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Correlating the asphalt-binder high-temperature properties (DSR) to HMA permanent deformation (RLPD) and field rutting: A laboratory-field study
Abstract
Asphalt-binders are part of the key material constituents affecting the performance of hot-mix asphalt (HMA), and ultimately, the field performance of flexible pavement structures. Quite often, it is desired/ useful to predict the HMA permanent deformation (viscoelastic) properties and field rutting from the asphalt-binder properties. Using the Texas flexible pavements and overlays database, namely the Texas Data Storage System (DSS), as the data source, this laboratory-field study was conducted to correlate the asphalt-binder properties to HMA permanent deformation (viscoelastic) properties and field HMA-layer rutting performance of in-service highway sections. Data extracted from the Texas DSS included asphalt-binder high-temperature rheological properties measured using the dynamic shear Rheometer (DSR) test, HMA permanent deformation (PD) and viscoelastic properties from the repeated load permanent deformation (RLPD) test, and field rut depth (RD) data for the HMA layers of in-service highway test sections. Two Texas asphalt-binder types, four HMA mixes, and four in-service field highway sections were used in the study. For some parametric comparisons, the corresponding results indicated good statistical correlations among the asphalt-binders, HMA mixes, and field rutting performance, with a coefficient of determination (R 2) over 60%. Overall, the study findings indicated that the HMA PD properties and field HMA-layer rutting can be predicted from the asphalt-binder high-temperature rheological properties, with a linear or logarithmic model, to an accuracy exceeding 60%.
... The accumulation of compressive and shear strains in the asphalt mixture is considered one of the major sources of asphalt-mixture layer rutting in flexible asphalt pavements and is often simulated as a stress-controlled cyclic loading phenomenon [4,51,52]. During the deformation of the asphalt mixture and due to its viscoelastic nature (i.e., the asphalt-binder in it), the work expanded by traffic loading is partially recovered by the [53,54]. ...
... Mathematically, Equation (1) indicates that the work dissipated per loading cycle is inversely proportional to the rutting resistance parameter. Thus, the larger the rutting resistance parameter is in magnitude, the greater the rutting resistance the asphalt-binder (or asphalt mortar) is at high temperatures and vice versa [51]. The corresponding DSR test results for the high-temperature rheological properties of two asphalt mortars are shown in Figure 2. As shown in Figure 2, when the DSR test temperature was increased, the complex shear modulus of the asphalt mortars decreased, with an exponential decline in the rutting resistance parameter (G*/sin δ)-indicating a decay in deformation resistance. ...
To explore the applicability of steel slag porous asphalt mixture, the interaction capability and microscopic interfacial mechanism between asphalt-binder and steel slag aggregate-filler were investigated in this laboratory study. These objectives were accomplished by comparing and analyzing the differences between steel slag and basalt aggregates in interacting with the asphalt-binder. The study methodology involved preparing basalt and steel slag asphalt mortar to evaluate the penetration, ductility, softening point, toughness, and tenacity. Thereafter, the interaction capability between the asphalt-binder and aggregates was characterized using the interaction parameters of the asphalt mortar obtained from dynamic shear rheometer (DSR) testing. For studying the functional groups and chemical bonding of the asphalt mortar, the Fourier Transform infrared (FTIR) spectrometer was used, whilst the interfacial bonding between the asphalt-binder and aggregates was analyzed using the scanning electron microscope (SEM). The corresponding test results indicated that the physical and rheological properties of the two asphalt mortars were similar. However, whilst the FTIR analysis indicated domination through chemical reactions, the interaction capability and interfacial bonding between the asphalt-binder and steel slag aggregates exhibited superiority over that between the asphalt-binder and basalt aggregates, with pronounced adsorption peaks appearing in the steel slag asphalt mortar spectrum. On the other hand, the SEM test revealed that, compared with the basalt, the micro-interfacial phases between the steel slag and asphalt-binder were more continuous and uniform, which could potentially enhance the interfacial bond strength between the asphalt-binder and aggregates (filler).
... In the study, the DSR test was conducted at a temperature of 20 C in a controlled stressloading mode at 0.4 MPa. 30,31 Like the RTFOT and PAV aging tests, four SRAA sample replicates were prepared and tested in the DSR test device per rejuvenation dosage. ...
... Asphalt-binder is comprised of four key components, namely saturates (S), asphaltenes (A), resins (R), and aromatics (A), which is often denoted as SARA. 31,[38][39][40] The chemical models for SARA are shown in Figure 1. ...
To improve the self-healing properties and reduce the reaction energy barrier during the self-healing process of aged asphalt-binders, this study utilized residual oil extracted from soybean to regenerate the aged asphalt-binder and enhance its rheological properties including the self-recovery potential. The self-healing properties from the reaction energy barrier and chemical structure were characterized using molecular dynamic simulations. In addition, the rheological properties were measured and quantified using the dynamic shear rheometer test device. From the study results, the least reaction energy (30.16 kcal·mol⁻¹) barrier registered during the self-healing process of the regenerated asphalt-binder occurred at 5.8 wt% residual Soybean-oil, and was thus, deemed as the optimum oil content. The results further indicated that the residual soybean-oil had a significant influence on the spatial configuration of the molecules in the aged asphalt-binder, particularly on the saturates and aromatics components. Overall, the study findings indicated that residual Soybean-oil can potentially reduce the reaction energy barrier of aged asphalt-binders and enhance the self-healing properties including fatigue life.
... Some basic asphalt binder indicators were often used for the performance description of the high temperature such as penetration, softening point, and rotational viscosity [1,161]. However, in the early 1990s, the Strategic Highway Research Program proposed a new specification known as the Superior Performing Asphalt Pavements (Superpave) that relates the physical properties of binders to the field performance [1,162]. ...
Rutting is one of the significant distresses in flexible pavements. Examining the methods to decrease permanent deformation is of considerable importance to provide long service life and safe highways. The main objective of this paper is to undertake a state-of-the-art review to combine the existing work on the permanent deformation of asphalt concrete pavements. For this purpose, the review synthesizes the evolution of the permanent deformation models, the tests methods used to evaluate and quantify the rutting potential of asphalt mixtures with a particular focus provided on the stress sweep rutting test which is gaining popularity as it tackles the shortcomings of its predecessor for the exact characterization and prediction of permanent deformation. Additionally, some advanced computational intelligence methodologies such as finite element model and soft computing are reviewed. Furthermore, the most common permanent deformation solutions are reviewed. It was found that efforts are put towards improving either the rheological properties of base asphalt by using modifiers or asphalt mixture by using selected aggregates to enhance the aggregate interlock and by implementing semi-flexible asphalt pavements which is expected to be a promising method against permanent deformation. This state-of-the-art work is expected to supply a comprehensive perception of the available models, rutting test, and solutions, and to suggest future studying areas related to the rutting of asphalt pavements.
... In evaluating the statistical correlation, any combination with a level of significance (R 2 ) greater than 60% was considered a good correlation. This R 2 threshold was selected based on similar thresholds used in the evaluation of asphalt binder parameters (49). Figure 9 presents the relationships between each performance measure and the carbonyl and sulfoxide indices. ...
Rejuvenators are used in the asphalt industry to improve the performance and durability of aged binders and facilitate the use of recycled asphalt materials. The purpose of this study was to evaluate the impact of rejuvenator type and dose on the laboratory performance of asphalt binders. For this study, recycled asphalt pavement (RAP) and extracted RAP binder were obtained from an airfield reconstruction project located in Atlantic City, NJ. One petroleum-based (aromatic extract) and three organic-based (corn oil, tall oil, and modified vegetable oil) rejuvenators were evaluated in this study. Each rejuvenator was used at two different rejuvenator doses (6% and 12% by total RAP binder weight) and was aged at three different levels. Performance grade testing, frequency sweep tests, critical temperature differential (ΔT c ), and Fourier transform infrared spectroscopy (FTIR) tests were conducted. Results showed that the use of rejuvenators lowered the high and low performance grade of extracted RAP binders, in particular organic-based rejuvenators had a greater impact on the performance grade. ΔT c was also improved through the use of rejuvenators. In fact, the extracted RAP binder exceeded the high severity ΔT c threshold (−5°C), whereas the rejuvenated RAP binders improved ΔT c to values greater than the low severity threshold (−2.5°C). Similar findings were observed from the Glover-Rowe parameter as well, in which rejuvenated RAP binders improved the cracking resistance of the extracted RAP binder. When assessing the aging susceptibility, modified vegetable oil and corn oil rejuvenators showed the smallest change in performance between aging levels.
... At high storage temperatures, the asphalt internal larger-scale polymer unit of motion (e.g., whole polymer chain) was activated in a flow state, inhibiting the rate of the polymerization reaction. Moreover, viscosity increased due to the high temperature, which led to light components of volatilization in the interior of the asphalt [29][30][31]. ...
