Long-term Oven Aging Research Articles

Insight into synergistic effect of zinc oxide/expanded vermiculite composite (ZnO/EVMT) on bituminous mixture performances under different aging conditions

Zinc oxide/expanded vermiculite composite (ZnO/EVMT) with synergistic effect can effectively retard bitumen aging behavior, but the effect on road and mechanical performance of bituminous mixture under different aging conditions is unclear, which hinders its application and promotion. Based on the above, this study is meant to reveal the synergistic effect of ZnO/EVMT on bituminous mixture, with the ultraviolet absorber (UVA) compounding with antioxidant (AO) (label as UVA+AO, the same component ratio as ZnO/EVMT) and hydrated lime (HL) modifier serving as comparison. Then, the influence of ZnO/EVMT on the laboratory performances, including road performance and mechanical properties, of bituminous mixtures under four different aging conditions (unaged, long-term oven aging, long-term continuous and long-term all-weather photo-oxidative aging conditions) were investigated. Results show that under unaged condition, the addition of ZnO/EVMT can enhance road performance of bituminous mixture, and has similar effect to that of HL modifier and more positive effect than that of UVA+AO modifier. Under long-term oven aging condition, bituminous mixture containing ZnO/EVMT and HL have similar deformation resistance. ZnO/EVMT and the other two modifiers can enhance the low-temperature property, water stability and fatigue property of bituminous mixture, and ZnO/EVMT modified bituminous mixture has the highest low-temperature property and the lowest property change sensitivity. Under two long-term photo-oxidative aging conditions, ZnO/EVMT modified bituminous mixture generally exhibits higher creep deformation and deformation growth rate but lower mechanical performance changing rate than base bituminous mixture. Therefore, ZnO/EVMT can improve bituminous mixture road performance and reduce its aging sensitivity under different aging conditions. And the expected service life and durability of bituminous pavement will benefit from its promotion practice.

Aging Resistance Evaluation of an Asphalt Mixture Modified with Zinc Oxide

The phenomenon of the oxidation and aging of asphalt binders affects the strength and durability of asphalt mixtures in pavements. Several studies are trying to improve the resistance to this phenomenon by modifying the properties of the binders with nano-particles. One material that shows promise in this field is zinc oxide (ZnO), especially in improving ultraviolet (UV) aging resistance. Few studies have evaluated the effect of these nano-particles on the thermo-oxidative resistance of asphalt binders, and, on hot-mix asphalt (HMA), studies are even more scarce and limited. Therefore, in the present study, the resistance to thermo-oxidative aging of an HMA manufactured with an asphalt binder modified with ZnO was evaluated. An asphalt cement (AC 60–70) was initially modified with 0, 1, 3, 5, 7.5, and 10% ZnO (percentage by weight of asphalt binder; ZnO/AC in wt%), and then exposed to aging in Rolling Thin-Film Oven tests (RTFOT) and a Pressure Aging Vessel (PAV). Penetration, viscosity, and softening point tests were performed on these binders, and aging indices were calculated and evaluated. Samples of HMAs were then manufactured using these binders and designed by the Marshall method, determining the optimum asphalt binder content (OAC) and the optimum ZnO/AC ratio. Control (unmodified) and modified HMA were subjected to short-term oven aging (STOA) and long-term oven aging (LTOA) procedures. Marshall, Indirect Tensile Strength (ITS), and resilient modulus (RM) tests were performed on these mixtures. LTOA/STOA results of the parameters measured in these tests were used as aging indices. In this study, ZnO was shown to increase the thermo-oxidative aging resistance of the asphalt binder and HMA. It also contributed to an increase in the resistance under monotonic loading in the Marshall and ITS tests, and under repeated loading in RM test. Likewise, it contributed to a slightly increasing resistance to moisture damage. The best performance is achieved using ZnO/AC = 5 wt%.

