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Asphalt overlays provide an economical means for treating deteriorated pavements. Thin bonded overlay (TBO) systems have become popular options for pavement rehabilitation. In addition to functional improvements, these systems ensure a high degree of waterproofing benefits. Conventional asphalt concrete fracture tests were developed for pavements with homogeneous asphalt concrete mixtures, and typically their thicknesses exceed two inches. The use of spray paver technology for construction of TBO leads to continuously varying asphalt binder content, up to approximately one-third of the layer thickness. The graded properties of asphalt concrete and thickness of the TBO (typically less than 50 mm) pose challenges for the use of conventional fracture test geometries. For example, obtaining the beams for SEN[B] specimens from pavement may not practical because of insufficient layer thickness of the TBO or may lead to excessive pavement damage. Applications of the other established test geometries, the DC[T] and SC[B] tests, are limited because of the material nonhomogeneity caused by nonuniform distribution of asphalt binder and smaller as-constructed thicknesses of TBO, which are usually less than 25 mm (1 inch) for gap-graded and 50 mm (2 inch) for dense-graded hot mix asphalt (HMA) mixtures. Both the DC[T] and SC[B] tests simulate movement of the crack fronts in transverse or longitudinal directions in the pavement. Use of these tests on field-procured samples of TBO yields a crack front that encounters nonhomogeneous material through the specimen thickness. The crack moves perpendicular to the axis of material nonhomogeneity, which makes data interpretation and fundamental material fracture characterization challenging. In addition, the crack in the specimens is correlated to a crack channeling across the pavement width rather than a more anticipated bottom-up or top-down direction. New test procedures for fracture characterization of graded asphalt pavement systems that have significant material property gradients through their thicknesses have been proposed. Suitable specimen geometry and testing procedures were developed using ASTM E399 and ASTM D7313-07 as a starting point. Laboratory tests were performed using an optimized compact tension C[T] test geometry for field cores as well as laboratory-fabricated composite specimens. Laboratory testing using the proposed procedure clearly showed distinction in the fracture characteristics for specimens prepared with varying material compositions. This capability of distinguishing different materials combined with stable crack growth makes the proposed testing procedure ideal for fracture characterization of thin and graded pavement systems. Statistical analysis of test data revealed that the proposed C[T] test procedure is capable of detecting differences in fracture energy results across a wide range of pavement systems and yields a low test variability. Finite element simulations of the test procedure further indicate the suitability of the test procedure as well as demonstrate a procedure for extraction of fundamental material properties. The suitability of the proposed C[T] test in the context of warmer temperatures was also evaluated. Changes in the loading rate were suggested to minimize the creep energy dissipation during the test at different test temperatures. Composite specimen fabrication procedure has been developed to optimize the design of TBOs. The proposed procedure can also be used to prepared composite specimens for interface bond strength and rutting resistance tests with emulsion and asphalt cement as tack coat material. Suggested wet application of tack coat emulsion on textured base, compacted with heated Superpave gyratory compactor top plate closely resembles field installation of TBOs. Moreover tack coat emulsion permeation effects on mixture fracture and bulk properties were also evaluated in an experimental study. Image analysis technique was utilized to characterize the tack coat emulsion impregnation gradient through the thickness of the overlays. An integrated approach to predict cracking performance of TBOs was presented combining laboratory test results, numerical simulations and early field performance.
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.
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.
Adhesion between asphalt-aggregate and cohesion within asphalt mastic has a significant effect on the performance of asphalt mixtures. Conventional testing methods and studies normally only focus on one of the damage modes (adhesion or cohesion), although in real asphalt mixtures (asphalt-aggregate system), these two failure modes can happen together depending on the material and loading conditions. The objective of this paper was to characterize the interface bonding characteristics of the asphalt-aggregate system using the thin-film interface test and the fracture property parameter, critical state energy density (CSED), and identify the key factors that could affect the interface bonding characteristics. The thin-film interface test simulated a more realistic bonding condition and monitored the damage between thin-film asphalt and aggregate. Experimental results showed that the effects of temperature and loading rate on the interface bonding characteristics were significant. The time-temperature superposition principle is found to work in both the linear viscoelastic range (dynamic modulus test) and the damage domain (interface bonding fracture test). Binder type, degree of aging, and types of aggregates all played an important role in the bonding performance for an asphalt-aggregate system.
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.
Proceedings of RILEM TC-PRC third conference on this subject. Papers from road authorities, engineers, researchers, contractors and manufacturers discussing the implementation and the long term behaviour of overlay systems. The following topics are covered: prevention and cracking assessment, choice and design of overlay systems, practical implemen