*2.1. Reuse and Rethreading*

The rethreading process is used for the repair of limited worn-out tyres because of the initial wearing and certification requirement of the damaged areas that need to be rethreaded [46]. It is one of the most ideal strategies that require the limited deployment of additional energy and resources, mainly rubber, which accounts for 50% of the material involved. It involves 20% usage in the damaged situation, whereas the remaining part constitutes a tyre carcass [47]. Practically, rethreading requires about 25% of raw materials and 30% of energy and only 30% of the energy needed to produce new tyres, which make this process economically profitable [48]. However, because of the safety issue at high speed, rethreading tyres is not used in automobile application [49].

#### *2.2. Recycling*

Recycling is also one of the widely used methods for managing waste tyre. Sienkiewicz et al. [22] referred to recycling that does not include any treatment, be it physical or chemical in nature, and only disintegration is important. Moreover, the role of the shape of the tyre, their initial development in terms of size, durability, elasticity, vibration capacity, high damping, etc., makes this material very useful and important in works of many other purposes. There are many applications for the tyres recycled; some of the end products

from recycled rubber include: manufacturing new tyres, tracks for athletics, insulation in buildings, matting surface, surfaces for playgrounds, marine non-slip surfaces, etc [50].

#### *2.3. Energy Recovery*

Various industrial processes rely on non-renewable energy sources, such as coal. The abundance of coal and the combustion process are sufficient to meet the demand. Recovery of waste tyres from other rubber products is one of the processes that can be used to deploy them as energy sources, such as fuel. Waste tyres can be used as an alternative fuel in cement kilns and for electricity generation, but their combustion and burning pollutes the environment. The cement industry uses tyres as a source of energy, making it a cost-effective way to meet their high-temperature requirements. However, compared to pollution levels in the air caused by the coal combustion process [22], this has a minor impact. Figure 2 shows that 53% of used tyres in the United States are capable of meeting fuel requirements [51]. Cement and paper mills use 68% of waste tyre for their energy needs, as shown in Figure 2.

**Figure 2.** US scrap tyre disposition.