Petroleum asphalt, which is the residue left after the distillation of crude oil, meets the characteristics of a mature physics technology of ultrasonic disposal used to reduce the viscosity of crude oil and improve the oil recovery rate. In this study, we analyzed changes in the viscosity of change trend of molten asphalt during ultrasonic disposal tests based on the viscosity-temperature properties of asphalt. We also investigated the effects of ultrasonic vibration on the chemical properties of asphalt by conducting microscopic and chemical tests. The results showed the following: (1) ultrasonic irradiation generated by the circulating vibration and cavitation effect can effectively reduced the viscosity of asphalt according to the law of specificity; 2) the MSCR test data changes showed that the viscosity recovery of ultrasonic disposal of asphalt increased over time, and the results showed that ultrasonic vibration had short-term adhesion reduction characteristics of matrix asphalt; and (3) four-component analysis shows that: the asphalt decreased the heavy component and increased the light component content after ultrasonic disposal, indicating that ultrasound can lighten the asphalt, which can be used as a new asphalt warm mix technology.
... At low temperatures, the stiffness of the asphalt binder rises, and the binder works as an elastic solid. Several studies have shown that asphalt mixture characteristics and performance are significantly impacted by high temperatures and sun radiation [15][16][17][18]. Shear deformation generated by substantial strains in the top regions of the HMA layers under traffic loads is the principal mechanism of rutting or permanent deformation (PD) in the HMA mix, particularly at increased temperatures. ...
A statistical model for predicting pavement surface temperature has been developed for the first time in this study. The main objective of this work is to analyse the impact of the input factors (solar radiation, ambient temperature, wind speed, and albedo) most affecting the conventional rigid pavement surface temperature. A multi-physics numerical model combining radiative, conductive, and convective heat transfers with a response surface methodology (RSM) model was created as an innovative and integrated approach. The numerical model of two-dimensional heat transport based on volume finite techniques is performed using FORTRAN software. Moreover, the analysis of variance (ANOVA) is used to establish the polynomial model or new correlation (quadratic regression) and analyse each input factor's statistical importance. Heat transfer model findings were in good agreement with the experimental data. For pavement surface temperature, the results show that the adjusted Radj2and predicted determination coefficients R2 achieved are 0.9912 and 0.9604, respectively. A good agreement is obtained between the statistical model's prediction values and the heat transfer model's numerical data. Based on the four analysed input factors, a simple polynomial statistical model is developed to forecast and reduce the conventional rigid surface pavement temperature. A wind speed of 1.215 m/s, an air temperature of 293.634 K, solar radiation of 222.305 W/m² and albedo of 0.782 were found to be the optimal operating conditions for obtaining the lowest possible temperature on the pavement's surface.
... For semirigid base pavement, the cumulative plastic deformation under repeated load is the main reason for rutting of asphalt mixture [1,2]. e cohesive force of asphalt and the extrusion force between aggregate constitute the rutting resistance of asphalt mixture, of which the contribution of cohesive force of asphalt accounts for about 40% [3][4][5]. Compared with the rutting test of asphalt mixture, it is much easier to predict the rutting performance of asphalt mixture by testing the permanent deformation resistance of asphalt binder. However, the difficulty lies in finding the most representative asphalt parameters to characterize the rutting resistance of asphalt mixture. ...
Using modified asphalt binder is one of the most effective methods to solve the rutting problem of asphalt pavement, but the traditional G∗/sin δ parameter is not enough to characterize the rutting resistance of modified asphalt in field use. In order to accurately evaluate the high temperature performance of asphalt and establish the relationship between the rutting resistance of binder and mixture, two kinds of matrix asphalt and three kinds of modified asphalt were selected for DSR and MSCR tests. G∗/sin δ, nonrecoverable creep compliance Jnr, recovery rate R, and other parameters were used to characterize the permanent deformation resistance of the binder, and the correlation between these parameters and the results of rutting test was analyzed. The results show that Jnr3.2 can accurately characterize the permanent deformation resistance of asphalt, while the stress sensitivity index Jnrdiff is not applicable to all types of modified asphalt. In contrast, Jnrslope can better reflect the stress sensitivity of asphalt, and Jnrslope is significantly correlated with the results of rutting test.
... As a viscoelastic material, the viscoelastic properties of the asphalt binder and the BRAA under different temperature conditions were quantified using the complex shear modulus (G*) and phase angle (δ), respectively [52]. In line with the Superpave asphalt binder's specification [53], the G*/Sin (δ) parameters for the original (unaged virgin) asphalt binder and the short-term-aged asphalt binder were limited to 1.0 kPa and 2.2 kPa, respectively [54]. ...
Soybean-derived bio-oil is one of the vegetable-based oils that is gaining the most interest for potential use in the rejuvenation of aged asphalt binders. This laboratory study was conducted to characterize and quantify the diffusion and rheological properties of bio-oil-rejuvenated aged asphalt binder (BRAA) using soybean oil. In the study, the chemical structure of the soybean oil was comparatively characterized using an element analyzer (EA), gel permeation chromatography (GPC), and a Fourier infrared (FTIR) spectrometer, respectively. Based on the chemical structure of the bio-oil, BRAA molecular models were built for computing the diffusion parameters using molecular dynamic simulations. Likewise, a dynamic shear rheometer (DSR) test device was used for measuring and quantifying the rheological properties of the aged asphalt binder rejuvenated with 0%, 1%, 2%, 3%, 4%, and 5% soybean oil, respectively. The laboratory test results indicate that bio-oil could potentially improve the diffusion coefficients and phase angle of the aged asphalt binder. Similarly, the corresponding decrease in the complex shear modulus has a positive effect on the low-temperature properties of BRAA. For a bio-oil dosage 4.0%, the diffusion coefficients of the BRAA components are 1.52 × 10−8, 1.33 × 10−8, 3.47 × 10−8, 4.82 × 10−8 and 3.92 × 10−8, respectively. Similarly, the corresponding reduction in the complex shear modulus from 1.27 × 107 Pa to 4.0 × 105 Pa suggests an improvement in the low-temperature properties of BRAA. Overall, the study contributes to the literature on the potential use of soybean-derived bio-oil as a rejuvenator of aged asphalt binders.
... According to related researches and comprehensive consideration of the AASHTO asphalt evaluation system, 64°C was adopted as the frequency sweep test temperature in this paper [19][20][21]. In this paper, the frequency sweep tests were carried out with a diameter of 25 mm and a gap of 1 mm at 64°C, and the frequency domain was 0.1-100 rad/s. ...
The performance of asphalt can be improved by adding styrene-butadiene-styrene (SBS) copolymer and crumb rubber (CR). This paper investigated the influence of the structure and content of styrene-butadiene-styrene (SBS) copolymer on the properties of SBS/CR modified asphalt (SBS/CRMA). These SBS/CRMA were prepared by mixing 90# matrix asphalt, 60 mesh CR powder, and SBS copolymers with two molecular structures, which were tested for penetration, softening point, ductility, and rheology. The complex modulus, phase angle, rutting factor, storage modulus, and dissipation modulus of SBS/CRMA were analyzed with the 64°C frequency sweep tests. The results revealed that the content and structure had significant impacts on the performances of SBS/CRMA, and the advantages of SBS polymer network structure in the modified asphalt system cannot be reflected when the amount of SBS was small. Meanwhile, the high-temperature stability, low-temperature tensile resistance, temperature sensitivity, and viscoelasticity of rubberized asphalt were further improved by adding a moderate amount of SBS copolymer. Furthermore, the properties of SBS/CRMA were better as the contents of SBS increased when the type of SBS doped was the same. The effect of modification improved by star-shaped SBS copolymer addition was more than that improved by linear SBS copolymer addition. As a conclusion, the content of 4 wt% star-shaped SBS and 20 wt% CR powder-modified 90# matrix asphalt has the best modification effect with the comparison of other groups.
... The principal rheological parameters obtained from the laboratory DSR testing are the complex shear modulus (G*) and phase angle (δ), respectively. G* is defined as the ratio of the maximum shear stress to the maximum shear strain, and it provides an indicative measure of the total resistance to deformation [61]. Phase angle, δ, is the phase shift between the applied shear stress and strain responses during a testit is a quantitative measure of the viscoelastic balance of the material response behaviour. ...
Styrene-butadiene-styrene (SBS) block copolymer modified asphalt-binder (SBSMA) is one of the commonly used asphalt-binders in the upper layers of asphalt pavements. Continuous environmental exposure along with the combined effects of traffic loading during the pavement's service life means high susceptibility to aging and degradation over time. Exploration of innovative methods to enhance the resilience of SBSMAs and improve the overall performance of asphalt pavements is thus inevitable. This study investigated the rejuvenation effects of poly-sulfide on aged SBSMA using molecular dynamic simulations and laboratory experimentation including the dynamic shear rheometer (DSR) and Fourier-transform infrared spectroscopy (FTIR) tests for evaluating the rheological properties and chemical compositions, respectively. In the study, the following parametric properties were determined and quantified, namely the diffusion coefficient, viscosity, solubility, and rutting factor of SBSMA. The corresponding results exhibited higher diffusion coefficient for the rejuvenated SBSMA over SBS and the asphalt-binder components. Overall, the study findings indicated that poly-sulfide, at dosages less than 8.0wt%, can potentially rejuvenate aged SBSMA and enhance its rheological properties. Additionally, the simulated results were found to be comparable to the laboratory test results. ARTICLE HISTORY
... The fundamental rheological parameters obtained from laboratory DSR testing are the complex shear modulus (G*) and phase angle (d), respectively. G* is defined as the ratio of the maximum shear stress to the maximum shear strain -the parameter provides an indicative measure of the resistance to deformation [32]. Phase angle, d, is the phase shift between the loading shear stress and strain responses during the DSR test -the parameter provides a quantitative measure of the viscoelastic balance of the material's response-behavior. ...
