**4. Principle of structural re-use**

In 2015 the Professorship for Polymer Engineering (Windesheim University of Applied Sciences) began to develop the principle of the structural re-use of EoL thermoset composite products [4, 12]. This method is based on keeping the composite structure of the End-of-Life product intact but machining it into smaller parts, e.g. strips or flakes. These smaller parts must have an oblong shape enabling it to act as reinforcing elements once embedded in resin while making new products. In this manner the good properties of the EoL composite, mechanical strength, stiffness and water resistance, remain unimpaired and can be used in the new product. An illustration of the use of EoL composite strips and flakes as reinforcing elements in new composite products is given in **Figure 2**.

To embed the strips or the flakes, additional virgin resin is required. This method implies that the new products will be relatively heavy and can only be simple in shape e.g. profiles, beams or plates. This combination of properties: high strength, high water resistance, relatively heavy and straight-shaped are extremely suited to infrastructural applications. Thermoset composites materials have outstanding resistance to outside conditions [1] and therefore will result in products with a long service life. The method of structural re-use of EoL thermoset composite products has been successfully proven in infra-structural demonstrators like retaining walls, guiding structures that funnel boats into canal locks, crane-mats and bridge decks as will be shown further on in this chapter.

### **5. Structural re-use in practice**

The method starts with the machining of the product into smaller parts, prior to the making of strips or flakes. In **Figure 3** an example is shown where an obsolete polyester boat is broken up into large panels.

In the second step, these panels are sawn into long strips or shredded into flakes, see **Figure 4**.

**Figure 2.** *New composite profiles reinforced with EoL composite strips or flakes [4].*

### **Figure 3.**

*Breaking up of a polyester boat into panels [4].*

**Figure 4.** *Panels sawn into strips or shredded into flakes [4].*

The processing of heavy and large windmill rotor blades into strips or flakes involves more effort than a thinner polyester boat hull. Abolished rotor blades are currently in the region of 30 meter long. Future lengths of abolished windmill rotor blades will be much longer still because currently windmills are installed with rotor blades of over 100 meter length. Abolished rotor blades must therefore be pre-cut preferably on location into transportable sizes, e.g. by mobile waterjet cutting ('cold cutting'), by concrete breaking tools or by diamond blade cutting. These pieces can then be transported to a location where they can be reduced in size still further before eventual shredding.

When rotor blades are shredded, a different material is obtained compared to shreds from boats, because a large part of this composite consists of high-oriented reinforcement. After the shredding process, the material is more needle-like, see **Figure 5** left, than when products with a more random reinforcement are shredded, such as boat hulls, the latter results in a more flake-like product, see **Figure 5** right.

During the process of machining the composite product into strips or flakes, other side products are obtained. First of all, dust is formed during cutting and shredding. But also other components occur originating from the original product such as adhesives, coatings, core materials (foam and wood) and metal parts. Also contaminations that were present on the product can be found back such as dirt, oil and specifically for boat hulls: anti-fouling and growth of shells. Generally these other components are not very harmful for the properties of the end product, provided their percentage is limited. Moreover, the harmful substances will not leach out because it is completely embedded in virgin ('fresh') resin. The company CRC in The Netherlands is specialised in industrial processing of EoL thermoset composites into grades of flakes that can be re-used for making new products.

Processing the strips or flakes into a new product can be done by different techniques. All techniques have in common that the re-used material (strips or flakes) is

**Figure 5.** *Shreds from rotor blades (left) and from boat hulls (right).*

embedded in virgin resin that binds it together. In most cases also a virgin composite layer is formed around the outside of the product.
