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Abstract: Fatigue cracking is a primary distress in asphalt due to repetitive stresses and strains caused by traffic. The main objective of this study is to investigate the use of the semi-circular bend (SCB) test as a quality assurance/quality control (QA/QC) measure for field construction. The SCB test parameters were determined using two methods, the first of which was cross-head movement (CHM), and the second was non-contact camera. In SCB CHM method the specimens were loaded monotonically until fracture under a constant cross-head deformation, while in none-contact camera method a camera was fixed in front of the SCB specimen to measure the crack length. In addition beam-fatigue test (BFT) was conducted according to AASHTO T-321 on the same mixtures. A comprehensive comparison between the test results is performed. The results of this study indicate that the SCB test has a great potential as a QA/QC test of fracture properties of asphalt mixtures.
This book discusses the applications of fracture mechanics in the design and maintenance of asphalt concrete overlays. It provides useful information to help readers understand the effects of different material and loading type parameters on the fracture properties of asphalt concretes. It also reviews relevant numerical and experimental studies, and describes in detail design parameters such as aggregate type, air void, loading mode, and additives, based on the authors experience and that of other researchers.
This volume highlights the latest advances, innovations, and applications in bituminous materials and structures and asphalt pavement technology, as presented by leading international researchers and engineers at the RILEM International Symposium on Bituminous Materials (ISBM), held in Lyon, France on December 14-16, 2020. The symposium represents a joint effort of three RILEM Technical Committees from Cluster F: 264-RAP “Asphalt Pavement Recycling”, 272-PIM “Phase and Interphase Behaviour of Bituminous Materials”, and 278-CHA “Crack-Healing of Asphalt Pavement Materials”. It covers a diverse range of topics concerning bituminous materials (bitumen, mastics, mixtures) and road, railway and airport pavement structures, including: recycling, phase and interphase behaviour, cracking and healing, modification and innovative materials, durability and environmental aspects, testing and modelling, multi-scale properties, surface characteristics, structure performance, modelling and design, non-destructive testing, back-analysis, and Life Cycle Assessment. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster new multidisciplinary collaborations.
A major cause of premature pavement deterioration has been the cracking of the asphalt materials. This study investigates the ability to apply fracture mechanics principles to study asphalt concrete cracking through experimental techniques. Single-edge notched beam (SE(B)) and disk-shaped compact tension (DC(T)) test geometries were developed to estimate the fracture energy of asphalt concrete. Fracture energy can be measured from these laboratory tests with adequate accuracy, which allows for the application of numerical models to accurately predict asphalt concrete fracture behavior. The fracture behavior of asphalt concrete at low temperatures can be described as quasi-brittle and the fracture properties are specimen size dependent within the size range tested for this study (25 mm up to 450 mm). The DC(T) test was applied to forensic studies of pavement structures and fracture energy estimated from the tests provided an alternative parameter for describing the cracking potential of the asphalt concrete mixtures.
Cracking in asphalt pavements is a challenging problem and has been the subject of numerous research studies for decades. To properly address this problem, suitable tests must be conducted to capture material behavior in cracking, such testing must be accompanied by proper mechanistic and empirical modeling of the material behavior in cracking. For mixture design and material quality control/assurance purposes, there is not a commonly accepted protocol for testing asphalt mixtures for cracking resistance characterization, due to variability of test results, non-uniformity in test specimens, and overall complexities of the tests that prevent them from being adopted for daily uses. On the other hands, for the tests that are popular for research purposes, the validity and sensitivity of such tests have not been fully witnessed and proven, due to lack of data quantity. Addressing these problems will help improve mixture design procedures and advance quality control and quality assurance of asphalt mixes, especially when complicated components, such as recycled materials and performance enhancing additives, are commonly incorporated into asphalt concrete nowadays. The overall goal of this research is to characterize the cracking resistance of various types of asphalt concrete mixes via a suitable candidate test. An additional goal is to provide guidelines for performing balanced mixture design on asphalt concrete with virgin and recycled materials when using such a test. Throughout the research, the selected fracture test, namely the semi-circular bend (SCB) fracture test, was first evaluated by investigating the sensitivity of performance indicators under various test conditions and proposing the most appropriate test conditions using a solid theoretical background. Then, the test was used to study fracture behavior of a wide range of asphalt paving materials including, but not limited to, various virgin asphalt mixes, crumb rubber modified (CRM) asphalt mixes, asphalt mixes with recycled materials such as reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS), together with asphalt mixes with recycling agents. Not only were these mixtures prepared in a single laboratory, specimens received from different laboratories and plants were also included in the test matrix to reduce bias and to investigate the variation of the performance indicators. Additionally, a method to conduct the performance-based balanced-design using only the SCB fracture test was explored. Finally, the effect of long-term aging on fracture behavior of asphalt mixes was investigated, in order to build foundations for performance prediction commonly used in asphalt pavement design procedures. The main contributions of this study are: 1) verification of the sensitivity of the SCB test using asphalt mixtures with controlled variables under the proposed test conditions that are suitable to the commonwealth of Pennsylvania, 2) investigation of the impacts of material variables and conditioning, namely aging process, on fracture behavior of asphalt concretes, 3) exploration of possibility of performing balanced mixture design on asphalt concrete using the SCB test as a stand-alone test. The SCB fracture test procedure is found to be suitable to qualify asphalt mixes to fulfill different traffic demands and pavement structural conditions. Reliable mix design and quality assurance of asphalt pavements with complicated rehabilitation histories and sophisticated material compositions can be performed with confidence using such a test.