Due to their superior characteristic properties, multi-layered carbon nanotubes (MCNTs) make ideal candidates for use as reinforcing materials, modifiers, or enhancers in asphalt-binders. With this background, this study was conducted to improve the mechanical properties of styrene–butadienestyrene (SBS) modified asphalt-binder (denoted as SBSMA) through injection of various MCNTs dosages into the SBSMA matrix. In the study, molecular dynamic simulations were used to model and quantify the elastic properties (i.e., bulk, shear modulus, etc.) of SBSMA as a function of MCNTs content. The mechanical response curves of the MCNTs reinforced SBSMA, denoted as MSBSMA, were evaluated using the atomic force microscope (AFM) device. The MSBSMA’s rheological properties (i.e., complex modulus and phase angle) were measured using the dynamic shear rheometer (DSR) test device. The corresponding results indicated that MCNTs had a profound impact on enhancing both the rheological properties and mechanical response-behavior of MSBSMA. Furthermore, the molecular simulations were found to be satisfactorily comparable to the laboratory experimentation results. Overall, the study findings substantiated that MCNTs can potentially be used to reinforce and enhance SBSMA.
... The complex shear modulus (G*) represents the ability of asphalt binders to resist permanent deformation at high temperatures [47]. In this study, the rheological properties, namely, the complex shear modulus (G*) and phase angle (δ) of the asphalt binders and TAPMA were measured using the DSR test device. ...
Due to its good piezoelectric and thermoelectrical properties, tourmaline anion powder
(TAP) can be used as a potential modifier to improve the piezoelectric, thermoelectric, rheological,
and mechanical properties of asphalt binders and asphalt mixtures, respectively. This study was conducted to investigate the functional, piezoelectric, and thermoelectric properties of a TAP-modified
asphalt binder (TAPMA) and the corresponding asphalt mixtures. In the study, the TAPMA’s
environmental friendliness, such as the volatile organic compound (VOC) adsorption and metal
immobilization, were investigated. Compared to TAP at 3.95 pC/N, the piezoelectric constant of
TAPMA was found to be 3.42 pC/N. In general, the results indicated that TAP could potentially
improve the functional properties of asphalt binders and asphalt mixtures, including the piezoelectric
and thermoelectrical properties. With respect to environmental enhancement, the asphalt binder
VOC emission reduced to 50% after TAP addition. In terms of metal immobilization, the heavy
metals Fe and Ti exhibited the best stability followed by the alkali metals Li, K and Na, and lastly,
Ca and Mg, respectively. Nonetheless, the emission concentrations of all the metals were below the
regulatory threshold. Furthermore, the study findings also indicated that TAPMA can potentially
adsorb the tail gas emissions of vehicles and heavy metals.
The feasibility of using recycled concrete powder (RCP) as fillers in asphalt mortar is explored in this study, to achieve a sustainable and economical asphalt production. The differences in physical properties between limestone powder (LSP) and RCP are compared and analyzed. Moreover, the interactions of LSP and RCP with asphalt are studied. The properties focused on this research include ductility, softening point, penetration, viscous and elastic behaviors of asphalt mortar. Compared to LSP, the RCP presented a rougher surface, additional pores, more complex pore structures, larger Brunauer, Emmett and Teller (BET) surface areas, and smaller particle size. At 0.6 and 0.9 of filler-to-asphalt weight ratio (F/A), the RCP is more effective for the performance enhancement of asphalt mortar compared with the LSP. When the F/A is 0.9 and LSP is completely replaced by RCP, the 15 °C penetration index (PI) and ductility of asphalt mortar decrease by 9.3% and 29.2%, respectively. The softening point increases by 5.4%. By contrast, the RCP causes a considerable decrease in PI, equivalent brittle point (T1.2) and ductility when F/A ratio is 1.2. After RCP completely replace LSP, the PI, T1.2, and ductility of asphalt mortar decrease by 47.1%, 44.0% and 29.0%, respectively. However, at F/A of 0.6, the asphalt mortar with 100% RCP replacement ratio presents both acceptable ductility and plasticity. Under the same temperature and F/A, the complex shear modulus G* and rutting resistance factor G* /sinδ of asphalt mortar raise with the increase of RCP replacement, which indicates that the RCP can better enhance the high-temperature rutting resistance of asphalt mortar than the counterpart LSP. This study found that the modification of LSP and RCP in asphalt mortar mainly depends on the physical interactions rather than the chemical reactions.
At upper service temperatures, rutting is one of the common ways through which asphalt pavements fail. The use of polymer modified binders (PMBs) significantly reduces the rutting tendency in asphalt pavements. Commercially, styrene–butadienestyrene (SBS) polymers with different molecular structures are used extensively for asphalt binder modification. Modified asphalt binders were prepared using four commercial-grade SBS polymers having different molecular structures (Linear, radial, high vinyl, and diblock) and at SBS content of 3, 4.5, and 7 wt%. Frequency sweep measurements (0.01–100 rad/s) were performed on the modified asphalt binders at 60 °C. Frequency sweep analysis reveals that the influence of molecular structure on the upper service temperature rheological properties is predominantly observed at lower frequencies (≤0.1 rad/s). At 0.01 rad/s frequency, the divergence in complex modulus and phase angle among the SBS modified binders with the four SBS polymers with different structures were ≈ 500 % and ≈ 25°, respectively. While at 10 rad/s, the variation in complex modulus and phase angle was only 60 % and 5°, respectively. The higher molecular weight (Mw), triblock structure, rigid polystyrene segments at the chain ends, and long radial branches in radial SBS polymer results in a stronger polymer network in the binder. The lower Mw and diblock structure in diblock SB polymer resulted in a weaker polymer network in the binder. The result implies that the rheological signature of the SBS polymer and its structure was predominantly observed at lower frequencies (<0.1 rad/s). Irrespective of the four SBS polymers, the correlation (R²) of the rheological properties with rutting was enhanced significantly at frequency ≤ 0.1 rad/s. This study illustrates the importance of lower frequencies in quantifying the effects of the SBS structure on the upper service temperature rheological properties of SBS-MABs. For a good correlation, effective grading, and quality control, the rheological variable at frequency ω ≤ 0.1 rad/s is important in modified asphalt binders.
The asphalt modifier formed by the miscibility of waste cooking oil and rubber is referred to as WRO. WRO modifiers prepared from waste tire crumb rubber (WTCR) and waste cooking oil (WCO) have the potential for solving the problems of segregation of rubber asphalt and the low recycling rate of waste cooking oil. The results of the Cole-Cole curve show that the WRO modifier can remarkably enhance the miscibility of WTCR and base asphalt. The Fourier transform infrared spectrometer (FTIR) tests proved that WTCR, WCO, and base asphalt were mainly physically miscible during the preparation of the WRO modifier and modified asphalt. In the process of preparing the WRO modifier and modified asphalt, the rubber undergoes devulcanization, conjugated double bond reduction, and oxidation reactions. The WRO modified asphalt presents great workability, storage stability, high-temperature elastic recovery, low-temperature crack resistance, and deformation recovery ability. In addition, the results of the multiple stress creep and recovery (MSCR) tests present that the WRO modified asphalt has desirable antirutting properties. The optimal preparation process of the WRO modifier preferred by orthogonal design is stirring 0.5 h at 260°C, and the mass ratio of WTCR and WCO is 6:4.
Current researches in the pavement engineering field are neglecting the influence of the chemical structure of curing agents on rheological properties of waterborne epoxy resin (WER) emulsified asphalt. The length of molecular chain and the number of active groups will affect the rigidity and flexibility of WER emulsified asphalt. In this study, three curing agents (TETA\DETA\593) with obvious differences in molecular chain length and number of active groups were selected to modify emulsified asphalt. The three kinds of WER emulsified asphalt were subjected to the conventional properties, DSR, BBR, SEM and FITR test. The research has found that the addition of WER system makes emulsified asphalt produce three-dimensional network structure, which significantly improves the high-temperature performance and temperature sensitivity of emulsified asphalt. Whereas, the low-temperature performance of WER emulsified asphalt deteriorates. This indicates that the high-performance of WER emulsified makes it more suitable for the adhesive of micro surfacing or cold mix asphalt used in heavy-load traffic in medium and high temperature areas. Curing agent TETA has the greatest impact on WER emulsified asphalt at high-temperature while 593 has the least adverse influence on the low-temperature performance. The results demonstrate that the more active groups in the curing agent, the higher the crosslinking degree and complexity of the three-dimensional network structure in WER emulsified. And it will lead to the better high-temperature performance of WER emulsified. The longer the molecular chain of curing agent, the more flexible chains in WER emulsified. And it will lead to better flexibility of WER emulsified.