Effects of rejuvenators and aging conditions on the properties of blended bitumen and the cracking behavior of hot asphalt mixtures with a high RAP content

The utilization of Reclaimed Asphalt Pavement (RAP) in asphalt pavement has obtained global popularity because of its cost-efficiency, technical advantages, and positive environmental influence. However, incorporating RAP requires careful consideration of cracking resistance because of the existence of age hardening of bitumen in RAP. For the mixtures containing high RAP contents, rejuvenators are often applied to enhance the performances of aged bitumen and the cracking of mixtures. This research aims to evaluate the effects of different rejuvenators on the rheological properties of bitumen and the cracking resistance of the mixture under short and long-term aging conditions. To achieve this goal, three rejuvenators - namely, RA1 (petroleum-based), RA2 (waste vegetable oil-based), and RA3 (modified soybean oil-based) were evaluated at contents of 0%, 4%, 12%, and 20%, respectively. The dynamic shear rheometer (DSR) test results show that, under unaged and rolling thin-film oven (RTFO) aging conditions, blended bitumen with RA1 and RA3 have higher G*/sinδ than RA2. Conversely, under pressure aging vessel (PAV) aging conditions, blended bitumen with RA1 and RA3 has lower G*sinδ than that with RA2. Regarding the cracking resistance, the indirect tension asphalt cracking test results show that, under short-term oven aging (STOA) conditions, the mixture using RA2 and RA3 has a higher cracking tolerance index (CTIndex) than the one with RA1. However, under long-term oven aging (LTOA) conditions, the mixture using RA1 has the highest CTIndex value. In addition, the high correlations between G*sinδ with CTIndex and post-peak slope (|m75|) and between the CTIndex and |m75| are observed.

Effects of asphalt binder type, aggregate type, and gradation characteristics on fracture properties and performance of asphalt mixtures at intermediate temperatures

This study aimed to design and evaluate asphalt mixtures by considering various factors including different binders, aggregate types, and gradation characteristics of the fine portion of mixtures, referred to as the interstitial component (IC). The mixtures were compacted to 93% of maximum theoretical density to prepare specimens for Superpave IDT tests, which included resilient modulus, creep compliance, and fracture tests. Parameters such as failure limit (fracture energy), damage rate (dissipated creep strain energy per cycle), and the relative cracking performance indicator (number of cycles to failure) were assessed for test specimens subjected to the long-term oven aging and the cyclic pore pressure conditioning. The results showed that mixtures with styrene–butadiene–styrene modified binders exhibited slightly higher failure limits but significantly lower damage rates compared to mixtures with unmodified binders, indicating improved cracking performance. Similarly, the limestone mixtures demonstrated equivalent failure limit but much lower damage rate to the granite mixtures, attributed to the porous surface morphology and inherent weakness of limestone aggregates. Notably, even small changes in the IC characteristics of the mixtures yielded substantial differences in fracture properties and performance, a phenomenon believed to be linked to the distribution of asphalt binder and the structure of air voids within the mixture. In conclusion, a thorough examination confirmed the impact of polymer modification and aggregate type on fracture properties and, notably, highlighted the pivotal role of the fine portion's characteristics in determining mixture cracking performance.

Understanding the Sensitivity of Mixture Cracking Performance Tests to Binder Properties and Long-Term Aging

The asphalt community is focused on the paradigm shift in mixture design from volumetrics to an optimization procedure based on performance tests called balanced mixture design (BMD). Laboratory performance tests are being assessed for their relationship to binder properties and field performance. However, existing BMD practice does not account for long-term oven aging (LTOA). This gap limits the appropriateness of thresholds and the potential of BMD for improving pavement performance. The Federal Highway Administration’s Asphalt Materials Research Program has launched a three-phase study to provide insights into relevant performance testing. Phase I compared seven cracking performance tests after short-term aging, whereas Phase II evaluated the sensitivity of selected performance tests to LTOA. Phase III, in which seven loose mixtures collected from Montana, Vermont, Ohio, and Florida were subjected to LTOA, is presented in this paper. The indirect tensile cracking, Illinois Flexibility Index, dynamic modulus, and cyclic fatigue tests were employed before and after two proposed LTOA conditioning protocols. Additionally, chemical, rheological, and fracture properties were obtained from extracted binders to obtain a better understanding of the impact of binder properties on mixture performance indices. Results illustrate that LTOA is critical for a comprehensive BMD framework and, thus, some of the testing protocols, indices, and thresholds need to be refined further.

