*2.1. Mechanomutable Asphalt Materials as Improved Materials for Constructing Pavements*

Mechanomutable asphalt materials were born from the principle of the functioning of the magneto-rheological (MR) fluids applied to asphalt binders [4,5]. As shown in Figure 2, the characteristics of magneto-rheological fluids provide a medium (in this case a bituminous matrix) in which to magnetically suspend active particles during the absence of magnetic fields. However, when magnetic fields are present, these materials have the capacity to behave as a quasi-solid material, increasing the apparent viscosity of the material [35,36], modifying its rheological behavior from Newtonian to viscoelastic [37] and impeding the movement of the magnetically active particles, which produce an internal stress tensor in the mixture [5].

Research studies that have specifically focused on mechanomutable asphalt materials have confirmed that, at the binder scale (Figure 3, MAB1, MAB2, MAB3), the higher intensity of the magnetic field and higher quantities of magnetically active particles can increase the modulus and decrease the phase angle of the mechanomutable binder [5]. Related studies that have simulated the dynamic demands of traffic (creep and recovery tests) have revealed that the cumulative deformations in these materials are due to a decrease in their propensity to deform rather than an increase in their recovery capacity (which is more strongly influenced by the penetration grade of the bitumen) [4]. In order to scale those findings to practice, later studies at the mortar scale (Figure 3, MAM1) confirmed the increase in modulus values, depending on the increase in the intensity of the magnetic field and the quantity of magnetically susceptible materials [6].

**Figure 2.** Functioning mechanism of mechanomutable asphalt materials (MAMs) as improved materials for pavements.

**Figure 3.** Key studies regarding the structural applications of MAMs in pavements [3–6,38].

Finally, studies regarding the piezoresistivity of electrically conductive asphalt base composites reveal that there is a correlation between this parameter and the stress–strain responses of the pavement, which could be useful for weighing, traffic monitoring, border monitoring and structural vibration control [39,40]. Therefore, the aforementioned capacities of these materials point to their potential use in the construction of airport runways, the high loading areas of airports, ports and parking lots, bus stops and exclusive lanes for heavy traffic.
