Subject matter

Cold bitumen emulsion (CBE) technologies play a key role in the development of environmental friendly and sustainable bituminous pavements. The bitumen/water emulsification process reduces the binder viscosity allowing mixing, laydown and compaction of CBE mixtures to be carried out at ambient temperature and without aggregate drying. This leads to important energy savings and reduction of atmospheric pollution.

CBE technologies are currently used for both non-structural (microsurfacing, slurry seals) and structural (surface, base and sub-base layers) paving applications. However, their application range is frequently limited to secondary or low-traffic roads.
This is mainly due to the lack of fundamental knowledge concerning the mechanical behaviour and the development of the long-term performance of CBE mixtures. As a consequence, the use of CBE technologies is often associated to higher technical risks with respect to those related to the use of traditional hot-mix or warm-mix technologies.

Based on this background, this TC aims to foster the use of CBE technologies as a sustainable and environmental friendly alternative to traditional hot technologies for both new construction and maintenance activities. The main goals of the TC are:

• to collect, summarize and improve the fundamental knowledge related to chemical and physical mechanisms that control the mechanical behaviour and the performance of CBE materials;
• to evaluate testing methodologies for the physical and mechanical characterization of CBE materials and suggest worldwide harmonisation of existing standards.

In order to tackle these goals, the TC will focus on the multiphase and evolutive nature of CBE materials. Such distinctive features are basically due to the presence of free water (low-viscosity liquid) which is essential for dispersing and distributing the bitumen droplets (thermo-viscoelastic solid) and to reduce the internal friction between aggregate particles (rigid solid).
Breaking of the bitumen emulsion and reduction of free water content are the basic time-dependent phenomena that, after construction, control the evolution process of CBE materials, i.e. the curing process, towards the long-term cured state.
The TC will also consider the role of emulsifier type and dosage, both in the curing process and in the development of adhesion with different aggregate substrates, as well as the effect of potential co-binders (Portland cement and other hydraulic binders) which have the capability of improving the mechanical performance of the mixtures throughout their service life.

Terms of reference

With regard to the practical application fields of emulsion-based materials within a pavement structure, the work of this TC With regard to the multiphase nature of CBE materials and to their practical application fields within a pavement structure, the work of the TC will be organised in the following two task groups (TG). The TG topics described below are preliminary and subject to changes according to the specific objectives defined by each TG.

TG1: EMULSIONS AND EMULSION-BASED COMPOSITES. [TG Leader: Miomir Miljković]

TG1 is going to focus on theoretical knowledge and laboratory testing aimed at obtaining a fundamental characterisation of bitumen emulsion (as a binder); CBE mastics composed of bitumen emulsion and filler-sized particles (including Portland cement and other hydraulic binders) and CBE mortars composed of mastics and fine aggregate will also be analysed as essential structural phases of CBE mixture. The interaction with emulsifiers and prospective co-binders (Portland cement and other hydraulic binders) will be of particular interest.

The characterisation is going to include comprehensive physical, chemical, and mechanical properties, as well as key processes like water evaporation and cement hydration. The rheological properties of bitumen emulsions, CBE mastic and CBE mortars at different formulations, stages of curing and environmental conditions are going to be of a particular interest.
The emulsion breaking process, with its possible scenarios, adhesion to mineral aggregates and the time-dependent character of these phenomena are also to be studied. In this regard involving a multidisciplinary approach with collaboration of specialists form several fields would be strongly preferred.

TG2 COLD BITUMEN EMULSION MIXTURES. [TG Leader: Cesare Sangiorgi]

TG2 will focus on mixtures and technologies employed both non-structural and structural paving applications.
With regards to non-structural layers, such as chip seals, slurry seals, micro-surfacings, and other surface treatments, mix design methodologies using traditional (natural aggregates) and alternative constituent materials (rubber, glass, etc.) will be first addressed in order to provide a consistent approach to practitioners. Laboratory and in-situ characterization will then follow, aiming to deliver new standards, specifications and guidelines encompassing the wide set of existing practices. Specific interest will be allotted to the evaluation of the impact of the proposed construction and maintenance methodologies on the pavement life, both in terms of structural and functional aspects. Ties with TG1 will mainly focus on binder-aggregate affinity as one of the most important topics related to the layer durability.

