*2.2. Mechanomutable Asphalt Materials for Improving Road Safety and Service Conditions*

Mechanomutable asphalt materials are electroconductive; thus, they have the capacity to produce and conduct Foucault currents generated from the effect of magnetic fields (Figure 4). In turn, these currents are the source of the energy losses transformed into heat through the Joule effect. Thus, mechanomutable asphalt materials can also be regarded as thermomutable asphalt materials, which makes them ideal for two types of road maintenance operations: 1) clearing ice and snow from the surface of the road (Figure 4), and 2) healing the cracks produced from the dynamic loads of traffic, temperature and moisture changes (Figure 5).

**Figure 4.** Schema of the thermomutable asphalt materials under magnetic fields for use in de-icing and producing anti-snow roads.

**Figure 5.** Schema of the healing capacity of thermomutable asphalt binders.

To achieve the first type of maintenance activity, the temperature of the electroconductive layer is increased with the goal to heat up the whole pavement system though conduction. This has the effect of melting possible snow and ice on the road and increasing user safety. For the second maintenance activity, a magnetic field is applied to the MAM to produce a controlled increase in temperatures between 30 ◦C and 70 ◦C, via induction [19,41] and microwaves [19], which is the interval of temperatures between which the binder flows as a Newtonian fluid and is then able to seal potential cracks in the pavement [22].

To achieve both aforementioned maintenance operations, an electroconductive smart layer can be placed inside the bituminous layers of the pavement. As shown Figure 4, the surface course would be applied on top to protect vehicle tires from possible damage caused by magnetically responsive materials in the mechanomutable asphalt layer; these materials, such as steel fibers obtained from end-of-life tires, typically have sharp edges. This surface layer would be an ultra-thin layer, to ensure the structural performance of the pavement and resist the temperature increase produced in the electroconductive layer by the activation of a magnetic field.

Table 2 describes recent strategies for managing snow- and ice-related maintenance activities on road pavements. These strategies have considered the use of electroconductive materials, as in this study, as well as other alternative systems. For example, the use of infrared heating, hydronic heating systems and embedded heating wires to melt the snow and ice in various public areas, such as pedestrian walkways, emergency entrances, loading dock ramps, hotel lobby entrances, bridge decks, sidewalks and pavements. These snow-melting systems are each composed of an energy source (which can be electric, geothermal and/or magnetic), heat exchanging elements, sensors (for measuring actual weather conditions) and a system control. The power consumption of these strategies varies depending on the current development of the system, which demonstrates that these solutions still require further research in order to optimize their performance and, finally, bring their use into practice.

Given that hazardous weather conditions can increase the susceptibility of traffic accidents, especially with snowfall being a particularly high risk factor in road accidents [42], these solutions can be used as environmental-friendly and smart alternative strategies for traditional "de-icing salts". While these salts have been shown to be economically accessible and effective, they affect the roadside soil, underground and surface water and vegetation integrity [43,44], as well as the long-term structural performance of the road infrastructure and vehicle health [45].


**Table 2.** Strategies for managing snow and ice in road surfaces.

With respect to the second type of maintenance operation, with the aim to transform roads into more resilient structures through self-healing, recent research efforts have designed and evaluated the use of encapsulated healing agents (oily rejuvenators) [54–56] and the effect of resting periods [57]. As it stands, this area is somewhat newer and has undergone less research.
