61 research outputs found

    Asphalt Binder Laboratory Short-Term Aging

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    The Rolling Thin Film Oven (RTFO) is widely used to simulate asphalt binder short-term aging. However, there is a general interest to improve the current short-term aging protocol especially for reducing the aging time. Besides, there are some doubts about the capability of RTFO in the simulation of aging of highly polymer modified asphalt binders which is mainly due to improper dispersion of such binders in the bottles during rotating and creeping of highly viscous binder out of the bottles during rotation. This work addresses the effect of time, temperature, airflow rate, and weight of asphalt binder on the laboratory short-term aging of asphalt binders and proposes an alternative protocol that can reduce the aging time and resolve some of the current short-term aging protocol shortcomings. In the first part of this study, two asphalt binders, from different sources, were examined in RTFO at different combinations of the above-mentioned test parameters. The high-end continuous performance grading temperature (estimated by dynamic shear rheometer), and carbonyl index (estimated by Fourier transform infrared spectroscopy) were considered as the two responses for quantification and qualification of laboratory aging. The statistical analysis showed that the first order terms of time, temperature, and weight as well as their interactive terms were statistically significant. However, the effect of airflow rate, within the studied range, was insignificant. Based on the findings of the first part of study, an alternative protocol was proposed for the study of short-term aging in a RTFO. One unmodified and three highly modified binders were aged in a RTFO under the current and proposed aging conditions for comparative purposes. According to the obtained rheological (high- and low-end continuous performance grading temperature and viscosity) properties as well as the chemical characteristics (carbonyl index, saturate-aromatic-resin-asphaltene fractions, and oxygen content), it was shown that the proposed laboratory short-term aging protocol not only can reduce the aging time of the conventional protocol, but also that it is applicable to both neat and polymer-modified modern asphalt binders

    Optimizing In-Place Density of Asphalt Pavements During Cold Weather Paving in Nebraska

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    Late season paving is common and often performed in colder temperatures, which is the most challenging environment for attaining optimal in-place density/compaction The in-place density of asphalt pavement greatly affects the lifespan of the pavement. It is also a key factor in preventing major pavement distresses, such as rutting, cracking, stripping (due to water damage) and aging. This research project aims to evaluate and compare the effectiveness of different compaction, delivery, and mix design characteristics to ensure the optimization of in-place asphalt pavement density. To this end, various laydown methods (i.e., Standard Pick-up Machine (SPM) and Material Transfer Vehicle (MTV)) and compaction equipment (i.e., double drum steel rollers, pneumatic rollers, and combination rollers with both steel and pneumatic tires), using both static and vibratory modes were employed. In addition, the effect of different aggregate blend combinations (i.e., using less coarse ledge rock) and asphalt binders (i.e., PG 58V-34, PG 40-40, and PG 52-40) on in-place density were studied. Four test sections were constructed over four separate days of paving, during cold weather conditions. The in- place density was measured using four methods: 1) Conventional/traditional cut roadway cores, 2) Combination of Infrared Continuous Thermal Scanning (ICTS) with conventional/traditional cut roadway cores, 3) Pavement Quality Indicator (PQI), and 4) Rolling Density Meter (RDM) utilizing Ground Penetrating Radar (GPR). The obtained results were compared and contrasted to the current testing, acceptance and construction methods system at Nebraska Department of Transportation (NDOT) and recommendations for future construction specifications and best practices were presented

    Research on High-RAP Asphalt Mixtures with Rejuvenators and WMA Additives

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    Effect of Antioxidant Additives and Recycling Agents on Performance of Asphalt Binders and Mixtures - Phase I

