The current asphalt binder performance grading system employs Dynamic Shear Rheometer (DSR) testing to determine high and intermediate temperature Theological properties. In recent years, the ability to measure DSR instrument compliance has allowed researchers to reliably measure low temperature binder properties as well. Low temperature characterization using DSR requires substantially smaller amount of binder as compared to the currently employed binder testing method, Bending Beam Rheometer (BBR). For these reasons and the possibility of using one piece of equipment for full characterization of asphalt binders, previous research has investigated DSR as an alternative to replace BBR testing by determining equivalent creep stiffness (S) and slope (m-value) from shear complex modulus. Different methods have been proposed to determine BBR specification parameters from DSR data and their viability has been evaluated primarily for virgin binders. The objective of this paper is to further assess the applicability of different methods to determine S and m-values from DSR data for four neat binders as well as extracted and recovered binders from eighteen different mixture samples. The variables within the matures include lab versus plant production, aggregate size and gradation, binder PG and source, and recycled material type and content. The methods employ different interconversion methods, ranging from exact interconversions to regression-based estimates. The shear relaxation modulus or creep stiffness and slope are correlated to S and m-value measured from BBR testing. The study also investigates the impact and differences due to use different interconversion methods. The results show that the Christensen approximate interconversion is adequately able to predict parameters from DSR results that are equivalent to S and m-value determined from BBR testing. The exact interconverted shear creep stiffness and shear relaxation modulus using generalized Maxwell model are compared to lab measured S and m values, results show that a linear relationship exists between these parameters. Finally, a simple equation is developed to enable estimation of BBR S and m-value from a single point measurement of complex shear modulus and phase angle. This contribution is expected to have a practical use by providing a platform to estimate low temperature specification parameters from a single point DSR measurement.
© 2019 Association of Asphalt Paving Technologist. All Rights Reserved.

To address asphalt pavement thermal cracking, researchers have developed performance-based evaluation tools for asphalt mixtures. A minimum fracture energy obtained from a disc-shaped compact tension test and Black space parameters determined by the stiffness and relaxation properties of asphalt mixtures are two such methods to ensure good thermal cracking resistance. Mix specifiers and producers strive to meet the requirements set by these performance-based criteria by adjusting their mix designs. However, there is a lack of information and consensus on the effect of mix design variables (such as binder grade and mix volumetrics) on thermal cracking performance of mixtures as it relates to fracture energy and Black space location. This study strives to fill this gap by quantifying the effect of: (1) recycled asphalt content, (2) effective binder content, (3) air voids, (4) asphalt film thickness, (5) voids in mineral aggregates, and (6) PG low and high temperature grades on thermal cracking resistance. A large dataset, 90 mixtures from the Minnesota Department of Transportation and 81 mixtures from University of New Hampshire database, was used for the study. The results indicate a strong correlation between binder related properties (binder content, asphalt film thickness, PG spread) and fracture energy. The correlation coefficients obtained from this study for PG spread, effective binder content, and air void can be confidently employed to achieve targeted fracture energy thresholds. The same can be achieved for the Glower-Rowe parameter at 15ºC by employing the correlation coefficients obtained for PG low temperature, virgin asphalt content, and voids in the mineral aggregate.
© National Academy of Sciences: Transportation Research Board 2018

Aging affects the properties of asphalt mixtures in different ways; increase of stiffness, decrease of relaxation capability, and the increase of brittleness, resulting in changes in cracking behavior of asphalt mixtures. In this study, ten plant-produced, labcompacted mixtures with various compositions (recycled materials, binder grades, binder source, and nominal maximum aggregate size) are evaluated at different long-term aging levels (24 hours at 135°C, 5 days at 95°C, and 12 days at 95°C on loose mix and 5 days at 85°C on compacted specimens). The asphalt mixture linear viscoelastic properties (|E*| and d) and master curve shape parameters measured from complex modulus testing and fracture properties (measured from discshaped compact tension and semi-circular bending fracture testing) are compared at different levels of aging. The results indicate that the mixture exposure time to aging is proportional to the dynamic modulus and phase angle changes. Generally, the fracture parameters of mixtures become worse when aging level changes from 5 to 12 days aging. In spite of the similar viscoelastic properties, the mixtures with 24 hours at 135°C and 12 days at 95°C aging do not show similar fracture parameters.
© National Academy of Sciences: Transportation Research Board 2018.

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.
© 2017 Elsevier Ltd

This recommendation describes how to evaluate the presence of potentially active bitumen in recycled asphalt (RA) materials through the cohesion test. The experimental protocol is designed according to the research performed by the RILEM Technical Committee 237-SIB ‘‘Testing and characterization of sustainable innovative bituminous materials and systems’’ with the purpose, to develop a new, simple and fast method for the characterization of RA while limiting the need for conventional rheological tests. The guidelines in this recommendation focus on the testing procedure including specimen preparation, data analysis and provide information on the preparation of a tests report.
© 2018, RILEM.

This recommendation proposes an experimental protocol to characterize recycled asphalt materials. The guidelines presented in this document are based on the results of a round robin test organized by the RILEM Technical Committee 237-SIB “Testing and characterization of sustainable innovative bituminous materials and systems” and provide information on the testing procedure, data analysis and indications for the preparation of a test report.
© 2018, RILEM.

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.