278-CHA : Crack-Healing of Asphalt Pavement Materials
Technical Committee 278-CHA
Deputy Chair: Prof. Orazio BAGLIERI
Cracking is one of the most prevalent deterioration modes of flexible pavements. It is caused by traffic loading, low temperature and can be accelerated by oxidation of the asphalt or when the asphalt material performs poorly. In research on asphalt pavement, these issues have often been addressed separately due to the varied reasons for the cracking. The service life of asphalt can be increased significantly if these issues could be addressed with one or a combination of solutions focussed on the prevention and healing of asphalt cracks.
Fatigue and thermal cracking are the most dominant cracking distress modes in flexible pavements resulting in structural and functional failures of pavements. The mechanisms behind the two modes are very different. Fatigue is a traffic-induced damage that results under repeated tension stresses, induced by heavy vehicles. This creates infinitesimal damage at the bottom of the layer and initiates micro-cracks. Progressively, the cracks propagate which leads to failure of the pavement. On the other hand, when the temperature of the pavement drops, thermally induced tensile stresses build up in the asphalt layer and lead to its cracking when the thermal stress exceeds the threshold of the tensile strength. This phenomenon is generally referred to as Low Temperature Cracking. In both cracking modes, the role the viscoelastic properties of the asphalt binder is crucial.
There are various mechanisms affecting the viscoelastic properties of asphalt binders. Age hardening, which is an irreversible process, is widely considered the most important. Even though asphalt binder is only one component of the asphalt mix, the overall performance of the asphalt pavement is largely dictated by the viscoelastic properties of this binder. Several factors have been cited to explain the phenomenon of age hardening in asphalt binders. The major causes of age hardening commonly cited include oxidation, volatilization, polymerization, syneresis, and separation.
Researchers are increasingly looking to nature as a source of inspiration for solving complex technological, societal, and environmental challenges. Biological systems, processes, and designs have already influenced innovation in the energy, transportation, and communication sectors, among others. Similarly, the pavement industry, which is under constant pressure to produce longer-lasting, yet high-performing materials, can take inspiration from the mechanisms that underlie the human body’s ability to heal itself. Self-Healing Materials (SHM) have actually been explored to help create asphalt mixes that can close their own cracks or even prevent cracks before they happen.
Self-healing of bituminous materials may happen naturally during rest periods (Baaj, 2002) or may be provoked through the use of self-healing materials or techniques (Schlangen et al., 2010). Self-healing has been defined as the ability of a material to heal damage automatically, without any intervention and autonomously (without external triggering). Some previously studied healing methods of bituminous and cement-based materials have included the use of microcapsules (Su et al., 2013; Yang et al., 2009), bacteria (Jonkers and Schlangen, 2008), fiber reinforcement (Schlangen and Sangadji, 2013), phase change materials among others. Other methods for healing asphalt cracks use exterior triggering such as induction (Garcia et al., 2009), microwave heating (Gallego et al., 2013).
The TC will deal with healing phenomena of asphalt, a subject which becoming more and more popular in the last decade. The focus is on the development of test methods for the induction of asphalt cracking, quantification of intrinsic self-healing properties as well as on ways to enhance the healing properties of asphalt. The work of the TC should lead to improved durability of structures with less maintenance. It is a subject which becoming more and more popular in the last decade.
The scope of the committee will be built around three primary areas of work:
1. Literature Review
- Evaluation through literature study of the pathologies and effects of cracking, as well as the effects of pavement design, aggregates, binder source and binder modification on the cracking. Particular focus will be given to low temperature and fatigue cracking;
- Determination of the most efficient ways to induce cracking in a laboratory environment, based on the real-life mechanisms of cracking;
- Determination of the analysis methods available for evaluating healing in asphalt pavement;
- Determining the most promising self-healing techniques available, which could be applied to asphalt pavement;
2. Laboratory Experimentation
- Evaluation of methods for crack induction in asphalt pavement;
- Evaluate different test methods, used by the different participant laboratories, to characterize healing in asphalt pavement;
- Preparation, with the help of industrial partners, asphalt samples with healing materials that will be used in a round-Robin campaign to evaluate their effectiveness;
3. Numerical Modelling
- Investigate simulation programs and modelling techniques to predict cracking in asphalt based on various cracking influences;
- Define the best modelling strategies for the predication of the effectiveness of crack healing techniques.
Terms of reference
The preliminary timeline for the committee will be approximately 4-5 years. The principal tasks of this committee will be divided into 3 TGs based on the literature review, laboratory experimentation and the numerical modelling. More technical groups could be foreseen if there is the possibility of interesting divergent studies during the course of the committee.
TG1 – This group will focus on the production of state of the art reports and will be subdivided into two subgroups. The reports will serve as the theoretical basis for the two subsequent groups TG2 and TG3. The members of the committee will contribute their expertise into the compilation and evaluation of these studies.
TG1a – This subgroup will review the nature of cracking in asphalt pavement, with particular focus on low temperature and fatigue cracking;
TG1b – This subgroup will review the experimental and modelling techniques that have been used or have the potential to be used with self-healing asphalt mixes with specific focus on the determination of how self-healing in asphalt will be evaluated and quantified;
TG2 – This group will be responsible for the laboratory experimentation. The experimental methods will focus on evaluating methods of crack propagation in laboratory asphalt pavement, along with the healing methods for these materials. The evaluation of the various crack propagation techniques – as well as the evaluation of their healing – will be implemented in a round-robin testing program. They will also evaluate and compare various test methods (i.e. NDT, 3 pt bending, fatigue, IDT, ductility, CT Scan, microscopy…) for evaluating self-healing techniques for asphalt pavement.
