Strengthening Concrete and Repairing Water Tanks with FRP
For the past two decades and more, fiber-reinforced polymers (FPR) have been used in the U.S. for concrete strengthening, as well as in its capacity as a standard construction material. It has steadily been gaining broader acceptance among professionals who are becoming aware of its outstanding properties, especially when compared to conventional strengthening processes and techniques. That being so, FRP composites are now being used in many more applications requiring strengthening, such as in water tank repair and in tank linings in general.
What is FRP?
FRP composites are materials which contain a polymer matrix which acts as a protector for a specific high-strength fiber which is continuous in nature, for example glass, steel wire, or carbon. It is these continuous fibers which provide the reinforcing quality to a structure, and they are embedded in the polymer, which binds them all together and transfers load between them. While carbon-based FRP is somewhat rigid in structure, other types of FRP are more flexible, and can be used to wrap around almost any shape of object for water tank or structural concrete reinforcement.
Applications for FRP
FRP systems offer a very useful and practical method for strengthening concrete structures, and are most commonly used in situations which call for ductility improvement and/or column confinement, shear strengthening, or flexural strengthening. FRP systems are a good choice for the seismic upgrading of concrete structures, for instance to confine columns so as to resist the buckling of steel bars, to prevent the shear failure of columns, to avoid failures of unconfined beam/column joints, and to mitigate lap splice failures. By increasing energy dissipation and global displacement of a given concrete structure, its overall behavior and strength can be significantly increased. Compared to using conventional steel reinforcement, a carbon FRP system could provide as much as five times greater strengthening capacity for concrete and tank linings.
Limitations of FRP
It is very important in FRP applications such as shear or flexure strengthening, that the concrete substrate being bonded to has sufficient existing strength to transfer stresses to the FRP system at the bond line. This of course is not an issue in FRP column confinement, which is more of a contact-critical application that basically depends on the connection between the concrete and the FRP system.
There is also a fire or heat limitation associated with FRP systems, since adhesives typically have a low threshold for heat damage. If the concrete being bonded to is capable of withstanding high heat without the FRP system, then it’s not worth taking any extra precautions with the FRP material. If the concrete cannot withstand fire damage, then the cost of fire-proofing the FRP system should be evaluated, to determine whether it’s justifiable or not.
FRP is a Great Option for Concrete Strengthening and Water Tank Repair
While FRP systems have been successfully used in a wide variety of applications like tank liners, tank leak repair, and many other strengthening scenarios, some companies have avoided the use of FRP materials for strengthening because of the relatively higher cost, compared to conventional techniques. However, those higher costs are entirely offset by the reduced labor costs, the shortened downtime during installation, and the lesser need for specialized equipment – all of which makes FRP materials the most cost-effective solution for strengthening applications.