Subject matter

Bituminous binders are complex organic materials by nature. As the last product in crude oil refinery, bitumen exhibits a complex chemical composition and a time- and temperature-dependent viscoelastic response to loading. In addition, bituminous binders show a distinct microstructure that affects its mechanical behaviour, which is on the other hand affected by chemical composition. Due to its organic nature, bitumen is prone to oxidation and other environmental effects over its lifetime. Ageing alters the chemical setup, microstructure and mechanical behaviour and can be a limiting factor for the service-life.

Recent developments including, but not limited to, an increase in recycling rates and the need for energy efficient constructions have added to this complexity due to the thriving market of various additives to achieve certain production and performance goals. Among them are different polymers, rejuvenators and production temperature-reduction agents. Traditional rheological methods are limited to characterize the materials mechanically. Tracing or quantifying certain additives in a binder or explaining the interaction between base binder and additives are hardly possible with these rheological test methods.

Thus, physico-chemical methods are increasingly used to analyse bituminous binders. Links between data gathered from these methods and rheological methods have been established, including past RILEM TCs, i.e. RILEM TC 231 NBM, RILEM TC 237 SIB and RILEM TC 252 CMB. However, physico-chemical methods have not been standardized yet and were mostly used for qualitative analysis of materials in the past. For engineering purposes, these methods are now employed for quantification purposes, and this requires calibration and standardization.

Thus, this proposed RILEM committee will be focusing on bringing knowledge on linking rheological and physico-chemical analysis (known as chemo-mechanics) developed by past RILEM TCs and the community together to have a sound basis and not reinvent the wheel. The experimental work of the committee will include bituminous binders, polymers and other additives. The boundary conditions (i.e. potentials and limitations) of widely used physico-chemical methods for binder analysis (FTIR, GPC, DSC) regarding their applicability on modified binders will be studied. Based on the results, recommendations for a standardized use of these methods and chemo-mechanical links will be provided.

More specifically, the TC will be concerned with:

• Gathering existing knowledge on physico-chemical analysis of bituminous binders and chemo-mechanics (literature study)
• Improving the methodology and developing data for statistical information of FTIR on bituminous binders as a basis for future standardization (round robin)
• Identifying potential methods for chemo-mechanical fingerprinting of modified binders (experimental)
• Recommendations for standardization of FTIR and methods for fingerprinting (recommendations)

RILEM Cluster F – the proposed home of this proposed TC – has already a high number of active TCs compared to the size of the active scientific community. Thus, this proposed TC will be very focused and establish strong links to other active TCs. To keep this TC focused, the TC will comprise of 2 TGs. Basis for round robin testing and other experimental works will be existing material from other active TCs to establish links to these committees from an early stage on. The materials will be limited to base bitumen and modified bitumen with polymer and rejuvenation agents.

Terms of reference

The proposed TC will be active for five (5) years from 2020 to 2024. The TC will perform a combination of literature review, round robin tests and other experimental work. It will aim at establishing a sound statistical foundation for subsequent standardization of FTIR on bituminous binders and describe further potential methods for fingerprinting of base and modified bituminous binders.

The TC is sought to be inaugurated at the RILEM International Symposium on Bituminous Materials to be held in June 2020 in Lyon, where a wider audience will be exposed to the intentions of this TC and have the opportunity to join in on the efforts. In addition, the current experts in the field will be invited to participate through mailings and personal contacts. The TC will concluded its work in 2024 and the findings will be presented at the RILEM International Symposium on Bituminous Materials, in which the TC will act a co-organizer.

The following two task groups (TG) are intended:

TG 1 Reproducibility of FTIR

TC CMB has started to work on statistical analysis (repeatability, reproducibility) of FTIR to trace oxidative ageing. A test program has been carried out, however with some drawbacks: e.g. ageing was carried out by each lab before FTIR analysis. Thus, by comparing results from different labs, the differences in binder handling and ageing devices were biasing differences produced by different FTIRs. This should be overcome by an efficient round-robin test, in which one lab will prepare and age all samples and the other labs will run FTIR tests on the prepared samples. Before the round robin test, the TG will review the state of the art from past RILEM TC STAR reports and scientific publications. This work will be done in 2020 and finished in 2021. The round robin test will be prepared in 2021 and executed in 2021 and 2022. Data evaluation will be carried out in 2023 and recommendations developed and published in 2023 and 2024.

