Industry opinion: strengthening seaside infrastructure

US-based Exel Composites’ Francesco Ierullo considers if composite materials can replace steel for strengthening seaside infrastructure

Ageing infrastructure is a well-documented global problem on seafronts, where salty, humid ocean air causes metals to corrode rapidly. Local governments must carry out frequent, time-consuming and disruptive repair jobs, costing billions of dollars, so that structures remain safe and durable. According to CNN, the cost of fixing America’s crumbling infrastructure could be as much as $2.6trn.

Thankfully, the USA’s Composite Standards Act outlines the requirement for facilitating the adoption of composite technology in infrastructure projects. Furthermore, in 2022, the American Concrete Institute (ACI) passed a new code for rebar. While these documents aren’t specific to coastal and civil infrastructure, they will hopefully encourage civil engineering companies to use composites for their corrosion resistance, all contributing towards strengthening seaside infrastructure.

Concrete’s biggest weakness is its low tensile strength, traditionally remedied by using steel rebar reinforcements. A major disadvantage of using steel in a concrete structure is that it is susceptible to corrosion. When rust forms around a steel rebar, the internal pressure will increase and the concrete will crack, exposing the steel to more moisture, salt and humidity.

Swapping out steel rebar for composites in seaside environments provides several key advantages. Firstly, carbon fibre and fibreglass composites are naturally corrosion resistant, which is ideal for short- and long-term immersion in seawater. This property is determined by choosing high-performance premium-grade resins, which ensure low water absorption and protection from aggressive chemicals.

Furthermore, composites don’t require additional coatings, such as electroless nickel plating or zinc galvanisation for stainless steel, to tackle corrosion. Traditionally used to treat steel rebar, the protective layer wears away over time, adding an extra step in production and adding to ongoing maintenance costs.

Secondly, because composites are lightweight, they are much easier to install as reinforcements in bridges and walkways. A fibreglass rebar is approximately one-quarter of the weight of a steel rebar, meaning companies can transport more profiles to the site, saving on transportation costs, and it’s easier for installation crews to carry, helping to promote job site safety. Modern composites also perform better regarding torsion and tension. Fibreglass has a higher tensile strength compared to steel, making it ideal for structural support in a bridge or walkway.

For seaside applications with cyclic loading, reinforcing materials must have good fatigue resistance. Seawalls, for example, must endure persistent, high-energy forces from waves to protect land from flooding and coastal erosion. Because of their tensile strengths, composite sheet piles thrive because they can withstand exceptional force without fragmenting.

Through a process called pultrusion, fibres are pulled through a resin bath and cured in a heated die, before being cut to their desired lengths. The process is highly automated, which ensures continuous, high-volume production of composite sheet piles and rebars at a consistent quality compared to manual manufacturing techniques.

If the USA’s Composite Standards Act 2021 pilot programme succeeds, it will encourage civil engineering companies to use composites in their infrastructure projects, enabling structures such as bridges, walkways and seawalls on seafronts to stand the test of time. 

Find out more at bit.ly/exelcomposites

For more on the USA’s Composite Standards Act, visit bit.ly/Congress_CSA

About Exel Composites

Headquartered in Finland and with a factory in Erlanger, Kentucky, Exel Composites offers over 60 years of experience in composite solutions. Its products are used in applications from wind power and transportation to building and infrastructure.

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