Nondestructive and destructive evaluation of FRP composite wrapped concrete cylinders with embedded debonds

Abstract

A major application of composite materials in the reinforced concrete industry is to wrap columns with Fiber Reinforced Polymer (FRP) composite fabric which results in increase in the columns’ axial compressive strength and ductility. Presence of debonds between the FRP wrap and the underlying column surface inhibits the proper confinement of the column by the composite wrap.The objectives of this research are: (a) to evaluate the feasibility of using Active Infrared Thermography for qualitative as well as quantitative evaluation of debonds in Fiber Reinforced Polymer (FRP) wrapped columns, (b) to understand of influence of heat flux, debond width and debond depth on various thermal response parameters, and (c) to study the effect of debonds on stress-strain behavior of FRP wrapped columns.All laboratory tests were conducted on concrete cylinders of size 6’’ x 12’’ (152.4 mm x 304.8 mm). Simulated air-filled debonds, water-filled debonds and debonds made from Teflon sheets of various sizes were placed on the concrete cylinder’s surface prior to wrapping with FRP fabric. Active Thermography technique was used to locate these simulated debonds and to quantify the debond width and debond depth. Infrared thermography tests were conducted using a digital infrared camera capable of acquiring radiometric images with capture speed of up to 60 frames/s. In this research, the effect of debond area in terms of percentage of total area on the stresses and strains of concrete columns wrapped with FRP composite fabric was also studied using destructive compression testing.The results reveal that Infrared Thermography is an effective nondestructive evaluation tool for qualitative and quantitative evaluation of subsurface debonds in concrete columns wrapped with Fiber Reinforced Polymer (FRP) composites. Also, a significant decrease in axial compressive strength with an increase in area of debonds was observed, and appropriate reduction factors have been proposed for use in strength computations. Both GFRP and CFRP composites were found to be effective in arresting the lateral dilation of the underlying concrete. Also, considerable ductility enhancement was evident due to the wrapping of cylinders with FRP composites, particularly with CFRP composites.