The purpose of this paper is to study the effect of high viscosity petroleum resin (HV-PR) on the microstructure and macro properties of styrene–butadiene–styrene block copolymer (SBS) modified bitumen. SBS modified bitumen was prepared with different content of HV-PR in this paper. The microscopic images were obtained by fluorescence microscope and were analyzed qualitatively and quantitatively with MATLAB and image-pro software. The dynamic shear rheometer test was used to study the dynamic shear properties of SBS modified bitumen with different HV-PR content. The effect of different HV-PR content on the aging resistance of the modified bitumen was studied. The other technical properties of SBS modified bitumen with different HV-PR content, such as segregation softening point difference etc. were also tested. The research results show that: HV-PR can help SBS to be sheared into smaller particles during the shearing process, effectively improve the swelling degree of SBS modifier, improve the spatial distribution of cross-linking structure, and form a more compact cross-linking structure. The addition of HV-PR can effectively improve the high-temperature deformation resistance and fatigue damage resistance of SBS modified bitumen, the higher the HV-PR content, the more obvious the improvement effect. The addition of HV-PR can also significantly reduce the loss of ductility and the gain of viscosity of SBS modified bitumen during the long-term aging process. The higher the HV-PR content, the more significant the effect. HV-PR can effectively improve the viscosity, low-temperature performance, and storage stability of bitumen.
High viscosity asphalt (HVA) has been widely utilized in the paving of large-void asphalt pavement, and it will be affected by thermal aging and exhibit different pavement performance. In this study, through a series of macroscopic and microscopic experiments, the change behaviors of cohesion, adhesion, high- and low-temperature rheological properties, microscopic phase structure and functional groups of HVA under different thermal aging conditions were first analyzed—in comparison with the three asphalts viz. styrene-butadienestyrene (SBS) modified asphalt (SBSMA), crumb rubber modified asphalt (CRMA) and neat asphalt (NA). Further, the relationship between macro-micro properties of asphalt binders was investigated by grey correlation theory, and the comprehensive performance of HVA at different aging stages and its aging resistance were contrastively evaluated via using radar chart analysis method. Results showed that aging degraded the cohesion and adhesion of asphalt binders as well as the water stability of asphalt-aggregate systems, and weakened the low-temperature property of asphalt binders—compared to the unaged sample, the short- and long-term aging reduced the cohesion work of HVA by 1.10% and 3.41%, respectively, and decreased the water stability index of HVA-limestone system by 0.54% and 1.86%, respectively. However, the variations of viscoelastic properties, temperature sensitivity, creep recovery ability and rutting resistance of HVA under aging were inconsistent with those of SBSMA, CRMA and NA. Aging decreased the microscopic surface roughness Ra of HVA and altered the intensity of functional groups at different wavenumbers, and the short- and long-term aging diminished its Ra by 21.26% and 37.85% compared to the unaged sample, respectively. Grey correlation analysis showed that the microscopic surface roughness Ra and the functional group indexes at different wavenumbers correlated well with several macroscopic indexes, which successfully explicated the variations of macroscopic properties of HVA from the micro perspective. Radar chart analysis displayed that the comprehensive performance of HVA in the original and short-term aging stages was second only to CRMA, but its comprehensive performance after long-term aging was only superior to NA; overall, HVA exhibited the most favorable anti-aging performance.
The effect of hydrophilic SiO2 content on the rheological property of bitumen (B)/ polyethylene glycol (PEG)/4,4′-diphenylmethane diisocyanate (MDI)/SiO2 composite was investigated. The multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests were applied to analyze the rutting resistance at high temperature and fatigue life at intermediate temperature of bitumious composites, respectively. The low temperature property was evaluated by glass transition temperature and tensile behavior. All the results suggested that the optimal SiO2 loading for modified bitumen with the best service performance was around 1%. The mechanism for these results was explored by the competitive and coupling effects of SiO2 nanoparticles networking themselves, polyurethane reaction between MDI and PEG, as well as urethane reaction between MDI and SiO2. The intrinsic nature of network structure played a key role in the performance of B/PEG/MDI/SiO2 composite.
MoS2 produced by naturally existing molybdenite has excellent potential as nano-fillers for improving matrix properties of cementitious materials. In this study, following the co-deposition of diethylenetriamine-tannin (DETA-TA) coating on the surface of MoS2, an environment friendly modifier i.e. DETA-TA-MoS2 was prepared, which was in turn applied to prepare DETA-TA-MoS2 incorporated linear styrene–butadienestyrene (SBS) polymer modified asphalt (LSPMA). Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy confirmed that DETA-TA rough coating was successfully deposited on the surface of MoS2. Its multi-tentacle structure and synergistic bionic design awarded the modifier with rougher surface and increased number of potential reaction sites, thus forming a stronger mechanical interlocking with LSPMA. Fluorescence microscopy results indicated that a good spatial network structure of DETA-TA-MoS2/LSPMA was developed as compared with that of LSPMA. Conventional performance tests, dynamic shear rheological and multi-stress creep recovery tests revealed that the viscoelasticity and rutting resistance of LSPMA were significantly improved after the addition of DETA-TA-MoS2 modifier. Compared with LSPMA, the storage modulus (G′) of 0.07%DETA-TA-MoS2/LSPMA increased by 26.4%, while average creep compliance of 0.07%DETA-TA-MoS2/LSPMA decreased by 61.7% (0.1 kPa) and 39.6% (3.2 kPa). This study provides important guidelines for the fabrication of DETA-TA-MoS2/LSPMA modified asphalt as an efficient alternative to conventional SBS modified asphalt for practical applications in highway and construction industries.
The selection and specification of asphalt binder is one of the factors that ultimately affect the long-term performance of asphalt pavements. Many agencies currently follow AASHTO M320 for their binder specifications, where the ratio of dynamic modulus to the sine of the phase angle, |G*|/sinδ, is the binder rutting parameter. However, an alternative now exists, AASHTO M332, which uses the non-recovered creep compliance, Jnr , for this purpose. In this paper, the relative merits of these two parameters are compared using experimental results from 21 different asphalt mixtures from Arizona. The rutting parameters according to AASHTO M332 and M320 were determined for each of the binders in these mixtures and, for each mixture, two rutting performance tests were conducted: Hamburg wheel tracking test and repeated load permanent deformation test. The two binder rutting parameters demonstrated very high correlation to one another for non-polymer modified asphalts, but inconsistent correlation for polymer modified asphalts. Both Hamburg wheel tracking tests and repeated load permanent deformation tests showed positive correlations to both |G*|/sinδ and Jnr. It was concluded that, while both parameters showed good correlation, the Jnr of the binder relates better to mixture rutting than does |G*|/sinδ. Considering the results in this study, it is believed that Jnr is a slightly better rutting parameter for binder specifications.
Abstract During the last decades by increasing vehicle number and weight on roads, road pavement has been subjected to greater damages which in many cases occurred even before expected pavement service life. Rutting is one of the major distress mechanism in flexible pavement placed due to that increasing tire pressure and axial loads further to climatic condition such as increasing of temperature. This study aims to evaluate the effect of binder types and differential of temperatures on the HMA mixtures in term of rutting resistance in four steps. In the first step, rheological properties of different binders (80-100, 60-70 and PG76) were assessed by using DSR test to identify the gradation of the binders and comprehend of the rheological properties of binders in addition to conventional tests. In the second step, HMA cylindrical specimens (100 mm) was prepared by utilizing Superpave mix design. 9 samples were prepared for each type of binder in order to determine the optimum asphalt content (OAC). In the third step, mixtures which contained different types of binder was exposed to the repeated-load indirect tension test at variable temperature levels (30˚C30˚C, 40˚C and 50˚C) in order to compare the resilience behavior of HMA under the influence of temperature variety as well as forecast the performance of mixture with variable types of binder. Finally, repeated load axial test (RLAT) was performed using MATTA machine to identify the potential of rutting for HMA mixtures. 27 HMA specimens each 9 samples contain different type of binder were tested, Three testing temperature levels (30˚C30˚C, 40˚C40˚C and 50˚C) were considered, (1H z) loading frequency and 100 KPa axial stress was repeated 3600 times.The results from the DSR test, resilient modulus test and the RLAT showed a trend that the HMA mixes that contain stiffer asphalt binder (higher elasticity) had superior performance under three different temperatures and considerably improved their rutting resistance.
Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It is more severe for pavements subjected to high pavement temperatures, slow moving, uphill in mountainous areas and heavy traffic loads. A number of binder rutting parameters have been proposed by different researchers for ranking/grading of the binders in terms of their rutting resistance. The suitability of different binder rutting parameters for explaining the rutting resistance of unmodified binders as well as modified binders has been a topic of research for several years. Considering that asphalt mixes in pavement layers are subjected to different conditions of temperature, loading time/frequency and stresses/strains, it is expected that these conditions will affect the way binder rutting resistance is judged. This study was conducted to examine the suitability of different binder rutting parameters for ranking of binders (unmodified as well as polymer and crumb rubber modified), distinguish modified binders from unmodified binders and for their ability to correlate with mix rutting. For this purpose, nine binders (four unmodified and five modified) were evaluated in oscillation and creep and recovery modes and various rutting parameters were examined. Oscillation tests were performed at varying frequencies and multiple stress creep recovery test was performed at different stress levels. The binder parameters were correlated with wheel tracking rut depths of bituminous concrete mix with NMAS of 19 mm. The frequency sensitivity of oscillation parameters and stress sensitivity of creep and recovery parameters were examined. Jnr and% recovery have been found to be stress sensitive whereas |G∗|, δ and |G∗|/sinδ were frequency sensitive. Some of the binder parameters have distinctly different ranges of values for unmodified and modified binders. The rankings produced by ZSV and Jnr closely matched the ranking of the mixes identified based on wheel tracking rut depths. While both oscillation and MSCR parameters correlated well with mix rutting for unmodified binder mixes, the correlation of oscillation parameters with mix rut depth was not good for modified binder mixes.
