Search

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. [ABSTRACT FROM PUBLISHER]

Mechanism of fracture in a viscoelastic heterogeneous composite with thermo-rheological properties such as, asphalt mixture is quite involved and cannot be correctly simulated with simpler linear elastic fracture mechanics constitutive laws. Over the last decade and half, a number of researchers have adopted use of cohesive zone (CZ) fracture models for simulation of fracture in asphalt mixtures. CZ interface elements are utilised in finite element (FE) models for representation of crack path, these elements follow traction- displacement relationships that allow for gradually degrading traction capabilities along the crack path with increasing level of crack opening. This paper presents a review of CZ modelling approach for simulation of asphalt pavement and overlay cracking performances. Suitability of CZ modelling approach for capturing discrete fracture in asphalt mixtures at low temperatures is presented through simulation of lab scale test. An example is also presented to demonstrate applicability of CZ-based modelling effort in capturing the crack initiation and propagation in asphalt mixtures at low temperatures. Thereafter, an FE-based pavement simulation approach is discussed that can be utilised in design of asphalt overlays to lower the propensity of reflective cracking. A case study of designing asphalt overlay systems for four real-life pavements in Minnesota is presented to demonstrate the applicability of the CZ-based modelling approach in conducting mechanistic design of asphalt overlays. [ABSTRACT FROM AUTHOR]

Towards developing a method capable to assess the efficiency of rejuvenators to restore embrittlement temperatures of oxidized asphalt binders towards their original, i.e., unaged values, three gyratory compacted specimens were manufactured with mixtures oven-aged for 36 hours at 135°C. In addition, one gyratory compacted specimen manufactured using a short-term ovenaged mixture for two hours at 155°C was used for control to simulate aging during plant production. Each of these four gyratory compacted specimens was then cut into two cylindrical specimen 5 cm thick for a total of six 36-hour oven-aged specimens and two short-term aging specimens. Two specimens aged for 36 hours and the two short-term specimens were tested using an acoustic emission approach to obtain base acoustic emission response of short-term and severelyaged specimens. The remaining four specimens oven-aged for 36 hours were then treated by spreading their top surface with rejuvenator in the amount of 10% of the binder by weight. These four specimens were then tested using the same acoustic emission approach after two, four, six, and eight weeks of dwell time. It was observed that the embrittlement temperatures of the short-term aged and severely oven-aged specimens were -25°C and -15°C, respectively. It was also observed that after four weeks of dwell time, the rejuvenator-treated samples had recuperated the original embrittlement temperatures. In addition, it was also observed that the rejuvenator kept acting upon the binder after four weeks of dwell time; at eight weeks of dwell time, the specimens had an embrittlement temperature about one grade cooler than the embrittlement temperature corresponding to the short-term aged specimen. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) have become the primary methods for enhancing sustainability in the asphalt industry in recent years. To further enhance sustainability benefits, asphalt producers have begun using RAP and WMA in combination. Research to date has focused on evaluating WMA-RAP mixtures in terms of moisture sensitivity and permanent deformation characteristics as measured in laboratory performance tests. In the present paper, the authors investigate a set of WMA mixtures that encompass a variety of variables, including four WMA additives (Evotherm 3G, Rediset LQ, Sasobit, and Advera) and three RAP contents (0, 15, and 45%). A common belief among practitioners is that the reduced aging in the asphalt binder associated with lower production temperatures in WMA mixtures leaves additional headroom for the incorporation of higher amounts of RAP, which is generally a stiffer, more brittle material. To fully characterize the performance of WMA-RAP mixtures, the authors evaluated the low-temperature, cracking behavior of these mixtures in conjunction with moisture and rutting resistance characterization. They achieved the low temperature testing of WMA-RAP mixtures through the disk-shaped compact tension [DC(T)], indirect tension (IDT) creep compliance, and acoustic emission (AE) tests. Test results showed that chemical additives improved moisture susceptibility according to the AASHTO T 283 standard test and fracture and bulk stress relaxation characteristics using the DC(T) and IDT tests, respectively. The organic Fischer-Tropsch wax-modified WMA mixtures performed the best among the WMA mixtures in terms of rutting resistance. The introduction of RAP led to the increased resistance to permanent deformation and moisture damage. Conversely, RAP reduced thermal cracking resistance according to the low-temperature performance tests in both HMA and WMA. The authors observed the same trend in AE test results as WMA-RAP mixtures exhibited warmer embrittlement temperatures as compared with control mixtures and are therefore expected to be more prone to thermal cracking. On the basis of these findings, thermal cracking resistance remains an issue to be considered in WMA mixtures containing RAP. Additionally, performance testing has shown to be a valuable tool for the evaluation of RAP and WMA mix designs to avoid performance issues in the field. [ABSTRACT FROM AUTHOR]