Evaluation of long-term oven aging protocols on field cracking performance of asphalt binders containing reclaimed asphaltic materials (RAP/RAS)

This study compared two loose mixes’ long-term oven aging (LTOA) protocols (i.e., 5-day at 95°C and 8-hour at 135°C) based on asphalt binder rheological and chemical properties. The protocols were then correlated with field aging conditions. Extracted and recovered asphalt binders from four asphalt mixtures were tested in the Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Double-Edge-Notched-Tension (DENT) Test, and Fourier Transform Infrared Spectroscopy by Attenuated Total Reflectance (FTIR-ATR). Based on the research results, the loose mix aging protocol of 5-day at 95°C replicates the effects of 2- and 3-year field oxidative aging on the rheological and chemical properties of the binders. The laboratory protocol of 8-hour at 135°C yielded a higher level of aging to the binders compared to the 5-day at 95°C protocol. Additional testing is planned to determine if these loose mix LTOA protocols can simulate 4–5-year field aging in Alabama.

Aging and temperature effects on the dynamic characteristics of asphalt mortar under impact loading

Asphalt pavement structures are subjected to impact loading during the milling process. This study aims to investigate the dynamic behavior of asphalt mortar under high strain rates ranging from 281.7 to 830.3 s−1 through the Split Hopkinson Pressure Bar (SHPB) experiments. The effects of temperature and long-term oven aging on the dynamic properties of asphalt mortar under impact loading were statistically analyzed. The results indicated that the dynamic strength and the impact toughness are both enhanced with the increase in the strain rate and temperature. Laboratory oven aging of asphalt mortar at 85 °C for 72 h indicates a significant increase in the carbonyl and sulfoxide indices, a decrease in compressive strength, and rising in elastic modulus. The failure patterns show a strong correlation with the strain rates. An increase in the temperature produces a better gradation of the fragments at higher strain rates regardless of the aging state.

Characterization of mortar film distribution of asphalt mixtures containing reclaimed asphalt pavement and its relationship with fracture performance using image analysis method

Fatigue cracking is an important pavement distress caused by repeated traffic loading that is known to be very sensitive to aging and climate conditions. A thorough understanding of the relationship between binder rheological and morphological characteristics and cracking resistance parameters of mixtures can contribute to the effective establishment of binder specifications. Therefore, this study aims to evaluate mortar film distribution and fatigue parameters of asphalt binder on fracture resistance of both virgin mixtures and recycled mixtures containing various softening oils and Reclaimed Asphalt Pavement (RAP). The mixtures were subjected to the short-term oven aging (4 h), long-term oven aging (8 h), and extended-term oven aging (16 h) using loose mix aging protocol at 135 °C. The mortar thickness was analyzed by using the 2D image from the sliced asphalt mixture samples. The statistical analysis was conducted to investigate the factors affecting the fracture performance of both asphalt binder and asphalt mixture. The results indicate the CT index of the mixture from the indirect tensile asphalt cracking test (IDEAL-CT) is significantly related to the parameters A and B of asphalt binder from linear amplitude sweep (LAS) test and the thickness of mortar. The mortar film thickness cannot judge the performance of the asphalt mixture alone. It is clearly shown in this study that thicker mortar film thickness within the RAP mixture can delay the weakening of fatigue fracture performance due to aging effect at intermediate temperature. The findings of this study might lead to a better cross-scale understanding of the fracture behavior of RAP mixtures.

