Fiber Reinforced Polymer (FPR) materials are utilized to improve flexural strength, shear strength, and ductility of existing sub-standard structures. Concrete elements strengthened by FRP sheets at tension zone are good example. FPRs improve the tensile strength of concrete. Another great example is to improve the flexural capacity of columns through lateral confinement.
Problematic of FRP Installation
Despite the advances in frp material design and fabrication, the quality control and monitoring of FRP installation remains a huge challenge. The performance of FRP sheets is defiantly correlated to the quality of FRP installation. In simple words, the FRP sheets cannot provide the expected performance if the bond between the FRP sheets and base element is loose. The following parameters can affect the quality of FRP installation:
1- Use of proper mixed amounts of each resin component
2- Storage environmental conditions of resin components
3- Surface temperature, moisture and exposure
4- Atmospheric conditions during application
5- Curing of the resin (Ref)
Bond Quality Control
Non-destructive testing (NDT) methods are good solution to examine the quality of bonding between FRP sheets and base concrete. Different non-destructive testing methods are used for quality evaluation of FRP installation, including:
1- Infrared Thermography
Infrared thermography keeps tracks of electromagnetic wave surface radiations related to temperature variations in the infrared wavelength. This method is effectively used to detect delamination or discontinuities in the shallow depth. Anomalies such as delamination and material changes can be detected on the basis of variable thermal conductivity and specific heat capacity. Infrared (IR) thermography can be a fast, reliable and confident non destructive testing technique for the evaluation of bonding defects in FRP – reinforced concrete structures (Read more).
2- Fiber Optic Sensors
Fiber optics are among the latest technologies that are used for quality assessment of FRP installation. Fiber optics are used to evaluate the degree of curing of the resin. In this application of fiber optics, the sensors are embedded into the laminates in order to monitor the progress of the curing of the resin and temperature variations over time.
3- Acoustic Methods
Acoustic methods provide an ideal non-intrusive approach for evaluating the quality of bond. The reflection of test area to acoustic (stress) wave in frequency domain is one of the best method for such examinations. Indeed, the stiffness of test area to stress wave perturbations change if a detachment occurs between FRP sheets and base concrete. A perfect bond shows higher stiffness when compared to a poor connection between the FRP and base concrete.