This study explores effect of binder grade variation on the performance parameters of stiffness, fatigue, and permanent deformation using different asphaltic concrete paving mixtures. Two penetration grade binders (40/50 and 80/100), four gradations (two wearing and two base courses) and single limestone aggregate source were used. Superpave Gyratory Compactor (SGC) was employed to fabricate specimens for Dynamic Modulus |E∗| test, Repeated Load Deformation Test (Flow Number Test, FN) and Static Creep Test (Flow Time test, FT) using Asphalt Mixture Performance Tester (AMPT). The |E∗| test was carried out for a range of temperatures (4.4–54.4 °C) and a frequency sweep (25–0.1 Hz), while FN and FT tests were performed at a single effective temperature of 54.4 °C and 300 kPa stress level. The |E∗| test results were subjected to the non-linear optimization technique to develop the stress-dependent master curves which reveal that the grade of bitumen significantly influences the stiffness of mixtures. The combination of the |E∗| and the phase angle pronounced into fatigue parameter which describes the fatigue behavior of a mix, and results indicate that the softer grade translates into higher fatigue resistance and vice versa. We observe that the 40/50 binder, on average, is 1.8 times more rut-resistant than the 80/100 binder. Further, this study also develops a non-linear regression model to express |E∗| as a function of testing temperature, loading frequency, and mixture volumetric parameter.
Rutting in bituminous layers is a major mode of distress, especially in pavements with thick bituminous layers. Different binder and mix rutting specifications are adopted by agencies worldwide to address the issue of rutting in bituminous mixes. The wheel tracking test is also widely used to evaluate the rutting potential of bituminous layers which depends on the aggregate gradation, binder type and also on the method of mix design adopted. The present study was conducted to examine the relationship between laboratory wheel track rutting and field rutting of different mixes prepared with different aggregate gradations, binder types and binder contents selected using different compaction efforts. Fifteen pavement sections with different surface mixes were constructed on a national highway. Loose bituminous mixes collected from the field were compacted to prepare specimens for wheel tracking tests. Two sets of specimens were prepared to have (a) 7% air voids and (b) an air void content similar to that observed in the field 1 day after construction. The rut depths measured using a wheel tracking machine correlated very well with field rut depths measured after 1 year when the laboratory specimens were prepared at the same initial air void content as achieved in the field. As expected, the rut depth measured in the laboratory wheel tracker for specimens prepared with 7% air voids did not correlate well with 1 year rut depths of field mixes which had different initial air void contents. Limiting wheel tracking test rut depths have been identified on the basis of comparison of the field rutting performance of different mixes and the corresponding laboratory rutting performance of the mixes. Limiting criteria have been proposed for two limiting rut depths of 10 and 20 mm and for different traffic levels.
The development of permanent deformation in flexible pavements has been a research topic for several decades. Currently there are models included in the structural design of pavements that can predict this type of failure. However, the variables required for the prediction of this distress are complex or difficult to obtain in the field, making its application in pavement evaluation also difficult. Measurement of the deflection of pavement structures by means of non-destructive testing is a technique used to assess the condition of the pavement. This research study seeks to correlate data from deflections of the pavement surface with probable permanent deformation in time. In addition, prediction of the remaining life of the pavement structure using a specified criterion is also analyzed. In order to accomplish these objectives, data acquired from 4 different full scale accelerated pavement test tracks was used to develop a permanent deformation model as a function of deflection, load repetitions and pavement layer thickness. The developed model considered a time series model that incorporates an Auto-regressive parameter of order 1. The proposed model presents an advantage over currently available models because it reduces the required parameters to predict the permanent deformation and/or remaining life in the structure and because these variables can be easily found and updated in a pavement management system.
Rutting has been one of the major distresses observed on asphalt pavement in China, due to increasing traffic volume, heavy axle load, continuous hot weather, etc., especially in long-steep-slope section, bus stops, etc. Many factors would affect rutting resistance of asphalt pavement, including material properties, climatic condition, traffic volumes, speed, and axle types, and construction quality. The orthogonal experimental design method was used in this study to reduce the number of tests required, without comprising the validity of the test results. The testing variables and their levels were selected according to investigations and field test results. Effects of various factors on asphalt pavement rutting performance were evaluated, including the asphalt binders, mixture type (aggregate gradation), axle load, vehicle speed and temperature. In this study, the wheel tracking test was used to evaluate rutting performance, as represented by the parameter Dynamic Stability (DS), of the various asphalt mixes. Test results were analyzed using range analysis and analysis of variance (ANOVA). All four factors evaluated in this study had significant effects on pavement rutting performance. The ranking of the significance was asphalt mixture type, temperature, loading frequency, and tire-pavement contact pressure. Asphalt mixture type was the most important factor that affects rutting resistance. Within the asphalt mixtures, asphalt binder had significant effects on rutting performance of mixes more than aggregate gradation. Rutting resistance of SBS modified asphalt mixes was significantly better than neat asphalt mixes, and skeleton dense structure mixes were better than suspended dense structure mixes.
Permanent deformation has conventionally been described by the viscosity-temperature relationship of bitumen at the high in-service pavement temperatures. However, the increase in traffic loads and widespread usage of polymer modified binders (PMBs) has necessitated more accurate predictions of bitumen creep performance. The US Strategic Highway Research Programme (SHRP) attempted to improve rutting predictions through the introduction of the rutting parameter, G*/sinδ. An overview of the SHRP rutting parameter is presented in this paper and improved creep predictions based on Anderson's and Shenoy's equations as well as the dissipated to stored energy ratio are considered. The aforementioned Linear Visco-Elastic (LVE) relations are calculated from frequency sweep data measured with a dynamic shear rheometer (DSR) and used to rank six bitumens in terms of creep performance. These LVE relations are then compared to the non-recoverable creep compliance parameter, J nr , in predicting the ranking of laboratory tested hot mix asphalt (HMA) specimens in terms of rutting resistance.
Flexible pavement structures are subjected to heavy traffic loading and repetition of such loading deteriorates the pavement. Fatigue cracking and permanent deformation (rutting) in pavement layers are the results of this deterioration. These problems arise due to improper characterization of asphalt binder. The conventional testing procedure does not provide deeper picture about behaviour of asphalt. It is required to characterize the asphalt after making some polymer modification and by using some advance testing protocol. This paper tries to evaluate the temperature susceptibility behavior of virgin and polymer modified asphalt and suggests some practical implication considering local industry use. Six polymer modified asphalt samples were prepared in the laboratory and tested with two virgin grades and one factory polymer modified sample using Dynamic Shear Rheometer (DSR). The testing results revealed that polymer modification has significant impact on reheological properties of asphalt binder. Viscosity-temperature susceptibility changes with the addition of polymer which makes asphalt suitable to use in warmer and colder regions in order to control the various distresses in flexible pavements. The finding of this paper would be helpful for local road construction industry for characterization of locally available asphalts and their modified versions.
In this chapter, a state of the art on the basics of the fatigue phenomenon of engineering materials is presented, with special attention to asphalt materials and bituminous binders. Since engineering materials are exposed to complex mechanical and environmental loadings (e.g. temperature and humidity variation etc.) asphalt mixture fatigue tests have been developed and widely used in the last decades. These tests are time consuming and relatively expensive. Hence, binder fatigue tests might be an effective preliminary evaluation of material helpful for mixture fatigue life testing.
Binder fatigue tests are used to investigate the fatigue behavior of bituminous binders and mastics, to compare different binder types, and to investigate the role of the binder in mixture fatigue behavior. The most common equipment for binder fatigue tests has been the plate-plate Dynamic Shear Rheometer (DSR). Other test geometries have been proposed as well. Even if DSR testing has become popular, there are up to now little data available on the reproducibility of this test. Task Group 1 (Binders) of the RILEM TC 206-ATB (Advanced Testing of Bituminous materials) undertook the task of organization of the RILEM Round Robin Binder Fatigue Test (RRRBFT). The purpose of this interlaboratory test was to investigate the repeatability as well as the reproducibility of binder fatigue tests.
