Influencia de la temperatura y el tiempo de mezclado en la modificación de un cemento asfáltico

Abstract

Based on the literature consulted to date, when an asphalt is modified wet with thermoplastic polymers (elastomers or plastomers), a remarkable increase in its rigidity is usually obtained, expressed through the decrease in penetration and ductility, and the increase in the softening point, the viscosity, the degree of operation (PG) at high service temperatures, the cutting module (G *) in rheology tests, among others. When the asphalt cement is wet modified, it is mixed with the additive at elevated temperatures for a predetermined time. The temperature and time of mixing of both components depends mainly on the type of additive used. During this process of exposing asphalt to high temperatures, its physical-chemical properties change, mainly due to a process of oxidation and aging of the binder, which directly affects the increase in stiffness and the decrease in ductility (Fernández, Rondón, & Reyes, 2011), (Rondón and Reyes, 2015). In general, the studies carried out on modified asphalts in the world, do not discriminate what is the real contribution of the additive in the stiffening process of the asphalt, and what is due to the processes of exposure of the binder at high temperatures for long periods of time when the asphalt is modified wet. The present study tries to generate a contribution in that sense, trying to evaluate, the influence that has the temperature and the times of exhibition to which the asphalts are submitted, when they are modified by wet way. For this purpose, physical characterization tests (penetration, softening point and specific gravity) were carried out on an asphalt 60-70 subjected to three temperatures and three exposure times. The times and temperatures at which the asphalt cement was subjected were chosen based on the literature review, trying to reproduce the wet modification conditions. It is considered necessary to specify that the mixing speed was not controlled during the process of submitting the samples, since it was not possible to obtain the means to carry out said control. Likewise, on MDC-19 mixtures manufactured with these thermally treated asphalts, resistance tests were carried out under monotonic load Marshall (INV E-748), maximum load with indirect traction (INV E-725-13) and loss by wear by half of the Cantabro trial (INV E-760-13). Based on the results obtained from the laboratories carried out in the present study, it is possible to conclude that, the temperatures and the exposure times to which the asphaltic cements are subjected during the process of modifying them by wet process, influence in a direct in the mechanical response that a MDC-19 mix experiences. Additionally, high temperatures used to mix the asphalt, generates a remarkable increase in the consistency of the asphalt, expressed through the decrease of the penetration and the increase in the point of softening and the specific gravity, however, the manipulation of this material in the mixture with the aggregates becomes complex, every time the material loses binder conditions and its cohesion with the aggregates decreases. Finally, the aging phenomenon on the asphalt cement product of the thermal treatment generated a change in its composition and its rheological behavior. This was seen in the results obtained, is characterized by a hardening of the asphalt and had two effects on the mixture: first, increase the support capacity of loads generated, and second, increase the resistance to deformation of the mixture, product of an increase in rigidity. However, this handling of the asphalt cement reduces the flexibility of the mixture due to loss of ductility, leading to the mixture being prone to damage by fatigue and loss of recovery potential.