Evaluating the Sensitivity of Intermediate Temperature Performance Tests to Multiple Loose Mixture Aging Conditions Using the FHWA Accelerated Loading Facility’s RAP/RAS Experiment

With the advancement of Balanced Mixture Design (BMD), laboratory performance tests for asphalt materials are being assessed for their relation to cracking performance in the field. However, most BMD applications do not account for long-term aging. This gap limits the appropriateness of thresholds and the potential of BMD to improve pavement performance as more amounts of the additives and reclaimed materials available can behave in drastically different fashions between early, intermediate, and late stages of service. In this study, five mixtures with documented field performance from the Federal Highway Administration’s Accelerated Loading Facility were subjected to long-term oven aging (LTOA) protocols. In addition to reheating loose mixtures containing reclaimed asphalt pavement and shingles, the two LTOA methods were 8 h at 135°C and 3 d at 95°C. The objective of this paper is to compare aging approaches, particularly whether equivalence between long-term aged procedures exists, and to highlight the sensitivity (or lack thereof) of common laboratory mixture performance tests. The Indirect Tensile Cracking (IDEAL-CT), Illinois Flexibility Index, Asphalt Mixture Performance Tester cyclic fatigue, and dynamic modulus tests were employed. The results show a collapse in mixture cracking indices when LTOA is incorporated, raising concerns over BMD implementation using criteria established exclusively with short-term oven aging. Use of [Formula: see text] presented a universal and logic shift in response from the reheated to LTOA state, affirming utility as an aging index. Blending insights can possibly be gleaned from the data, although 95 and 135°C LTOA procedures yield mostly equivalent linear viscoelastic and cracking indices.

Mechanical Behavior of Low-Density Polyethylene Waste Modified Hot Mix Asphalt

The use of polymeric waste in the modification of asphalt binders for the construction of road pavements is a technique studied several years ago. However, the use of these materials involves high temperatures close to 190 °C, which generate large environmental impacts due to their emissions. In this study, an asphalt cement (AC) with low-density polyethylene (LDPE) residue contents of 5%, 7%, and 10% with respect to the mass of the AC was modified by the wet method. The modification was carried out using a temperature of 150 °C with the aim of preventing the oxidation of the AC and reducing the emissions generated at high temperatures. Based on the physical-rheological properties of the modified asphalt binder, it was found that 5% LDPE produces the best performance. Subsequently, a hot-mix asphalt type HMA-19 control without a modified asphalt binder and another with a modified asphalt binder were manufactured in order to evaluate the mechanical behavior by means of the Marshall test, an indirect tensile strength (ITS) test, resilient modulus (RM) testing, resistance to fatigue testing, permanent deformation testing, and the Cantabro test. Additionally, the asphalt mixtures were tested under the conditions of short-term aging (STOA, Short-Term Oven Aging), long-term aging (STOA + LTOA, Long-Term Oven Aging), and partial saturation with water (STOA + LTOA + water). Based on the results, an ANOVA analysis of variance was performed to assess whether the changes in the mechanical response of the modified mixture are statistically significant with respect to the control mixture. As a general conclusion, it is reported that mixtures with LDPE can be used for thick layers in high-temperature climates in order to control rutting.

Influence of Gradation on the Mechanical Properties of Aged Hot-Mix Asphalts

When a hot-mix asphalt (HMA) ages, its mechanical properties, resistance, and durability change. Several studies have been conducted throughout the world to evaluate the effects of aging in HMAs. However, few studies have analyzed the influence of gradation. The main objective of this study was to evaluate the influence of gradation on the mechanical properties of aged HMA mixes. For such purposes, three HMA mixes with different gradations were manufactured (named HMA-10, HMA-19, and HMA-25), which were conditioned in STOA (short-term oven aging) and LTOA (long-term oven aging) by following the guidelines established by the AASHTO R30 specification. Marshall, Indirect Tensile Strength (ITS), resilient modulus, permanent deformation, fatigue (under controlled-stress condition), and Cantabro tests were performed. These tests were carried out to evaluate resistance under monotonic and cyclic load as well as the resistance to moisture damage and abrasion. The best performing mix in the test was HMA-19. There is no clear trend about the influence of gradation over the susceptibility of mixes for aging. This susceptibility changes depending on the test performed and the property measured. Furthermore, in resilient modulus tests, it is observed that the influence of gradation on aging susceptibility changes depending on the test temperature.