Granted that most distresses in asphalt (flexible) concrete (AC) pavements are directly related to fracture, it becomes clear that identifying and characterizing fracture properties of AC mixtures is a critical step towards a better pavement design. This thesis examines the testing variables of a reliable and practical semicircular bending (SCB) test for evaluating the fracture characteristics of asphalt concrete mixtures at intermediate service temperature conditions. The first part of this thesis investigates the repeatability of the SCB fracture test method by integrating a statistical-experimental approach to identify testing variables of the SCB test that result in repeatable test results. Toward this end, five testing variables (the number of testing specimens, specimen thickness, notch length, loading rate, and testing temperature) of the SCB test were investigated due to their significant effects on mixture fracture characteristics. After statistical analysis of 18 specimens tested a typical testing variables, approximately, five to six specimens/replicates were found to be a reasonable sample size that could properly represent asphalt concrete fracture behavior using the SCB test method. The coefficient of variation (COV) of the mixture fracture energy was used to evaluate the effect of each variable on the repeatability of test results. A range of 1 mm/min. to 5 mm/min. for the loading rate, a notch length from 5 mm to 25 mm, and a specimen thickness of 40 mm to 60 mm and a testing temperature of 15-40°C showed the lowest variation of fracture energy. The second part of this work is to investigate the sensitivity of the SCB test using the previously determined testing variables. Fourteen different asphalt concrete (AC) mixtures collected from 12 field construction projects in Nebraska were used in this task. The ANOVA test showed statistically significant differences between mixtures at a 95% confidence level. Tukey’s HSD multiple-comparison analysis found similarities within mixtures of same types and significant difference between mixtures types. In addition, the fracture energy of bituminous mixtures increased with increasing amount of virgin asphalt content in mixture. Overall, the SCB test method developed herein proved to be repeatable and sensitive to changes in mixtures, and thus a promising tool for evaluating the fatigue fracture resistance of AC mixtures.
Adviser: Yong-Rak Kim
Permanent deformation (or rutting) is a common distress in hot-mix asphalt (HMA) pavements. As part of the HMA mix and structural design processes to optimize field performance, the Hamburg wheel-tracking, dynamic modulus, and uniaxial repeated load permanent deformation tests have been developed to characterize the HMA rutting resistance potential. The primary objective of this study was to compare the three laboratory rutting tests of HMA mixes and to relate their rutting predictive potential to actual field performance. The research methodology incorporated a two-phase approach: laboratory testing and field performance monitoring of selected mixes under both conventional traffic loading and accelerated pavement testing. For the HMA mixes evaluated, a good correlation was observed in the three laboratory tests and in comparison with actual in situ field performance. Overall, the findings indicated that the Hamburg wheel-tracking test was the most feasible test for daily routine HMA mix design and screening, while both the dynamic modulus and repeated load permanent deformation tests exhibited greater potential for comprehensive characterization of HMA material property (e.g., modulus) and applications for pavement structural design as research-level test tools.
The effect of temperature level and its exposure time in hot mix asphalt production stages on the conventional and rheological properties of asphalt cements have been investigated through experimental study. A series of Rolling Thin Film Oven (RTFO) Test was conducted at the temperature/time combinations for 135, 150, 163 ºC and 40, 80, 120 minutes. Dynamic mechanical characteristics of the binders were detected by dynamic shear rheometer tests. The results show that the variations in exposure time and temperature distinctly changed the properties of binders in a wide range. It is recommended that for a better simulation of short term aging in production and construction stages, RTFO test temperature and curing time should be adjusted according to the real individual field conditions. Also, in order to give information about the aging behavior of a specific binder for possible field conditions, the test results should be presented for a number of temperature-time combinations.
It is clear that the purpose of mixture design is to select optimum asphalt content for a desired aggregate structure to meet the prescribed criteria. Aggregate makes up high proportion of volume and mass of mixtures; hence, it is considered as an important constituent of asphalt concrete. This study postulates that the gradation is an important characteristic of the aggregate in adoption of the optimum mixture. One aggregate source, three gradations and different percentages of Sasobit® was used to manufacture hot mix asphalt and warm mix asphalt. The test results indicated that the aggregate gradation affects the rutting resistance and especially the moisture susceptibility of the introduced mixtures, differently. Rutting resistance was evaluated using the flow number parameter, and in order to determine the moisture sensitivity mechanism, a mechanical and visual inspection tests were carried out. At the end, it is concluded that the optimum aggregate gradation for these two types of mixtures is different.
The primary objective of this study was to compare the flow number (FN), dynamic modulus (DM), and uniaxial repeated load permanent deformation (RLPD) laboratory tests, used to characterize the HMA mix rutting resistance potential, and establish if they could be reasonably related to each other, and whether, based on these correlations, one test method can be satisfactorily used in lieu of the others. In addition, the concept of FN Index was introduced to quantify the rutting resistance of HMA mixes. Laboratory test results indicated that the FN Index, in contrast to the classical FN (cycles) parameter, exhibited a better correlation with results of both the DM and RLPD tests.
The Superpave specification parameter |G*|/sind for high temperature performance grading of paving asphalts has not been found to be adequate in rating various binders, especially some polymer-modified ones, for their rutting resistance. This has led researchers to seek other possible parameters that may better relate to rutting resistance and also to search for ways to improve the existing parameter |G*|/sind so that it is more sensitive to pavement performance. Some researchers have suggested the repeated creep and recovery test, while others have used a semi-empirical approach as a means to refine the existing Superpave specification parameter.
The present work revisits the proposed refinements of the Superpave specification parameter and shows that the semi-empirical approach involving curve-fitting of experimental data is not necessary if the derivations are based on fundamental concepts. The final equations obtained through a theoretical development are verified using part of the same experimental data that were used by the earlier researchers.
Rutting is one of the common distresses occurring in hot-mix asphalt (HMA) pavements that can be mitigated through adequate laboratory testing during the HMA mix-design screening stage. The Hamburg Wheel Tracking Tester (HWTT) is one of the test methods widely used in the routine HMA mix-design screening and quantification of the HMA rutting resistance potential in the laboratory. However, the occurrence of premature field rutting failures have been reported for some surface HMA mixes (even after being satisfactorily screened with the HWTT test in the laboratory), mostly in high-temperature environments , heavy truck-trafficked areas, and high shear-stress zones such as intersections, curves, etc. In an effort to improve the HWTT's screening and performance predictive capabilities, new models and HMA rutting parameters such as the rutting area, normalized rutting area, shape factor, rut-depth ratio, rutting resistance index, and the equivalent remaining laboratory rutting life were evaluated to supplement the traditional rut depth and number of load passes criteria. The fundamental theory for formulating these new models and HMA rutting parameters is to better account for the currently prevailing traffic loading and climatic conditions. However, one key challenge associated with such enhancements and new model developments prior to industry implementation is correlations and validation with field performance data. Using the Texas flexible pavements and overlays database, namely the Texas Data Storage System (DSS) as the data source, this study was conducted to correlate and validate the HWTT laboratory test data to field rutting performance of in-service highways. As extracted from the DSS, three Texas commonly used HMA mixes (ranging from fine to coarse-graded) and five in-service highways were used for the study. Overall, the laboratory HWTT yielded good correlations with field rutting performance data with a coefficient of determination generally exceeding 60% for most of the HMA rutting parameters evaluated. In particular, the rutting area and normalized rutting area parameters exhibited statistical superiority in terms of correlations with all the field rutting performance data, with coefficient of determination values averaging 69.9%. Nonetheless, more field correlations and validation studies of this nature are strongly recommended, among others, to aid in defining and establishing the pass-fail screening crite-ria/thresholds for the proposed HMA rutting parameters.
Rutting or permanent deformation (PD) is one of the most critical distresses occurring in hot-mix asphalt (HMA) pavements. However, despite all of the recent efforts aimed at producing new test methods and better road materials, HMA rutting is still prevalent, particularly in hot regions and/or on highways with heavy truck-traffic loading. Laboratory testing to screen HMA mixes against rutting during the HMA mix-design stage thus constitute a vital step towards optimizing field performance. In this Texas case study, five laboratory test methods were comparatively evaluated for quantifying and screening four HMA mixes’ rutting resistance potential relative to their field performance on in-service highway test sections under conventional traffic loading and climatic conditions. The five test methods included the dynamic modulus (DM), flow number (FN), repeated load permanent deformation (RLPD), simple punching shear test (SPST), and Hamburg wheel tracking tester (HWTT), respectively. The four HMA mixes evaluated included commonly used Texas fine-, coarse-, and porous-graded mixes. The data for the study, both laboratory and field performance including climate (temperatures) and traffic loading, were all extracted from Texas flexible pavements and overlays database, namely the Texas Data Storage System denoted as the DSS. Overall, all the laboratory test predictions correlated well with the actual measured field performance data, with the HWTT and SPST tests exhibiting superiority over the other test methods. As theoretically expected, the coarse-graded HMA mix out-performed the other mixes, with the fine- and porous-graded mixes being at the lower end of the spectrum.
The Hamburg Wheel Tracking Test (HWTT) is a widely used routine laboratory test for identifying and screening hot-mix asphalt (HMA) mixes that are prone to rutting. The standard HMA pass-fail screening criterion under the current HWTT protocol is 12.5 mm rutting at 50°C. However, Texas has experienced record high summer temperatures in the recent years (i.e., over 122°F), and several rutting failures have occurred in the field with some surface HMA mixes that had passed the HWTT in the laboratory. These failures occurred mostly in high shear-stress locations, in particular with slow moving (accelerating/decelerating) traffic at controlled highway intersections, stop-go sections, in areas of elevated temperatures, heavy/high traffic loading, and/or where lower performance grade (PG) of asphalt binders have been used. This laboratory hybrid study was thus initiated to explore new data analysis methods and introduce new alternative rutting parameters to supplement the traditional HWTT pass-fail screening criteria (≤ 12.5 mm rut depth at 50°C) for surface HMA mixes. Several HMA mixes commonly used in Texas were evaluated in the laboratory and new HWTT analysis parameters, such as the rutting area (ΔA), the normalized rutting area (RutΔ), and the shape factor (SF) with the potential to capture the HMA rutting path-history, were formulated. In addition, a comparison between the newly formulated and traditional rutting parameters with field performance observations was conducted and yielded plausible results in terms of predicting the early-life rutting performance of HMA mixes.
