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Car tires can be recycled for secondary use. For example, the addition of crumb rubber increases the life of asphalt. Typically, tires are shredded to particles as small as a few millimeters. Further shredding is too energy-intensive. However, a new method has emerged — high-temperature shear shredding. It takes place with the help of a rotary disperser. The essence of its work is a strong compression (20-30 megapascals), as a result of which the material is cracked and destroyed. At the same time, the rubber is heated to temperatures close to devulcanization. A powder is produced, which is then cooled sharply. To increase the efficiency of the process, scientists add other polymers to the rubber.

“Among all possible applications of crumb rubber from worn out tires, the most interesting one is the use in road pavement. Crumb rubber as a modifier of bitumen and asphalt concrete mixtures increases their service life and has great potential in the road industry. This combines the problems of recycling used tires and increasing the durability of roads. In this way it is possible to reduce the consumption of primary natural resources,” — Alexander Vecher, PhD in Biology, Deputy Director of the Nanotechnology Research Center at RUDN.

Nanotechnologists prepared rubber crumbs from car tires and then ground them into powder together with butadiene-styrene rubber on a rotary disperser. The powder was added to hot bitumen heated to a temperature of 120-180鈩� and stirred for 1-40 minutes. This approach is called “dry” preparation method. It means that the dry powder is added to the mixture directly during preparation, rather than in a separate process step.

RUDN nanotechnologists have studied rubber particles before and after their interaction with hot bitumen using scanning electron microscopy. Grinding together with butadiene-styrene rubber leads to the formation of outwardly homogeneous hybrid particles. After a minute of stirring in hot bitumen, the powder particles split into 100-200 nanometer-sized pieces. This rapid splitting probably occurs because the bitumen penetrates into the pores of the particles and causes swelling in different directions. With increasing stirring time, complete particle breakup is not observed in the hot bitumen. On the contrary, a tendency to form gel-like structures is noticeable.

“Considering that one minute of mixing time corresponds to the technology of obtaining various asphalt concrete mixtures, it can be recommended to use additive powders in a ‘dry’ way, i.e. to introduce them into the asphalt concrete mixture during its production. This will be more economical. In further research we will conduct rheological studies of bitumen with modifiers,” — Alexander Vecher.

The results were in the journal Polymers.