For performance-based specifications and design processes, a number of cracking-related index parameters have been proposed for asphalt mixtures in recent years. A number of these parameters have been developed to utilise results from fracture tests. This study conducted a comprehensive evaluation of various fracture index parameters including fracture energy, Illinois flexibility index, stress intensity factor and toughness index. Over 200 tests from 61 distinct test data sets representing 21 asphalt mixtures are included. The focus of this study is on low-temperature cracking and all indices were evaluated using test results from the disk-shaped compact tension fracture tests conducted at low temperatures. The objective of this study was to determine if there is a relationship between various fracture index parameters as well as to determine typical measurement variability associated with each parameter. Comparisons were made between different indices and correlations were determined for the mix rankings provided by individual indices. The results indicate that fracture energy successfully captured the mix rankings and showed a strong correlation with other indices. In order to better capture post-peak softening behaviour of asphalt mixtures, the flexibility and toughness indices have been utilised; however, these parameters were found to have high variability. A new index called fracture strain tolerance has been proposed that was shown to provide the same level of distinction between mixtures as the flexibility and toughness indices while having considerably lower variability. Finally, several areas were identified for future extension of this research.

The need for a viscoelastic characterisation of hot mix asphalt is increasing as advanced testing and modelling is incorporated through mechanistic-empirical pavement design and performance-based specifications. Viscoelastic characterisation includes measurement of the mixture stiffness and relative proportion of elastic and viscous response. The most common method is to measure the complex modulus, where dynamic modulus represents the stiffness and the phase angle represents the relative extent of elastic and viscous response. Determination of phase angle from temperature and frequency sweep tests has been challenging, unreliable and prone to error due to a high degree of variability and sensitivity to signal noise. There are also large amounts of historical dynamic modulus data that are either missing phase angle measurements or have poorly measured phase angle data that inhibit their use in further evaluation. This paper evaluates the robustness of phase angle estimation from stiffness data for asphalt mixtures. The objectives of the study are to: (1) evaluate the procedure of estimating phase angle from the slope of log-log stiffness master curve fitted with a generalised logistic sigmoidal curve and compare it with lab measurements and the Hirsch model; (2) assess the effect of measured and predicted phase angles on a mixture Black Space diagram; (3) evaluate the effect of using predicted phase angles on SVECD fatigue analysis particularly regarding damage characteristics curves and fatigue coefficients and (4) evaluate the impact on layered viscoelastic pavement analysis for critical distresses (LVECD) pavement fatigue performance evaluation due to the use of predicted phase angles. Three sets of independent mixtures were evaluated in this study comprising a wide range of mixture conditions. The results indicate good agreement between measured and predicted phase angle values in terms of shape and peak master curve values. In terms of magnitude, the values from both matched very well for certain sets of mixtures and subsequently manifested in similar performance predictions. However, for other sets of mixtures, a considerable difference was observed between measured and predicted phase angle values as well as SVECD and LVECD results. The differences may be attributed to the use of different types of linear variable displacement transducers (loose core versus spring loaded). Another possible explanation for the difference could be the contribution of plastic strain, which may create a difference in phase angles of 1–2°.

In recent history, a number of State Departments of Transportation have looked at providing safer driving conditions on bridges. One improvement method is placing high friction overlays on bridge decks. This study analyzed crash data to evaluate the performance of high friction overlays in reducing crashes. This study was completed by analyzing 10 years of data for nine bridges encompassing four different proprietary overlay systems. Within one of the overlay systems, three different aggregate types were also compared. Crash characteristics analyzed included the crash time, weather conditions, bridge surface conditions, average annual daily traffic, and severity of crashes. This study is part of a comprehensive study that includes extensive field evaluation and comparative performance analysis between different systems to evaluate their effectiveness on bridge decks in Minnesota. While the data presented herein is from bridge sites located in Minnesota, the findings apply to most of the northern tier states in the United States as well as other countries with colder climatic conditions. The analysis of data suggests that although there is a reducing trend in overall number of crashes; a reduction in crashes on bridges cannot be completely attributed to the use of high friction overlays. Furthermore, the presence of high friction overlays are unable to play a role in winter crash prevention. Thus this study shows that forensic evaluation of accident data does not support commonly anticipated crash reduction benefit of high friction overlays.

