From recycled plastic to pulverized waste tires: recycled asphalt for more sustainable roads

To improve the current road network, there are several recycling techniques that reuse the foundational materials of the pavement. In addition, the industry, on its way to decarbonization and the promotion of the circular economy, is also working on the development of more sustainable paving alternatives.

Every day, millions and millions of people travel by road to get to their jobs, homes, or vacation destinations. And we move on pavement that is mostly made up of asphalt mixtures that incorporate oil-based bituminous binders in their manufacturing process, which is essential to achieve the performance of asphalt mixtures during their service life. Just as in other sectors, this industry also wagers on decarbonization and has been working for years to develop techniques that are just as efficient but more sustainable and respectful to the environment. 

The first thing we ask ourselves, then, is if asphalt pavement can be reused. The answer is yes. According to a study carried out by the UPC (Universidad Politécnica de Cataluña), in addition to conventional rehabilitation methodologies for solid surfaces that use virgin materials, there are various procedures that reuse spent materials from the pavement. UPC experts explain that for reuse, "along with these aged materials, other materials such as special binders, rejuvenating agents, new bituminous mixture, etc.) can be added," and that there is not just one way to carry out this process. 

In fact, depending on the deterioration of the asphalt pavement, whether it is superficial or, on the contrary, affects the pavement structure, the cost (not only economic, but also environmental and social), experience and availability of equipment or the required time, there are four most commonly used techniques: hot reuse; semi-hot; cold with cement; and cold with bituminous emulsions, either in situ or in a plant.

Affects traffic less and other advantages of reuse

Regardless of which circular economy system is used, the advantages of reusing a pavement range from using the available resources within the circular economy system, thereby avoiding the exploitation of new quarries, reusing existing granular materials in the aged mixture, producing no waste, to manufacturing yields. In addition, when this recycling is done on site , the operations related to transport of materials to a manufacturing plant are eliminated. 

At the same time, experts explain that these techniques avoid gauge problems, as the pavement does not "rise" with them; it facilitates making modifications related to vertical and horizontal alignment without the need for major actions; it allows for repairing structural failures without disposing of existing materials and improves surface bonding. In addition, there is less impact on traffic, because while one lane is being rehabilitated, the others can still be used and the time it takes for these operations is less than that of traditional techniques.

In this regard, Cepsa has several ongoing projects in which different reuse techniques are being applied, in order to rehabilitate the structure of damaged pavements. In the Basque Country, for example, highway GI 3591, to the Arantzazu Sanctuary has used 80% recovered material from aging roads. 

Alternative pavement projects

Beyond reuse, which is usually used to solve the deterioration of the current road network, the industry is looking for alternatives in terms of materials to manufacture new pavements, taking sustainability criteria into account. . 

Thus, we find pavements crated from plastic waste and recycled PET. PlasticRoad from KWS, for example, uses recycled plastic from bottles, cups, and other types of containers and packaging. In 2018, a section of the bicycle lane in the Dutch city of Zwolle became the first pavement made from this material. And in Philadelphia, Temple University experts use a mixture of PET plastic and mud “that functions as permeable concrete and porous asphalt,” explains one of its developers, Professor Naji Khoury. PlastiSoil, as its creators call it, can be used for sidewalks, bike lanes, highways, or parking lots.

In Spain, thanks to the work of Signus, more than 1,600 kilometers of asphalt roads are using rubber crumbs from end-of-life tires (EOLT) that the company collects to recycle. And, along the same lines, the University of Granada has been working for years on the Masai Project; sustainable, automated and intelligent asphalt materials that incorporate milling of aged pavement, used tires and other recycled materials. This project has generated interest from F1. 

On the other hand, the CETIM (Multi-sector Research Institute) of A Coruña is also researching mixtures with nanocellulose from wood waste. 

In addition, at Cepsa, the Asphalt area participates in several Eco-asphalt projects that follow “the principles of the circular economy and incorporate additives to reduce energy consumption and emissions.” These include methodologies for reducing manufacturing and on-site application temperatures, tests with new binders for higher performance that contribute to greater durability of the pavement, and the use of by-products derived from other refining processes.