Asphalt aging is recognised as one of the important factors causing cracking related failures in asphalt pavements. Asphalt aging occurs during production, construction, and service life of the ...asphalt surfaced pavements. Since constituents of asphalt mixtures are continuously increasing (increased recycled asphalt pavement (RAP), rejuvenators, compaction aids, warm-mix additives, fibres, etc.) and interactions between these constituents are complicating the mixture design process, relying solely on the volumetric mixture design is usually not resulting in asphalt mixtures with the highest possible performance. Thus, asphalt mixture test methods for rutting and cracking should be improved and incorporated into current mixture design methods to be able to develop more durable asphalt mixtures that last for their intended service lives. In this study, the most effective asphalt mixture long-term aging protocol was determined to achieve reliable semi-circular bend (SCB) test parameters that are correlated with in-situ cracking performance. The selected aging protocol will be integrated into the balanced mix design procedures that are currently being developed. Developed asphalt mixture design methods are expected to improve the longevity of asphalt materials, reduce life-cycle costs for agencies, and improve long-term road users' comfort.
AbstractFatigue cracking performance of asphalt mixtures is highly influenced by the binder and air-void contents, binder grade, binder modification, volumetrics, recycled asphalt pavement/reclaimed ...asphalt shingles (RAP/RAS) content, and aging. In Oregon, asphalt pavements commonly fail prematurely due to cracking-related distresses, necessitating costly rehabilitation and maintenance at intervals of less than half of the intended design lives in some cases. This study focuses on characterizing the cracking performance of asphalt mixtures used in Oregon by evaluating the impact of asphalt mixture variables, such as binder content, air-void content, aggregate gradation, and polymer modification, on cracking and rutting performance using semicircular bend (SCB) and flow number (FN) tests, respectively. The goal of this study is to provide a better decision-making structure during the pavement design stage to address fatigue cracking susceptibility, with the intent of avoiding premature pavement failure and expensive early maintenance and rehabilitation. Increased binder content improved the cracking performance, suggesting that increasing binder content of asphalt mixtures currently used in Oregon can create significant savings by improving pavement longevity. Additionally, reducing the density increases cracking performance; therefore, producing asphalt mixtures that are easy to compact and utilizing intelligent compaction technologies that are currently being implemented in Oregon can potentially create a significant improvement in the fatigue cracking resistance of asphalt mixtures.
Recycling highway construction materials and minimising the use of virgin materials can reduce the pavement life cycle costs, improve highway network condition, conserve natural resources, and ...protect the environment. However, aged binder in reclaimed asphalt pavement (RAP) and recycled asphalt shingle (RAS) makes asphalt pavements more brittle and creates long-term durability problems. In this study, the performance benefits of using softer virgin binder grade and increased virgin binder content strategies in RAP and RAS mixture production in Oregon were quantified. Semi-circular bend and flow number tests were conducted on prepared samples in laboratory to assess their cracking and rutting performance with low or no RAP (0% and 15%), high RAP (30% and 40%), and RAP&RAS, three binder contents (total binder contents with RAP/RAS and virgin binder - 6%, 6.4%, and 6.8%), and three binder grades (PG 58-34, PG 64-22, and PG 76-22). Moreover, possible combinations of RAP/RAS content, binder content, and binder grade to produce asphalt mixtures with high cracking and rutting performances were suggested using regression modelling and sensitivity analysis. The results of this study show that increasing binder content does not create any significant impact on the cracking performance of RAP&RAS mixtures but it is an effective strategy to improve the fatigue cracking resistance of 30% and 40% RAP mixtures.
AbstractIn the context of urban heat islands (UHI), sustainable solutions are being devised to craft greener built environments such as cooler roofs and pavements mainly to counter a variation of ...thermal flux within the urban climates. Modification of the pavement thermal properties is a potential strategy to render pavements cooler with different cooling mechanisms. The thermal behavior of pavements is largely dependent on the different but interactive thermal properties of pavement materials such as thermal conductivity, specific heat capacity, density, albedo, thermal emissivity, and not on one single property alone. The objective of this research study was to investigate the thermophysical properties of different pavement systems through the development of a comprehensive methodology that can quantify contribution of thermal properties on urban climates from laboratory-based measurements. Six different paving mixtures including conventional dense-graded, asphalt-rubber, and cement concrete mixes were prepared encompassing 96 sample data points for the experimental program. With an increase in specific heat capacity, thermal conductivity, thermal diffusivity, and albedo, there was a decrease in the maximum pavement surface temperature of the various mixes. Although the investigation of thermal behavior of pavement materials is complex in nature, this laboratory study has attempted to investigate all major thermophysical properties of different pavement systems in a comprehensive manner. It is envisioned that this research study will help advance the state of the art and knowledge related to pavements’ selection and contribution to urban climates, and in recommending a suitable UHI mitigation strategy from the pavements’ perspective.
•SCB and IDT tests are the most reliable tests to evaluate fatigue cracking.•Flexibility index parameter is effective in differentiating cracking resistance.•Mixing method does not have significant ...effect on measured cracking performance.•Compaction method significantly affects the measured cracking resistance.