With regards to structural layers, focus will be on the role of the aggregate structure, and its interaction with CBE mastics and mortars. A specific attention will be devoted to “grave emulsion” mixtures that can be distinguished from dense-graded cold mixtures (cold asphalt) because of the thin film of CBE mastic that surround the coarse aggregate particles. General aspects of grave emulsion mixture design will be considered such as emulsion formulation and breaking behaviour, residual bitumen content, aggregate properties and total water content.

METHODOLOGY

Both TGs will focus on fundamental material properties and on a performance-based approach comprising theoretical background, experiments, modelling and, if possible field observations.

The activities of the TGs will start with a through literature review aimed at collecting worldwide theoretical knowledge and experiences related to cold bitumen emulsion materials. Cold paving technologies based on bitumen emulsion are used in many countries for pavement construction. Various technologies have been developed worldwide for different pavement layers. They differ with respect to bitumen emulsion formulation, aggregate properties and use of functional additives. First, these technologies will be compared reviewing their “local” background, highlighting their benefits and aiming at a general classification and harmonization of terminology.

Each TG will then focus on a specific topic, possibly regarding application and/or comparison of testing and evaluation procedures. These activities may involve, for example: performing round robin tests (standard tests on reference materials), investigating different properties of specific materials (either emulsions or mixtures), performing tests using improved or innovative equipment or protocols, develop special purpose testing equipment or protocols.

Detailed working programme

The working programme of the TC will consist of the following individual activities:

• A kick-off meeting will bring together the perspective members along with external experts in the field of bitumen emulsion and CBE materials. Basically, it will be a workshop where TG leaders will present the terms of reference and propose a spectrum of possible goals. TC members and experts will also be invited to summarize their experience and outline their own view and goals about the TC topics. The first meeting of each TG will be fixed within 6 months.
• The main objective of the first individual TG meeting will be the identification of specific TG goals and propose working plans. Work on the literature review will also be discussed and organized. Possible synergies with other TCs and missing expertise will be identified.
• In the first Annual meeting of the new TC, the TG leaders will present the goals identified within the TG. The discussion within the whole TC will allow highlighting possible synergies and common strategies. Synergies with other TCs on Bituminous Materials will also be discussed. 
• During the second year, the TGs will finalize the literature review and select specific “major” topics, possibly regarding application and/or comparison of testing, evaluation or design procedures. The chosen topics will be selected to ensure as much collaboration between each TGs as possible. The working plan will also be finalised (e.g. material distribution, testing protocols, evaluation strategies, plan and organisation of workshops). 
• In the second Annual meeting of the new TC, the TG leaders will present the “major” goal identified within the group and the working plan. If available, preliminary results will also be presented. The literature review carried out by the TGs will also be dis-cussed and summarised in order to set the ground for a common review paper(s) to be submitted to a journal (e.g. Materials and Structures). The paper will also contain a general description of the TC, its goals and possibly the working plan of each TG. 
• During the third and fourth year, the TGs will pursue individual working plans. Individual or combined TG meetings will be held to present results, identify critical points, and propose amendments to the working plan.
• The third and fourth annual meetings will review progress and achievements of each TG. These will also be the time to plan and approve presentations of the TC activities, papers, recommendations and reports. Proposals for a final international conference or workshop will be discussed and finalized (location, steering committee, scientific committee, peer review process, etc.). 
• During the fifth year TGs will finalize their individual working plans and consider the production of draft papers or recommendations. 
• The fifth (concluding) annual meeting will discuss the contribution of each TG to the final STAR report. 
• The final international conference or workshop will be held.