It is recognized that the Superpave® binder rutting parameter (G*/sinδ) is not sufficient to evaluate binder contribution to asphalt mixture rutting. As a result of the NCHRP 9–10 project, a new dynamic shear rheometer test was introduced with promising results: repeated creep and recovery (RCR). For simplicity, the original RCR creep stress was 25 Pa so that the binder would stay in the linear range. However, there is evidence that stresses under traffic loads are high enough to make the binder reach the nonlinear range. This paper was prepared to cover the stress dependency of binders in the RCR test and the relationship with mixture performance. Eight different binders, modified and unmodified, were compared in the stress dependency. The relationship between binder and mixture performance was studied with mixtures prepared with two kinds of aggregates and seven different binders. Results show that the binder stress sensitivity varies significantly between binders on the basis of modification type and testing temperatures. Results of the mixture repeated creep show significant effects of modifier type and good correlation with results of the RCR of binders. For stresses until 10,000 Pa, the correlation between RCR and mixture permanent deformation is good in regard to the stress level selected. It was also noticed that binder samples that were able to withstand high levels of stress in the RCR test without collapse provided the mixtures with a lower amount of permanent deformation. The stress sweep using cyclic loading to measure G* relates well to the stress sensitivity measured with RCR.
This paper deals with laboratory and field evaluation of pure and polymer-modified asphalts (PMAs), in which one bitumen and one polymer type of different contents were used. Styrene-butadiene-styrene (SBS) modified asphalts were selected to evaluate which polymer concentration could offer cost-effective solutions on heavily trafficked highways. Polymer concentrations used were 0%, 3%, and 6% SBS by weight of binder. Asphalt cement containing 6% SBS was referred to as a highly-modified binder in this study. An in-service test road was constructed in 2012 to compare the performance of asphalt pavements built with PMAs while all other variables were held constant as possible. The results of laboratory testing indicated that the morphology of SBS modified binders was influenced by storage temperature and polymer content. The formation of an interlocked continuous network was shown to enhance the rheological properties of PMAs. Significant differences in resistance to rutting and cracking were noted between highly-modified and control asphalt mixtures. This observation was attributed to increased modulus and enhanced critical strain energy release rate of polymer-modified asphalt mixtures. Preliminary performance evaluations showed that none of the test sections evaluated exhibited obvious rutting. Notable differences were, however, observed in the cracking behavior. The test section with the highly-modified binder had a much better resistance to cracking. The field measurements on cracking corresponded well with the test results of the semi-circular bend test in the laboratory. The experimental results of the highly-modified asphalt were in good agreement with field performance. Future monitoring is needed to evaluate long-term trends in performance.
Permanent deformation, mainly referring to rutting, is one of the main distress modes of asphalt pavement. Exploring effective methods to mitigate the rutting distress is of great significance for providing a long-life and safe road. The rutting solutions were first reviewed. It was found that the efforts from academic and engineering industries focused on enhancing the rheological properties of asphalt binder by adding modifying powder, fiber or mixture into binder or mixture, as well as strengthening aggregate interlock and applying novel pavement structure. Semi-flexible asphalt pavement was suggested to be a promising method to fight the rutting distress, because it has a high mechanical property without scarifying the flexibility of asphalt pavement. In order to consider the influence of temperature on rutting occurrence, cool asphalt pavements, especially heat-transfer induced structures, were reviewed and deemed to be a new strategy for reducing rutting susceptibility of asphalt pavement. In order to evaluate the effectiveness of above rutting solutions, many tests, such as multi-stress creep recovery test for asphalt binder and wheel tracking test for asphalt mixture, were reviewed. By linking the reported results of wheel tracking test with high-temperature rutting mechanism it was advised to develop a test method that could reproduce the real field pavement environment, including multiple stress mode, temperature gradient control system and pavement structure, to assess the rutting response of asphalt mixture. This review is expected to provide an overall insight on the existing rutting solutions and test methods, and recommend future studying areas relevant to rutting distress.
This study assessed the sensitivity of the Simple Punching Shear Test (SPST) to different hot-mix asphalt (HMA) mix-design variables, as part of the TxDOT efforts to improve the screening of HMA prone to rutting, permanent deformation, and shear failure under heavy traffic loading, high temperature environments, and severe shear stress conditions. The SPST, which is simply a monotonic penetration of a 1.5-inch diameter solid steel block into a typical Hamburg Wheel Track Test (HWTT) HMA specimen, was further compared to Hamburg Wheel Track Test (HWTT) in order to validate its usefulness. Both the SPST and HWTT tests were comparatively conducted at the traditional 50 °C and elevated temperature of 60 °C. Three SPST-HMA parameters namely, shear strength, shear strain, and shear modulus, were identified to validate the SPST and only the shear strength exhibited a good correlation with HWTT rutting. Additionally, both the HWTT and SPST tests showed that the HMA shear strength and shear failure are sensitive to changes in asphalt-binder content/type, mix types, and test temperature. Most of the HWTT rutting tests failed prematurely when the temperature was elevated to 60 °C, whereas for the SPST, only the magnitude of the HMA shear strength reduced. This suggests that the SPST could be a good supplementary test to identify and screen HMA prone to rutting and shear failure, particularly in high-temperature regions under high shear stress conditions. In addition, the findings indicate that balancing and optimizing the HMA design variables with consideration of field temperature conditions is imperative to ensure adequate HMA shear strength and satisfactory rutting performance.
This study evaluates the influence of morphological properties of aggregates on the mechanical behavior of bituminous mixtures. For that, two aggregates with different characteristics, i.e., round river gravel and crushed gneiss, were used in the research. Laboratory tests were conducted to characterize morphological properties of the aggregates following traditional methodologies and using a modern image analysis system, AIMS 2. Six asphalt mixtures containing different proportions of gravel and crushed gneiss were designed according to the Superpave methodology and evaluated in mechanical performance tests. The results obtained indicated that aggregate morphological characteristics, especially those of coarse particles, are strongly correlated with the resistance to rutting of the asphalt mixtures. In addition, AIMS 2 was shown to provide more direct and scientific measurements of aggregate morphological characteristics that present higher correlations with the mixture performance than traditional methodologies. Finally, the results also demonstrated that the aggregate surface texture is highly correlated to the performance of the mixtures and should be carefully considered in aggregate and asphalt mixture specifications.
In the United States, a number of State Highway Agencies claim that the Superpave specification has some critical gaps, most of them related to the performance characterization of modified bitumens (D'Angelo, 2002). Recognizing this fact AASHTO sponsored project NCHRP 9-10 and in 2001 NCHRP 459 (Bahia et al., 2001a) report was published. The report offered a revised system for testing and evaluating asphalt bitumens based on damage behavior. A scheme to conduct bitumen rutting tests that would allow a more direct qualification of bitumens for specific climate and traffic conditions was presented. The proposal, however, was only conceptual and lacked the details required for implementation, such as specific criteria and limits. This paper addresses the implementation of NCHRP 9-10 for bitumen rutting resistance. It reviews why G*/sin delta has to be changed for a new parameter, called viscous component of the creep stiffness Gv. It is shown how a mechanistic system based on damage behavior can be transformed in a new riffling specification. A proposal for specification limits in terms of the new Gv parameter is given. To develop the proposal, 19 asphalts of several grades currently used or marketed in Wisconsin were tested. The results of the bitumen testing were correlated with field performance using the past experience in the state of Wisconsin. The proposed limits are tentative and are mainly based on the ranking of the PG graded bitumens included in the study. The trial specification limits presented in this paper represent one step forward from the existing PG grading system towards a more reliable bitumen rutting characterization.
The Strategic Highway Research Program developed the Superpave System, which is the new asphalt binder tests and specifications that rank binders based on performance and improve one's ability to select binders that will optimize cost effectiveness for the location, climate, traffic, and structure of the pavement. A discussion covers the Superpave specifications and test; test sites that validated several aspects of the binder specification and its limitations; and changes in testing for the high temperature properties of binders.
The shear strength of hot mix asphalt (HMA) was evaluated with a direct shear device in this research. The indirect unconfined compression test was adopted to calculate the cohesion and the angle of friction of HMA mixtures. The influence of asphalt content, loading rate, and testing temperature on the shear strength of HMA mixtures was also investigated. The shear resistance properties of asphalt mixtures were investigated by a direct shear device using five gradations (i.e., two intermediate-graded and three large-stone mixtures). The results show that the shear strength is highly related to rutting resistance of the HMA mixture at a high temperature. Testing parameters have great influences on the cohesion component and low influences on the angle of friction. The shear strength of asphalt mixtures has good correlations with the dynamic stability through wheel-tracking tests. The angle of friction is susceptible to the mixture gradations and their design methods. The well-interlocked gap-graded mixtures have greater friction angles than the continuously dense-graded mixtures.
