope operated in phase contrast mode. All bituminous binders show the same microstructural features, consisting of three distinct phases, the perpetua-, peri- and catana-phase. The perpetua-phase is soft and viscoelastic in nature, the peri-phase is relatively stiff and solid in nature and the catana-phase is alternatingly hard and soft in nature and is always found in the middle of the peri-phase. Experiments at different temperatures result in a quantitative picture of the changes/transitions between the different microphases upon heating. Phase formation is reversible with respect to temperature, upon heating homogenisation occurs and upon cooling re-formation of the phases can be observed.
Durability is one of the most important properties of an asphalt mixture. A key factor affecting the durability of asphalt pavements is moisture damage. Moisture damage is generally considered to be the result of two main mechanisms; the loss of adhesion between bitumen and the aggregate and the loss of cohesion within the mixture. Conventional test methods for evaluating moisture damage include tests conducted on loose bitumen-coated aggregates and those conducted on compacted asphalt mixtures. This paper looks at results from the rolling bottle and the saturated ageing tensile stiffness (SATS) tests in an attempt to better understand the underlying processes and mechanisms of moisture damage with the help of surface energy measurements on the constituent bitumen and aggregates. Combinations of materials were assessed using both the rolling bottle and SATS tests. The surface energy properties of the binders were measured using a dynamic contact angle analyser and those of the aggregates using a dynamic vapour sorption device. From these surface energy measurements, it was possible to predict the relative performance of both the simple rolling bottle test and the more complicated SATS test. Mineralogical composition of the aggregates determined using a mineral liberation analyser was used to explain the differences in performance of the mixtures considered.
Performance of asphalt pavements depends on the properties of its constituent materials, mixture volumetrics, and external factors such as load and environment. An important material property that influences the performance of an asphalt mixture is the surface free energy of the asphalt binder and the aggregate. Surface free energy governs the adhesive bond strength between the asphalt binder and the aggregate as well as the cohesive bond strength of the asphalt binder. These bond energies in turn influence the resistance of the asphalt mixture to distresses such as fatigue cracking and moisture induced damage. Asphalt binders undergo several types of engineering and natural modifications that influence their chemical and mechanical properties. Three common examples of modifications are the addition of polymers, addition of additives (e.g., antistrip agents), and oxidative aging of the asphalt binder. This paper is part of a study conducted to examine the effect of different types of modifications on the surface free energy components of the asphalt binder. The change in surface free energy was used to calculate parameters that are related to the performance of the asphalt mixtures. Results from this study demonstrate that the magnitude and nature of change to the surface free energy and concomitant performance-related parameters varied significantly among different asphalt binders. For example, certain modifications improved the performance of some binders while adversely affecting the performance of others. The experiment and analysis methods presented in this study can be used to examine the influence of modifications on performance and optimize the engineering properties of binders and asphalt mixtures.
The influence of natural wax in asphalt binders and hot-mix asphalt has been studied for decades, with consideration of both negative and positive effects. Recent advances in warm-mix asphalt (WMA) have spurred interest in the use of commercial waxes such as Sasobit and Asphaltan B as additives in asphalt binders to achieve certain positive effects. Despite a number of previous studies, the effect of Sasobit on wettability and adhesion between asphalt binders and aggregates is not fully understood, likewise, the effect of water vapor released from Aspha-Min, another WMA additive, at production temperatures is not adequately understood, although such water may negatively influence the behavior of WMA. In the present study, the effect of Sasobit and Aspha-Min on wettability and adhesion was investigated using the surface free energy (SFE) method. Dynamic advancing-wetting contact angles were measured for wettability (coating) and dewetting-receding contact angles were measured to evaluate adhesion. It was observed that Sasobit increases the wettability of asphalt binders over aggregates, as indicated by the change in the spreading coefficient. Conversely, a general trend is that Sasobit reduces the adhesion (free energy of adhesion) between asphalt binders and aggregates. In this study, moisture susceptibility is defined as the amount of spontaneously released free energy due to the breaking of the binder-aggregate bond with water. For PG 64-22, a small or no reduction in moisture susceptibility was observed; for PG 70-28, an increase in moisture susceptibility was observed. In case of the Aspha-Min, the overall SFE results are insignificant.