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    The use of reclaimed asphalt pavement (RAP) in asphalt mixtures has notably increased in recent times. Nevertheless, the inherent stiff and aged characteristics of RAP materials have consistently raised concerns regarding cracking performance. The use of recycling agents (RAs) has gained popularity in recent years since they can effectively modify the engineering properties of the aged asphalt binder. Besides that, the combination of RA with antioxidant (AO) additives has shown promise in enhancing the long-term performance of RAP mixtures. This research aims to investigate the effect of various RAs and one AO additive on performance of asphalt binders and high-RAP mixtures. Five RAs (paraffinic oil, naphthenic oil, aromatic extracts, triglycerides/fatty acids, and tall oils) and one AO (zinc diethyldithiocarbamate - ZnDEC) were selected. Initially, the effects of RA and AO were analyzed at the binder level considering chemical (SARA, FT-IR, CHNOS) and rheological as well as physical (DSR, BBR, and Wihelmy Plate) testing results. Secondly, following the findings at the binder level, two specific RAs (naphthenic oil and triglycerides/fatty acids) were chosen and utilized in combination with ZnDEC to modify the binder used in producing high-RAP mixtures. The studied mixtures were subjected to semi-circular bending test (SCB) and Hamburg wheel tracking test (HWTT) to evaluate cracking, rutting and moisture damage resistance of the mixtures, respectively. The chemical analysis of the RAs showed that those based on triglycerides/fatty acids and tall oils demonstrated pronounced peaks near the 1740 cm-1 region and a greater oxygen content relative to other RAs. As expected, the RAs had a softening effect on the binder blends. Additionally, ZnDEC helped retard the oxidation of the RA-modified binders, and its effectiveness depended on the RAs\u27 susceptibility to aging. At the mixture level, the simultaneous use of RAs and ZnDEC in the high-RAP mixture improved cracking performance and reduced oxidative aging but might negatively affected rutting and moisture damage resistance

    Optimizing Chemical & Rheological Properties of Rejuvenated Bitumen

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    Bitumen has long been a material used in the construction of roadways, yet new pavement only consists of low fractions of recycled materials due to poor compatibility of aged bitumen and new materials. Thus, rejuvenators, chemical additives, have been used in an attempt to re-balance the chemical composition and restore the physical properties of aged bitumen back to its virgin state. A fundamental understanding of how one particular rejuvenator, soybean oil, revitalizes bitumen was investigated using a multi-scale approach. Fourier-transform infrared spectroscopy (FTIR) was used to determine the changes in chemical properties of pure and rejuvenated virgin and aged samples. Samples were artificially short term aged using a rolling thin film oven (RTFO) procedure or long term aged using a pressure aging vessel (PAV). Rejuvenator concentrations were tested at both 7.5% and 15%. FTIR results reveal carbonyl (IC=O), sulfoxide (IS=O), branched aliphatic (IB), and aromatic (IAr) indices decrease in RTFO and PAV samples from rejuvenation with soybean oil, suggesting that the aging process in the aged bitumen has been reversed. A linear amplitude sweep (LAS), a mechanical procedure using a dynamic shear rheometer (DSR), was employed to investigate rheological properties. LAS analysis of PAV samples manifests fatigue resistances of bitumen samples increase at every applied shear strain as a result of increasing concentration of rejuvenator. The relation of FTIR and LAS results indicates rejuvenation of aged bitumen with soybean oil reverses the aging process at a molecular level and, as a result, increases the fatigue life of the bitumen