The use of recycled asphalt pavement (RAP) in hot-mix asphalt leads to significant environmental and economical benefits. The major benefits are realized through reduced demand for new or virgin aggregates and asphalt binders. A limited amount of research has been performed to investigate the effects of RAP on the low temperature fracture characteristics of asphalt mixtures. However, this is an important subject, since the inclusion of RAP in Hot-Mix Asphalt (HMA) has the potential to increase mixture stiffness and brittleness unless properly compensated for. Most design procedures for mixtures consisting of RAP recommend an asphalt binder grade adjustment to compensate for the aged binder through the use of a softer virgin binder. This study evaluates the validity of this grade adjustment procedure in the context of four RAP materials using mixture fracture testing. The RAP materials used in this study were chosen from a larger database of materials to represent a wide variety of binder aging levels. Various fracture tests for asphalt concrete were identified through literature review. The disk-shaped compact tension (DC(T)) test, as standardized in ASTM D7313-07b, was used in this study to characterize mixture fracture energy. DC(T) fracture tests were conducted on various asphalt mixtures, namely: a control mixture with no RAP, manufactured with PG 64-22 asphalt binder; four mixtures containing 30% RAP from different sources, with an adjusted virgin binder grade of PG 58-28, and; a reference mixture containing no RAP, manufactured using PG 58-28 binder. The test results indicate significant reduction in the fracture energy of asphalt mixtures with 30% RAP and no virgin binder grade compensation. The reduction in fracture energy was surprisingly consistent between the four RAP sources irrespective of the significantly different RAP binder stiffnesses that were determined to be present in these mixtures through binder recovery and testing. However, when the RAP mixtures were produced using a softer virgin binder (PG 58-28), the measured fracture energy was higher than the control mixture. The study provides some assurance that adequate cracking resistance can be maintained in mixtures containing 30% RAP when designed properly, and demonstrates how fracture testing with ASTM D7313-07b can be used in the design and control of RAP mixtures, particularly where cracking is of concern. [ABSTRACT FROM AUTHOR]

Asphalt concrete is one of the most widely used materials in transportation infrastructure, covering the surface of approximately 94% of more than 4 million miles of highways in United States. Asphalt pavements located in cold regions or in milder climate areas with large daily temperature fluctuations encounter thermal cracking manifesting itself in the form of several transversely oriented surface-initiated top-down cracks of various lengths and widths. Self-healing as an intrinsic property of asphalt materials mitigates the thermal cracking process in asphalt pavements and extends pavements' service life. However, self-healing properties of asphalt pavement gradually diminishes with aging. The present study utilizes the Acoustic Emission (AE) technique and the fracture-based Disk-shaped Compact Tension (DCT) test to provide quantitative assessment of self-healing of thermally-induced damage in asphalt concrete materials at the micro (AE test) as well as macro (DCT test) levels. Asphalt concrete specimens were subjected to eight controlled cooling cycles and effects of resting, i.e., dwell time, between cooling cycles on self-healing were investigated. The Felicity effect phenomenon was observed in this study indicating occurrence of self-healing in the material. The AE test results showed gradual degradation in self-healing capability of asphalt mixtures as the material was exposed to cooling cycles. However, it was observed that the rate of self-healing degradation was not constant as it was higher at the beginning and then gradually reduced until it reached almost zero after the fourth cooling cycle. Moreover, AE results also indicated that the 12 hours dwell time between cooling cycles significantly increased the self-healing by more than 30% and allowed the material to regain most of its self-healing capabilities. DC(T) fracture energy results were consistent with the findings from AE test. Results also demonstrated that, on the average, 12 hours resting time increased fracture energies of asphalt mixtures by about 13%. [ABSTRACT FROM AUTHOR]

Thin bonded wearing courses (TBWC) provide an efficient treatment option for deteriorated rigid and flexible pavement systems. As a surfacing layer placed over existing, deteriorated pavement, the overlay system should be designed to resist various forms of cracking, including: thermal, block, reflective, and top-down. Recent developments in fracture testing and numerical simulation techniques have provided stronger links between material fracture properties and field cracking performances of asphalt pavements. However, little work has been directed towards applying these tools to thin bonded wearing courses and overlay systems, This paper describes fracture characterization of TBWC through testing of cored field samples and laboratory prepared specimens. The fracture characterization was performed using the ASTM D7313-07b test protocol, which is currently one of the most widely utilized test specifications for low temperature fracture energy measurement of asphalt concrete. Laboratory samples were prepared to evaluate the effects of the tack-coat application rate, compaction effort (air void level), and overlay thickness on the fracture properties of the gap-graded asphalt concrete mixes and TBWC. The fracture energy results for field cores are compared with laboratory compacted specimens of plant produced hot-mix asphalt mixture, which was sampled during construction. Moreover comparisons of fracture toughness are made between typical dense-graded asphalt mixtures, laboratory compacted gap-graded mixture, and TBWC samples, The results indicate a higher fracture resistance of the gap-graded TBWC when compared to the typical wearing course mixtures. This is a significant finding since the greater air void levels of gap-graded mixtures are typically associated with lower fracture toughness. More work is needed to further explore the fracture behavior in TBWC, especially to study the effects of crack propagation orientation. The fracture characterization results and the testing techniques presented herein provide a laboratory analysis tool for design, control, and characterization of TBWC. [ABSTRACT FROM AUTHOR]