Het gedrag van asfalt (ACRe): bepalen, modelleren en voorspellen

Civil Engineering and Geoscience

Over Wegen

Intreerede prof.dr.ir. S.M.J.G. Erkens. Rede in verkorte vorm uitgesproken op 19 september 2014 in een gecombineerde ceremonie met de intreerede van prof. dr. Tom Scarpas.Structural engineeringCivil Engineering and Geoscience

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

Cracking in asphalt concrete

Fatigue resistance of asphalt concrete is usually evaluated by means of fatigue tests, like repeated load four point bending tests. These tests are rather time consuming and, therefore, not suited for performance based specifications. In this article a new, faster procedure to determine the fatigue characteristics is introduced. The procedure is based on a combination of theory and experiments. Both the theorectical background and the experiments that were used are discussed in this article. Furthermore, fatigue relations that were developed using the new procedure and relations developped using classical fatigue tests, are compared.Road & Railroad Research LaboratoryCivil Engineering and Geoscience

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

Determining and Modeling Asphalt Concrete Response (ACRe)

In road engineering research and design the principles of material mechanics have not yet become a standard tool. In this contribution a project aimed at applying these principles to asphalt concrete is presented. Attention is paid to the differences between the standard test procedures and those based on mechanics considerations, presenting examples of the disturbances that can occur to illustrate the need for mechanically sound testing. The general approach in the ACRe project is introduced, showing the material model utilised and the parameters that have to be determined. The physical meaning of the model parameters is mentioned the tests used for the model parameter determination, uniaxial tension and compression tests and four-point shear tests, are introduced. The uniaxial compression test is discussed in more detail, to illustrate the approach used in the test programme. The results from this test are also presented, as well as the way in which a general expression for the compressive strength of the material was determined on the basis of these results. Finally, an example of the application of the model for damage predictions in road engineering constructions is presented. In this example two different pavement structures are analysed, illustrating that this kind of analyses can show the different damage patterns that will occur. In current day road engineering design approaches for every structure the same location is considered normative. From observations in practise it is known that this is not the case and the differences observed in the simulations agree rather well with these observations.Road & Railway Research LaboratoryCivil Engineering and Geoscience

De meerwaarde van structureel, langjarig bemonsteren

Vanwege het grote aantal variabelen dat een rol speelt bij het gedrag van asfaltverhardingen, is het cruciaal om bij het volgen van het gedrag in de tijd gedetailleerde gegevens te hebben over de samenstelling, aanlegcondities en het gedrag en verloop in eigenschappen in de tijd. Op basis van ervaringen uit het verleden, kan men lessen leren over hoe het gedrag van materialen het beste gemonitord kan worden. Puntsgewijs incidenteel of structureel meerjarig bemonsteren? Het kan tot verrassende conclusies leiden. Deze paper gaat in op de ervaring die is opgedaan met de opzet en uitvoering van het monitoren van de veroudering van de ZEBRA vakken bij het Innovatie Programma Geluid.Pavement Engineerin

Het healingmechanisme van bitumen nader verklaard

Asfalt heeft de aantrekkelijke eigenschap dat het zichzelf kan herstellen na schade. Er is echter tot op heden geen betrouwbare methode om de healingcapaciteit van een asfaltmengsel te bepalen. Bij het healingproces van een discrete scheur spelen twee processen een rol, namelijk het in contact komen van de oppervlakken van de scheur; het zogenaamde bevochtigen, en het vermogen van deze oppervlakken in contact om kracht over te dragen; de intrinsieke healing. In dit artikel wordt een testmethode gepresenteerd welke in staat is om de verschillende parameters die een rol spelen gedurende de healing te variëren om zo het belang van de processen in healing bloot te leggen. Met behulp van deze testmethode is de mate van healing van bitumen in de tijd onderzocht en de invloed van normaalkracht gedurende healing. Op basis van de gepresenteerde resultaten kan worden geconcludeerd dat bevochtiging van het scheuroppervlak tenminste 50% van de macroscopisch geobserveerde healing bepaalt voor pure bitumen. Dit inzicht kan worden gebruikt om een materiaalmodel voor healing van asfalt te formuleren, op basis waarvan een relatief eenvoudige healingtest kan worden ontworpen waarmee de healingcapaciteit van asfaltmaterialen onderling kan worden vergeleken.Pavement Engineerin

Samengestelde appels als referentie voor dichte peren?

Tussen de Eisen 1978 en Standaard 2015 is de regelgeving vele malen aangepast. Proeven, definities, eisen en toleranties zijn allen aangepast. Maar nog veel belangrijker is dat gestart is met het vervangen van het vertrouwde empirische technisch kader voor asfaltverhardingen door een nieuw functioneel kader. Voor asfaltbeton is hiermee in 2008 begonnen en met de nieuwe versie van de Europese Normen volgen mogelijk ZOAB en SMA.De Werkgroep Asfaltverhardingen (WGA) van CROW beheert de regelgeving voor asfalt in de Standaard RAW Bepalingen en heeft de interne afspraak dat wijzigingen in de regelgeving alleen worden doorgevoerd als deze door middel van onderzoeksresultaten onderbouwd kunnen wordenVoor het beoordelingskader van asfalt is het van belang de relatie te kennen tussen de doelsamenstelling voor het typeonderzoek, de samenstelling voor de productiecontrole en de samenstelling voor de controle van gerealiseerde werk. Evenzo is de relatie tussen de streefdichtheid voor het typeonderzoek, de dichtheid van proefstukken in warme toestand tijdens de proefstukvervaardiging in het laboratorium en de dichtheid van proefstukken voor controle van gerealiseerd werk van groot belang. De huidige kluwen van doelsamenstelling, samenstelling na extractie en referentiesamenstelling en van streefdichtheid en referentie-dichtheid, platen, balkjes, gyratortabletten, gyratorproefstukken en boorkernen wordt in deze bijdrage beschreven evenals de knelpunten die hiervan momenteel in de praktijk het gevolg zijn.Vanuit een integrale veiligheidsbeschouwing voor asfaltverhardingen van ontwerp tot en met realisatie moet herijking plaatsvinden van toleranties voor samenstellingen ten opzichte van de doelsamenstelling en van dichtheden ten opzichte van de streefdichtheid voor de beheersing van de kwaliteit van asfalt bij productie en verwerking. Op basis van een theoretische analyse wordt hier een voorzet voor gegeven en wordt een aanpak voorgesteld voor de validatie van de voorgestelde wijzigingen.Pavement Engineerin

Chemo-mechanics of ageing on bituminous materials

Ageing of bitumen is a complex process. It is accompanied by major chemical and mechanical changes. In this study, Fourier Transform Infrared (FTIR) spectrometer and Dynamic Shear Rheometer (DSR) tests were utilized to investigate the effect of ageing on the chemical and mechanical properties of bituminous materials. Bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the materials. The FTIR tests results were used to quantify the changes in the chemical functional groups and to calculate ageing indices (carbonyl index and sulfoxide index) of bitumen. In addition, the DSR tests results were analysed to determine the evolution of the rheological properties of bitumen. A linear relationship was made between the ageing indices and complex shear modulus, providing thus a chemo-mechanics framework to describe bitumen ageing. The results were validated by using data of field aged samples. Finally, the influence of ageing on the parameters of two viscoelastic models was determined