TG3 – This group will be responsible for the development and adaptation of models for pavement cracking prediction, along with the prediction of the effectiveness of various self-healing techniques. The starting point of these projects will be largely derived from the literature review of TG1. A number of modelling tools will be used in the round-Robin campaign based on the expertise available in the committee. The tools used could possibly include Finite Element modelling, constitutive modelling and others. The correctness of the models will be compared with the laboratory derived results of TG2 where possible.
The scope of the membership of this committee includes academics, PhD students, and asphalt materials researchers along with government and industry representatives around the world.
Detailed working programme
General TC: The TC will organize a kick-off meeting in September 2016 in Montreal, Canada during Cluster Meetings. The meeting will be among the committee members and other interested parties to determine the available expertise, competencies and abilities of the committee. The leading members for the TGs will be decided with one chair for each group. The TGs will also be assigned secretaries from the midst of the committee with TG1 being assigned two (responsible to each subgroup) and TG2 along with TG3 being assigned one each. These assignments will be subject to change based on change in availability or priority.
TG1 Literature Review – The completion literature review will be the first task of the committee and will be completed in a timeframe of approximately 1 year. The reports will cover i) the cracking of asphalt pavement and its simulation in a laboratory environment and ii) self-healing in asphalt and its evaluation in laboratory conditions, performed simultaneously by TG1a and TG1b, respectively.
TG2 Laboratory Experimentation – This group will begin with a meeting to discuss a number of experimental techniques with the goal of evaluating and simulating cracking in asphalt pavement in a laboratory environment. The development of crack inducing methods will allow for work on the evaluation of the asphalt pavement self-healing. The preliminary work of this group is expected to begin several months after the first TC meeting and continue for the length of the project.
TG3 Numerical Modelling – This group will likely begin their work shortly after the completion of TG1 and the publication of its findings and continue throughout the existence of the TC. The literature reviews will determine a number of existing theories related to asphalt cracking and self-healing. These theories will be put to the test in a number of research labs focused on numerical modelling. The work produced here will be compared to the results of TG2 where possible.
This technical committee will build on the work of Dr. Erik Schlangen and TC 221-SHC, which studied “Self-healing phenomena in cement-based materials”, completing their work in 2013. Some members of this committee will be solicited to participate in the current one, or to provide their expertise.
The work of Technical Committee 241-MCD under Prof. William G Buttlar will be consulted for they work on “Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements”. The final report is due in Spring 2016, which coincides well with the beginning of the current proposed project.
This research coincides very well with each of the three main goals of RILEM in terms of:
- “to promote sustainable and safe construction, and improved performance and cost benefit for society”, as self-healing asphalt pavement would be a more sustainable building material, and would provide superior performance service-life along with a clear cost-benefit of society in that scope;
- “to stimulate new directions of research and its applications, promoting excellence in construction”, as self-healing asphalt pavement would constitute a superior construction material which has yet to be implementing on an industrial level;
- “to favour and promote cooperation at international scale by general access to advanced knowledge”; as the committee will built on the findings of four RILEM committees. It will also base a RILEM committee on a continent with generally less RILEM participation. The goal of course would be to promote the participation across nations and continents for this committee.
The committee will deliver state of the art reviews on the subjects of:
- Cracking in asphalt pavements, and the testing needed to induce as well as evaluate it;
- Self-healing methods for asphalt pavement.
An experimental study will be completed for the following:
- A laboratory procedure for producing asphalt with accelerated cracking;
- A laboratory procedure for determining the effectiveness of self-healing materials;
- Numerical prediction of asphalt pavement cracking and self-healing of asphalt pavement.
An international symposium will be organized close to the conclusion of this study, along with a final report summarizing the main findings.
Group of users
- Academics, PhD students, asphalt researchers, and standardization committees;
- Testing laboratories, asphalt producers, paving companies and government transportation agencies.
Specific use of the results
The impact and benefits of this research program are multifold. First, the increased service life of asphalt pavement through the use of self-healing materials will reduce the cost of road construction and maintenance. In addition to this direct financial impact, there is an indirect impact through the preservation of scarce raw materials, such as high quality aggregate and asphalt binder. The high demand on asphalt in recent years led to a significant increase, and volatility, in its price. Not only will this allow for the reduction in the consumption of virgin materials (binder, aggregates) on a per year basis, it will reduce the environmental pollution associated with the repair and replacement of roads. Additionally, it will reduce the human cost associated with the repair of roads, allowing for these labours to be transferred to other needs in society. In addition, the developed mix will be compatible with the use of recycled materials which means less solid waste and fewer landfills. The global CO2 emissions of the asphalt industry would then be reduced.
The expected impact of this research on the field of pavement materials is also significant. In addition to developing innovative materials and solutions, the work will lead to the development of new tests and techniques on cracking that are needed by the scientific community. As there has been considerable research done on self-healing materials in the previous decade, this will allow for a re-examination of progress that has been made along this path. The findings of this work will be published in scientific journals and venues and would lead to scientific collaborations with national and international scientific researchers from different areas.
Finally, he program will contribute to a new generation of highly technically qualified engineers who are sensitive to sustainable development and environmental issues. They will have the opportunity to work on innovative projects, think out of the box and develop their critical thinking. They will also develop technical knowledge on the different aspects of pavement materials engineering and design and learn how to deal with some advanced and innovative techniques in this field. In the near future, these personnel will contribute, with other peers, to lead the change towards more sustainable civil engineering infrastructures through their work in academia, construction and building materials industries, engineering firms and governmental transportation authorities.