Collaboration with Repsol, with the companies Abertis and Tecnofirmes, in the design of bituminous mixtures manufactured using recycled material for application in the AP-61 highway

Asphalt News 02/03/2016

At the request of the companies Abertis—operator of the AP-61 highway—and Tecnofirmes—as contractor company for the manufacture of mixtures—the collaboration of Repsol's Department of Technical Assistance and Development of Asphalts in designing the work formulas of AC2 S- and BBTM11B-type bitumen mixtures., to which recycled material from the milling of bituminous mixture in the percentages of 25 % and 10 %, respectively, is added.

The two types of mixtures were applied to a test section of the AP-61 Freeway, using AC22S as an intermediate layer and BBTM 11B as a wearing course.

The recycled material stems from the demolished freeway surface, which makes it possible to ensure its origin and evenness, in addition to guaranteeing the characteristics of the aggregate of which it forms part.

The binders supplied correspond to a 50/70 bitumen for the AC22 mixture and a modified PMB 45/80-65 bitumen for the BBTM 11B mixture.

The main work consisted of classifying and controlling the demolished material for the purpose of ensuring that the grading of the mixture fits into the spindle in each case, to which end three fractions were used: 0/6, 0/12 an 6/22.

Fractions 0/6 and 6/22 were used in the AC22S mixture and the fraction 0/12 in the BBTM11B mix. The demolished material was added to the manufacture of the mixture directly in the dryer drum, behind the flow of the lighter flame to prevent the binder from becoming overheated, and mixed with the hot virgin aggregate, thereby allowing the drying of the demolished material and the homogenization of the temperature of all the granular material.

The working formula was prepared with the collaboration with the Asphalts laboratory of the Repsol Technology Center which, based on the samples supplied by the customer, defined the most adequate dose and assessed the characteristics of the mixtures manufactured.

In order to verify the behavior of the two mixtures manufactured using demolished material, a comparison was made with mixtures without addition of recycled product, obtaining similar characteristics in both cases and fulfilling the requirements for the two types of mixtures in all cases.

The work was not only limited to the design of the mixture, but also to control the executed sections in order to validate, on a real scale, the production and installation process on the basis on samples taken at the plant.

Such actions, in which it is verified that the addition of demolished material from bituminous mixtures for different percentages and types of mixtures produce results that fulfill the characteristics required for a bituminous mixture, make it possible to validate and demonstrate the use of demolished material, where applicable.