A Mechanics based Computational Platform for Pavement Engineering

Civil Engineering and Geoscience

Experimental Characterization of Asphalt for an Elasto-Visco-Plastic Constitutive Model

This paper describes a range of uniaxial creep tests that have been undertaken for a proprietary polymer modified asphalt, the procedure used to determine the parameters required for an elasto-visco-plastic constitutive model. Uniaxial compressive creep testing and creep recovery testing have been undertaken over a range of temperatures and stress conditions. Procedures used to determine the model parameters from the test data are detailed and parametric equations are developed to describe the model parameters as functions of the test conditions. Particular attention is given to the determination of the parameters related to visco-plastic flow and damage accumulation at high strain levels. The model has been implemented in to the CAPA- 3D Finite Element (FE) program and preliminary verification has been undertaken

Physical and mechanical moisture susceptibility of asphaltic mixtures

AbstractMoisture has for a long time been recognized as a serious contributor to premature degradation of asphaltic pavements. Many studies have been performed to collect, describe and measure the moisture susceptibility of asphaltic mixes. Most of these aimed at a comparative measure of moisture damage, either via visual observations from field data or comparative laboratory tests. The research presented in this paper is part of an ongoing research effort to move away from such comparative or empirical measures of moisture induced damage of asphaltic materials and develop a fundamental approach via a comprehensive energy based computational framework. Such a framework would enable realistic predictions and time assessment of the failure pattern occurring in an asphaltic pavement under the given environmental and traffic loading, which could be rutting, cracking, raveling or any combination or manifestation thereof. The paper discusses the fundamental moisture induced damage parameters and demonstrates the developed model

Aging of Asphalt Symposium: Delft, the Netherlands September 17th 2014

Technical specifications for the asphalt concrete properties are developed to be able to specify mixtures that will perform well in pavement applications. Being able to identify and determine properties related to pavement performance in practice is crucial for both road authorities and contractors, since it allows for design and risk management by determining design life times and reliability. However, the properties of Asphalt Concrete (AC) change over its lifetime and since most pavement layers last for a decade or more these changes are crucial in determining the performance in practice.For many of the standard materials the effect of aging is implicitly dealt with in the safety factors that also account for other effects such as the variation rest periods/healing and variations in traffic and weather in the design methods and specifications. Rapid changes in the materials used (increasing percentages reclaimed asphalt, bio‐bitumen, rejuvenators, waste materials) and in theproduction of both bitumen (new refining methods resulting in different composition of bitumen) and asphalt concrete itself (warm mix asphalt, porous asphalt concrete, rubber asphalt mixtures) lead to increased uncertainty in the effects of aging. As a result, the uncertainties in pavement performance increase, which means the prediction of maintenance and the necessary budgets is getting more inaccurate.In order to maintain the ability to reliably design and maintain pavements and determine the most cost‐effective solutions for a given situation, a better understanding of the aging processes and objective methods to take into account aging effects on material properties is needed. This need is widely recognized, in the USA the Mechanical Empirical Design Guide takes aging into account through aging tests on the bitumen used and in Europe CEN TC227 works on establishing a method to assess the aging sensitivity of asphalt mixtures. This symposium aimed at combining the existing information and insights from ongoing research into recommendations that will allow thedevelopment of methods to determine aging sensitivity and the impact on pavement performance, facilitate the exchange of obtained data and stimulate further developments The resulting recommendations are: Do make long term aging sensitivity of binders part of the bitumen standards and take the results from the aging sensitivity of binders into consideration when assessing AC properties.Be aware that RTFOT testing only gives an indication of the sensitivity of a penetration grade binder to aging during hot mix production and construction, it doesn’t work for hard grades, PMB’s or warm mixes. Because of the many variables involved, developing one test method to characterise aging sensitivity seems improbable. However, PAV aging is both practical and, if tests at various conditions are carried out, able to give kinematic properties. A PAV protocol for testing at two temperatures and time intervals could provide practical characterisation information forthe short term and enable model development and validation on the long term. RCAT and other aging procedures could also be used in this sense, but considering the availability of equipment and the wide spread experience, PAV is the best candidate to allow the rapid development of international experience with the approach.Based on the current standards and the work presented during the symposium, PAV tests at 90 and 100 degrees Celsius and 20 and 40 hours, respectively, are suggested. The low values for temperature and duration are based on the current standards and fit both the USA and CEN procedure, while research shows that after 40 hours at 100 degrees the chemical (FTIR) and rheological (DSR) properties of laboratory aged and field samples were similar (Section6.5 and 8.5). At 100oC the temperature is low enough so that the effect of secondary reactions is negligible. As such, these conditions are appropriate for kinetic expressions for in service pavement performance. For high temperature processes and possibly also for repeated recycling (very long term) more sophisticated methods are needed. Set‐up and maintain field monitoring of temperature and UV radiation in various climate zones, as well as regular sampling over time and height to keep checking the predicted changes (from both tests and models), versus the actual changes in properties order to ensure reliability of the data as well as the applicability for pavement performance prediction. In setting up field tests, it is important to get both the composition of the virgin bitumen and the composition after mixing, transport and placement in the pavement. Thesecompositions provide the starting points from both the material and pavement structure point of view and can be used to assess the development of aging products over time. There is a lot of discussion about the impact of binder recovery methods on the observed composition, so until it is proven that this does not have an influence, for comparisons the same recovery method should be used. Set up a coordination and support action on AC‐Aging to continue to exchange information and experiences, both in research and in construction projects. develop an IR testing protocol, to facilitate the exchange of results and information. Compare the bitumen composition that is found through various recovery methods toestablish if there is an effect and if so, develop a procedure to address this. To further understanding of aging, a Round Robin test on the differences in test conditions between US and EU, allowing better access to each other’s data and knowledge would be seful. When developing aging tests for AC, it would be useful to look at the US experience. As long as there is no fundamentally correct method for assessing the aging, it would be preferable to standardize it as much as possible in order to allow cooperation and exchange of data

