Everything you want to know about wood in civil engineering

Wood has been used for centuries in civil engineering (civil works). The material offers unique advantages in terms of sustainability, strength, and environmental friendliness. Due to the increasing focus on the circular economy and CO₂ reduction, wood is regaining ground in infrastructure projects. This article examines in detail the reasons for using wood in civil engineering, the most commonly used wood species, key players in the market, competing materials, and an environmental comparison.

Why use wood in civil engineering?

Wood is used in the civil engineering sector because of its versatility, environmental friendliness, and technical properties. Here are some key reasons:

Renewable and sustainable
Wood is a renewable resource, provided it comes from sustainably managed forests. Certifications like FSC® and PEFC guarantee responsible forest management, with new trees being planted for every tree felled.

Long lifespan
Hardwoods such as Azobé, Angelim vermelho, and Bilinga have natural resistance to fungi and insects, meaning they can last for decades in outdoor applications.
CO₂ storage
As trees grow, they absorb CO₂ from the atmosphere and store it in their wood tissue. This makes wood an excellent choice for climate-friendly construction projects.
Strength and flexibility
Wood has an excellent strength-to-weight ratio. It's lighter than concrete and steel, yet has a high load-bearing capacity. This makes transport and handling easier and more efficient.

Aesthetic value
Wood gives infrastructure projects a natural look and integrates well with the surroundings. This is especially important for projects in nature and recreation areas.

What can you make from wood in civil engineering?

Wood is used in various civil engineering projects, including:

Bridges

Both pedestrian and other traffic bridges use hardwood for its strength and durability. Wood species used for this purpose include Azobé, Angelim vermelho, and Bilinga.

Sheet piles

Wooden sheet piles are used for water barriers, revetments and banks.

Wooden sheet piles have been used for hundreds of years to protect our country from water. Due to its specific properties, wood is an extremely suitable material for sheet piles. Wood is light, strong, readily available, and has a low environmental impact. It is a bio-based resource that stores CO2, is renewable and recyclable, and fits perfectly within the circular economy. Numerous wood species, sourced from sustainably managed forests, are suitable for sheet piles. To ensure a long lifespan, it is important to pay attention not only to design, detailing, and maintenance, but also to the structural properties.
The wood species suitable for sheet piling, such as Azobé, Angelim vermelho, and Okan, are highly resistant to fungal attack and therefore belong to the highest durability classes DC1 and DC2 according to the 2016 NEN-EN 3501 classification (DC1 = very durable, DC5 = not durable). These durability classes apply only to heartwood. Sapwood is always considered 'not durable'. The durability of the wood naturally affects the lifespan of the sheet piling. NEN 5461:1999 specifies that wood with durability class 1 (DC1) has a minimum lifespan of 25 years in freshwater and ground contact.

Reusing sheet piles

The Vallei en Veluwe Water Board recently converted old sheet piling into new sheet piling in Vorchten, a village in Gelderland about 20 kilometers south of Zwolle. The wood had previously served as a water inspection board in the Eem River near Eemnes. According to the Vallei en Veluwe Water Board, the wood was still of such good quality that throwing it away would have been a real shame. "Our water board operates as circularly as possible. In this case, only the top sections of the planks were worn out. They have been shortened and can be reused, resulting in a strong, durable sheet piling that will last for years and contribute to a circular future," the water board states.

Braking structures and dolphins

These structures protect bridges, locks, and quays from collisions. A wood species we often see here is Basralocus.
Braking systems are constructed to slow down vessels when they approach a lock or bridge and are in danger of colliding with it.
For this reason, fenders are almost always made of wood. This causes the least damage to steel vessels and prevents sparks. Because shipping traffic in the Netherlands is becoming increasingly heavy, fenders also need to be increasingly stronger. For this reason, steel structures are increasingly clad in hardwood to serve as fenders.

Scaffolding and decking

Wood is popular in hydraulic engineering projects because of its natural appearance and anti-slip properties.

Which types of wood are commonly used in civil engineering and why?

Not all wood types are suitable for use in civil engineering. Below is an overview of the most commonly used types:

Tropical hardwood

Ekki
Extremely durable (durability class 1) and resistant to both fresh and salt water. Ideal for sheet piles and retaining walls.
Angelim Vermelho
Very strong and hard, often used for sheet piling.
Badi
Lightweight, yet durable and water-resistant. Often used in bridges and jetties.
Basralocus
Pileworm resistant and widely used for underwater constructions.

