Disk-shaped Compact Tension Research Articles

A comprehensive evaluation of crumb rubber modified asphalt-aggregate interfacial behavior and the effect of water: Molecular dynamics simulation and experimental investigation

The incorporation of crumb rubber (CR) makes the asphalt-aggregate interfacial properties highly complex and uncertain, while water is a key environmental factor causing interfacial failure. This paper aims to evaluate the characteristics of crumb rubber modified asphalt (CRMA)-aggregate interaction and the interfacial failure mechanism under the influence of different material properties and water at ambient temperature. Firstly, the CRMA-aggregate interfacial behavior before and after water intrusion is investigated using molecular dynamics simulations at the molecular scale. Next, the failure process and characteristics of the CRMA-aggregate interface were analyzed using the disk-shaped compact tension (DCT) test at the macro scale. Finally, the effect of water intrusion on the interface failure mode was analyzed through image processing. The results show that CR enhances binder cohesion and significantly affects its adhesion to aggregates with high CaO and MgO contents regardless of the presence of water. The asphalt concentration distribution on the CaO and MgO surfaces is more concentrated with higher peak concentration, leading to superior interfacial adhesion and water damage resistance with binder, while Al2O3 and SiO2 were inferior. The use of asphalt with higher creep stiffness, high-strength alkaline aggregates, and smaller CR particle size is beneficial for enhancing the CRMA binder-aggregate interfacial fracture performance. Water intrusion severely affected the interfacial adhesion, resulting in a significant increase in the proportion of adhesion failure, which is the main cause of the deterioration of the interface properties. The findings of this study provide insights into the factors affecting the CRMA-aggregate interfacial behavior, which facilitate the accurate design and application of high-strength durable CRMA mixtures.

Establishing Strategies to Improve Cracking Resistance of High Recycled Binder Ratio Asphalt Mixtures

This study aims to investigate promising mitigation strategies for improving the cracking performance of high recycled binder ratio (RBR) asphalt mixtures. Moisture-resistant aggregates that do not require anti-stripping agents, reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS) were sampled for this study from sources in two climatic zones, south and north. The south-moisture-resistant (SR) mixtures were designed with 0.16 and 0.29 RBRs with RAP, while the north-moisture-resistant (NR) mixtures included 0.21 and 0.37 RBRs with RAP and 0.44 RBR with RAP/RAS. The mitigation strategies evaluated included a softer binder, a different binder source with higher ΔTc, a recycling agent (RA), reduced recycled binder availability (RBA), polymer-modified asphalt (PMA), and hybrid approaches including softer binder + RBA and PMA+RBA. The Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and Disc-Shaped Compact Tension (DCT) test were conducted to capture intermediate-temperature and low-temperature cracking performance, respectively. In addition to the cracking tolerance index (CTindex), an IDEAL-CT interaction diagram analysis was added to further understanding the effect of mixture variables on cracking performance. The findings suggest that while no single strategy works for all RBR mixtures tested, RA, RBA, softer binder, or their combinations yield adequate cracking performance depending on factors including RAP binder stiffness and quantity, RA dose, climatic zone, and RBA.

Emphasis of Cyclic Loading on the Fracture Mechanism and Residual Fracture Toughness of High-Performance Concrete Considering the Morphological Properties of Aggregate

