Reclaimed Asphalt Shingles Research Articles

Morphological and Nanomechanical Characterization of Industrial and Agricultural Waste–Modified Asphalt Binders

AbstractFor the past several decades, researchers around the world have used nanoindentation techniques to characterize different materials for biological, medical, and polymer science applications. In recent years, nanoindentation techniques have been explored by some pavement professionals to characterize asphalt materials. This study used the atomic force microscope (AFM)–based PeakForce quantitative nanomechanical mapping (PFQNM) technique to evaluate nanoscopic properties of asphalt binders modified with four different types of industrial and agricultural waste materials, which included ground tire rubber (GTR), reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and rice husk ash (RHA). Three scan sizes (20 × 20, 10 × 10, and 5 × 5 µm) were used to map the properties of the aforementioned binder samples. Mechanistic properties such as adhesion, energy dissipation, deformation, and Derjaguin, Muller, and Toropov (DMT) moduli of modified binder samples were estimated at different morph...

Evaluation of low temperature viscoelastic properties and fracture behavior of bio-asphalt mixtures

The overall national emphasis on sustainability in pavement construction has led to the promotion of recycled materials such as reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles. In general, the inclusion of these materials has led to reduced performance at low temperatures leading to thermal cracking. Previous research by the authors showed that the application of bio-binder from swine manure could alleviate the effect of RAP while improving the overall low temperature bulk viscoelastic and fracture properties of the asphalt mixture. The current paper expands on the previous research on bio-modified asphalt mixtures by investigating three additional bio-asphalts produced by introducing wood, miscanthus and corn stover based bio-oils to a neat asphalt. These bio-asphalt mixtures were introduced in both virgin and reclaimed asphalt pavement mixtures to evaluate interaction between the bio-oils and reclaimed asphalt pavement, with a focus on properties related to low temperature pavement performance. Low temperature characterization was conducted using disk-shaped compact tension fracture (DC(T)) and indirect tension (IDT) bulk viscoelastic characterization tests. The IDT test, completed in accordance with AASHTO T-322, evaluated the creep compliance of mixtures at 0, −12 and −24 °C to examine the ability of the mixture to relax thermal stress development. The DC(T) test was completed according to ASTM D-7313 to determine the fracture energy of the mixtures at −12 °C. Test results demonstrate that the bio-asphalt mixtures had superior physical properties in terms of fracture resistance and creep compliance. Furthermore, the effect of increased RAP contents was less detrimental to low temperature properties in the bio-asphalt mixtures as compared to the reference hot-mix asphalt mixture.

Laboratory characterisation of asphalt mixes containing RAP and RAS

Due to its economic and environmental benefits, using reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in new hot-mix asphalt (HMA) has become an integral part of today's asphalt industry. The advantages of using RAP and RAS in HMA are not limited to economic and environmental benefits, and may result in improving a number of mix performance characteristics including rutting and resistance to moisture-induced damage. Despite aforementioned benefits, concerns over premature pavement distresses resulting from using RAP and RAS limit their usage in HMA. Furthermore, because of the lack of mechanistic performance data, use of new mixes containing RAP and RAS remains limited. Therefore, the present study was undertaken to investigate the effects of using different amounts of RAP and RAS on laboratory performance of HMA, and to generate valuable input design parameters for implementation of the mechanistic-empirical pavement design guide (M-EPDG), using local materials. Four types of base course mixes containing 0% RAP, 25% RAP, 40% RAP and 20% RAP+5% RAS, and three types of surface course mixes containing 0% RAP, 25% RAP and 20% RAP+5% RAS were tested. Laboratory tests were conducted to evaluate stiffness, low-temperature cracking, fatigue life, rut and moisture-induced damage potential of the mixes. It was found that dynamic modulus and creep compliance of the asphalt mixes increase and decrease, respectively, with an increase in the amount of RAP and/or RAS used in the mix. Fatigue life was found to increase with increasing RAP content up to 25%, and to decrease when the RAP and/or RAS content exceeded 25%, or when RAS was used in the mix. It should be noted that this conclusion was drawn based on a 15% increment in RAP content. Hamburg wheel tracking (HWT) test results showed increased resistance to rutting and moisture-induced damage, with an increase in the amount of RAP and/or RAS. However, the tensile strength ratio test results were not confirmed by HWT. The findings of this study are expected to be helpful in understanding the effects of using different amounts of RAP and RAS on the performance of asphalt mixes produced using local materials. Furthermore, valuable design input parameters, developed in this study for new mixes containing RAP and RAS, may be used for calibration of the M-EPDG input parameters, with local materials.

Laboratory Performance of Asphalt Mixtures Containing Recycled Asphalt Shingles

The use of recycled asphalt shingles (RAS) as a partial replacement for petroleum-based virgin asphalt binder has received considerable attention in recent years. The objective of this study was to conduct a comprehensive laboratory evaluation of asphalt mixtures containing RAS, including stone mastic asphalt. Mixes were designed to meet Superpave® design criteria. A suite of laboratory tests was conducted to capture the mechanistic behavior of the mixtures against major distresses. Laboratory testing evaluated rutting performance, moisture resistance, and fracture resistance of laboratory produced mixtures by using the Hamburg loaded wheel-tracking test, semicircular bending test, and thermal stress restrained specimen tensile strength test. Results of the experimental program indicated that the draft revision of AASHTO PP 53, Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in New Hot-Mix Asphalt, overestimated the shingle asphalt binder availability factor. In addition, asphalt mixtures containing 5% RAS performed as well as the control asphalt mixture containing no RAS at high, intermediate, and low temperatures. Furthermore, the inclusion of RAS showed an improvement in rutting performance by resulting in a lower rut depth as compared with the control mixture containing no RAS.

