Sustainability is currently a hot topic, both in general and in relation to composite materials. Assessing the environmental impact of structures is a relatively new and complex field. An essential message here is that when assessing structures, even in terms of environmental impact, the full lifespan of the structure must be considered.
Life Cycle Analysis
Clients and manufacturers find it valuable to be able to compare products based on their environmental impact. Life Cycle Analysis, abbreviated as LCA, is the umbrella term for methods used to evaluate the environmental impact of structures. These methods identify and analyze environmental impacts during three key life stages:
This method analyzes a structure by breaking it down into individual parts and determining for each part how much material, energy and water is used, and whether harmful substances are emitted. This process is quite detailed. Take a metal part for example: this requires the extraction and transportation of iron ore, the use of machinery and personnel, and all these steps are included in the analysis.
During the lifespan of a structure, such as inspection and maintenance, energy is also consumed and harmful substances can be emitted. Ultimately, every structure has a certain lifespan, and when it ends, there must be a plan for the structure’s removal or repurposing.
The central element of LCA is the Life Cycle Inventory (LCI), a database containing information about the environmental impact of various construction materials. Although LCIs are carefully constructed, they are sometimes based on assumptions. While the amount of heat released when burning a given material can be accurately measured, aspects such as the commute of miners or maintenance workers, for example, may vary from situation to situation and therefore needs to be estimated.
The results of an LCA can be displayed in different ways, with various impact indicators, such as tonnes of CO2 emissions, energy consumption, or combined scores such as Eco or MKI score.
The assumptions made during a Life Cycle Assessment (LCA) are often the subject of discussion. For new and diverse materials such as composites, knowledge about their environmental impact is in many cases limited. Especially in the production and end-of-life phases of composites, there are many discussions about their environmental friendliness.
In general, composite structures have advantages in terms of environmental impact during their use, as there are several options to design them energy-efficiently. These options will be discussed below.
A composite material usually consists of fibers and a polymer. The production of glass fibers and carbon fibers requires significant amounts of energy, and most polymers are produced from petroleum.
It is also possible to make composites from natural materials. Many resins can be combined with natural fibers such as flax, hemp, wood and bamboo. Although the mechanical properties of natural fibers are usually less than those of synthetic fibers, composites made from natural fibers can still have good specific strength and stiffness due to their low density. Another advantage of natural fibers is that they are often transparent to radar radiation, for example.
Matrix materials based on natural sources are also available, where vegetable oils can be used instead of petroleum to make polymers. A major challenge in using natural resources for construction materials is potential competition with food crops, similar to the problems faced by biofuels.
In addition, different production methods of composite materials have different environmental impacts. For example, production with an open mold can lead to more emissions of VOCs (Volatile Organic Compounds) than with a closed mold. However, in a closed mold many tools are often used (such as vacuum foil) that generate waste after removing the product.
Composite structures generally require less maintenance than steel and wooden structures. In civil engineering there are examples where the lifespan of concrete structures has been extended by external reinforcement with composite materials.
Repairing a composite structure usually involves removing damaged areas and replacing them with new layers of composite material, which can usually be done on site. Curing a repair can be done, for example, with the help of an electrically heated blanket. For superficial or cosmetic repairs, with the right expertise, excellent results can be achieved. However, for heavily loaded structures, repair does not always lead to the same original strength.
A trend that appeals to architects is the use of composite facade panels. These panels offer a lot of design freedom and enable bold designs with a low weight. In renovation projects, this means that the existing support structure does not need to be reinforced or only minimally reinforced. Light support structures can be designed for new construction. In addition, the good thermal insulation properties of fiberglass and plastic, as well as the possibility of using facade panels as a sandwich construction, contribute to energy-efficient buildings.
Composites are often used in moving structures because of their lightweight design, which leads to energy efficiency. An example of this can be found in the transportation sector, where ships, trains, airplanes and truck trailers are used to transport cargo. The energy requirement in all these forms of transport is highly dependent on weight. Reducing weight results in reduced rolling and water resistance, which improves energy efficiency. In automotive applications, the lightweight design is also beneficial because vehicles often accelerate and decelerate while driving, and lightweight designs lead to fuel savings and more profitable payload.
Suppose a truck-trailer combination becomes 5% lighter and this leads to an assumed fuel saving of 5% per trip. Over 10 trips this would result in a total saving of 5%. However, if the weight loss means 10% more paying load can be carried per trip, one trip out of 11 trips could be saved, giving almost a 10% savings.
In addition, composite flywheels can be used to store braking energy, which is efficient due to their high specific strength. In industrial applications such as pick-and-place machines and robots, increasing production speed can be achieved by using lighter and stiffer structures. Depending on the product, the investment in lightweight designs can pay for itself through increased production output.
The design freedom that composites offer can also indirectly save energy, for example by creating aerodynamic shapes, such as lightweight fairings on truck cabins. In general, energy savings, especially in transportation applications, can be achieved through lightweight construction, often using composite materials.
End of lifespan
When a composite structure reaches the end of its lifespan, there are several options available, but in general the options for recycling or disposing of composite structures are even more limited than for older building materials. Depending on the type of resin and reinforcement used, recycling is sometimes an option. Incineration in cement kilns is a method recognized by the European Union as a way to process composite waste. Composite waste is considered inert and therefore not considered more harmful than regular household waste.
* Nijssen, R. (2015). Composieten Basiskennis. Retrieved from Composites NL: https://compositesnl.nl/wp-content/uploads/2020/03/Composieten-Basiskennis-3e-druk-NL-CNL.pdf