This research investigates the fatigue behaviour and fracture mechanics of high-performance concrete (HPC), including various compositions such as HPC with basalt aggregates (HPC-B), HPC with gravel (HPC-G), and high-strength coarse mortar (CM) under static and cyclic tensile loading within the special priority program SPP 2020. The study aims to integrate fracture mechanics into structural analysis to enhance design guidelines for slender cross-sections and safety-related high-performance structural components. The experimental investigations reveal HPC-B’s remarkable superiority, displaying its higher compressive strength, modulus of elasticity, and tensile strength compared to HPC-G and CM. A modified disk-shaped compact tension (MDCT) based on ASTM standards, aided by digital image correlation (DIC) unveils fracture behaviour, emphasizing fracture energy as a crucial parameter. HPC-B exhibits improved crack resistance and notch sensitivity reduction attributed to crushed basalt aggregates and an enhanced interfacial transition zone (ITZ). The research scrutinizes factors like material characterization, aggregate morphology, stress levels, and the displacement rate on crack formation. High-cycle fatigue tests show HPC-B’s superior performance, and the post-fatigue analysis reveals enhanced residual fracture toughness attributed to nano-level structural changes, stress redistribution and aggregate-matrix interaction. A 3D image analysis via Computed Tomography (CT) scans captures mesostructural crack propagation and provide quantitative insights. This research marks a significant shift from conventional aggregate-focused approaches and introduces a novel approach by integrating excess paste theory and mesoscale analysis, highlighting the critical role of aggregate choice in material characterization and mesoscale design in enhancing the structural efficiency of HPC. Furthermore, the study advances the understanding of HPC fatigue behaviour, emphasizing the interplay of aggregate types and morphologies and their dynamic response to cyclic loading, offering valuable insights for optimizing design guidelines and fostering innovation in structural engineering.

Interfacial characteristics of fiber asphalt mastic and aggregates: Impact on mixture crack resistance performance

The interfacial characteristics between fiber-modified asphalt mastics and aggregates play a crucial role in the performance of asphalt mixtures. To explore these interfacial interaction characteristics, three types of fibers (basalt, glass, and polyester), five levels of fiber content (ranging from 0.1% to 0.5% by mixture mass), and two types of aggregates (limestone and basalt) were selected, and an optimal mixture design was established. Contact angle tests, binder bond strength tests, and disk-shaped compact tension tests were conducted to investigate the impact of fiber type, fiber content, and aggregate type on interface characteristics. The results indicate that the addition of fibers can enhance the interfacial strength, with basalt fibers exhibiting superior reinforcement effects. As fiber content increases, the influence of aggregate type on interfacial strength decreases. Under ambient conditions, a composite failure mode was observed, while at low temperatures, cohesive failures dominated. The incorporation of fibers led to an increase in interfacial cohesion strength. The interfacial interaction strength between fiber asphalt mastic and aggregates exhibits a favorable linear correlation with the fracture energy and peak crack mouth opening displacement of the asphalt mixture. Overall, this study elucidates the microscopic mechanisms involved in fiber asphalt mixtures, laying the foundation for further in-depth research.

Comparative fracture resistance assessment of rubber-modified asphalt mortar based on meso-and macro-mechanical analysis

ABSTRACT This study investigates the effects of ground tire rubber (GTR) on the cracking resistance of asphalt mortar from different analysis scales. Furthermore, the effectiveness of different fracture test methods was compared for GTR-modified asphalt mortar, including the indirect tensile cracking test (IDEAL-CT), disk-shaped compact tension test (DCT) and Illinois flexibility index test (I-FIT). To achieve this, a mesoscopic fracture test based on the SEM-Servo Plus device was proposed firstly to obtain the micro-parameters of constitutive models in discrete-element modelling (DEM). A unified fracture modelling procedure that can avoid any interference factors was carried out for comparative fracture analysis. Results from the tests and simulations show that rubber filler plays a positive role in enhancing the fracture properties of the asphalt mortar. The fracture energy measured by IDEAL-CT is almost 5–6 times of the DC(T) test and 1.5–2 times of the I-FIT test. It is not an inherent attribute of material and can only be regarded as a relative index for fracture resistance evaluation. The FI and CTindex obtained from the I-FIT and IDEAL-CT test show a weak correlation of fracture resistance, especially when comparatively evaluating the GTR-modified asphalt mortar with minor difference in filler content.

Experimental and theoretical framework for illustrating the dependency of fracture toughness with tensile, bending, and compression loading in asphaltic samples

AbstractOpening mode fracture behavior of asphalt mixture is studied experimentally and theoretically using three full disk‐shaped specimens, namely, edge‐notched disk bend (ENDB), disk‐shaped compact tension (DCT), and center‐cracked Brazilian disk (CCBD). While the ENDB sample is subjected to pure bending, the BD and DCT specimens are loaded by diametral compression and pin loading tension, respectively. The experimental results showed the noticeable role of loading type on the cracking resistance of asphaltic mixtures such that the specimen loaded in diametral compression showed significantly smaller fracture toughness than the DCT specimen (that is loaded under tension). The KIc results determined from the ENDB also lie between the KIc of DCT and CCBD testing methods. The discrepancies observed between the experimental results of the three specimen types were related to different signs and magnitudes of T‐stress in these test samples. Accordingly, by taking into account the effect of such stress term via employing modified maximum normal strain theory, the mode I test data were predicted theoretically. Finally, the test data obtained from the CCBD and DCT samples were estimated in terms of the KIc of the ENDB specimen (as the reference sample).