An evaluation of reclaimed asphalt shingles in hot mix asphalt by varying sources and quantity of reclaimed asphalt shingles

The practice of incorporating reclaimed asphalt pavement (RAP) into hot mix asphalt (HMA) is common within the paving industry as a cost-effective source of quality paving binder and aggregate. Recently, research efforts have focussed on investigating the potential of using reclaimed asphalt shingles (RAS) in HMA. This study provides a comparison of the laboratory performance of several HMA mixtures with varied RAS sources and contents. Performance testing for the mixtures included dynamic modulus and phase angle. Fatigue testing was also performed for several of the mixtures. Mixtures with higher amounts of binder replacement from RAS showed stiffer performance at high temperatures and less stiff performance at low temperatures. The mixture with greater amounts of RAS showed better fatigue performance. The mixtures with various sources of RAS, whether pre- or post-consumer, showed similar low-temperature performance, while the mixture with a blend of both sources was stiffest at high temperatures. A set of mixtures comparing different RAS sources was also compared with a mixture containing RAP as the only recycled binder source. The results of testing of these mixtures showed that the RAP mix was stiffer at intermediate and high temperatures but had similar results to the RAS mixtures in low-temperature performance.

Evaluating the effect of rejuvenators on the degree of blending and performance of high RAP, RAS, and RAP/RAS mixtures

The objective of this study was to examine if asphalt rejuvenators can offset the stiffness attributed by the hardened binder from reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in mixtures that incorporate high RAP and RAS content without adverse impact on the performance of the mixtures. Also, to assess, if rejuvenators can help the hardened binder from the RAP/RAS comingle with the virgin binder. Overall, the results showed that asphalt rejuvenators can mitigate the stiffness of the resultant binder. The cracking characteristics of the mixture improved by the addition of the rejuvenators, however, the rutting and moisture susceptibility were adversely impacted at the dosage and the testing conditions used. Also, the tests results at 4°C generally showed that there was blending of the rejuvenated and virgin binder, however, no conclusion could be made at the higher temperatures.

Permanent Deformation Characterization of Asphalt Mixtures by Using Incremental Repeated Load Testing

Currently, flow number (FN) is being used for measuring the permanent deformation resistance of asphalt mixtures. The provisional AASHTO TP 79 test method specifies the requirements of the FN test; however, there are undefined levels of test variables, such as temperature, axial stress, and confinement. Agreeable FN criteria that can reliably discriminate between various mixtures have not been established. As the asphalt industry continues to develop more sophisticated mixtures (warm mix, reclaimed asphalt pavement, and reclaimed asphalt shingles), the FN value has failed to capture the true complexity of the asphalt mixtures. These shortcomings and the unpredictable testing time of the FN test have affected its usefulness for evaluating high-temperature performance of asphalt mixtures. A new test procedure for evaluation of the rutting susceptibility of asphalt mixtures is being proposed. The new procedure is conducted at one temperature and three stresses on the same replicate in three increments of 500 cycles and takes only 25 min to complete. The property of the test is the permanent strain attributable to the last cycle of each test increment (minimum strain rate, MSR). A master curve is developed by plotting the MSR values versus parameter TP, which is a product of temperature and pressure. The MSR master curve represents the unit rutting damage (rut per axle) of asphalt mixtures at any stress and temperature and can be used in the laboratory for material characterization, mix design verification, mixture ranking, or pavement design applications to predict rut depth for project climate and design traffic.

An Evaluation of Reclaimed Asphalt Shingles for Beneficial Reuse in Roadway Construction

Abstract A large-scale recycling and reuse application of scrap shingles would utilize an otherwise wasted resource while clearing landfill space and creating new business opportunities. One potential reuse application is the use of reclaimed asphalt shingles (RAS) as an additive or substitute for the earth materials typically used in the aggregate base (AB) and subbase (ASB) layers of roadway pavements. The purpose of this study was to determine the technical specifications of RAS, the effect of fly ash stabilization on RAS strength, and the practicality of the widespread implementation of RAS in the AB and ASB layers of roadway pavements. RAS, fly ash stabilized RAS (S-RAS), RAS-aggregate mixtures, and RAS-silt mixtures were evaluated for particle size characteristics, compaction characteristics, CA Bearing Ratio (CBR), unconfined compressive strength, and resilient modulus. According to the results of the testing protocol, unstabilized RAS is unsuitable as base material although RAS could potentially be used as subbase or general fill material. RAS-aggregate mixtures are suitable for use as subbase and are potentially suitable as base course in an unstabilized state; however, RAS-aggregate mixtures exhibited decreasing resilient modulus with increasing RAS content. Fly ash stabilized RAS (S-RAS) was less susceptible to penetrative deformation than unstabilized RAS, however, S-RAS was still highly susceptible to penetrative deformation when unpaved. Fly ash stabilization of RAS generally provided less improvement in resilient modulus compared to fly ash stabilized low-plasticity clays. This may be due to the high asphalt content of RAS particles and resulting diminishment in pozzolanic activity and/or the diminished particle interconnectedness for cementation. Other forms of stabilization, such as cold asphalt emulsion, may be more effective in strengthening RAS. Further evaluation of alternative stabilization methods and additional studies to evaluate the practicality of RAS in other geotechnical applications such as embankment fill, filter, and/or drainage material are recommended.