The questions to be answered by TG item are:

• How well can oxidative ageing be quantified by FTIR in terms of reproducibility when results from more than one lab should be compared?
• What is the optimal test procedure and data analysis to maximize reproducibility?
• Can an analytical description of the FTIR spectra increase the benefit from spectral analysis?

Methods to be used by each participating lab are FTIR and DSR (for the benefit of combining mechanical with chemical information). Participating labs are welcome to further other methods, e.g. BBR, GPC, NMR, other spectroscopic and microscopic methods, etc.

The goal of this TG is to provide recommendations on how to prepare samples, run FTIR tests and process and analyse data in a standardized way. These recommendations can be taken over by international standardization committees and set a common ground for future work with FTIR to make results from different groups more comparable.

TG 2 Bituminous Binder Fingerprinting

Fingerprinting of bituminous binders by FTIR and other methods have been discussed in a small number of scientific papers recently. In addition, TC 237 SIB has also worked in this field. The idea is to distinguish bitumen from same grading but different source or refinery process and quantify additive contents (especially SBS, other polymers and rejuvenation agents) by FTIR or a combination of FTIR and other methods. The work in this TG again includes a review of the state of the art (2020, 2021), experimental works (2022), evaluation and recommendation (2023, 2024)

The questions to be answered by this work item:

• Can a commonly available method be used to identify bituminous binders from different sources?
• How comparable is such a method when data from different labs are merged?
• Can a method or set of methods be defined to quantify certain bitumen additives and how precise are the derived results?

Methods to be used by each participant are FTIR, GPC, DSC and DSR. Further methods are welcome.

The goal is to define methods for fingerprinting and quantification of certain additives with commonly available methods. This can again be seen as a pre-standardization step to make sure that future research in this area provides comparable results.

TG 1 and TG 2 will work in close collaboration to make best use of the produced data and ensure the succesful achievement of their individual objectives. The TG work has been organized in such a way, e.g. there is an overlap in the testing methods and studied materials, to allow for maximum interaction.

Detailed working programme

Spring 2020: Approval of new TC by TAC

June 2020: Kick-off meeting in Lyon during the RILEM International Symposium on Bituminous Materials. Approval of work program and assignment of group leaders.

Fall 2020: Meeting to discuss its plans with the other Asphalt Scientists during the Annual RILEM Asphalt TC meeting.

During 2020: Individual meetings by TG’s, finalizing proposal of working plan, evaluation of other possible synergistic activities, identification of missing expertise/experts that could be affiliated with the TC.

2020 to 2021: Review and gathering of state of the art for TGs

During 2021: Individual meetings by TG’s, finalizing proposal of working plan, starting of round robin test (TG 1) and experimental work (TG 2)

Fall 2021: Annual TC meeting in the course of the Annual RILEM Asphalt TC meetings.

2021 – 2022: Executing and finalizing round robin test and experimental work. Start of data evaluation.

During 2022: Workshop of the TC: Bring together experts from the bituminous binder and mixture community and key experts from materials science, polymer science, and material chemistry to define best candidate laboratory characterization techniques for binders and mixtures, along with optimal specimen preparation methods for chemo-mechanical characterization of bituminous materials.

Fall 2022: Annual TC meeting in the course of the Annual RILEM Asphalt TC meetings.

2023 – 2024: Data evaluation and developing recommendations for both TGs as a basis for further use in standardization.

Fall 2023: Annual TC meeting in the course of the Annual RILEM Asphalt TC meetings.

Spring/Summer 2024: Co-organizing the RILEM International Symposium on Bituminous Materials

Fall 2024: Final Report and Recommendations and closing of the TC during the Annual RILEM Asphalt TC meetings.