Mitigation Strategy Selection for Asphalt Mixtures with High Reclaimed Asphalt Pavement Content

Economics and sustainability goals have driven higher use of recycled asphalt materials (RAMs), such as reclaimed asphalt pavement (RAP) and recycled asphalt shingles, in the pavement industry. Owing to the brittle nature of aged binders found in RAMs, a mitigation strategy is usually needed to ensure adequate cracking performance. Determining a proper mitigation strategy is vital to designing long-lasting asphalt concrete (AC) pavements with balanced performance. This study explored the use of mitigation strategies on AC mixtures with intermediate and high RAP contents, using materials from four mixtures that were part of a mill and overlay project in Milford, Delaware. This project included one standard mixture and three experimental mixtures with 25%–40% RAP. This paper presents performance data for field cores, plant-mixed laboratory-compacted specimens, and laboratory-mixed laboratory-compacted specimens. The effects and benefits of using a softer binder versus a recycling agent and the effects of using both a softer binder and a recycling agent to mitigate the stiff RAP binder are explored. To understand the effects of each mitigation strategy with aging, data from one-year field-aged cores and from laboratory-aged specimens are shown. Adjusting only one variable to mitigate the increased stiffness and brittleness of recycled binders yielded the best results in this study. Additionally, some test parameters were found to be sensitive to aging, including the flexibility index from the semicircular bend test and the cracking test (CT) index from the IDEAL-CT, while others were not observed to be sensitive to aging, including the fracture energy measured by the low-temperature disk-shaped compact tension test.

Performance Assessment of Bioasphalt Mixtures Containing Guayule Resin as an Innovative Biobased Asphalt Alternative

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of 0.65–0.69 kJ/m2 compared to 0.46 kJ/m2 for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, 400 J/m2). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered 591 J/m2 at its performance grade low temperature (−16°C) and 409 J/m2 at −22°C compared to 429 J/m2 for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Evaluation of the state of practice asphalt binder and mixture tests for assessing the compatibility of complex asphalt materials

The present study aims to evaluate binder and mixture testing methods for capturing the compatibility of complex asphalt materials consisting of different virgin binder sources, reclaimed asphalt pavement (RAP) materials and recycling agents (RA). Binder evaluation methods include the saturate, aromatic, resin and asphaltene (SARA) fractionation, advanced polymer chromatography (APC) analysis, differential scanning calorimeter (DSC) and rheological measurements. Mixture performance tests include the complex modulus (E*), direct tension cyclic fatigue (DTCF), disk-shaped compact tension (DCT) and semi-circular bending (SCB) fracture tests. The results from the testing and analysis indicate that the rheological characterisation of asphalt binder or mixture may not capture the incompatibility between virgin binder, RAP and RA. Binder DSC analysis as well as mixture fracture tests have shown promise to evaluate the compatibility of complex asphalt materials with different virgin binders, RAP and RA, as well as the effect of incompatibility on mixture performance.

Investigation of the Effect of Oxidative Aging and Temperature Sensitivity on the Illinois Flexibility Index and Disc-Shaped Compact Tension Tests

