HOW TO REJUVENATE AGED BITUMEN AS INDICATED BY A LABORATORY METHOD --BITUMEN, FLEXIBLE AND DURABLE. 3RD EUROBITUME SYMPOSIUM 1985, THE HAGUE, NETHERLANDS, SEPTEMBER 11-13, 1985

Plants producing recycling mixes are sufficiently reliable to guarantee the production of materials with the characteristics envisaged by the new specifications. These results are more frequently obtained by fixed plants, where the recovered material is about 50%. The mechanical tests, to which the recycled concrete are submitted, give partial information on the behaviour of the material in the long run, except in case of macroscopic errors of application; in that case the causes of the troubles are easily recognizable. Those errors are mainly due to the necessity of employing sophisticated laboratory methods, not able to exactly reproduce the conditions in which the new binder in the recycled mix will work. A great importance is attached to the preliminary study of bitumens in the laboratory for the purpose of defining correct operations. The amount and the kind of binder to be added and the necessary chemical additives are defined through laboratory tests that reproduce changes occurring in the industrial plant. The evaluation of the physical and rheological characteristics and the composition of mixed bitumens depends largely on the method of extraction. The homogenizing of the aged bitumen with new bitumen as produced in the laboratory allows the reconstruction of a chemical structure, which can be compared to a bitumen suitable in grade and viscosity suited to the requirements of the pavement. In the plants this process is hypothetical; in the asphalt concrete, in fact, the possibilities that the regeneration of aged bitumen take place in a shorter time than the time expected from laboratory tests depend on the production rate and the mixing cycle adopted. In practice the regeneration of the binder is based on assumptions that cannot be easily attained. It is therefore necessary that the laboratory method pay less attention to the binder but considers the characteristic of final asphalt concrete. For this aim it is necessary that at least the laboratory operates separately on the recycled mix and on the new mix through different processes: -to restore the aged bitumen characteristics with the new bitumen and chemical additive in suitable proportions to reach the expected mechanical characteristics of recycled asphalt-concrete, -to evaluate mechanical characteristics of new asphalt-concrete by the optimization of new binder to be added, -to manufacture the final mixture as expected by the project and to evaluate the mechanical behaviour after mixing in the right proportion, new mix with recycled material, -in this way the binder will be regenerated and this will allow a better diffusion in the mix and the final product will be an asphalt-concrete with the required characteristics, -as regards bitumen quality, the methods to be followed to regenerate the aged bitumen remain the same as employed at present, particularly those employed for the evaluation of the final viscosity, as regards the amount of new bitumen to be added, it must be