Advanced composite materials are playing a major role in the building industry
Advanced composite materials are playing a major role in the building industry
by Girum Urgessa, PhD, PE
Center for Real Estate Entrepreneurship (CREE) Fellow and Associate Professor of Civil Engineering at George Mason University
The choice of construction materials in the building industry is very limited. The four available options in the industry include concrete, steel, wood, and masonry. While some of these traditional construction materials exhibit composite properties, they possess limited strength, stiffness, or durability. For example, wood is a natural composite made from fibers and lignin matrix. However, it is vulnerable to water damage and decay. Similarly, concrete is a composite made from aggregate, cement, water, and chemical additives. However, it has low tensile strength, and its weight to strength ratio is relatively high.
Recently, the use of advanced fiber reinforced polymer (FRP) matrix composites have shown promise in the building industry and they are regarded as having the potential for transforming the construction of new buildings, producing spectacular new shapes and forms, and resulting in more efficient and attractive structures. FRP composites mainly consist of reinforcing fibers embedded in a polymer matrix. The reinforcing fiber provides stiffness and strength, and they can be made from glass, carbon, or aramid. The polymer matrix protects the reinforcing fibers from environmental effects and allows proper load transfer between the reinforcing fibers. The polymer matrix can be polyester, vinylester, or epoxy resins. FRP composites are light weight, corrosion resistant, durable, and have high strength. They are also anisotropic, having different strength properties in different directions, which can be tailored to meet complex design requirements by engineers or architects.
The use of FRP composites in building construction started by implementing them in tandem with traditional construction materials. For example, FRP reinforcing bars have been used in concrete construction in lieu of traditional reinforcing steel; FRP sheets have been used to wrap concrete columns to increase strength properties or add confinement; FRP roof panels, siding panels, or decks have been used on traditional wood framed residential buildings.
The International Code Council, who is responsible for developing the International Building Code, permitted the use of FRP composites in both interior and exterior parts of building construction. Owing to that fact, the use of FRP composites has increased rapidly on a larger scale where major structural or architectural elements, and even a complete residential building is solely made out FRP composites. This article highlights three world-wide examples in which large-scale FRP composites were used in the building industry. The examples encompass FRP composites used in structural load resisting systems, in architectural cladding materials, and in framing an entire residential building in which they are the exclusive construction material of choice.
1. Structural load resisting elements exclusively made from FRP composites
The construction of basement walls is a good example where the use of advanced composites is gaining popularity. Concrete walls have been the dominant choice for basement wall construction. However, there are many disadvantages in using concrete basement walls, including longer installation time, poor insulation properties, and the associated heavy weight. In addition, concrete cracks are often common in basement walls leading to water seepage and mold generation. Recent advances in FRP composites have made it possible to construct entire basement walls that are lighter, durable, and energy efficient with little required insulation. For example, consider the Epitome wall system developed by Composite Panel Systems LLC here in the US.
The Epitome wall, as shown in Figure 1, is an all-in-one system combining a vertical wall structure, continuous insulation, a double top plate, integrated stud cavities, waterproofing, and a vapor barrier. Epitome walls are factory assembled, fiberglass-faced structural insulated panels with a preformed polyurethane foam core. The panels are manufactured with 1-5/8 in. wide studs on the interior surface spaced 16 in. on center. The composite walls can be used as load bearing or non-load bearing walls. The panels can be delivered to a site in one trip and can be installed in under three hours.
The Epitome walls have passed rigorous testing, and met building code requirements and compliance for residential foundations. It was reported that the wall system can carry 25 kilopounds of downwards force per lineal foot. In addition, the panels have an insulation value 16 times more than that of the traditional concrete walls, making them attractive for energy efficiency. Advanced FRP composite structural elements, such as the Epitome wall, may cost extra upfront. However, if life-cycle cost is considered, the benefits of such systems are far superior to the traditional construction options.
Figure 1. Basement walls made from FRP composites
2. Architectural cladding materials exclusively made from FRP composites
The San Francisco Museum of Modern Arts underwent major expansion and renovation, and reopened its doors in 2016. This renovated building featuring a 10-story rippled, undulated, and curved facade, is the largest architectural application of FRP composites in the US. The facade consists of more than 700 FRP panels covering 54,000 ft2 surface area. Some of the individual FRP panels measure 5.5 ft wide by 30 ft in length, while the skin thickness is only 3/16 in. The FRP composites were mechanically fastened and bonded using customized aluminum extrusion. The FRP composite system successfully passed the National Fire Protection Association (NFPA) 285 fire testing for use on high-rise building applications. There were many reasons why FRP was chosen in this particular project including its durability, very high strength-to-weight ratio compared to steel, overall shorter schedule for construction completion, and inherent form shaping capability into complex shapes as shown in Figure 2.
The FRP composites ability to offer significant energy savings when used as a thermal bridging between the exterior and the interior of a building is also praised by the architectural and engineering community. This project’s success is considered a monumental step for the use of FRP composite in future cladding designs that strive to stay ahead of the traditional curtain wall systems.
Figure 2. Cladding made from FRP composites
3. Residential buildings exclusively constructed from FRP composites
Sustainability considerations, including resource limitations and cost, are increasingly demanding new solutions in residential building construction. As such, FRP composites are poised to be the most attractive solutions for replacing traditional construction materials that are used in residential building construction. For example, consider the Starlink system. This system is a modular construction for low-cost thermally efficient dwellings made entirely from FRP composites with pultruded profiles connected through bolts or snap-fitting mechanisms for rapid assembly. The parts, which are prefabricated to fit neatly together without the need for cutting, have been shown to be environmentally friendly, reduce labor cost, and eliminate waste on construction sites.
The FRP modular building does not require thermal bridging; it can be easily reconfigured for reuse on another site; it can also be altered or extended to accommodate the growth in family size in residential buildings. Figure 3 shows an example of a full-scale building made from the Starlink FRP composite system in the UK in 2012. It is striking that the all-FRP house weighs only 18 tons compared to a conventional house of the same size weighing 40 tons.
Figure 3. A full-scale house made from FRP composites (white building on the left)
In summary, FRP composites have unlimited potential for transforming the state of practice in building construction. They are shown to be more sustainable than existing construction materials; they are durable and corrosion free; they can be handled, lifted, and installed easily given their light weight; and they are energy efficient. The interest of incorporating FRP systems in building construction has accelerated due to their proven performance to pass national fire tests and their inclusion in building codes. It is anticipated that FRP composites will become the construction material of choice in the future as sustainable building construction alternatives are sought out by clients, developers, architects, and engineers alike.
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