The moisture damage in polymer modified asphalts has been studied for decades, yet the effects of chemical functional groups on moisture sensitivity are not known. In this study, a nanoscale experiment is conducted to measure these effects in terms of adhesive/cohesive forces using an atomic force microscopy (AFM). A base asphalt binder and two polymers such as styrene-butadiene (SB) and styrene-butadiene-styrene (SBS) modified asphalts are used to prepare an AFM sample on glass substrates. The AFM samples are conditioned under dry and wet conditions. In the AFM, these samples are probed by silicon nitrite (Si(3)N(4)), carboxyl (-COOH), methyl (-CH(3)), and hydroxyl (-OH) functionalized AFM tips and nanoscale pull-off or adhesion/cohesion forces between asphalt and tip molecules are measured. Based on the ratio of wet to dry adhesion/cohesion forces, it is shown that the polymer modification makes binders less susceptible to moisture damage. Among the four tips, the -COOH tip shows almost no difference in adhesion forces between wet and dry samples. Using -OH tips, it is shown that the cohesion in SBS modified wet asphalt samples is significantly higher than the cohesion in SB modified wet asphalt samples. The Si(3)N(4) tip shows higher adhesion in SB modified wet samples than that in the SBS polymer modified wet samples. Based on the adhesion/cohesion force, 3% polymer is found to be the optimum for both SB and SBS polymers. In addition, this study determines the methodology for sample preparation and testing parameters for nanoscale AFM testing on asphalt binders.
In this study, thermal degradation of amine-based liquid anti-strip additives was evaluated due to RTFO-aging and PAV-aging according to AASHTO T 240 and AASHTO R 28 test methods, respectively. The surface free energy (SFE) characteristics of asphalt binders before and after aging were used as a tool for this evaluation. Two asphalt binders, namely PG 64-22 and PG 70-28, and two anti-strip additives, namely AD-Here HP Plus and Redicote E-6, were evaluated. It was observed for 0.75% AD-Here HP Plus in PG 64-22, mixing at 163°C is more effective than mixing at 145°C with respect to increase in SFE. Also, both RTFO and PAV-aging decrease the total SFE of asphalt binders; both the aging processes are more effective in PG 64-22. In addition, the beneficial effect of anti-strip additives in acid-base characteristics of asphalt binders is severely reduced by RTFO and PAV-aging. Finally, the chemical model of asphalt binder, proposed by Wasiuddin et al., was expanded to include the SFE characteristics of asphalt binders due to aging.
The mechanical properties of bitumen, such as elasticity/Young's modulus, stickiness/adhesion, hardness and energy loss, and sample deformation were acquired quantitatively and simultaneously with the topology at the microscale, discriminating clearly two separate phases within the bitumen. Temperature-dependent measurements revealed detailed and specific data about the changes of these properties with temperature, enabling the development of predictive models for the performance and durability of asphalt.
Asphalts used in the construction of pavements exhibit unique properties at the micron and nanometre scale. Atomic force microscopy (AFM) images of asphalts and asphalt chromatographic fractions prepared as thin films clearly show that a variety of ‘microstructures’ can develop on the surface of these types of materials. Structure develops to different degrees and in different forms depending on the residua crude source from which the asphalt or asphalt fraction is derived, the thermal history of the sample and the sample thickness. Based on our current best interpretation of a very large number of AFM images obtained over several years, we hypothesise that the interaction between crystallising paraffin waxes and the remaining asphalt fractions is responsible for much of the structuring, including the well-known bee structures (Loeber et al. 1996, Journal of Microscopy, 182 (1), 32–39), which has been observed with asphalt materials.
