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The present work investigates low-temperature cracking performance of fiber-reinforced asphalt concrete (FRAC) materials. Different asphalt mixtures containing various amounts of fiber were explored. Disk-shaped compact tension (DC(T)), indirect tensile (ID(T)), and acoustic emission (AE) tests were conducted to evaluate cracking performance of FRAC materials. In addition, the AE test was utilized to investigate low-temperature fracture in fiber-modified asphalt binders. Results demonstrated that incorporating fibers improved low-temperature cracking behavior of asphalt mixtures by increasing the fracture energy by 4.3% and tensile strength by 5.1% per ounce of fiber added to the material. Moreover, it was observed that presence of fibers enhanced fracture softening behavior of FRAC mixtures. Asphalt binder results showed that fiber-modified binders consistently exhibited lower embrittlement temperatures indicating higher resistance against thermal cracking. The AE hit counts in both FRAC mixtures and asphalt binders significantly decreased at the average rate of 8.3 and 9.6% per ounce of fiber added to mixtures and asphalt binders, respectively. Finally, a cracking performance prediction model was developed for FRAC materials using the machine learning elastic-net regression approach. [ABSTRACT FROM AUTHOR]

A novel approach for the fracture characterization of soft adhesive materials using spiral cracking patterns is presented in this study. This research particularly focuses on hydrocarbon polymeric materials, such as asphalt binders. Ten different asphalt materials with distinct fracture characteristics were investigated. An innovative integrated experimental–computational framework coupling acoustic emissions (AE) approach in conjunction with a machine learning-based Digital Image Analysis (DIA) method was employed to precisely determine the crack geometry and characterize the material fracture behavior. Cylindrical-shaped samples (25 mm in diameter and 20 mm in height) bonded to a rigid substrate were employed as the testing specimens. A cooling rate of −1 °C/min was applied to produce the spiral cracks. Various image processing techniques and machine learning algorithms such as Convolutional Neural Networks (CNNs) and regression were utilized in the DIA to automatically analyze the spiral patterns. A new parameter, "Spiral Cracking Energy (ESpiral)", was introduced to assess the fracture performance of soft adhesives. The compact tension (CT) test was conducted at −20 °C with a loading rate of 0.2 mm/min to determine the material's fracture energy (Gf). The embrittlement temperature (TEMB) of the material was measured by performing an AE test. This study explored the relationship between the spiral tightness parameter ("b"), ESpiral, Gf, and TEMB of the material. The findings of this study showed a strong positive correlation between the ESpiral and fracture energies of the asphalt materials. Furthermore, the results indicated that both the spiral tightness parameter ("b") and the embrittlement temperature (TEMB) were negatively correlated with the ESpiral and Gf parameters. [ABSTRACT FROM AUTHOR]

• Self-healing of thermal cracks in asphalt materials was investigated. • Acoustic emission and disk-shaped compact tension testing approaches were utilized. • The Felicity effect was observed indicating occurrence of self-healing in material. • Healing Index parameter was introduced to assess extent of self-healing in material. • Results showed occurrence of intrinsic healing at intermediate temperatures. 30% increase in HI% was observed due to 12 h of resting period between cooling cycles. As an intrinsic property of asphalt material, self-healing could reverse the cracking process in asphalt pavements and extend their service life. This study provides quantitative assessment of self-healing of thermally induced damage in asphalt concrete materials using Acoustic Emission (AE) as well as Disk-shaped Compact Tension (DCT) tests. Asphalt concrete specimens were subjected to eight cooling cycles and the effects of resting time between cooling cycles on self-healing were investigated. The AE test results showed gradual degradation in self-healing capability of asphalt mixtures as the material was exposed to increasing number of cooling cycles. In addition, AE results indicated that the 12 h resting time between cooling cycles significantly improved the self-healing by more than 30% and allowed the material to regain most of its self-healing capability. DC(T) results also showed that the fracture energies of asphalt mixtures were increased on the average by 13% due to the 12 h of resting time. DC(T) test results were consistent with the findings from the AE tests indicating that both approaches could successfully capture the effect of resting times on the material fracture properties. [ABSTRACT FROM AUTHOR]

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]

