One of the most influential variables in determining the performance-based properties of the asphalt mixtures is the specimen fabrication method. This study investigates the impact of specimen fabrication methods through a comprehensive study of six test sections constructed in 2011that include a range of RAP contents and two different virgin binders. Complex modulus and fatigue characterisation was conducted on asphalt binders and mixtures. Three specimen fabrication methods were evaluated: specimens compacted from plant sampled loose mix with and without reheating, and specimens fabricated from raw materials in the laboratory. Predicted performance from lab tests were compared to field performance. The mixtures with PG 58-28 binder showed expected trends with increasing RAP content (higher modulus, lower phase angle); however, mixes with PG 52-34 did not. Similar trends were observed for specimens fabricated with plant mix (not reheated), and the specimens fabricated with raw materials in the lab. Binder results and performance prediction using the plant mix agree with the observations in the field.
Dave EV, Botella R, Marsac P, Bodin D, Sauzeat C, Nguyen ML.
Cracking in Asphalt Pavements
. In: Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements: State-of-the-Art of the RILEM TC 241-MCD. Vol. 28. Springer International Publishing ; 2018. pp. 33-102. Publisher's VersionAbstract
This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.
Premature cracking in asphalt pavements and overlays continues to shorten pavement lifecycles and creates significant economic and environmental burden. In response, RILEM Technical Committee TC 241-MCD on Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements has conducted a State-of-the-Art Review (STAR), as detailed in this comprehensive book. Cutting-edge research performed by RILEM members and their international partners is presented, along with summaries of open research questions and recommendations for future research.
This book is organized according to the theme areas of TC 241-MCD - i.e., fracture in the asphalt bulk material, interface debonding behaviour, and advanced measurement systems. This STAR is expected to serve as a long term reference for researchers and practitioners, as it contributes to a deeper fundamental understanding of the mechanisms behind cracking and debonding in asphalt concrete and composite pavement systems.
Abstract Dynamic modulus (|E∗|) and phase angle (δ) are necessary for determining the response of asphalt mixtures to in-service traffic and thermal loadings. While a number of |E∗| and δ predictive models have been developed, many of them require lab measured properties (e.g. binder complex modulus). The majority of previous work has focused only on prediction of |E∗|, limited models exist for prediction of δ. This research utilized generalized regression modelling of lab measurements (from 81 asphalt mixtures) to develop and verify prediction models for |E∗| and δ using only nominal asphalt mix properties that are readily available during the initial mixture design and specification process.
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.
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.
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.