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Introduction -- Objectives and summary -- Theoretical background -- Test methods -- Materials and specimen fabrication -- Uniaxial testing -- Determination of viscoelastic properties from IDT test -- Development of a simple performance test and validation -- Conclusions and recommendations -- Implementation and technology transfer plan -- References -- Appendices.
Fatigue cracking in asphalt concrete (AC) is of immense importance to pavement design and analysis because it is one of the most important forms of distress that can lead to structural failure in pavement. Once started, these types of cracks can be combined with other environmental factors leading to detrimental effects such as faster rates of pavement deterioration and shortened pavement life and functionality. Currently AASHTO TP101, also known as linear amplitude sweep (LAS) specification, is being widely used to evaluate the ability of an asphalt binder to resist fatigue. The LAS method, although mechanistic in its approach, has certain drawbacks. First, the test is performed on an aged 2-mm thick binder sample, which in reality may never exist in the AC where there is a varying non-uniform thickness of the binder across the components of the AC. Secondly, the test methodology predicts an increased fatigue resistance at lower strain levels of load when the binder ages. This is in contrast to the general belief among researchers that aging is one of the primary contributors to the acceleration of pavement cracking. This study aims to evaluate fatigue resistance in a more realistic approach that is more likely to exist in AC by incorporating sand asphalt mixtures. First, the linear viscoelastic properties of binder and sand asphalt mixture samples were evaluated to obtain the material properties under the influence of aging. Later, the fatigue tests on the sand asphalt mixture were investigated to understand the influence of a thin film of binder on the fatigue resistance. It was observed that based energy dissipation criterion for the binder evaluated a reasonable estimate for fatigue damage at relatively lower temperatures, but was limited to capture the influence of aging. Moreover, it was observed that fatigue testing on a binder at an intermediate temperature of 25 °C could cause edge effects to dominate as seen in the plateau regime for the phase angle in the time sweep tests. In order to overcome the edge effects in the binder LAS tests, the sand asphalt mixture testing was used for analyzing the binder fatigue resistance. Sand asphalt mixture testing could capture the microcracking and macrocracking phases more distinctively when compared to binder testing. In the case of pressure aging vessel (PAV) aged samples, it was observed that the macrocracking phase disappeared and was replaced by sudden changes in the material properties, indicating that the PAV aged mixture was more susceptible to fatigue cracking. By using the simplified viscoelastic continuum damage approach, the fatigue resistance of the binder and sand asphalt mixture was evaluated. The sand asphalt mixture testing was better to capture the influence of aging and changes in the microstructure during fatigue in comparison to binder fatigue tests..
Fatigue cracking is one of the primary modes of distress in asphalt pavements that has an important economic impact. Fatigue resistance characterization of an asphalt mixture is a complex issue due to: (i) composite nature of the material, (ii) gradation of aggregate particles, (iii) variation of asphalt film thickness, (iv) air voids distributions, (v) asphalt binder nonlinear viscoelastic behavior, (vi) effects of binder oxidative aging as a function of time, and (vii) micro crack healing during rest periods. Different methods to assess fatigue cracking in asphalt materials are available in the literature. However, there is no methodology to characterize fatigue cracking behavior of asphalt materials that is independent of the mode of loading (controlled-strain or controlled-stress). The objective of this research is to develop a new methodology to characterize fatigue cracking of the fine aggregate matrix (FAM) portion of asphalt mixtures using dynamic mechanical analyses (DMA). This is accomplished through different, but related, approaches. The first approach relies on identifying the various mechanisms of energy dissipation during fatigue cracking that are manifested in: (i) nonlinear viscoelastic deformation, (ii) fracture, and (iii) permanent deformation. Energy indices were derived to quantify each of these energy dissipation mechanisms and to quantify fatigue cracking irrespective of the mode of loading. The first outcome of the approach is a fatigue damage parameter (crack growth index) that provides comparable results for a given material even when tested under different modes of loading and different load (strain or stress) amplitudes. The developed fatigue characterization method has a lower coefficient of variation when compared to conventional parameters (number of load cycles to failure or cumulative dissipated energy). The crack growth index parameter was also qualitatively and quantitatively compared to three dissipated energy methods available in the literature. The second outcome of this research is a constitutive model that can describe both asphalt mixtures' nonlinear viscoelastic response and fatigue damage in one formulation. Nonlinear viscoelastic as well as damage parameters were obtained for both modes of loading. This second approach has the advantage that the constitutive model can be implemented in a numerical framework to describe the response of asphalt mixtures under various boundary conditions.
Bituminous Mixtures and Pavements contains 113 accepted papers from the 6th International ConferenceBituminous Mixtures and Pavements (6th ICONFBMP, Thessaloniki, Greece, 10-12 June 2015). The 6th ICONFBMP is organized every four years by the Highway Engineering Laboratory of the Aristotle University of Thessaloniki, Greece, in conjunction with
This book offers a collection of 17 scientific papers about the computational modeling of fracture. Some of the manuscripts propose new computational methods and/or how to improve existing cutting edge methods for fracture. These contributions can be classified into two categories: 1. Methods which treat the crack as strong discontinuity such as peridynamics, scaled boundary elements or specific versions of the smoothed finite element methods applied to fracture and 2. Continuous approaches to fracture based on, for instance, phase field models or continuum damage mechanics. On the other hand, the book also offers a wide range of applications where state-of-the-art techniques are employed to solve challenging engineering problems such as fractures in rock, glass, concrete. Also, larger systems such as fracture in subway stations due to fire, arch dams, or concrete decks are studied.
Bituminous Mixtures and Pavements VIII contains 114 papers as presented at the 8th International Conference ‘Bituminous Mixtures and Pavements’ (8th ICONFBMP, 12-14 June 2024, Thessaloniki, Greece). The contributions reflect the research and practical experience of academics and practicing engineers from thirty-four (34) different countries, and cover a wide range of topics: Session I: Bitumen, Modified binders, Aggregates, and Subgrade Session II: Bituminous mixtures (Design, Construction, Testing, Performance) Session III: Pavements (Design, Construction, Maintenance, Sustainability, Energy and Environmental consideration) Session IV: Pavement management and Geosynthetics Session V: Pavement recycling Session VI: Pavement surface characteristics, Pavement performance monitoring, Safety Session VII: Biomaterials in pavement engineering Session VIII: Prediction models of pavement performance Bituminous Mixtures and Pavements VIII covers recent advances in highway materials technology and pavement engineering, and will be of interest to scientists and professionals involved or interested in these areas. The ICONFBMP-conferences have been organized every four years since 1992. This 8th conference was jointly organized by: Laboratory of Highway Engineering, Aristotle University of Thessaloniki, Greece; Built Environment Research Institute (BERI), University of Ulster, UK; University of Texas San Antonio (UTSA), USA; Laboratory for Advanced Construction Technology (LACT), Technological Institute of Iowa, USA; Technological University of Delft (TUDelft), The Netherlands, and University of Antwerp, (UA), Belgium.
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 development process included a number of phases, which are described in the report. Included in this report are the following: 1) a state-of-knowledge review for fatigue response of asphalt aggregate mixes, 2) a description of a pilot test program and its results, 3) a description of an expanded test program using the equipment and methodology selected in the pilot test program, and 4) a description of a mix analysis and design system, which can be used to mitigate fatigue cracking.