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Fatigue failure can be attributed to cyclic (dynamic) loading energy which induces stresses and/or strains below the allowable strength and/or fracture strain level of a material. Since fatigue failures evolve over time, damage theories have been postulated to describe the mechanism by which this failure occurs. When a crack exists or forms early in the life of a pavement, fracture mechanics becomes the most relevant theory to explain the damage process. If conditions prevail to promote brittle fracture, the stress intensity factor and its critical value, Kc (or Gc) , becomes the most relevant parameter controlling the cracking and fatigue damage process. If conditions prevail to promote ductile fracture, the ductile fracture parameter, Jc, becomes the parameter for consideration. If conditions prevail to promote creep fracture, the C* - Line Integral offers the most relevant fracture criteria. Since the definition of Jc or C* in fracture mechanics imposes the condition that either parameter will degenerate into Kc (or Gc) when brittle fracture conditions, prevail, the utilization of Jc or C* provides the user with a powerful tool to characterize the fatigue/fracture process in a more general form. Since asphaltic mixtures can exhibit brittle and/or creep fracture, it is apparent that the C* - Line Integral can more closely capture the fatigue/fracture damage process than Kc or Jc. In this paper, a simple laboratory procedure to determine the C* - Integral, which is interpreted as the energy release rate, is presented. In addition, a mixture efficiency factor (`?*) is introduced. The mixture efficiency factor is used to examine and compare the efficiency of asphaltic concrete mixture in resisting fracture cracking using different aggregates and asphalt cement binders.
Resulting from the Symposium on [title], held in December 1991, at the ASTM Standardization Meetings in San Diego, this volume comprises 19 papers in four sections: aggregates; mineral fillers; mixture evaluation; and fatigue, modeling, and theoretical. Member price, $52. Annotation copyright Book N
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
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.
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
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.
The level of research activity in the highway sector as a whole has declined precipitously in recent decades, whilst the challenges facing US state highway agencies have escalated. As a result, a Strategic Highway Research Program - SHRP) was initiated to establish collaboration with research bodies tackling similar highway problems in countries worldwide. This collection of reports from around the world presents SHRP`s progress towards providing research-based new products from which the international highway engineering community may benefit. SHRP concentrates on six high-priority research areas: asphaltic materials; pavement performance; cement and concrete; maintenance cost effectiveness; concrete bridge component protection systems and the chemical control of snow and ice.