Low-temperature cracking is a major form of distress that can compromise the structural integrity of asphalt pavements located in cold regions. A review of an Acoustic Emission (AE)-based approach is presented that is capable of assessing the low-temperature cracking performance of asphalt binders and asphalt pavement materials through determining their embrittlement temperatures. A review of the background and fundamental aspects of the AE-based approach with a brief overview of its application to estimate low-temperature performance of unaged, short-term, and long-term aged binders, as well as asphalt materials, is presented. The application of asphalt pavements containing recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) materials to thermal cracking assessment is also presented and discussed. Using the Felicity effect, the approach is capable of evaluating the self-healing characteristics of asphalt pavements and the effect of cooling cycles upon their fracture behavior. Using an iterative AE source location technique, the approach is also used to evaluate the efficiency of rejuvenators, which can restore aged asphalt pavements to their original crack-resistant state. Results indicate that AE allows for relatively rapid and inexpensive characterization of pavement materials and can be used towards enhancing pavement sustainability and resiliency to thermal loading. [ABSTRACT FROM AUTHOR]

An acoustic-emission approach to evaluate the low-temperature cracking performance of asphalt binders is presented. The acoustic activity of a thin film of asphalt binder bonded to a granite substrate is monitored while the layer is exposed to decreasing temperatures from around 20°C to approximately -50°C. Results of eight different asphalt binders at three different aging levels, i.e., unaged (TANK), short-term aged (RTFO), and long-term aged (PAV), are presented. The acoustic emission (AE) embrittlement temperatures are found to be sensitive to binder type as well as binder aging level. Results show that for most binders, their AE-based embrittlement temperature is a few degrees lower than their bending beam rheometer (BBR) critical cracking temperatures. [ABSTRACT FROM AUTHOR]

The present work for the first time reports observations and modeling to characterize three-dimensional spiral-shaped fracture patterns in a bi-axially stressed layer of asphalt material bonded to an aluminum substrate. Five different asphalt materials with different fracture characteristics are investigated. A logarithmic spiral model was found to mathematically represent the 3D helix-shaped cracks observed. A spiral tightness parameter is proposed for the characterization of spiral fracture patterns in asphalt. Results of acoustic emission and compact tension tests are also presented and employed in the evaluation of observed spiral cracks. The shape of spirals are found to be influenced by the fracture properties of the asphalt materials tested and appear to be independent of the thickness and shape of the test sample. The embrittlement temperature and fracture energy of tested asphalt materials were found to correspond to the characteristic parameters of spiral cracks. [ABSTRACT FROM AUTHOR]

An acoustic emission (AE) approach to evaluate the effectiveness of rejuvenators in restoring aged asphalt concrete to its low-temperature performance grade is presented. Specimens, oven-aged for 36 h at 135 °C, were treated with rejuvenators (10% of binder weight). After 2, 4, 6, and 8 weeks of dwell time, the specimens were tested using AE while being cooled down to −35 °C. It was observed that after four weeks of dwell time, the rejuvenated-treated specimens had recuperated the original embrittlement temperatures. After eight weeks, the specimens’ embrittlement temperature were about three grades (∼18 °C) lower than those of the aged temperatures. [ABSTRACT FROM AUTHOR]

The present study focuses on the application of an acoustic emission (AE) based laboratory test to evaluate low-temperature cracking performance of several types of asphalt materials in the context of a recently completed national pooled fund study on low-temperature cracking (LTC). Comparisons are made between AE test results and the critical cracking temperature of asphalt binders determined from Bending Beam Rheometer (BBR) test and Direct Tension Test (DTT), which are in turn compared to field observed thermal cracking in the corresponding test sections. Based upon our findings, recommendations are made as to the potential use of the AE-based technique in asphalt binder specification. [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]

Highlights: [•] The results supported the use of RAS modified mixtures in warm climates. [•] The warmer embrittlement temperatures due to RAS is critical in cold climates. [•] Nodules of RAS form due to partial blending between the RAS and virgin binders. [•] RAS nodules accumulate damage first and thus govern the embrittlement temperature. [•] Higher RAS content leads to higher peak loads and lower fracture energy in DC(T) test. [Copyright &y& Elsevier]

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]

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]