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As many markets place more focus on temperature reductions for asphalt production and laying, cold-mix asphalt techniques are receiving renewed interest.
By learning to control complex interactions between bitumen emulsions and different minerals, researchers aim to develop techniques that will enable cold asphalt to be used on a large scale.
“There is a lot to be gained from using cold asphalt rather than the conventional hot mix. And whereas soft bitumen emulsions have been shown to work well with all kinds of different stone, hard bitumen emulsions work perfectly well with some minerals, but not at all with other ones,” says Oleg Antzutkin, professor of Chemistry of Interfaces at Luleå University of Technology (LTU) in the north of Sweden.
Oleg Antzutkin is part of a research team set up to solve the mysteries of cold-mix asphalt. Bringing together the expertise of different disciplines and industries, it is a joint project involving scientists at LTU and the Royal Institute of Technology (KTH) in Stockholm, as well as NCC Roads and Nynas.
“Asphalt is a very complex system that is dependent on many different parameters. The mineral composition of the stone seems to play an important role in making the bitumen stick to it. It is our aim to nd a way to improve the compatibility between certain rocks and bitumen,” he explains.
So far, calcium-rich minerals have been identified as particularly problematic. However, ambient weather conditions such as temperature, rain and sun will also in uence the result.
“We are trying to identify the correlation between the various parameters and the success or failure of different bitumen/stone mixtures. This will help us to predict which mixtures will work, and also to understand why they work,” says Oleg Antzutkin.
His LTU colleague Dr Andrei Filippov is developing a new methodology for studying the breaking process of the cold-mix bitumen emulsion that enables it to stick to the stone. Diffusion NMR (nuclear magnetic resonance) is employed to study bitumen emulsions confined between polished plates of different minerals.
At LTU, Dr Tommy Edeskär has also devised a self-learning machine system that can handle and make sense of all the different variables. The aim is to develop a predictive tool that will prove valuable to both bitumen producers and road builders.
At KTH, professor Mark Rutland’s research group contributes to the project with their expertise in surface chemistry and advanced techniques, such as atomic force microscopy (AFM).
Tommy Edeskär (left) and Oleg Antzutkin are two of the scientists hoping to perfect cold-mix asphalt. So far used to a limited extent, cold-mix asphalt offers benefits in terms of energy consumption, carbon emissions, working conditions and recycling.