Debunking Myths about Composites in Construction
Since 1980, when the first European bridge was documented to employ composite materials as reinforcing tendons, an increasing number of civil engineers in the US and abroad are specifying carbon and glass systems for structural use. The orthotropic properties and high strength-to-weight ratio of composite materials are of great value for seismic retrofit, capacity upgrades, or concrete reinforcing materials. However, given composites’ relatively short history in civil engineering, lack of building design codes, and short list of available documented case examples, there are some common misconceptions.
Composites are too expensive
Composites saves people a significant amount of money over the life of the application. While the initial material cost can be more, various areas of cost savings make composites the more economical choice. Composite products have a low installation cost. The light weight of composite products eliminates the need for heavy lifting machinery thus saving you money. Composites can also be fabricated onsite.
Composites are a fire hazard
A significant concern in any application utilizing composite materials is the possibility that the material may ignite and release potentially harmful toxic smoke. However, the use of composites in building structures, which have stringent fire regulations, shows they are in compliance as with other more conventional construction materials. Moreover, composites are generally poor conductors and discourage the spread of fire.
Composites can’t handle UV radiation
The effect of UV radiation on composites is well documented. It is well known that with prolonged exposure to sunlight, the polymer matrix may harden and color change or pigment loss may occur. However, these effects of UV exposure are limited to the top few microns of the exposed surface, and are generally abated with the simple application of a UV resistant coating to the surface. Consequently, in thicker sections the UV degradation effect on structural properties is minimal. Highly light stable resins and pigments have now been developed which further enhance the long term stability of composite structures.
There aren’t any design guides available
A common error is assuming that there are currently no design aides for composite materials in the US. Current design guides are now available for composite materials in civil engineering applications. Documents such as the American Concrete Institute’s "Guide for the Design and Construction of Externally Bonded Composite Systems for Strengthening Concrete Structures, ACI 440.2R-02" (ACI, 2002), and "Guide for the Design and Construction of Concrete Reinforced with COMPOSITE Bars, ACI 440.lR-01" (ACI, 2001) were produced by the American Concrete Institute 440 Committee and are available. These publications are by definition design guides and not codes.