This study investigated the sensitivity of the Illinois flexibility index test (I-FIT) and the disc-shaped compact tension [DC(T)] test with respect to oxidative aging and testing temperature. For this purpose, five plant-produced surface course asphalt mixtures covering a wide range of performance-graded asphalt cement (PGAC) were utilized. As for oxidative aging sensitivity, two methods of forced-draft oven aging, at 85°C for 120 h and at 95°C for 72 h, were utilized. Furthermore, to measure the temperature sensitivity, the I-FIT test was conducted at 23°C, 24°C, 25°C and PGAC intermediate temperatures, while the DC(T) test was conducted at −18°C, −24°C, and −30°C. In this study, the analysis of the I-FIT test results from oxidative aging showed that both methods of aging caused a reduction in flexibility index values of asphalt mixtures, and the flexibility index values after two methods of aging were statistically comparable. Moreover, even though oxidative aging caused a reduction in DC(T) fracture energies of asphalt mixtures containing hard PGAC, the fracture energies before and after the two methods of aging were statistically similar for asphalt mixtures. The analysis of the I-FIT test results from testing temperature sensitivity showed that the flexibility index values of asphalt mixtures containing hard PGAC at 23°C were statistically dissimilar to those at 25°C when the testing temperature dropped from 25°C to 23°C. Consequently, regarding the I-FIT test, the comparable flexibility index values from the two methods of oxidative aging suggested utilization of forced-draft oven aging at 95°C for 72 h as a less time-consuming method compared to forced-draft oven aging at 85°C for 120 h to evaluate the effect of oxidative aging. In addition, the variability in flexibility index values due to the drop in testing temperature suggested exercising caution when conducting the test on asphalt mixtures containing hard PGAC.

A case study of the comparison between rubberized and polymer modified asphalt on heavy traffic pavement in wet and freeze environment

Ground tire rubber (GTR) usage in asphalt pavement with the dry process has gained more prominence in recent times. The objective of this work is to investigate the pavement performance of GTR-modified asphalt pavement and polymer-modified asphalt pavement on heavy volume of traffic conditions in Michigan's wet and freeze environment. A suite of laboratory tests was done to evaluate the pavement performance of GTR-modified and polymer-modified asphalt mixtures. To reveal the strain and stress relationship under different frequencies and temperatures, the dynamic modulus test was applied. The Hamburg wheel tracking device (HWTD) was used to assess the high-temperature deformation resistance. The disc-shaped compact tension (DCT) test was used to evaluate the low-temperature cracking characteristics. The characteristics of the asphalt binder were assessed by the dynamic shear rheometer (DSR) for high-temperature properties and the asphalt binder cracking device (ABCD) for low-temperature properties. After the construction, a field noise test was conducted. The experimental results stated that the polymer-modified asphalt mixture and GTR-modified asphalt mixture showed higher dynamic modulus and better ability to prevent cracking than the conventional asphalt mixture at low temperatures, as well as better permanent deformation and stripping resistance than the conventional asphalt mixture. The fracture energy of the GTR-modified hot mix asphalt (HMA) is 13–16 % larger than the polymer-modified HMA. The number of passes to the stripping point of GTR-modified was 510–518 % higher than the conventional HMA. When compared to the field core, the lab-compacted HMA offers superior pavement performance. The extracted asphalt binder test results show the GTR-modified asphalt has better rutting resistance and cracking resistance than polymer-modified asphalt, and the results in the noise test demonstrated that the rubber-modified asphalt pavement mitigated the noise level by 2–3 dB on the road at different vehicle speeds. Moreover, the pavement condition was noticeably enhanced after the reconstruction of the surface course. The total number of passenger tires to be used in this project is about 2270. To summarize, better rutting and cracking properties in asphalt pavement are shown by the project's utilization of rubber technology. And the GTR-modified HMA is comparable to polymer-modified HMA. Therefore, it may be appropriate to utilize rubber technology on high-traffic volume asphalt pavement in Michigan's wet and freeze climate.

Disk-shaped compact tension test for fracture analysis on pharmaceutical tablets

Pharmaceutical tablets must meet a number of requirements and among them, the mechanical strength plays an important role. The diametral compression test is generally used to evaluate it but can generate unstable failures. Thanks to load-unload cycles applied to the tablets subjected to a DCT test, it was shown that the concept of equivalent linear elastic fracture mechanics usually, can be successfully applied to the Mode I fracture behavior. Within this framework, the equivalent elastic crack growth resistance, commonly called resistance curve (R-curve), of the studied material was obtained and revealed the development of a Fracture Process Zone (FPZ) which is symptomatic of a quasi-brittle behavior. Moreover, the cyclic loading applied during the fracture test revealed the existence of a second dissipative mechanism leading to residual crack opening which seems to be mainly caused by friction phenomenon in the FPZ. • Fracture behavior of pharmaceutical tablets is a key issue for their manufacturing. • An alternative to the diametral compression test is proposed here. • No instability issues using the notch opening displacement controller. • A quasi-brittle behavior identified through equivalent LEFM theory. • Presence of dissipative mechanisms like micro-friction inside the process zone.

