Exploring damage recovery in bituminous mixturesAn analysis of healing technologies

Resumen

In recent years, the analysis of the recovery capability of bituminous mixtures has become an important research topic in the field of pavement engineering. This capability is recognized as a foundation for the development of long-life asphalt pavements. Nonetheless, if this ability is to be exploited to develop new rehabilitation techniques for road infrastructures, there still remain some questions that need to be addressed. The recovery of properties in bituminous materials mainly produced by various phenomena: reversible phenomena (e.g., thixotropy and heating,) and the healing phenomenon (understood as the reestablishment of the broken molecular bonds). However, in spite of the fact that there are many studies that have assessed the effect caused by these phenomena, relatively little is still known about their real efficiency, or which of these have the greatest impact on recovery capacity along with their repeatability (if they are to be used as a basis for developing rehabilitation techniques, these phenomena should be able to produce a similar level of damage recovery several times). In this respect, it is also interesting to consider that these phenomena are highly related to the damage state of the material (reversible phenomena are more prominent before crack initiation, whilst the healing phenomenon can appear when the crack is produced), and consequently it is necessary to determine the optimal damage state at which the rehabilitation techniques should be applied. Finally, it should be considered that the majority of rehabilitation techniques based on the recovery capability of asphalt materials are primarily affected by three variables (duration, temperature, and external forces), and because of this, it is of critical importance to determine the optimal conditions for these variables. These optimal conditions will be directly related to the characteristics of the asphalt material, and therefore it is also necessary to know the relationship between time, temperature and external forces, and the various types of bituminous binders. Based on these considerations, this research aims to study the recovery capability of bituminous materials at various levels of damage, taking into account the influence of several variables such as time, temperature, external forces, and rest periods. Thus, to explore the recovery due to healing phenomenon, different types of asphalt mixtures were tested under various conditions until their macro-failure by employing the University of Granada Fatigue Asphalt Cracking Test (UGR-FACT), after which various conditions were applied in order to induce their recovery (applying heating and external forces) under different treatment durations. In addition, to explore the role of recovery capability due to reversible phenomena, the asphalt material was tested using UGR-FACT by introducing different types of rest periods. The results indicated that among the variables that could affect the recovery capability of the material at the macro-crack level, the duration of the healing treatment has little impact, while the type and amount of binder could have more influence than temperature. Additionally, the presence of external forces during the healing treatment could increase the rate of recovery, but it is not sufficiently effective to recover the initial properties of the material. Thus, regardless of the type of treatment, the amount of fatigue life recovered in macro-damaged asphalt mixtures is low, prompting the suggestion that although applying these healing techniques can close the macro-crack, completely effective healing appears to be more difficult to achieve. Furthermore, the results indicated that the presence of rest periods in the loading regime could lead to an increase in the fatigue life of asphalt mixtures when they are included before the appearance of cracks. In particular, it appears that an increment in the rest period duration and if they are included before the capacity to deform of the material is consumed could improve the resistance of the materials tested against cyclic loading. In this respect, the recovery produced during rest periods are not only related to reversible phenomena, but also to the delay of damage because of an increment in the plastic deformations produced (the inclusion of rest periods could increase the amount of deformations produced in the material, leading to a more ductile response and subsequently more number of load cycles can be supported).