Ditecpesa continues to carry out research and promote the manufacture of asphalt mixtures using rubber powder from used tyres, with the aim of improving those currently used and marketed by Ferrovial Agroman.
Rubber dust or powder from old tyres, when mixed with asphalt bitumen using both dry and wet processes, has been shown to provide interesting applications. Ditecpesa has further developed its application to hybrid bitumen mixtures by incorporating rubber powder on site to a bitumen mixture already been previously modified with elastomers in its own plants. Satisfactory results have been achieved both in manufacture and use of the mixture, as well as through the added value of recovering waste materials, as explained by José Miguel Martínez Macedo Head of Operations and Development.
“The properties of bitumen mixtures containing recycled tyre rubber (RTR) are better than those of asphalt mixtures with penetration grade or modified bitumen”, explains José Miguel. “Comparing mixtures with traditional polymers and mixtures with RTR, the latter show better performance in terms of resistance to fatigue, rutting and cracking, with the added value of recovering a waste material such as tyre powder.”
Another advantage of modified bitumens containing rubber powder (RTR-MB) is their good environmental performance. On the one hand, they reuse the rubber waste resulting from management of end of life tyres (ELTs), and can thus be included in new internal policies on the circular economy. On a global, external level, they protect the environment by reducing noise generation, and are highly efficient as an additive to improve the properties of asphalt mixtures.
Regarding asphalt mixtures modified with rubber powder, different methods can be used when incorporating the powder. Ditecpesa has extensive experience with all methods, applying the best solution for each project:
- Dry process: the rubber powder is added directly to the mixer in the asphalt plant through a hopper and feeder.
- Wet process: Rubber powder is already incorporated in the bitumen, in proportions of around 8% to 12% of the total bitumen. It is supplied in a tanker truck in the traditional manner; problems with sedimentation are easily resolved through augers in the holding tanks within the asphalt plant.
- Hybrid bitumens: this is a solution developed by Ditecpesa (and used in the Olivar – Jaén motorway). The asphalt bitumen is first modified with a traditional polymer, and RTR is subsequently added on site (in a proportion of approximately 10%) using mobile mixing units. The resulting bitumen would be equivalent to a PMB 45/80-65.
In addition to laboratory research, Ditecpesa takes part in specialist annual congresses, such as the Technical Sessions on Tyre Dust held in Toledo. This brought together top representatives of Spain’s leading companies in the manufacture and management of new mixtures for application on roads. Ditecpesa is one of such companies, and was a keynote speaker at the roundtable on the general outlook of bitumen mixtures incorporating rubber powder.
José Miguel Martínez took part in the said roundtable, together with representatives from PTC, COLLOSA, EIFFAGE, REPSOL and SACYR, discussing the benefits of these mixtures and current and future trends for the industry.
The event, organised by Signus, was attended by professionals from Valoriza and Asefma, who contributed their own experiences, as well as representatives from the public administration. All of them highlighted the importance of a solid regulatory framework and adequate planning for the production of these types of bitumen.