Investigation of low-temperature cracking resistance of asphalt mixtures by conducting Disc-Shaped Compact Tension (DC(T)) and Semi-Circular Bend (SCB) tests

This research was focused to investigate the low-temperature cracking resistance of five plant produced SP12.5 surface course asphalt mixtures by conducting the Disc-Shaped Compact Tension (DC(T)), Semi-Circular Bend (SCB) and Bending Beam Rheometer (BBR) tests. The DC(T) and SCB testing were conducted at three temperatures, −18, −24 and −30℃, to characterize the cracking resistance and determine the mixture-based low-temperature Performance Grade (PG) of asphalt mixtures by using the suggested minimum threshold values of DC(T) fracture energy. Moreover, BBR testing was conducted on the recovered asphalt binders from the same asphalt mixtures. The analysis of tests results showed that the DC(T) and SCB fracture energies at three temperatures were statistically comparable and characterized the low-temperature cracking resistance similarly. Even though, the low temperature PG of the recovered asphalt binders were within the Superpave specifications, in some cases, they were mismatched with the mixture-based low-temperature PG. Dissimilar to the SCB fracture energies, the DC(T) fracture energies had better relationships with the low-temperature properties of the recovered asphalt binders. Considering the low-temperature PG of the recovered asphalt binders and the mixture-based low-temperature PG, the DC(T) and SCB tests are essentially needed to reliably evaluate the low-temperature cracking resistance of asphalt mixtures. Moreover, the relationships between the DC(T) fracture energies and the recovered asphalt binder properties revealed that there was a better correlation between the DC(T) fracture energies at three testing temperatures and the recovered asphalt binders’ temperatures corresponding to the stiffness value of 300 MPa.

Evaluation of the significance of different mix design variables on asphalt mixtures’ cracking performance measured by laboratory performance tests

Cracking is one of the primary distresses for asphalt pavements. This study is motivated to investigate the significance of the various mix design variables in determining the cracking performance of asphalt mixtures including both intermediate and thermal cracking performance, contributing to a better understanding of the mix design to improve the mixture cracking performance and promoting the development and implementation of the performance related specification and performance based specification. Total 20 mixtures were tested and evaluated in this study. The most current state of the practice mixture performance tests, including the Complex Modulus (E*) test, Semi Circular Bending (SCB) test, Disk Shaped Compact Tension (DCT) test and Direct Tension Cyclic Fatigue (DTCF) test were conducted on these mixtures for characterization of their cracking performance. The advanced statistical analysis methods were employed on the generated data base to investigate the significance of the mix design variables on determining the cracking performance parameters measured from the laboratory tests. The correlations between the various cracking performance parameters measured from the tests were also evaluated in this study. The results show that the binder related mix variables play the significant role for determining both the low temperature and durability cracking performance of asphalt mixture. For evaluation of the mixture fatigue cracking performance, several aggregate related variables in addition to binder variables are identified as the significant factors. Correlation analysis shows that mixture rheological based cracking parameter G-Rm does not show the strong correlations with neither the facture indices measured from the DCT and SCB tests nor the fatigue parameters measured from the DTCF test. This study also develops a simplified linear regression model as a predesign tool for evaluation and prediction of mixture cracking performance in general.