The Young-Dupre equation for the work of adhesion of a liquid drop to a solid surface, where the solid surface is in equilibrium with the vapor of the liquid, is given as W = (gamma L)(1 + cos theta), where (gamma L) is the surface tension of the liquid and theta the contact angle. This work (W) has generally been identified with the free energy of adhesion. It is shown here that it constitutes the total work of adhesion only under the artificial condition that the sessile drop retains its shape after detaching from the solid surface. Under ''real conditions, W represents only one component of the total free-energy change taking place when a drop is separated from, or attached to, a vapor-equilibrated smooth solid surface. In the present work, a Net Free Energy of Adhesion, Delta F-N, is derived which gives the total free energy necessary to separate a sessile drop from a smooth solid surface to form a free sphere (its negative, of course, is the free energy of attachment of the sphere). It is given by Delta F-N = pi r(2) (gamma L)[(2a/sin theta)(2/3) - alpha], where r is the radius of the solid-liquid interface and a, called the ''effective area'', is [2/(1 + cos theta)] - cos theta. The Net Free Energy of Adhesion and Young-Dupre work of adhesion are compared as functions of the contact angle. This is done for systems of constant solid-liquid interfacial area and for systems of constant drop volume.
Bitumen is a complex mixture of hydrocarbons for which microstructural knowledge is incomplete. In an effort to detail this microstructure, 13 bitumens were analysed by phase-detection atomic force microscopy. Based on morphology, the bitumens could be classified into three distinct groups. One group showed fine domains down to 0.1 µm, another showed domains of about 1 µm, and a third group showed up to four different domains or phases of different sizes and shapes. No correlation was found between the atomic force microscopy morphology and the composition based on asphaltenes, polar aromatics, naphthene aromatics and saturates. A high correlation was found between the area of the ‘bee-like’ structures and the vanadium and nickel content in bitumen, and between the atomic force microscopy groups and the average size of molecular planes made of fused aromatics. The morphology and the molecular arrangements in bitumen thus appear to be partly governed by the molecular planes and the polarity defined by metallic cations.
The present paper focuses on a physico-chemical analysis of five different types of bitumens, both before and after aging. These bitumen samples were chosen based on: the original crude oil (straight-run bitumens with different asphaltene and crystallized fraction contents), mode of refining (straight-run vs. half-blown bitumen), and modifier characteristics (straight-run vs. polyphosphoric acid (PPA)-modified bitumen). The aim of this study is to determine both the aging effect on chemical species and the chemical organization as a function of the type of bitumen sample.
In this study, the characteristics and performance of three commonly used catalysts used for alkaline-catalyzed transesterification i.e. sodium hydroxide, potassium hydroxide and sodium methoxide, were evaluated using edible Canola oil and used frying oil. The fuel properties of biodiesel produced from these catalysts, such as ester content, kinematic viscosity and acid value, were measured and compared. With intermediate catalytic activity and a much lower cost sodium hydroxide was found to be more superior than the other two catalysts. The process variables that influence the transesterification of triglycerides, such as catalyst concentration, molar ratio of methanol to raw oil, reaction time, reaction temperature, and free fatty acids content of raw oil in the reaction system, were investigated and optimized. This paper also studied the influence of the physical and chemical properties of the feedstock oils on the alkaline-catalyzed transesterification process and determined the optimal transesterification reaction conditions that produce the maximum ester content and yield.
Effect of aging on the morphology of bitumen was investigated. Two bitumens were aged according to the thin film oven test (TFOT), pressure aging vessel (PAV) test and ultraviolet (UV) radiation, respectively. The morphology of the binders before and after aging was characterized by atomic force microscopy. The physical properties and chemical compositions of the binders were also measured. The results showed that aging affected the bitumen morphology significantly. Aging increased the overall surface stiffness of the bitumen and made the bitumen surface more solid-like. The extent of these changes was dependent on aging conditions. TFOT decreased the contrast between the dispersed domains and the matrix, which contributed to the single-phase trend of the binders. The effect of PAV aging on morphology of the binders was dependent on the base bitumen. In one case, it further accelerated the single-phase trend of bitumen in comparison with that after TFOT. In the other case, it caused the phase separation of bitumen. In both cases, PAV aging increased the surface roughness of the binders obviously. As a result of UV aging, the contrast between the matrix phase and dispersed phase was increased due to the difference in sensitivity to UV radiation of the bitumen molecules, which caused or further promoted the phase separation in the binders. Regardless of the aging procedure carried out, a strong correlation was observed between the changes in morphology and physical properties as well as chemical compositions of the binders before and after aging.