Coplanar Strip Line based Technique for the measurement of Defects in GFRP Wrapped Concrete Structures

Abstract

The introduction of FRP (Fiber Reinforced Polymer) composites in civil engineering applications has resulted from the need for structural rehabilitation of aging infrastructure such as bridges, roads, buildings etc. The structural integrity of FRP bonded systems is dependent on proper bonding between the FRP wrap and the underlying members. The bond integrity may be adversely affected when air and water voids occurs. Therefore, it is important to evaluate the FRP retrofitted structural members using non destructive evaluation techniques such as infrared thermo graphic, ultrasonic, microwave method, acoustic, radiographic technique and capacitive sensor based technique. An NDT (Non Destructive Testing) method would not only locate a defect, but it would also be useful for determining characteristics of the defect such as its size, shape, and orientation. Many NDT techniques have the ability to detect and characterize defects in structures made entirely of composite materials and also structures rehabilitated with FRP wraps. All above mentioned NDT techniques has some advantages as well as disadvantages. This thesis presents a new non destructive evolution technique for measuring the defects and delamination in Glass Fiber Reinforced Polymer (GFRP) wrapped CONCRETE using coplanar strip lines. CPS based technique is cost effective and locate the defects very easily. If there is presence of air and water void in the GFRP and CONCRETE then the change in the capacitance & electric field of CPS at low frequency and change in the reflection coefficient and resonant frequency at radio frequency (RF) takes place. As the width of air or water void increases the change in capacitance of CPS (Coplanar Strip Line) at low frequency can be measured. That’s why CPS based method is most suitable to measure the capacitance. To find the capacitance due to air or water void in FRP and concrete different models are made using Maxwell 2D software at low frequency. At high frequency, the alternation in the resonant frequency due to addition of moisture on CST Microwave studio 9.0 is studied. Keywords: GFRP, NDT, FRP, FEM, Composites, Air void, Water void, Capacitance, Coplanar strip lines, Reflection coefficient, Capacitive imaging.