Comparison of Rubber Asphalt with Polymer Asphalt under Long-Term Aging Conditions in Michigan

The objective of this study is to compare the long-term aging performance of dry-processed rubber-modified asphalt mixture with styrene–butadiene–styrene polymer-modified asphalt mixture on heavy traffic volume roads in the wet-freeze environment of Michigan. The rutting performance was evaluated using the Hamburg wheel track device. The disc-shaped compact tension test was used to assess the fracture energy. The dynamic modulus experiment was used to estimate the load and displacement relationship. The asphalt binder properties were evaluated using multiple stress creep recovery and the linear amplitude sweep test. The pavement distresses were evaluated using the pavement mechanistic–empirical design. All three types of asphalt mixture show excellent rutting resistance after long-term aging conditions, while the fracture energy of the rubber mix is 17.1% to 30.5% higher than that of the control mix and 6.8% to 9.1% higher than that of the polymer mix. The rubber and polymer incorporated with the asphalt binder improved the resistance to permanent deformation and improved the fatigue life of the asphalt binder. In summary, the rubberized asphalt technology using the dry process shows better cracking resistance and fatigue life. Therefore, rubberized asphalt using the dry process will exhibit adequate performance when used for high-volume roads in the wet-freeze environment of Michigan.

Application of Balanced Mix Design Strategies to Missouri Dense-Graded Asphalt Mixtures

This study focused on the improvement or redesign of dense-graded mixtures in Missouri by applying various strategies typified by a balanced mix design (BMD) approach. Briefly, the BMD approach involves designing mixtures using appropriate thresholds of mixture performance tests to control major distresses. In this study, two existing dense-graded mixtures from Missouri were adopted with 33% binder replacement by recycled asphalt pavement (RAP). Appropriate thresholds from three commonly used cracking tests, namely the disk-shaped compact tension test, or DC(T), the Illinois Flexibility Index Test (I-FIT), and the indirect tensile asphalt cracking test (IDEAL-CT), were paired with the Hamburg wheel track test (HWTT) toward the improvement or rebalancing of mixes designed before the availability or specified use of these tests. Preliminary test results showed that the existing mix designs did not satisfy the cracking thresholds adopted in this study, and thus the following modifications were made to the mixtures: (a) replacing the base binder with a softer grade binder, (b) adding a rejuvenator, and (c) adding ground tire rubber (either 10% or 20% by weight of base binder). According to the results, modification with rubber and softer binder was the most efficient strategy for improving and balancing DC(T) fracture energy and HWTT performance. On the other hand, the use of a softer binder or rejuvenator led to the best success in meeting semicircular bend (SCB) (I-FIT) and IDEAL-CT test requirements in balance with HWTT requirements.

Long crack propagation and closure in DC(T) specimens of Ni-based superalloy Inconel 718 and stainless steel AISI 301 after shot peening

In this study, the effects of severe shot peening on ambient temperature long crack growth, threshold and closure behavior in Nickel-based superalloy Inconel 718 and stainless steel AISI 301 were investigated. To assess the relationship between shot peening, crack tip shielding and crack growth, pre-cracked disk-shaped compact tension (DC(T)) specimens were treated at distinct locations around and ahead of the crack front. A beneficial influence of shot peening on crack propagation and closure was only identified in Inconel 718, albeit limited to shot peening of the entire area around the crack front. In contrast, the applied shot peening treatments had detrimental effects on crack growth properties in AISI 301. While the effective threshold of Inconel 718 was not affected by shot peening, AISI 301 featured a decreased intrinsic resistance against the onset of crack propagation. Strain-induced near-surface α′-martensite formed due to shot peening of AISI 301 was found to promote martensite formation during crack growth, giving rise to embrittlement of the material.

Comprehensive Laboratory Evaluation of Recycling Agent Treated Plant-Produced Asphalt Mixtures

Recycling agent (RA) is typically used to restore or rejuvenate the properties of aged asphalt to desired properties. This study was motivated to comprehensively characterize the performance of asphalt mixtures treated with RA. The overarching goal of the research project is to provide guidance to agencies for revising asphalt mixture specifications to include RAs. Ten plant-produced mixtures were evaluated including three control mixtures (with 30 and 40% reclaimed asphalt pavement [RAP]) and seven 40% RAP mixtures treated with different RA products. Mixture testing was conducted with and without laboratory conditioning of loose mixture for 6 h at 135°C. Testing included the mixture Complex Modulus (E*) test for viscoelastic characterization, Direct Tension Cyclic Fatigue test for fatigue performance evaluation, Tensile Strength Ratio test for moisture susceptibility evaluation, and Semi-circular Bending test, Cracking Index Test and Disk-shaped Compact Tension test for mixture cracking and fracture behavior at different temperatures. In addition, the Hamburg Wheel Track Testing was conducted for rutting performance characterization on the unaged mixtures. Results show that addition of different RAs can improve the properties of asphalt mixtures by softening the mixtures with RAP and improving the cracking performance as compared with the control mixtures. However, addition of RA could severely deteriorate the rutting performance of mixtures and increase the moisture susceptibility as compared with the control mixtures. In addition, addition of certain RAs can also decrease the aging resistance of asphalt mixtures, specifically in context of cracking performance.