Use of Blended Binder Tests to Estimate Performance of Mixtures with High Reclaimed Asphalt Pavement/Recycled Asphalt Shingles Content

The purpose of this study is to assess the use of blended binder tests to estimate mixture performance properties of high reclaimed asphalt pavement (RAP)/recycled asphalt shingles (RAS) mixtures utilizing recycling agents as a means to evaluate different recycling agents and estimate their doses for a given mixture. Blended binder properties are measured by using standard performance grading (PG) and PG+ test methods and correlating the results with corresponding performance properties of mixtures. Blended binders consisting of virgin and recovered binders and recycling agents were prepared and tested for PG grading properties, multiple stress creep recovery grades, and linear amplitude sweep fatigue life after the rolling thin-film oven and pressure aging vessel aging. Mixtures were tested for rutting resistance and cracking resistance at intermediate temperature and at low temperatures after being subjected to short-term oven aging and long-term oven aging. The correlation between the blended binder properties and mixture performance properties is used to identify the binder test parameters that can be used to predict the long-term performance of high RAP/RAS mixtures and the effects of various recycling agents. Results generally indicate that use of direct testing of recovered binders with recycling agents is an effective means to estimate required initial dose for recycling agent, and testing actual blended binders can be used to predict mixture performance-related properties for the testing conditions used in this study.

KAJIAN DURABILITAS DAN PENUAAN ASPHALT CONCRETE-WEARING COURSE (AC-WC) ASBUTON PRACAMPUR TERHADAP VARIASI LAMA RENDAMAN

The fundamental problem in roads construction is the road damage that occurs before the road’s designted time is reached. Causes of such a damage consist of weather, water, temperature, or the reduction in the quality of pavement layers due the aging process. The manufacture of test object for Short-Term Oven Aging (STOA) was carried out by heating the test object in loose condition with 135°C of temperature for 4 hours before compaction, while the manufacture of test piece for Long-Term Oven Aging (LTOA) was carried out by heating the test object for 2 days in 85°C temperature after the specimen was compacted. The durability parameters of the AC-WC mixture was observed from Residual Streght Index (RSI), First Durability Index (FDI), and Second Durability Index (SDI). Based on the findings of Pre-Blended Buton Asphalt AC-WC mixture produced 6,0% of Optimum Bitumen Content (OBC). The RSI of the test object in normal, STOA, and LTOA obtained 97,11%, 94,82%, and 95,77% respectively. Furthermore, the FDI of the test object in normal, STOA, and LTOA obtained r value of 0,42%, 0,74%, and 0,60% respectively. Meanwhile, the SDI of the test in normal, STOA, and LTOA obtained a value of 4,87%, 9,75%, and 7,73% respectively. In addition, the Sa of the test object in normal, STOA, and LTOA in 96 hours of soaking were 95,13%, 90,25%, and 92,27% respectively. All in all, the finding showed that the AC-WC mixture with Pre-Blended Buton Asphalt in normal condition attained 72 hours of durability, while for the test specimen which is subjected to aging (STOA and LTOA) attained 48 hours of durability.

Extended aging performance of high RAP mixtures and the role of softening oils

ABSTRACT Recently, there is a growing interest in increasing content of reclaimed asphalt pavement (RAP) material in the production of Hot Mix Asphalt (HMA) pavements to further reduce material costs and to preserve non-renewable resources. This study aims to evaluate the long-term performance of high RAP mixtures containing various softening oils. Both petroleum-based and bio-based oils were applied in preparing the 30% RAP and 50% RAP mixtures. The mixtures were subjected to the short-term oven aging (4 h), long-term oven aging (8 h), and extended-term aging (16 h) in the laboratory. Their performance, including the rutting, fatigue cracking at intermediate temperature, and low temperature cracking, were measured and compared with the control mixtures. The results indicate that the softening oils in this study can be used to produce asphalt mixtures containing high percentages of RAP with similar performance to a virgin mixture utilising the same aggregates and mixture design. In addition, the results show that making decisions to compare, qualify, or otherwise accept mixtures using the short-term aging results alone can be very risky. It is clearly shown in this study that relative ranking of mixture performance can change based on the level of aging.

