The use of carbon fiber reinforced polymer strips in residential foundation reinforcing has become more common. Products such as Carbon Armor, by Basement Systems, and The Reinforcer, by thereinforcer.com, are being used more frequently. Carbon fiber external reinforcing has been used for a long time in commercial applications, such as seismic retrofits, but only recently has become widespread in the residential foundation reinforcement sector.
Carbon fiber reinforcing strips consists of strips approximately 4” wide by ¼” thick that are epoxied to the interior face of the wall. Additional items, such as connections to the floor and to the slab on grade and the first floor diaphragm, as well as blocking to thicken the wall, may be necessary. In general, installation of these strips costs 1/3 to ½ of many other methods. That being said, they are not always feasible, such as in situations where the wall is stepped or damage to the face of the wall will prevent proper adhesion. Here, they may not be a good choice. An Engineer should always evaluate the conditions to assess if carbon fiber reinforced strips are a suitable repair. We are often asked if these are strong enough to reinforce the wall, as they visually appear minimal. In actuality, the mechanics are the same as steel rebar within the wall, but actually in this case the straps are more effective since the distance from the compression side to the tension reinforcement in the wall is greater than if a reinforcing bar had been installed within the wall. In general, the glue is not the weakest component of the wall and the products are generally warrantied by the manufacturer against future movement. An older type of repair designed by an Engineer, such as installing rebar, I-beams or pilasters, is typically not warrantied in the way that a manufacturer’s product is.
It is important that you work with the manufacturer to be sure that the installation meets all their requirements and that the warranty will be valid. Provided that the project is applicable to the use of carbon fiber strips and that they are properly designed, installed and warrantied, they are inexpensive, effective and quick way to significantly increase the capacity of the foundation wall.