Evaluating effect of rejuvenators on high RAP mixtures through laboratory performance tests and construction of field test sections

Although thirty-one US states utilize 20% recycled asphalt pavement (RAP) or greater in asphalt pavements, Iowa limits the usage of RAP to 20%, and 30% with a softer binder in the surface layer. Because high RAP mixtures can cause asphalt mixtures to stiffen due to the hardening effect of the aged binder, rejuvenators should be used to improve the cracking resistance of high RAP mixtures. Due to increasing demand for sustainable, and environmentally materials, two bio-based rejuvenators, Invigorate and Tufftreck, were considered for this study. To evaluate effect of rejuvenators on high RAP mixtures, field test sections were constructed in Cerro Gordo County, Iowa, 2020. The field test consists of six different sections with two rejuvenators and three different RAP contents of 22%, 34% and 45%. Performance grading (PG) of asphalt with rejuvenators adopted for the field test sections lowered both high and low temperatures of the virgin asphalt. Based on the eight cores for each test section, all six test sections with or without rejuvenators exhibited field densities between 93.6% and 95.2%, exceeding the minimum requirement of 93%. First, loose field samples were compacted at the laboratory for Hamburg wheel tracking test, semi-circular bending test, and disc-shaped compact tension test. Second, the laboratory test results were analyzed to determine if rejuvenators were effective in mitigating rutting, moisture damage and cracking. Based on the analysis of limited laboratory test results, Tufftrek was effective in lowering rutting and moisture damage whereas, for minimizing cracking, using a soft binder was most effective. Third, a condition survey on test sections was performed in one year after construction. Based on a condition survey of six test sections, no rutting was observed from all test sections, but some low-severity cracks were observed in sections without rejuvenators. Based on the limited condition survey results, it can be concluded that rejuvenators were effective in delaying the initiation of cracking.

Evaluation of lab performance of stamp sand and acrylonitrile styrene acrylate waste composites without asphalt as road surface materials

Acrylonitrile styrene acrylate (ASA) plastic and stamp sand are both waste materials that impose a significant burden on the environment. This study investigates the potential of using stamp sand and ASA plastic composite as the pavement structure. It should be noted that this new material does not use the asphalt binder. A series of lab tests usually used for asphalt pavement materials were employed for the stamp sand and ASA plastic composite material. The high-temperature properties were analyzed by the Hamburg wheel tracking device (HWTD), while the low-temperature performance was measured by the disc-shaped compact tension (DCT) test. The tensile strength ratio (TSR) was used to determine the moisture susceptibility and the dynamic modulus was used to assess the deformation characterize under various loads and frequencies, the coefficient of permeability was estimated by the water permeability test, and the mass loss of aggregate was estimated by the Cantabro loss test. The dynamic modulus results showed that the ASA mixtures have improved high-temperature deformation resistance as compared to the asphalt mixtures. The ASA mixture with 40% sand showed higher stiffness than the ASA mixture with 30% sand. The ASA mixtures have excellent rutting resistance and moisture damage resistance. The fracture energy of the asphalt mixture is 42–77% higher than the ASA mixture. The tensile strength ratio of the ASA and asphalt mixture are all larger than 0.8 and therefore satisfy the Superpave specification. The average coefficient of permeability of the ASA mixture is 6–10 times higher than the asphalt mixture in the same air void level. The average aggregate loss percent of the ASA mixtures is 9.2–10.8 times higher than asphalt mixtures. In summary, the implementation of stamp sand and ASA plastic mixtures may be a successful solution to mitigate the environmentally harmful effects of waste plastic and stamp sand, as well as assist in offsetting the cost and negative effects of the asphalt mixtures typically used for road surfaces.