Review and analysis of advances in functionalized, smart, and multifunctional asphalt mixtures

Abstract

Road pavements are designed to withstand road traffic and weathering actions while ensuring comfortable and safe riding conditions as well as low costs and damage to the environment. When a road pavement has additional abilities or reacts to an external stimulus, it is considered to be smart and multifunctional. Examples of such abilities that have been investigated in asphalt mixtures are photocatalytic, superhydrophobic, self-cleaning, deicing/anti-icing, self-healing, thermochromic, and latent heat thermal energy storage abilities. These abilities are developed using different materials such as nano/microparticles (including semiconductor materials and microcapsules), fibers, phase change materials (PCMs), and dyes, often using dissimilar techniques such as spray coating, volume incorporation, spreading, and asphalt binder modification. Owing to their large surface areas, road pavements are true recipients for large amounts of nano/micromaterials, and consequently, act as important "tools" to stimulate an emerging sector related to the scale of production of materials in the form of nanoparticles. Moreover, smart and multifunctional road pavements can be included in the domain of clean technology (e.g., photocatalytic pavements that promote the environmental depollution of NO x -type gases emitted as vehicle exhaust gases). In this context, they can contribute to materializing the transition to a novel socioeconomic model known as "Green Recovery" that is environmentally friendly, sustainable, and inclusive. This model is a very important path toward economic and employment recovery, a vision to which many countries are strongly committed. Therefore, this work reviews new capabilities imparted to asphalt mixtures and provides recommendations.

Functionalization of Smart Recycled Asphalt Mixtures: A Sustainability Scientific and Pedagogical Approach

“…In this specific case, the selection of the SS for the composition of the asphalt mixture was based on the fact that iron is commonly used to dope TiO 2 and, therefore, increase the photocatalytic efficiency since the nature of aggregates can affect the efficiency, according to previous conclusions [34]. Furthermore, the use of SS can promote new capabilities, such as self-healing and anti-ice [5]. RAP is the most common recycled material introduced in asphalt mixtures [35].…”

“…Both gases are produced in motor vehicles and also industrial processes. Recently, alternative techniques to improve urban air quality have arisen, such as capturing or reducing pollutants based on photocatalytic materials [5]. Among the photocatalysts, titanium dioxide (TiO 2 ) is one of the most studied and applied semiconductors to functionalize dissimilar materials; it allows the degradation of harmful gases due to the redox photocatalytic properties when activated by UV radiation [6][7][8].…”

“…The presence of water, ice, and snow over the surface drastically reduces friction contributing to the increase of road accidents [21][22][23]. Thus, it is essential to drain or repel the surface water quickly and remove/avoid ice and snow, which can be performed by promoting the superhydrophobic capability with the application of particles as TiO 2 [24,25] TiO 2 or combined with ZnO [25], SiO 2 [26], PTFE [27], fluorine polymer with nano-CaO [28], magnesium-aluminum layered double hydroxides [29], among others, over asphalt pavements usually by spraying coating [5,25,[27][28][29]. A superhydrophobic surface is characterized by a high-water contact angle (higher than 150 • ) [22,25,27].…”

“…As for the photocatalytic asphalt mixtures, the immobilization of the particles remains a challenge for the spraying coating of superhydrophobic asphalt mixtures. In addition, this capability must be evaluated in real-scale conditions to test its effectiveness [5]. How-ever, there is evidence that superhydrophobic coatings form an impermeable layer on the material's surface, preventing water damage [24].…”

“…In addition, the application of these capabilities on recycled asphalt separately is rare, and together as a multifunctional material is nonexistent or unknown. However, it is strongly recommended as the eco-social friendly dimension of the civil engineering material is enhanced and the production cost reduces due to the reduction of raw materials use [5,[30][31][32][33].…”