Crack attenuating mixtures, denoted as CAM, are some of the mixes commonly used in the State of Texas (USA) to mitigate reflective cracking in overlays, both in flexible—hot mix asphalt (HMA) and rigid concrete pavements. Typically designed at 98% lab density, with high quality aggregates, these fine-graded HMA mixes are rich in asphalt-binder (minimum 6.5%), predominantly using PG 76-22. In this study, three PG 76-22 asphalt-binders from three different sources (denoted as A, B, and C) were evaluated in the laboratory for their potential to meet the CAM Balanced Mix-Design (BMD) requirements when used in combination with limestone aggregates and 1% hydrated lime. Laboratory tests conducted included the Hamburg wheel tracking test (i.e., for rutting and moisture damage [stripping] evaluation), the Overlay test (i.e., for cracking evaluation), and the asphalt-binder rheology, namely the dynamic shear rheometer (DSR) and the bending beam rheometer (BBR). The corresponding results indicated that not all PG 76-22 asphalt-binders are manufactured equally and that material source has a profound influence on both the asphalt-binder rheological properties and the overall performance of the resulting HMA mix. In fact, one of the PG 76-22 asphalt-binder graded out as a PG 82-22 and could not meet the BMD performance requirements for a CAM mix-design. As part of the quality control/assurance protocols and to ensure that the right materials “as designed and specified” are utilized, the overall findings of study suggests that it is imperative that all asphalt-binders delivered to a given construction site must be sampled and tested for its rheological properties and graded accordingly. Provided high quality materials are used, the study also indicated that a CAM mix could satisfactorily be designed at a lower lab density than 98% (i.e., 96.5 - 97.5%); which translates into cost savings in terms of the asphalt-binder content.
The inadequacy of the Superpave high temperature specification parameter, G*/sin δ, to correctly grade the superior field performance of modified asphalt binders has been demonstrated by several researchers. A new parameter that is blind to modification type and is performance based is now needed. As a replacement for the existing high temperature binder test (G*/sin δ), the FHWA has developed an easy to use Multiple Stress Creep and Recovery Test (MSCR) that measures fundamental characteristics of asphalt binders. In this study, several binder parameters proposed to replace the existing Superpave rutting parameter were validated using hot-mix testing. Several different binder tests were evaluated to determine which would provide a replacement for the Superpave high temperature binder criteria. The new test and criteria will have to be performance related and blind to modification. The results from these binder tests were compared against hot-mix rutting results from the Asphalt Pavement Analyzer, the Hamburg Wheel Tracking, the ALF test sections and actual roadway sites. The results from the mixture rut testing showed that different rut testers will provide completely different ranking of binders. This difference is related to the stress level applied by the different testers. This hot-mix testing indicates that the different binders, specifically the polymer modified binders, have different stress dependencies. The binder criteria currently used to specify the high temperature properties are specifically intended to be run in the linear viscoelastic range and therefore can not determine the stress dependency on binder materials. The multi step creep and recovery test can be run at multiple stress levels and can characterize the stress dependency of polymer modified binders. The MSCR test was developed as a result of these findings and other results from various internal studies conducted by FHWA. A separate sub-study was also conducted in this research to understand the effect of stress and strain on the microstructure of polymer modified binders. It was found that in MSCR data there is a clear relationship between %recovery and %strain in the creep portion of the test. In some cases, at least, this is the dominant relationship. Very high strain causes yield behavior in polymer modified asphalt binders (PMA). After high strain, PMAs still exhibit recovery but the rate of recovery is reduced. At high strain, binder morphology, tensile and shear properties change. A test procedure was developed to run creep and recovery testing on one sample at multiple stress levels (MSCR). This test procedure makes it easy to evaluate how the binder response will change under different stress conditions. A property called nonrecoverable compliance Jnr was developed based on the nonrecovered strain at the end of the recovery portion of the test divided by the initial stress applied during the creep portion of the test. The Jnr value normalizes the strain response of the binder to stress which clearly shows the differences between different polymer-modified binders.
The rutting resistance of hot mix asphalt (HMA) Superpave™ mixes in surface course materials was investigated using asphalt material characterisation tests and a digital imaging processing (DIP) technique. The effects of the type of aggregate, the type of binder and the binder content on rutting resistance were quantified. Two types of aggregate were examined: Superpave™ SP12.5 and high friction SP12.5 FC2. Both a modified (PG Plus) and an unmodified binders were considered at the optimum binder content and the optimum content plus an additional 0.5%. To accurately identify the effect of each variable, the shear upheave of these mixes was also quantified. The DIP technique involved estimating the number of aggregate contacts, the total contact length and internal structure index of two-dimensional images of the experimentally tested samples. The results showed that both the rutting resistance and stiffness of HMA surface mixes were sensitive to aggregate type, binder type and binder content. A hig...
In this research, three different methods of rutting resistance evaluation of asphalt binders were compared using high temperature characteristics of rubber-modified binders. For this purpose, implementing dynamic shear rheometer, frequency sweep test and repeated creep and recovery test were conducted on neat and modified samples at 60°C. Rutting resistance of asphalt binders were determined by three approaches: the Superpave specification parameter, G*/sin δ, the cross model for calculating zero shear viscosity, and the Burgers model to determine viscous component of creep stiffness. Utilising these three approaches, rutting resistance of modified asphalt binders were determined and then normalised to rutting resistance of the neat asphalt binder in order to calculate rutting resistance improvement ratio. Results showed that ranking of modified asphalt binders according to three approaches is the same while the quantity of improvement was significantly different. Also, based on these methods, it was observed that crumb rubber has better anti-rutting properties than reclaimed rubber.
As a result of the research conducted for the Strategic Highway Research program (SHRP), a set of new testing methods to characterize the rheological, failure, and durability properties of asphalt binders has been developed. These methods use testing devices that either are completely new or that have been used before only for research purposes. The methods also call for measuring mechanical response parameters that are not very common for asphalt pavement engineers or for many asphalt producers. The purpose is to discuss the following points: (a) the viscoelastic nature of asphalts and its relation to pavement performance, (b) the concepts behind selecting the new test methods and the new characteristic properties, and (c) how the new measured properties compare with the conventional properties. These points are addressed by providing a theoretical-conceptual background about the conventional and new tests and by comparing new and conventional data measured for a large number of asphalts that vary in their sources and their grades. The comparison identifies the advantages of the new testing methods and the need to implement the proposed testing and specification system.
This paper describes the results of a research that was conducted to investigate the contribution of the different components in an asphalt mixture to the resistance to permanent deformation. As part of this research, extensive triaxial tests were performed on the stone skeletons of dense, stone mastic, and porous asphalt concrete. An extensive characterization of the bituminous mortar was also performed using the dynamic shear rheometer and the direct tension tests. The results showed that aggregate skeletons exhibit a high tendency to dilate implying tensile stresses and strains in the bituminous mortar. The results also showed that plastic deformation is much more important than viscous deformation for the stone skeleton mixtures and that viscous deformation is more important for the dense mixture. The findings of the research were used to analyze the permanent deformation that occurred in accelerated pavement test sections.
In the United States, a number of State Highway Agencies claim that the Superpave specification has some critical gaps, most of them related to the performance characterization of modified bitumens (D'Angelo, 2002). Recognizing this fact AASHTO sponsored project NCHRP 9–10 and in 2001 NCHRP 459 (Bahia et al., 2001a) report was published. The report offered a revised system for testing and evaluating asphalt bitumens based on damage behavior. A scheme to conduct bitumen rutting tests that would allow a more direct qualification of bitumens for specific climate and traffic conditions was presented. The proposal, however, was only conceptual and lacked the details required for implementation, such as specific criteria and limits. This paper addresses the implementation of NCHRP 9–10 for bitumen rutting resistance. It reviews why G*/sinδ has to be changed for a new parameter, called viscous component of the creep stiffness Gv. It is shown how a mechanistic system based on damage behavior can be transformed in a new rutting specification. A proposal for specification limits in terms of the new Gv parameter is given. To develop the proposal, 19 asphalts of several grades currently used or marketed in Wisconsin were tested. The results of the bitumen testing were correlated with field performance using the past experience in the state of Wisconsin. The proposed limits are tentative and are mainly based on the ranking of the PG graded bitumens included in the study. The trial specification limits presented in this paper represent one step forward from the existing PG grading system towards a more reliable bitumen rutting characterization.
This article evaluates the effects of linear viscoelastic properties of asphalt on pavement rutting and fatigue cracking.
The parameters in the binder specification recently developed by the Strategic Highway Research Program (SHRP) were also compared
for pavement performance. Two studies were conducted for asphalt-aggregate mixes. The first study was the wheel tracking test
to evaluate the rutting of mixes containing three asphalts. The second study was a detailed field study of the effects of
binder properties on the pavement performance of eight different sections. Results of both investigations indicated that SHRP
parameters were not sufficient indicators for predicting the rutting and fatigue cracking of pavements. The discrepancies
between performance data and existing parameters of the binder mainly resulted from the inherited assumptions made during
the specification development, that is, stress- or strain-controlled mode and traffic loading frequency. In order to directly
relate the linear viscoelastic properties of asphalt binders to pavement performance, calculating the dissipated energy per
traffic cycle, W
d, became imperative. Fundamental derivation of W
d was developed in this study. Results indicated that W
d could predict the rutting and fatigue cracking of pavements reasonably well. This study, proposed the dissipated energy,
W
d, as the single parameter for evaluating pavement rutting and fatigue cracking.
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