Effect of long-term aging on waste tire rubber and amorphous poly alpha olefin compound modified asphalt binder and its mixtures

The aging resistance of asphalt mixture has an important impact on the long-term quality and service life of asphalt pavements. This research aims at studying the effects of long-term aging on waste tire rubber (WTR) and amorphous poly alpha olefin (APAO) modified asphalt binder and mixtures. The prepared compounds included, 12%WTR + 4%APAO and 15%WTR + 4%APAO modified asphalts, were used as experimental objects. Base asphalt binder (70 penetration grade), 15%WTR modified asphalt and styrene–butadiene-styrene (SBS) modified asphalt were the reference objects. First, pressure aging vessel (PAV) and long-term oven aging (LTOA) were used to simulate the long-term aging of asphalt binder and mixture, respectively. Secondly, the performance tests of asphalt binder and mixture were carried out, and the evaluation indexes of the effects of long-term aging on performance were proposed. For the asphalt binder, the results show that the incorporation of WTR and APAO significantly improves the post-aging conventional properties, rheological properties and fatigue properties. The Fourier transform infrared spectroscopy (FTIR) results were found to correlate to the physical tests results. In the asphalt mixture part, the results show that 15%WTR + 4%APAO modified mixture has better high temperature and fatigue performance after aging, among the rubber-based asphalt mixtures. The low-temperature performance of WTR/APAO asphalt mixture was not compromised after aging. Compared with the SBS modified asphalt mixture, the high and low-temperature performance of 15%WTR + 4%APAO asphalt mixture after aging are better. Overall, 15%WTR+4% APAO asphalt mixture has better advantages to counteract the influence of oxidative aging.

Influence of the Long-Term Oven Aging on the Performance of the Reinforced Asphalt Mixtures

The long-term aging of the asphalt mixtures has become a major concern because it decreases the lifespan of the asphalt layer. In this study, the asphalt mixtures incorporating steel slag aggregates were reinforced with synthetic fibers as a novel contribution in terms of decreasing the effect of aging on the performance of the asphalt mixtures. However, different mixtures—namely, Mix0, Mix1, and Mix2—were subjected to long-term oven aging to study the effect of the aging on the performance of the asphalt mixes. Mix0 consisted of coarse and fine granite aggregates, while Mix1 was composed of coarse steel slag aggregate and fine granite aggregate. Mix2 represents the reinforced asphalt mixtures incorporating coarse steel slag aggregate and reinforced with the synthetic fibers of polyvinyl alcohol, acrylic, and polyester at the proportion of 0.3% by weight of the aggregates. The conducted performance tests were resilient modulus, rutting depth, and cracking resistance. The outputs of the performance tests for the unaged asphalt mixes displayed that the mixtures incorporating coarse steel slag aggregate exhibited better performance than the mixtures containing granite aggregate. Meanwhile, the reinforced asphalt mixtures have shown a lower resilient modulus and a higher permanent deformation than the unreinforced asphalt mixes due to the elastic behavior. Otherwise, the reinforced asphalt mixtures have shown superior resistance to cracking in comparison to the unreinforced mixtures. On the other hand, the performance of the aged asphalt mixtures demonstrated that the mixtures containing granite aggregates exhibited a lower susceptibility to aging than the mixtures incorporating steel slag aggregate. Meanwhile, the performance of the aged reinforced asphalt mixtures showed that introducing synthetic fibers has decreased the effect of the long-term oven aging.

Effect of laboratory long-term oven aging on the stiffness of asphalt mixtures

This study evaluates the effect of laboratory long-term oven aging (LTOA) on the stiffness of asphalt mixture using laboratory dynamic modulus test. A large variety of materials was subjected to diverse LTOA conditions including different aging temperatures and durations with loose mixture and compacted samples. Dynamic modulus master curve and dynamic modulus ratio (DMR) data shows that the aging of loose mixture at 95 °C could be an ideal LTOA procedure with the efficiency and capability to characterize the long-term aging in the field. The variety of materials including the use of recycled asphalt pavement, warm mix asphalt technologies and asphalt binder performance grade was also found to have appreciable effect on the LTOA properties.