New developments in mixing, testing, modeling Research findings on sustainable asphalt technology Bitumen use and specifications in Europe Fully-searchable text on accompanying CD-ROM Asphalt Paving Technology 2013, a series volume, contains 26 original research papers devoted to the formulation, chemistry, mixing, modeling, testing and optimization of asphalt—with applications to highway and infrastructure engineering. Written by leading civil and structural engineers from universities and government agencies around the world, the book offers information for designing and producing higher-quality asphalt. Selected keywords: photocatalytic asphalt; fatigue loading; skid-resistance; low-temperature cracking software; long-term aging; fracture properties; moisture damage; RAP; rejuvenators; binders; flexible pavement; healing. The CD-ROM displays figures and illustrations in articles in full color along with a title screen and main menu screen. Each user can link to all papers from the Table of Contents and Author Index and also link to papers and front matter by using the global bookmarks which allow navigation of the entire CD-ROM from every article. Search features on the CD-ROM can be by full text including all key words, article title, author name, and session title. The CD-ROM has Autorun feature for Windows 2000 with Service Pack 4 or higher products along with the program for Adobe Acrobat Reader with Search 11.0. One year of technical support is included with your purchase of this product.
Asphalt concrete is commonly used as the surface layer in many pavement structures. One of the most important characteristics of asphalt concrete is its cracking resistance. At present, the conventional engineering material parameters such as tensile strength and dynamic modulus are the parameters used in the process of flexible pavement designs. In order to improve the design process, development and use of mechanistic-based design methods are necessary. These methods require characteristics that accounts for fracture resistance of asphalt concrete materials such as fracture energy. Thus, the use of a fracture mechanics approach and the development of valid fracture tests which are able to extract fundamental fracture properties of asphalt concrete are crucial. The goals of this research were to first introduce and evaluate a new and more practical fracture test, called single-edge notched disk (SEND) test, that can be easily used to characterize fracture properties of asphalt concrete, and second, to describe testing and analysis technique used in this investigation. As compared to other available fracture tests, the SEND test had several advantages, including capability of using field specimens, easy specimen preparation and test procedure, simple load configuration and test fixtures, big fractured surface area, and capability to induce cracks to propagate across the pavement thickness. Since the SEND test combined materials' visoelastic deformation with fracture, it was able to simulate real life failure in pavements more accurately as compared to other existing fracture tests. The scope of this study was on laboratory and field compacted, dense graded asphalt mixture specimens. The results of the study clearly showed the ability of the SEND test to characterize fracture properties of various types of asphalt concrete mixtures at different testing temperatures, loading rates, and air void levels.
Several different types of modifiers are increasingly being used to improve the performance of asphalt binders or to achieve desired mixture production characteristics (e.g., Warm Mix Asphalt). However, current Superpave performance specifications do not accurately reflect the performance characteristics of these modified binders. The main objective of this study was to evaluate the inherent fatigue cracking resistance of asphalt binders in the form of a matrix with rigid particle inclusions. The underlying rationale for this approach was to subject the binders to a state of stress that is similar to the one in a full asphalt mixture. This was achieved by fabricating and testing composite specimens of the asphalt binders and glass beads with a specified gradation. Four asphalt binders with similar true temperature grades but different modifiers were used in this study. The viscoelastic and fatigue cracking characteristics of the binders were measured using the glass bead-binder composite specimens in a dynamic shear rheometer at an intermediate temperature. The results demonstrate that the four asphalt binders modified using different methods had different damage characteristics despite the fact that these four binders were rated to have a similar performance grade based on the Superpave specifications. Fatigue cracking characteristics of the glass bead-binder test specimens used in this study were qualitatively very similar to the fatigue cracking characteristics of full asphalt mixtures using the same binders. The rank order of fatigue cracking resistance for the four glass bead-binder mixtures compared reasonably well to the rank order of fatigue cracking resistance for the full asphalt mixtures that incorporated these asphalt binders.
The purpose of this study is to examine potential relationships between fatigue and fracture parameters obtained from standardized laboratory tests. A flexural bending beam test was used to obtain two fatigue parameters, which include a traditional fatigue criterion based on stress or strain to find number of cycles to failure and a new fatigue criterion based on an energy approach known as the plateau value (PV). Similarly, a disk-shaped compact tension DC(T) fracture test was used to obtain fracture energy parameters, including: fracture strength, pre-peak fracture energy, post-peak fracture energy, and total fracture energy. A factorial of the eight possible correlations was computed to determine the strongest association between the fatigue and fracture parameters for the asphalt mixtures investigated. The study was motivated by the desire to investigate the feasibility of predicting time-consuming fatigue test results with fracture test results, which can be obtained much more rapidly. Based on the results obtained in this study, it was shown that a potentially strong correlation exists between fatigue and fracture mechanisms in asphalt concrete, as characterized by parameters associated with dissipated or consumed energy. As presented through the statistical analysis, the plateau value (PV) and the pre-peak fracture energy (Gf-pre) are the most highly correlated parameters from the fatigue and fracture tests, respectively. This study is based upon limited experimental data and is explored an initial starting point to find relationships between fatigue and fracture mechanisms. Much more experimented and analytical work will be needed to fully understand these relationships and to develop a standardized interconversion scheme.