Subject matter

It is well established that currently a considerable amount of waste is produced and a major part of the resources are wasted through the mainly linear process of material use in our economies: raw materials are extracted, used or further processed into products where they are used and then disposed of in landfills and incinerators. A “circular economy” on the other hand turns goods at the end of their service life to be used as resources for other industries. This process improves resource efficiency and reduces climate and environmental impacts, through promoting waste reuse and recycling and by phasing out disposal or incineration of waste. A significant share of waste materials is recycled back into the same product where they came from (closed-loop recycling). However, despite considerable progress in recycling of waste materials generated, in many instances their quality or technical requirements do not allow for the materials to be recycled into the same product. As a result the waste materials are landfilled or incinerated. This provides a substantial opportunity to recycle wastes produced as precious secondary raw materials for example in road pavements. Various types of waste materials such as crumb rubber, glass and construction & demolition waste have been successfully used in road pavements. However, as the current literature shows, this use has remained for the most part at the research level or limited to some countries and therefore, there is an urgent need to develop and broadly demonstrate such solutions in order to promote widespread market uptake. Rilem technical committees present an optimal international cooperative opportunity to address all aspects pertaining to the use of waste and marginal materials in roads. This can span from materials choice to laboratory performance up to in situ performance of selected materials. This technical committee will develop a robust and fundamental understanding for evaluation of the use of waste and marginal materials as performance enhancing alternatives for the traditional road materials. The use of waste, marginal and secondary materials is sometimes limited based on the perception that there could be possible polluting elements in these non-conventional materials for road construction. As the roads are placed in the natural environment, these potential pollutants have the possibility to contaminate the ground water and soils around the roads.

The goals of this TC can be realized and solutions can be sought only through interdisciplinary research; this will inherently increase Rilem membership and its reach beyond the traditional civil engineering and materials science fields as demonstrated by the interdisciplinary list of interested parties at the end of this proposal.

This TC aims to facilitate the use of waste, marginal and secondary materials for roads by investigating the performance of road materials containing waste through round robin tests and through development of standard procedures for their selection, preparation and use.

The new TC aims to achieve the following:

(i) Identify waste, marginal and secondary materials that are suitable as performance and/or durability enhancing components in road materials
(ii) Investigate suitable binder additives and performance of the modified binders
(iii) Investigate suitable aggregate substitutes and performance in mixtures
(iv) Investigate possible pollutants
(v) Recommend suitable waste materials and limit amounts to be used in roads

Terms of reference

The TC will be active for 5 years (2017-2021). A combination of literature review, experimental work including waste materials treatment techniques will be done. At the end of the TC a symposium will be organised to disseminate the findings of the TC. The TC will perform its tasks in the following task groups:

TG1: Asphalt Binder Additives
A number of waste materials can be used as performance enhancing additives for asphalt binders. The most promising are chemically processed PET, which is traditionally used as anti-stripping agent, PET fibres, glass fibres, textiles, PU, which is conventionally selected for preparing low temperature bituminous foam, and crumb rubber from vehicle tires. The use of binder additives and the effects on the physical, chemical and mechanical properties of the material will be investigated with different techniques as listed below.
Physical –chemical characterization: The impact of the recycled material additives on the structure and on the properties of the modified binders will be addressed through advanced experimental methodologies. The molecular weight distribution of the waste modifier will be first evaluated with gel permeation chromatography (GPC) on the binders. Fourier transform infrared spectroscopy (FTIR) will be used to determine potential changes in the functional groups of the modified binders. Using differential scanning calorimetry (DSC) any shifting in the glass transition temperature and in the melting temperature that may affect the mechanical behaviour will be quantified and determined. In addition the potential inhomogeneity of the structure of the waste modified asphalt binder will be evaluated at the nanoscale based on atomic force microscope (AFM) measurements and at the microscale through X-Ray tomography which allows for a three-dimensional reconstruction of the materials microstructure.
Mechanical characterization: Together with more advance techniques, classical rheological characterization will be used to determine the properties of the different virgin and waste modified asphalt binders for identifying potential critical behaviours. For this purpose, Dynamic Shear Rheometer and Bending Beam Rheometer tests will be conducted to evaluate the material response over a wide range of temperatures. The fatigue and healing behaviour of asphalt binder containing recycled additives will be experimentally evaluated through an advanced multi scaling approaches. Limitations associated to the use of extraction and recovery procedures will be also addressed and solutions proposed to be implemented for routine forensic and quality control tests in asphalt research institutions, road authorities and in the industry for verifying the final waste-modified products.

