The power of the sea is legendary. When someone asks, “What can withstand the power of the sea?” the expected answer is, “Nothing.”
But the real answer is: fiberglass composite.
Glass fiber reinforced polymer (GFRP) is often used in architectural applications because of the ability to mold it into exotic shapes with very light weight. Those are made by laminating of glass-fiber fabric or mats. Pultruded GFRP is the more industrial cousin in the FRP family. While the laminates usually get the headlines (like the façade of the new expansion of the San Francisco Museum of Modern Art), pultruded GFRP has been quietly expanding its uses in more structural applications for decades.
One of the places pultruded fiberglass has made itself at home is in the seawall business. Composites resist the corrosive and chemically degrading condition of water, including salt water, very well. Marine applications are generally considered the ultimate aggressive environment for most construction materials. Sea-water corrodes steel, which affects both steel construction and steel-reinforced concrete. Since concrete is somewhat porous, and often acquires cracks (or at least micro-cracks) due to drying shrinkage, earth movement, or freeze/thaw activity, sea water penetrates the concrete and corrodes the steel rebar inside. The corrosion products occupy a larger volume than the original steel, so the concrete gets cracked more, and corrosion increases. When new, those materials may be strong enough to withstand the pounding of the sea, but in the end, the water makes them weak.
Composite sheet piles are offered by a number of US companies, including Lee Composites, Everlast Synthetics, Crane Materials International (CMI), and Gulf Synthetic Products. The piles are pultruded in a crenellated profile that gives them high vertical stiffness, stiff enough to be driven into the soil. It also give them good resistance to in-plane loads, such as crashing waves.
makes pultruded composite seawalls, bulkheads, sheet piles, and retaining walls that do not corrode. Sea-water does not weaken their chemistry, so they maintain their strength over decades of exposure. For FRP, the sea is not really an aggressive environment at all.
These materials have been in service in many locations for a considerable period of time, and have established a track record for durability. Lee Composites’ seawall system, for example, has been on the market for over 20 years. Their first installation, on Galveston Island, TX, was installed in 1993. It withstood Hurricane Ike in 2008 (a category four hurricane). It is still in service and continues to pass its yearly inspections.
This kind of extremely demanding structural application points out that FRP can combine architectural versatility with high structural value. Unlike many conventional finish materials that rely on a separate structural element for support, FRP can combine the two functions into one, it can be both designed and engineered.
Or, to put it another way, if it can stand up to the ocean, imagine how it will perform on the side of your building.