As published in previous post tensile strength is a mere fraction of compressive strength. Sometimes a compression concrete member may fail when an unexpected loading like earthquake produce stress normal to axial direction to which it is designed properly. Such members which are damaged but managed to keep standing without failure need to be repaired to make structure serviceable. In this purpose, a repair technology of wrapping these members with suitable materials is required.
This conception was developed long ago but the key materials of wrapping have found recent years. Durability, ductility and stiffness and response to creep is the key feature for a wrapper. If the strengthening wrapping somehow is torn the capacity of the repaired section reduced dramatically. Moreover where wrapping is exposed to environmental attack like corrosive nature, it is important to have a property of remain unchanged against any condition of corrosiveness. Considering durability fact the steel, the most common and strong material, steel is removed from the list of wrapping materials.
The purpose of wrapping is to prevent tensile cracks. Wrapped concrete element is several times stronger than non-wrapped one. Now its time to know what is the wrapping material? This is fiber reinforced concrete. Due to light weight and non-corrosive properties it can strengthen any element without increasing self weight of element or structure. Being light weight it can handle easily.
It is noticed that one layer of fiber reinforced polymer concrete can increase the ultimate strength of an element by a factor of 2.5. However increase of layer doesnot incrase ultimate strength linearly. Ultimate strength increased 8 times with 8 layer of wrapping. Whereas one layer of wrap can increase the ultimate strain 6 times. These discussions indicate that with one layer increase ductility many times as ultimate strain increased many times. This feature makes fiber reinforced polymer concrete more suitable for earthquake rehabilitation projects.
With High ultimate strain, it is required to have low stiffness. Glass fibers that have considerably lower stiffness than the carbon fibers and higher ultimate strain is desirable. The unfavorable creep behavior of glass fiber poses little adversity in earthquake resistant .applications as earthquake forces are seldom encountered. Moreover, glass fiber is much less expensive than carbon fiber. Therefore, glass fiber has been used in rehabilitation and retrofitting of structures in Gujarat.
Wrapping can be applied to strengthen concrete beams in compression and shear composite but in this purposes fabric wraps are used in concrete beams.
Now-a-days FRCs are getting popular in india. Indian earthquake seismic design and construction were developed rapidly after 2001 Gujarat earthquake. FRCs bring speed in repairing structures and its members. A 5000 sqm of fertilizer plant has been repaired and left for operation within 45 days. Indian manufacturer were supplied all repair materials. Now many manufacturer produce frc materials leaving great opportunity for design, construction and rehabilitation with fiber reinforced concrete.