Rheology rethink

A proposed new method for studying the rheology of bitumen and binders at low temperatures proves promising. Hilde Soenen explains the method’s potential.

The objective is to obtain a consistent method for determining the rheological behaviour of bitumen binders at the lowest service temperatures,” says Hilde Soenen, Bitumen Research Manager and responsible for Nynas lab at the University of Antwerp in Belgium, after evaluating a new method together with two PhD students.

Presently, two standard methods are used to determine the rheological behaviour of bitumen - at medium to high temperatures a Dynamic Shear Rheometer (DSR) is used, and at low temperatures a Bending Beam Rheometer (BBR). The DSR method, which involves samples being placed between parallel plates, is more versatile and enables tests to be performed using smaller samples than the BBR.

Current DSR methods are based on 25 and 8 mm diameter plates, and for bitumen this allows testing to around 0° C, due to rheometer equipment limitations. By using plates of a diameter of only 4 mm, it seems possible to extend the temperature range to -20° C or even -30° C. A smaller sample size is also an advantage when testing recovered and aged binders, as these are difficult to obtain in larger quantities.

“A student from Aalto University in Helsinki, Olli-Ville Laukkanen, looked into the 4 mm DSR method during his Master’s and PhD study. He’s been optimising the testing, for instance the sample loading procedure and the necessary calibrations, using equipment at the University of Massachusetts in Amherst,” says Hilde Soenen.

Another visiting research student, Judita Gražulytė from the Road Research Institute at Vilnius University in Lithuania, developed the 4 mm DSR method for use with equipment at the Nynas lab, producing test results comparable with those obtained in the US lab.

“That suggests a level of repeatability and reproducibility, which is a prerequisite for any test measurement used in a performance-based selection system for bituminous binders for road applications.”

However, the 4 mm DSR method also presents a number of challenges, for example with regard to temperature control and the preparation and placement of samples.

“We are working to solve these issues and there is still a lot more to be done.”

The relevance of rheological information is also widening. Low temperature rheological properties can, for instance, provide insight into the durability or ageing of a binder. A specific parameter (delta Tc), used for such evaluations, is calculated from rheological data.

“We believe that the new 4 mm method will have an important role to play, also here.”

Projects

Sokndal, Norway

The recently opened Motorcenter Norway offers everything from go-carting to drag racing. Nynas was involved in the project by supplying Nypol HF 105, a polymer-modified bitumen ideal for pavements that are subjected to high stresses.

Projects

Gothenburg, Sweden

The Älvsborg Bridge spans the estuary of the Göta Älv river at the entrance to Gothenburg and the biggest port in Scandinavia. The bridge, officially opened in 1966, has a total length of 930 m and a suspended span of 418 m. To guarantee the bridge's functionality and extend its useful life, extensive maintenance work has been under way since 2019, the third and final stage being completed this summer.

Talking point

Road infrastructure in North-Western Europe

Even though many successful road projects have been completed in Western Europe in recent years, the durability and availability of the road infrastructure needs to be improved.

Interview

Paving the way for asphalt 4.0

Digitalisation is making inroads in the asphalt industry. The latest Eurasphalt & Eurobitume (E&E) Congress was held virtually in June. It was a success, but the next E&E event will allow industry stakeholders to meet face-to-face.

Noted

All the key players are working together to achieve the best possible result.

Katri Eskola, Specialist Road Maintenance Finnish Transport Infrastructure Agency

Talking point: The COVID-19 pandemic


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