TG2: Aggregate and Filler Substitute
TG2 will work on the possibility of replacing conventional aggregates with recycled waste materials such as C&D waste, ceramics, PET granulates, steel slag, glass powder, PU foamed waste, and ceramic filler will be included in this TG. The task is divided into the following.
Testing and ranking: Recycled waste materials mentioned above will be tested and ranked according to the current standards for pavement granular materials in terms of mechanical, chemical and mineralogical properties. This includes bulk density, shape, resistance to fragmentation, strength, water absorption, resistance to freeze-thawing, volume stability and resistance to abrasion. Within this subtask, the general applicability of the considered materials can be assessed and a pre-selection for the next subtasks can be made.
Adhesion to binder: Subsequently, the substitute granulates will be characterized with respect to their adhesion and interaction with asphalt binder. For this, a number of standardized and recently developed methods will be employed to assess the adhesion with and without the presence of water. This includes the rolling bottle and static tests as well as contact angle measurements and the Wilhelmy Plate method. Thus, a second pre-selection can be made to make sure that only those materials will be employed in the further study that show high binder adhesion quality.
Mixture mechanical performance: In this subtask, the behaviour of asphalt mixtures prepared with single waste materials will be evaluated through mechanical performance characterization, while limits on the amount of each recycled waste material will be proposed by parametric studies. For this purpose, low temperature behaviour, fatigue resistance, resistance to permanent deformation, stiffness and water sensitivity of asphalt mixture will be investigated. In addition, long-term performance and durability will be assessed by laboratory aging of the asphalt mixtures and subsequent performance testing.

TG3: Characterization of Combined Mixtures
In cooperation with TG1 and TG2 combined “products” will be developed and characterized chemically and mechanically.
Chemical characterization: Techniques such as gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), contact angle measurements for adhesive properties will be used to chemically characterize the combined binder additives.
Mechanical characterization: For the mechanical characterization of the combined binder additives, the dynamic shear rheometer (DSR) will be used to obtain rheological characteristics of the binders as well as industry standard tests such as penetration and softening point.
Characterization of mixtures: Significant advancements shall be made in terms of combined use of different recycled waste materials within one mixture. By parameter studies, limit amounts for each recycled waste material for combined use in asphalt mixtures will be determined based on the performance of the mixtures. In the mixing process conventional and low energy mixing procedures will be considered. Various scenarios of combined waste materials will be developed. These scenarios will depend on the geographic areas and availability of particular products.
Recycled mixtures can be susceptible to brittleness and therefore the particle loss tests will be performed within this task. Dynamic mechanical tests for fatigue, low temperature cracking and dynamic modulus will be used to rank solutions with respect to standard mixtures. Various combinations and scenarios will be investigated based on the performance of the waste materials and compatibility with other ingredients with the goal of maximizing waste use.

TG4: Environmental Assessment
The aim of this TG is to identify the potential sources of pollutants of the recycled materials, their release processes and their effect on health, soils, water and air, in order to take the necessary precautions to ensure safe application of recycled materials in road construction.
To this end, the determination of the polyaromantic hydrocarbons (PAH) content as well as leaching behaviour of the specific materials under specified conditions based on different scenarios (normal and exceptional conditions) will first take place. Leaching is the primary process through which contaminants from road construction materials enter the environment; thus leaching tests will be used to evaluate the possible environmental risk. The methodology that will be deployed will be based on the European Standard EN 12920:2006+A1:2008 which focuses on characterising the release mechanisms through which contaminants from asphalt materials are leached.

Detailed working programme

Spring 2017: Kick-off meeting and Approval of work program and assignment of group leaders
Fall 2017: Annual meeting, discussion and approval of work plan
Spring 2018: Meeting of TGs, update of deliverables and work plan
Fall 2018: Annual meeting, discussion of results, presentation of achievements
Spring 2019: TG meetings, data evaluation, presentations, papers
Fall 2019: Annual meeting, discussion of results, presentation of achievements
Spring 2020: TG meetings, data evaluation, presentations, papers
Fall 2020: Annual meeting, discussion of results, presentation of achievements
Spring 2021: International symposium
Fall 2021: Annual meeting, concluding remarks, final report, presentations of final results