Fracture Properties of Aged Asphalt Mixtures Incorporating Recycled Tire Rubber and Styrene-Butadiene Rubber at Low Temperatures

ABSTRACT A laboratory investigation was conducted to evaluate the fracture properties of aged asphalt mixtures containing recycled ground tire rubber (GTR) and styrene-butadiene rubber(SBR) modifiers at low temperatures. Asphalt mixtures were compacted by the gyratory testing machine and aged according to the SHRP short term oven aging (STOA) and long term oven aging (LTOA) procedure. An experimental program was to evaluate the effects of different modifiers and aging conditions on the indirect tensile strength, creep compliance, resilient modulus, and fracture energy of compacted asphalt mixtures.The results indicate that the fracture energy of asphalt mixtures at -10°C decreases slightly after the STOA or LTOA process in general, but the SBR-modified asphalt mixtures tend to increase at ultimate compaction condition.The GTR-modified asphalt mixtures have lower elastic stiffness (higher creep compliance intercepts) as compared with the unmodified mixtures before and after the LTOA process.The SBR-modified asphalt mixtures have higher fracture energy at -10°C than that of mixtures containing the unmodified AC-30 and the GTR-modified asphalt. Based on indirect tensile creep compliance, tensile strength, failure strain and fracture energy, the GTR and SBR-modified mixtures show a greater potential to resist low temperature cracking as compared with the unmodified mixtures.

Effect of low-temperature modifiers on HMA mixture aging and cracking resistance

The Superpave Performance Grade of an asphalt binder can be improved by adding different combinations of polymers and low-temperature modifiers. Although using various modifiers is not new, their effect, in particular softening oils, on long-term aging is not yet well understood. The objective of this study is to evaluate the effect of two widely-used oils to adjust binder grades on volumetrics, workability and fatigue cracking resistance of mixtures subjected to short- and long-term aging. Eight combinations of softening oils and polymers were used to prepare PG 58-34 binders. The mixtures prepared with these combinations were oven-aged for six and 14 h and used to compare their Flexibility Index (FI) results following Semi-Circular Bending Illinois FI test (SCB-IFIT) procedure. In addition, the effects of binder composition and aging on the compaction effort were assessed using the Superpave Gyratory Compactor (SGC) data. Furthermore, extracted and recovered binders of these mixtures were tested following the Linear Amplitude Sweep (LAS) test at intermediate temperature. Overall results indicate that oils used and aging susceptibility of the eight mixtures affected FI results differently. There is a good relationship (R2 = 83%) between the FI values and the absolute value of the LAS-B parameter of the extracted and recovered binders. This finding shows that FI sensitivity to aging is at least initially driven by the binder properties. The main finding from the analysis of the LAS-B parameter is that ΔTc measured for the 20-hr Pressure Aging Vessel (PAV) aging cannot be assumed to represent long-term oven aging of mixtures exceeding six-hours of oven aging at 135 °C.

Effect of Long-Term Aging on Fracture Properties of Virgin and Recycled Asphalt Concrete

Abstract Oxidative aging stiffens asphalt in the pavement, raising brittleness, cracking potential, and deterioration of pavement serviceability. Mechanical testing of long-term aged asphalt concrete in the laboratory has shown elevated stiffness, higher failure load (peak load), and reduced fatigue cracking resistance. Among the laboratory mechanical tests used to evaluate mix fatigue resistance and flexibility is the semicircular bend (SCB) test. This study was conducted to determine how the properties of the long-term aged asphalt mixes compare with those from short-term aged asphalt mixes tested under SCB test. Such comparison is important as a decision needs to be made by mix designers as to what aging level to apply when testing asphalt concrete to evaluate fatigue resistance. The mix variables included air void, binder content, and binder stiffness. The properties that were measured, i.e., the response parameters, included fracture energy, load at failure (peak load), mix stiffness, and flexibility index. A large number of mixes including various aggregates, gradations, and binder contents were included in the study. Results showed that long-term oven aging significantly changed flexibility index, peak load, and stiffness of tested specimens. Sensitivity of the parameters to aging was also evaluated in the context of an aging index and defined as the ratio of the measured property after long-term aging to that after short-term aging. In this respect, the aging index did not change as the binder content changed. However, the aging index was sensitive to variations in air void and binder stiffness.