European and domestic hardwood

Oak
High strength and wear resistance, suitable for bridges and noise barriers.
Robinia wood
Highly durable and a good alternative to tropical hardwood.

Handbook on wood in civil engineering

It Handbook Wood in Civil Engineering (2022) describes available wood species and applications for civil engineering. In 2022, the CROW knowledge platform published a revised version of the Handbook on Wood in Civil Engineering.

In recent years, important wooden bridges have been built, such as in Groningen, Sneek, and Harderwijk. There are also wooden lampposts and crash barriers. But a major breakthrough hasn't yet been achieved. That could change. After eighteen years, the CROW CUR manual "Wood in Civil Engineering" has been completely revised and offers a fresh perspective on this age-old and, above all, sustainable material.

This updated version contains numerous new details for the proper design and detailing of common applications, sheds new light on modifying wood and wood products, and highlights all its advantages. Wood stores CO2, often has a favorable environmental profile (ECI), is easily reusable, has a pleasant and natural appearance, is lightweight yet very strong, and is also easy to repair and process.

Management, maintenance and costs

The manual "Timber in Civil Engineering" addresses the extensive application possibilities of wood in civil structures. Wood has unique properties that help make civil engineering more sustainable, circular, and climate-neutral, and it offers an effective response to the anticipated resource scarcity. The manual provides information on potential applications, (modern) wood species and their properties, and examples of sustainable wood applications in construction. Cost aspects and the management and maintenance of wooden structures are also discussed.

The manual is like paper publication available.

Calculate how much CO2 wood stores in civil engineering

The Centrum Hout (Wood Center) has a special calculation module to calculate the CO2 content of wood products used in civil engineering. These products can consist of a single wood species, but can also be composed of multiple wood species or products. Wood (fibers) in different types of panel materials are also taken into account.

Calculate CO2 in wood products

Competitive materials in the civil engineering sector

Besides wood, other materials are used in civil engineering, such as plastic, concrete, and composite. Below is a comparison:

Prolock sheet piles
Prolock is a synthetic sheet pile system used as an alternative to wooden sheet piles. The material is rot-proof and low-maintenance, but has a higher environmental impact during production.
Concrete
Concrete is a popular construction material, but its production produces high CO₂ emissions. It is less flexible than wood and has a larger environmental footprint.
Composite
Composites combine wood fibers with plastic and are used for bridge decks and jetties. They are low-maintenance, but more difficult to recycle than solid wood.
Recycled plastic
Plastic sheet piling and retaining walls are increasingly used due to their long lifespan. However, plastic has a higher environmental impact during production and disposal.

Environmental comparison: wood versus alternative materials

Environmental impact is a crucial factor in choosing building materials. Wood outperforms competing materials on several fronts:

CO₂ storage and emissions
Wood absorbs CO₂ during growth and continues to store it throughout the lifespan of the structure. Concrete and plastic, on the other hand, have high CO₂ emissions during production.

Renewability
Wood is a renewable resource, while concrete and plastic are produced from non-renewable resources such as limestone and petroleum.

Energy consumption during production
The production of wood products requires significantly less energy than the production of steel, concrete or plastic.

End of life and reuse
Wooden structures can be reused or processed into new products after use. Plastics and composites are more difficult to recycle and often cause waste management problems.

Reusing wood from civil engineering

Wood used in a civil engineering project can often be reused for other purposes. For example, we mentioned earlier in this article that a water board processes sheet piles into (shorter) sheet piles for another project.

Boogaerdt Hout is running a special project, Waterwood, in which wood from the water lines is also reused. This wood is primarily hardwood from old lock gates, mooring posts, and sheet piles. Waterwood reclaims high-quality wood, carefully sourced from historic waterworks in the Netherlands and surrounding countries. The wood offers unprecedented possibilities, from facade cladding and sturdy picnic benches to viaduct cladding and promotional gifts. Basralocus mooring posts are processed into facade cladding with fire class B in collaboration with Waterwood and Houthandel Paulussen.

View Waterwood

Conclusion

Wood remains an indispensable material in the civil engineering sector due to its durability, strength, and environmentally friendly properties. While plastic, composite, and concrete are competing materials, wood remains the most environmentally responsible choice for many applications. With the growing focus on the circular economy and CO₂ reduction, the demand for sustainable wood in the civil engineering sector is expected to only increase.

Text: Everything you want to know about wood in civil engineering

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