Cracking is a common failure mechanism in asphalt concrete pavement structures. It is one of the main reasons for large road maintenance and rehabilitation expenditures, as well as reduced user comfort and increased fuel consumption due to high road roughness. The resistance of the pavement to this distress mechanism is dependent upon the ductility of the asphalt pavement mixture. The use of recycled asphalt materials in asphalt mixtures are also becoming increasingly common. A drawback of this practice is a reduction in ductility of the asphalt mixture, which causes a significant reduction in the fatigue life of the pavement in many cases. In Oregon, asphalt pavements are commonly failing prematurely due to cracking-related distresses, necessitating costly rehabilitation and maintenance at intervals of less than half of the intended design lives in some cases. For this reason, it is necessary to accurately quantify the impact of increasing the recycled asphalt content in asphalt pavement on the structural cracking resistance of the pavement through the use of low-cost and efficient testing procedures that can be implemented easily. This study focuses on characterizing the cracking performance of asphalt pavements in Oregon by considering four tests commonly used to evaluate fatigue cracking resistance and proposing the implementation of the most cost-effective and efficient test procedure for agencies and contractors.
The tack coat is a bonding agent applied between new and existing asphalt pavement layers. Roadway construction operations inherently introduce adverse conditions, such as dust on the pavement ...surface and nonuniform coverage (streaking), which can compromise tack coat bond quality. Climatic conditions such as heavy rainfall also create issues late in the construction season. Newly developed engineered tack coat emulsions, which utilize stiff asphalt binders and polymer modifiers, are purported to improve interlayer bonding characteristics and reduce the propensity of early fatigue cracking and pavement failure. This study evaluates engineered tack coats against conventionally used tack coats in a laboratory setting to identify their benefits when subjected to different pavement surface types, application rates, and commonly experienced adverse roadway construction conditions. Monotonic direct shear testing was employed to characterize interlayer bonding using two response parameters, interlayer shear strength and interlayer bond energy. This study advances the knowledge of engineered tack coat performance under real-world conditions and also employs a laboratory sample preparation methodology that is representative of pavement construction in the field.
Most state Departments of Transportation (DOTs) and asphalt contractors do not think that commonly used asphalt mixture properties, such as voids in mineral aggregate (VMA), voids filled with asphalt ...(VFA), and dust-to-binder ratio, reflect the long-term performance of asphalt mixtures. In addition, there are several new additives, polymers, rubbers, and high-quality binder types incorporated into asphalt mixtures today. Volumetric mixture design methods are not capable of capturing the benefits of using all these new technologies on asphalt mixture performance. Furthermore, the interaction of virgin binders with reclaimed asphalt pavement (RAP) mixtures with high binder replacement contents and the level of RAP binder blending into the asphalt mixture are still not well understood. Because of all these complications related to the more complex structure of asphalt mixtures, simple volumetric evaluations to determine the optimum binder content may not result in reliable asphalt mixture designs. Two volumetrically identical mixtures may provide completely different rutting and cracking performance according to laboratory tests. For all these reasons, in this study performance tests for rutting and cracking are incorporated into current asphalt mixture design methods to make it possible to validate or revise the optimum binder content determined by the volumetric mix design method (the only method currently used for asphalt mix design).
Deterioration of the concrete bridge deck is one of the most significant problems affecting the service life of bridges in the United States (U.S.). The early failure of asphalt pavement overlays on ...concrete bridge decks with spray-on waterproofing membranes has been recognized as a significant issue by the Oregon Department of Transportation (ODOT). Potential reasons for the failure of the asphalt overlays were thought to be the poor adhesion between the waterproofing membrane and the asphalt-wearing course, and the material properties of the asphalt layer. Moisture penetration into the asphalt overlay and standing water on the concrete bridge deck result in expansion and contraction at the interface on the bridge deck during freeze-thaw cycles. Expansion and contraction because of freeze-thaw cycles cause debonding at the interface and result in an increased rate of deterioration for the asphalt concrete overlay. Additionally, the de-icing salts used to prevent hazardous roadway surfaces in the winter permeate into the deck and cause corrosion of the steel reinforcement, weakening the structural integrity of the bridge. The main goal of this study is to develop an impermeable asphalt mixture with high cracking and rutting resistance that can seal and protect the concrete bridge deck by preventing water and de-icing salts from penetrating into the concrete deck. Permeability of developed asphalt mixtures was quantified by permeability testing and moisture sensor measurements. Rutting and cracking resistance of the developed impermeable asphalt mixture strategies were also evaluated by conducting flow number (FN) and semi-circular bend (SCB) tests in the laboratory.
•Established pavement temperature predictive models using thermophysical properties.•Utilized conventional and modified asphalt and cement concrete paving mixtures.•Correlated thermophysical ...properties with pavement temperature predictions.•Validated predictive models with field test results that had excellent correlations.•Adjudged models to be robust tools to assess urban climates in built environment.
This study developed pavement temperature predictive models based on the characterized thermophysical properties of different pavements to assess urban climates in the built environment. A database comprising of six pavement types including conventional and modified asphalt, and cement concrete mixtures was available with their thermophysical properties: specific heat capacity, thermal conductivity and material density. Models were developed to predict temperature at the surface, and at 40mm depth using the measured thermophysical properties, and recorded climatological parameters: air temperature, wind speed, and relative humidity. The two predictive models were robust and rational depicted by low bias and high precision. An increase in heat capacity increased pavement surface temperature indicating that higher energy is required to raise the pavement temperature, and also be able to release as much energy as stored, which would be best suitable at different times of the day to counter urban heat island (UHI) effects. An increase in thermal conductivity decreased pavement temperature illustrating that the pavement would store more heat within the system for a longer duration, and may release this heat at a particular timeframe changing the urban climate at that moment. An increase in wind speed by about 1m/s increased pavement temperature by 1°C, and this may increase UHI if there is already higher temperature in the environment. Overall, based on rational correlations between model predictions and actual field measurements it is recommended that the pavement temperatures of the systems be comfortably predicted for pavements using the developed models.