    Optimizing Chemical & Rheological Properties of Rejuvenated Bitumen

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    Bitumen has long been a material used in the construction of roadways, yet new pavement only consists of low fractions of recycled materials due to poor compatibility of aged bitumen and new materials. Thus, rejuvenators, chemical additives, have been used in an attempt to re-balance the chemical composition and restore the physical properties of aged bitumen back to its virgin state. A fundamental understanding of how one particular rejuvenator, soybean oil, revitalizes bitumen was investigated using a multi-scale approach. Fourier-transform infrared spectroscopy (FTIR) was used to determine the changes in chemical properties of pure and rejuvenated virgin and aged samples. Samples were artificially short term aged using a rolling thin film oven (RTFO) procedure or long term aged using a pressure aging vessel (PAV). Rejuvenator concentrations were tested at both 7.5% and 15%. FTIR results reveal carbonyl (IC=O), sulfoxide (IS=O), branched aliphatic (IB), and aromatic (IAr) indices decrease in RTFO and PAV samples from rejuvenation with soybean oil, suggesting that the aging process in the aged bitumen has been reversed. A linear amplitude sweep (LAS), a mechanical procedure using a dynamic shear rheometer (DSR), was employed to investigate rheological properties. LAS analysis of PAV samples manifests fatigue resistances of bitumen samples increase at every applied shear strain as a result of increasing concentration of rejuvenator. The relation of FTIR and LAS results indicates rejuvenation of aged bitumen with soybean oil reverses the aging process at a molecular level and, as a result, increases the fatigue life of the bitumen

    Research on High-RAP Asphalt Mixtures with Rejuvenators - Phase II

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    A previous study by the authors have demonstrated effectiveness of three rejuvenators: R1 (triglyceride/fatty acid: agriculture-tech based), R2 (aromatic extract: petroleum-tech based), and R3 (tall oil: green-tech based) on rejuvenating properties of the aged binder. In that study, it was observed that the rejuvenators made high-RAP mixtures softer and more compliant, which may increase the rutting potential, while they simultaneously improve cracking resistance of the high-RAP materials. Research outcomes and findings from the previous study resulted in consequential research needs for more specific investigation of high-RAP mixtures with rejuvenators in order to achieve realistic implementation into future high-RAP paving projects in Nebraska. This study thus aimed to investigate the effects of type, dosage, and treating methods of rejuvenators when they are added in aged asphalt materials. To meet the goal, we used the three rejuvenators (R1, R2, and R3) by conducting various binder-level and mixture-level tests in this study. For the binder-level testing, the performance grading (PG) method was used to primarily determine proper dosages targeting desired binder grades, and two chemical tests (i.e., Fourier Transform Infrared and Saturates-Aromatics-Resins-Asphaltenes analysis) were also conducted to examine chemical characteristics altered by rejuvenation and further aging process. The selected dosage levels from the binder testing were then applied to asphalt concrete (AC) mixture-level performance evaluation by conducting two tests: flow number for rutting and semicircular bending fracture with and without moisture conditioning for cracking. AC mixtures treated with rejuvenators at the dosage levels selected from the binder PG testing showed improved fracture resistance compared to unrejuvenated mixtures. Test-analysis results also indicated that PG binder testing, although it can successfully determine the proper dosage range of rejuvenators, is limited by only assessing the effects of rejuvenators in mechanical properties, which can be better aided by integrating chemical characterization that provides a more in-depth material-specific rejuvenation process. In addition, it appears that rejuvenation methods (e.g., blending and/or curing) can alter performance of aged mixtures. Therefore, the selection of rejuvenators and their implementation into practice should be carried out by considering multiple aspects not only by its PG recovery

    Effects of Rejuvenators on High-RAP Mixtures Based on Laboratory Tests of Asphalt Concrete Mixtures and Fine Aggregate Matrix Mixtures

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    Although the linear viscoelastic stiffness, fracture characteristics, and permanent deformation behavior of AC mixtures can be determined through experiments, it is generally time-consuming and expensive to reach statistically repeatable results. Thus, it is attractive to pursue alternative methods that are cheaper, faster, and repeatable in order to efficiently evaluate and predict asphalt mixtures’ core mechanical characteristics (such as stiffness, fatigue, and plastic deformation)

    Evaluation of Thin Asphalt Overlay Pavement Preservation in Nebraska: Laboratory Tests, MEPDG, and LCCA (17-2624)

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    Thin asphalt overlays offer an economical resurfacing, preservation, and renewal paving solution for roads that require safety and smoothness improvements. Recently, thin asphalt overlays have been used in Nebraska as a promising pavement preservation technique that needs evaluations
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