Durability of European Asphalt Mixtures Containing Reclaimed Asphalt and Warm-Mix Additives

This paper investigates the moisture susceptibility of European asphalt mixtures (SMA) containing reclaimed asphalt (RA) and warm mix (WMA) additives. Test sections of a typical SMA mixture have been laid, from which cylindrical samples were cored and utilized for laboratory testing. Four variants of the SMA mixture were prepared; a control HMA mixture with 0% RA, a mixture with 30% RA and no WMA additive, a mixture with 30% RA in which a WMA additive was added and a mixture with 40% RA and a WMA additive. The coring procedure and testing were carried out in two phases; first field cores were taken 24 hrs after the construction of the test section was completed and then once again 12 months later. In this way, the influence of field aging on the mechanical performance of the mixtures was considered. The samples were moisture conditioned at various combinations of water bath immersion and cyclic pore pressures by means of the Moisture Induced Sensitivity Tester (MiST). The degradation in strength due to moisture was quantified through indirect tensile strength tests. The results indicated that the use of RA in combination with WMA additives resulted to mixtures with improved durability characteristics, with respect to moisture damage, compared to the control HMA mixture. Based on the results, recommendations were made for characterizing and limiting moisture damage of asphalt pavements

HighRAC workshop

With the increasing drain on natural resources and resulting aim to reduce the environmental impact of road engineering, the use of reclaimed asphalt in fresh asphalt becomes more and more important. Despite the experience in using RAC, there are still many questions regarding the effect of RAC on the technical and environmental performance of mixes, especially with high RAC content. For the true impact of RAC to be quantified, a methodology is needed for the evaluation of the possible environmental and other benefits of asphaltic mixes containing high percentages of RAC (HighRAC). For such a methodology to be precise, it will require reliable data about the durability of pavements constructed with these new types of mixtures. The HighRAC Workshop aimed to serve as a venue for a gathering of a select group of national and international experts to exchange knowledge, ideas and experience on : (i) appraisal of the long-term performance characteristics of HighRAC mixtures (ii) enhancement of the engineering properties of HighRAC mixtures by constituent material selection and/or modification at various length scales (iii) comparison and validation of current mix design procedures for mixtures containing HighRAC (iv) a holistic Life Cycle Assessment based approach for evaluation of long term pavement life including environmental and sustainability considerationsStructural EngineeringCivil Engineering and Geoscience