Revealing structure

Employing an advanced analysis method, Nynas researchers are starting to unmask the chemical structure of bitumen. Xiaohu Lu explains how TOF-SIMS is used to analyse the surface structure of bitumen.

Using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) we have been able to characterise the chemical composition and structures of bitumen surfaces. We also compared wax-free bitumen with bitumen that contains natural wax and wax-free bitumen with added wax,” says Dr Xiaohu Lu, Senior Technical Specialist and leader of several bitumen R&D projects at Nynas.

The TOF-SIMS project has enabled the researchers to Revealing structure delve deeper into some of the unanswered questions regarding the chemical structure of different types of bitumen and their components. For instance, by opening a window into the surface structure of bitumen, their work has revealed the role played by wax.

The researchers established that the structures formed on bitumen surfaces are closely linked to the wax content. They could observe that wax is enriched and deposited on the bitumen surface, providing insight into the associated phase segregation phenomena.

Dr Xiaohu LuSenior Technical Specialist, manages various Nynas R&D projects on bitumen and bituminous materials. Prior to joining Nynas in 2002, he was an Associate Professor at the Royal Institute of Technology (KTH) in Stockholm, where previously he had obtained his PhD in Highway Engineering. 

“The surface of wax-free bitumen is characterised by a homogeneous distribution with no chemical variation or phase structures, but when natural wax is added there is segregation resulting in wax enrichment on the surface,” he explains.

However, the segregation is different from the one in the naturally waxy bitumen. For instance, in the bitumen with added wax, the researchers found none of the so-called “bee” structures (elongated and well-defined structures that resemble the stripes on a bee) commonly seen in bitumen containing natural wax.

“These findings will help us to understand and predict performance differences in bitumen. Building on our initial study, we are now using TOF-SIMS to look more closely at the effects of ageing,” says Xiaohu Lu.

Surface analysis

TOF-SIMS is used to collect chemical information about the surface of a sample from secondary ions that are emitted following bombardment by high energy primary ions. The collision between these primary ions and the sample results in the emission of a variety of particles. Most of the particles, such as atoms and molecules or parts of molecules, are neutral. However, some come off as either positively or negatively charged ions.

It is the mass spectroscopy analysis of these emitted secondary ions that help create a “picture” of the surface. By scanning the primary ion beam over the sample surface, separate mass spectra are acquired from each pixel within the analysed area. This provides information of submicron resolution that can be displayed in a variety of ways.

Safety

Safety assessment at asphalt plant

Nynas visits an asphalt plant operated by NCC, a construction company in the Nordic region, to assess its safe handling of bitumen.

Mats Wendel
Interview

Sustainable Development driving innovation

It is important to have both incentives and clear requirements to drive developments forwards and to make sure that the industry is making a positive contribution to sustainable development.

A90 Dundee
Projects

In good shape

Most local authorities in the UK think of cold mix asphalt as a new and relatively untested road construction material. But it has been used successfully in the UK for more than 10 years, including a section of trunk road in Scotland built with a cold mix asphalt base course in 2008.

Safety

Knowledge key to safe deliveries

Bitumen is delivered hot and therefore precise procedures are needed in order to minimise safety risks such as burn injuries. Safety is something on which the transport company Kördel maintains a constant focus.

Noted

A road so smart it will be able to charge your car.

Bloomberg on the development of intelligent highways in China.
More at: bloomberg.com


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