Efecto de las condiciones de fabricación en las propiedades de las mezclas bituminosas recicladas

Abstract

The use of bituminous material milled from the pavement (known as Reclaimed Asphalt Pavement, or RAP) in the manufacture of recycled bituminous mixtures is growing day by day due to the economic and environmental benefits that this technique of road maintenance entails. However, there is some concern about the resulting properties of the recycled mixture considering the manufacturing conditions. One concern is the blending of the asphalt binder from the RAP (the aged asphalt binder) with the virgin asphalt binder. The main factors that could affect the degree of mixing between the aged and virgin asphalt binders are: the production temperature, mixing time, final temperature of the mixture, origin of the RAP, the properties of the RAP, and the use of additives as rejuvenators to enhance the degree of mixing. Therefore, this thesis aims to analyze the effect of manufacturing conditions on the volumetric and mechanical properties of recycled bituminous mixtures. This objective was pursued by establishing two stages of research. In the first stage, the conditions for manufacturing test samples consisted in varying the temperature of the aggregate and RAP, as well as varying the mixing time. The effect of the rejuvenating agent on recycled bituminous mixtures with 60% RAP was also analyzed. The second stage consisted of changing specific characteristics from the first stage, for example, changing the origin of the RAP, extending the mixing time, as well as using different materials and laboratory equipment. The first stage was carried out at the Polytechnic University of Catalonia (UPC) and the second stage was held at the University of Nottingham. An experimental program was developed that includes tests to evaluate the properties in recycled mixtures, such as: void content, tensile strength, stiffness modulus, and Fenix test. Emphasis was placed on the use of the Fenix test developed at UPC, since it has proven to be a practical and efficient method to characterize the cracking behavior of bituminous mixtures at different temperatures. A test method has also been included to analyze the influence of the RAP mastic, the UCL (Universal Binder Characterization Method) developed at UPC and that has confirmed in different studies that it can give complementary information about the effect of the content and the temperature of the mastic on the mechanical properties of a recycled bituminous mixture. It has been possible to conclude that recycled mixtures can achieve a performance similar to that of conventional mixtures, provided that the appropriate treatment is taken into account in the design and manufacturing process. By preheating the RAP, it is possible to more effectively spread the rejuvenating agent which will mobilize a greater quantity of the RAP asphalt binder. Extending mixing time causes the RAP agglomerations to begin to separate and, therefore, a greater amount of bitumen is mobilized. The incorporation of a rejuvenating additive produces a positive effect on the properties of the recycled mixtures since it manages to restore the properties of the aged bitumen. However, in most cases, it is sufficient to apply any condition (preheating of RAP, increasing the mixing time, overheating aggregates or the use of the rejuvenators) to improve the properties, but in some cases to apply all the conditions simultaneously a synergistic effect is produced in the properties of the mixtures, inducing a positive effect on the behavior of the recycled mixtures.