Asphalt pavements in colder climates encounter significantly shortened service lives because of excessive transverse cracking. This paper presents the results for 26 pavement sections in Minnesota that were studied to evaluate the effects of asphalt mix designs on pavement cracking performance. The field performance is presented with various cracking measures and compared with mix design aspects such as amount of asphalt binder, binder grade, and amount of recycling. The disk-shaped compact tension (DCT) fracture energies measured on the field cored samples are also compared with cracking performance. In this study, asphalt pavement sections from several locations were evaluated to encompass various types of asphalt mixtures and asphalt construction types that were commonly used in Minnesota. The amount of transverse cracking for each section was converted into a newly proposed cracking performance measure that accounted for the amount, rate, and timing of cracking. The comparisons between asphalt mixture attributes and cracking performance measures showed that the amounts of total asphalt binder and recycled asphalt binder may not be sufficient. Performance testing, in addition to currently used controls (mix volumetrics and constituent properties), is recommended to ensure good cracking performance. The DCT fracture energy results for companion sections show that mixtures with higher fracture energies exhibit lower amounts of transverse cracking. © 2016, National Research Council. All rights reserved.

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. © 2016 Published by Elsevier Ltd.

Historically, asphalt mixtures in Minnesota have been produced with fine gradations. However, recently more coarse-graded mixtures are being produced as they require less asphalt binder. Thus, it is important that pavement performance for coarse gradations be evaluated. Within this research work, performance evaluation took place with the use of the dynamic modulus test in indirect tension mode on coarse-graded mixtures consisting of field cores from 9 different pavements located in five districts of Minnesota. From each pavement's surface layer, 3 specimens were tested at three temperatures; 0.4°C, 17.1°C, and 33.8°C each at nine frequencies ranging between 0.1 Hz and 25 Hz. Additional volumetric characterization of the field mixtures was done to determine asphalt content, air voids, and blended aggregate gradations. Asphalt binders were extracted and recovered for use in determining binder shear complex master curves. Through this information the modified Witczak model was used to create |E∗| master curves which were then compared against the indirect tension (IDT) test | E∗| experimentally created master curves. From the results the modified Witczak model needs to be modified for IDT collected dynamic modulus data. © ASCE.

Thermal cracking in asphalt pavements continues to be a significant pavement distress mechanism in cold climate regions. The formation of discontinuities due to thermal cracking causes extensive damage to the integrity of the pavement and forms pathways for intrusion of water into the base and subgrade layers. Current use of the performance-based binder specifications has not been shown to effectively lower the propensity for this distress. When this is combined with advent of newer asphalt mix manufacturing and construction technologies as well as desire for incorporation of greater amounts of recycled materials in paving mixtures, it has led to significant research and implementation efforts on asphalt mixture performance-based specifications. On the basis of various past research studies on low temperature cracking, a performance specification that utilises fracture energy of asphalt mixtures through use of disk-shaped compact tension (DCT) test has been developed. A significant number of present studies are underway to implement these specifications including two states which are in the pilot implementation stage. A major question that has been raised during the implementation of these specifications has been in the lack of information on sensitivity of pavement thermal cracking performance to the variations in fracture energy of the mixture. The present study focused on determining the effects on thermal cracking performance of pavements for variations in DCT fracture energy of asphalt mixtures. The sensitivity was determined through use of the IlliTC thermal cracking simulation system. The IlliTC system utilises asphalt mixture's fracture and viscoelastic properties to conduct finite element-based simulations using realistic pavement thermal loading conditions. Although this system has been validated in the past, the present study conducted further validation through comparison of predicted cracking performance with field-measured cracking performance. For sensitivity analysis, three types of asphalt mixtures for three climatic conditions and three pavement structures were evaluated. Apart from other things, the fracture mechanics in asphalt concrete at lower temperatures depend on the material's fracture energy as well as its tensile strength. In order to ensure that the effects of fracture energy variations were the focus, a critical tensile strength value was determined for each scenario (for each mix for each climate), which allowed researchers to conduct the simulations with varying fracture energies (six different levels). The results show that a variation of 25J/m² in the fracture energy could lead to significantly different pavement thermal cracking performances. This is a significant finding that will aid in continued implementation of the fracture energy-based material specifications and provides guidance to transportation agencies in development of the final version of their material specifications. © 2015 Taylor & Francis.

Over the course of their service life, concrete pavements undergo significant traffic and climatic loads, which lead to a gradual accumulation of damage. This accumulation of damage and distress comes from the effects of changing weather conditions (e.g., temperature, moisture) and continuous vehicular traffic. Repeated environmental and traffic loading leads to cracking and spalling of the concrete at the joint edges. States in the northern portion of the United States and the provinces of Canada have climates that fluctuate greatly in temperature throughout the seasons. Greater temperature differentials cause greater deflections in rigid pavements; these deflections lead to more prevalent spalling and a greater need for partial depth repair. Many U.S. state departments of transportation (DOTs) use partial depth repair as routine practice to maintain concrete pavements (e.g., the DOTs of Minnesota, North Dakota, South Dakota, Idaho, Montana, Washington, and Wisconsin). Enhanced acceptance criteria of rapid set cementitious materials for use in partial depth repair are needed. The purpose of this study was to investigate laboratory tests, recommended by ASTM C928 and others, for inclusion in the acceptance specifications for patching materials.