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The main objective of this study was to deduce and assess crack propagation parameters of twelve asphalt mixtures including: eight conventional dense graded, two polymer-modified gap graded, and two asphalt-rubber gap graded mixtures using the EN 12697-44:2010 based monotonic semi-circular bending (SCB) test. The asphalt mixes were prepared using different binder types, binder contents, and air voids levels totaling 72 samples with two replicates per mix type. Dense graded mixes had higher fracture toughness than rubber- and polymer-modified mixes at various temperatures. Total fracture energy and residual energy were higher for modified mixes than dense mixes. The share of residual energy in rubber-modified mixtures was 80 % of total fracture energy, indicating that even though a crack initiates in these mixes, it will take much more time to completely fail those materials. Predictive models for crack propagation parameters were developed and were based upon material properties. All three models had very good statistical goodness of fit measures (R2adj >= 0.80, and Se/Sy
Laboratory assessment of crack resistance and propagation in asphalt concrete is a difficult task that challenges researchers and engineers. Several fracture mechanics based laboratory tests currently exist; however, these tests and subsequent analysis methods rely on elastic behavior assumptions and do not consider the time-dependent nature of asphalt concrete. The C* Line Integral test has shown promise to capture crack resistance and propagation within asphalt concrete. In addition, the fracture mechanics based C* parameter considers the time-dependent creep behavior of the materials. However, previous research was limited and lacked standardized test procedure and detailed data analysis methods were not fully presented. This dissertation describes the development and refinement of the C* Fracture Test (CFT) based on concepts of the C* line integral test. The CFT is a promising test to assess crack propagation and fracture resistance especially in modified mixtures. A detailed CFT test protocol was developed based on a laboratory study of different specimen sizes and test conditions. CFT numerical simulations agreed with laboratory results and indicated that the maximum horizontal tensile stress (Mode I) occurs at the crack tip but diminishes at longer crack lengths when shear stress (Mode II) becomes present. Using CFT test results and the principles of time-temperature superposition, a crack growth rate master curve was successfully developed to describe crack growth over a range of test temperatures. This master curve can be applied to pavement design and analysis to describe crack propagation as a function of traffic conditions and pavement temperatures. Several plant mixtures were subjected to the CFT and results showed differences in resistance to crack propagation, especially when comparing an asphalt rubber mixture to a conventional one. Results indicated that crack propagation is ideally captured within a given range of dynamic modulus values. Crack growth rates and C* prediction models were successfully developed for all unmodified mixtures in the CFT database. These models can be used to predict creep crack propagation and the C* parameter when laboratory testing is not feasible. Finally, a conceptual approach to incorporate crack growth rate and the C* parameter into pavement design and analysis was presented.
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.
Internationally, much attention is given to causes, prevention, and rehabilitation of cracking in concrete, flexible, and composite pavements. The Sixth RILEMInternational Conference on Cracking in Pavements (Chicago, June 16-18, 2008) provided a forum for discussion of recent developments and research results.This book is a collection of papers fr
In the recent past, new materials, laboratory and in-situ testing methods and construction techniques have been introduced. In addition, modern computational techniques such as the finite element method enable the utilization of sophisticated constitutive models for realistic model-based predictions of the response of pavements. The 7th RILEM International Conference on Cracking of Pavements provided an international forum for the exchange of ideas, information and knowledge amongst experts involved in computational analysis, material production, experimental characterization, design and construction of pavements. All submitted contributions were subjected to an exhaustive refereed peer review procedure by the Scientific Committee, the Editors and a large group of international experts in the topic. On the basis of their recommendations, 129 contributions which best suited the goals and the objectives of the Conference were chosen for presentation and inclusion in the Proceedings. The strong message that emanates from the accepted contributions is that, by accounting for the idiosyncrasies of the response of pavement engineering materials, modern sophisticated constitutive models in combination with new experimental material characterization and construction techniques provide a powerful arsenal for understanding and designing against the mechanisms and the processes causing cracking and pavement response deterioration. As such they enable the adoption of truly "mechanistic" design methodologies. The papers represent the following topics: Laboratory evaluation of asphalt concrete cracking potential; Pavement cracking detection; Field investigation of pavement cracking; Pavement cracking modeling response, crack analysis and damage prediction; Performance of concrete pavements and white toppings; Fatigue cracking and damage characterization of asphalt concrete; Evaluation of the effectiveness of asphalt concrete modification; Crack growth parameters and mechanisms; Evaluation, quantification and modeling of asphalt healing properties; Reinforcement and interlayer systems for crack mitigation; Thermal and low temperature cracking of pavements; and Cracking propensity of WMA and recycled asphalts.
The main objective of this project was to develop and verify the overlay tester (OT) based fatigue cracking prediction approach in which the OT is used to determine fracture properties (A and n) of hot-mix asphalt (HMA) mixtures. This approach was developed based on fracture mechanics. However, not only was the fatigue crack propagation characterized by Paris' law fracture concepts, but the crack initiation described by traditional fatigue model was also included in this approach. In this approach, the fundamental HMA fracture properties (A and n) were used to estimate fatigue life of asphalt pavements including crack initiation and crack propagation.
When reinforcing existing cracked asphalt pavements, the design and evaluation of the durability of the reinforced structure are quite different from those of a new pavement generally based on fatigue criteria deduced from stress and strain fields computed for the undamaged pavement. For the design of reinforcement solutions, the presence of cracks and their propagation must be considered explicitly. To move in this direction, the present article aims at improving the understanding of bottom-up crack propagation in asphalt pavements. Some investigations relying on the interpretation of an accelerated full-scale fatigue test are presented as well as the numerical analysis of this test through the theory of linear elastic fracture mechanics and the Paris law. The tested pavement section is composed of four layers. The two uppermost layers are made of asphalt concrete (AC) materials whose modulus and fatigue performances are different. The pavement is subjected to repeated loads applied by the Fatigue du Béton Armé Continu (FABAC) traffic simulator of the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR), and the development of cracking in the AC layers is monitored using embedded instrumentation and Falling Weight Deflectometer (FWD) test campaigns. To better control the crack pattern that develops during the fatigue test, an artificial flaw (metal angle) is purposely placed at the bottom of the AC layers (in the transverse direction to the moving loads) to localize the initiation of cracking. A bottom-up crack is supposed to grow vertically from this defect in the AC layers. This is effectively detected and followed by the experimental measurements, which are combined to model for the analysis of the test. Finally, the kinetics of crack growth deduced from the Accelerated Pavement Test (APT) results and those computed using the Paris law calibrated from fatigue tests performed in the laboratory are compared.