Application of CFRP composite for sustainable solution of corroded slab system due to low nominal cover case study on nerd slab system

Abstract

Carbon Fiber Reinforced Polymer (CFRP) strengthening technique had been shown excellent performance in externally strengthening reinforced concrete (RC) elements due to their superior properties compared to the alternative strengthening techniques. A substantial number of studies have been done to study the behavior of externally bonded CFRP strengthened RC elements. However, as per the knowledge, while most studies have focused on the external strengthening of RC beams using CFRP, and very few studies have focused on strengthening the pre-stressed beams and slabs. Pre-stressed concrete is most popular building technique in construction buildings. Steel corrosion is recognized as the most serious and dominant mechanisms of deterioration for concrete structures. Subsequently, the capacity of the pre-tension elements decreases after exposure to corrosion. NERD center slab system faces such unacceptable losses in load carrying capacity, stiffness, and ductility due to severe corrosion in pre-stressed beams. This study focuses on how CFRP can go for a load increment after reaching its ultimate load carrying capacity. The test procedure was arranged in two stages. The first stage testing was used to show the performance/ behavior of composite slab specimen and pre-stressed beam, with the application of load. The second stage of testing was carried out to make comparison between the structural performance of retrofitted and strengthen specimens. Specimens were selected for retrofitting after application of loading in stage 1. The total of 12 specimens were exposed to the loading and behavior of each of the specimen were observed. Specimens were selected as slabs and eight number of them were composite slabs with or without shear links which have overall dimensions equal to 1800 * 600 mm and other four were pre-stressed beams with overall dimensions of 1800 mm in length. In this study, CFRP is proposed as the economical solution which does not touch the structural integrity of the structure. All the specimens were tested using universal loading machine. In stage 1, specimens were loaded up to its ultimate failure. In stage 2, all the tested specimens were retrofitted using CFRP. In total number of six specimens were used for retrofitting. Another six specimens were also strengthened using CFRP before loading. In each stage of loading several observations were done. Such as mode of failure, cracking width distribution, ultimate load, and each composite panel's corresponding deflection were also recorded. In stage 1, flexural and shear cracks propagated in the pre-stressed beam and the beam failed at the applied load of more than 50 kN. Stage 2 focused on the performance/ behavior of the retrofitted and strengthened specimen after application of CFRP. The results from stage 2 showed a considerable reduction (nearly 20%) in loading of retrofitted/ strengthened composite slabs compared to control specimens. Difference in failure pattern is caused for this discrepancy in load demand of second stage. The experimental results showed some satisfactory performance in regaining the lost strength of the composite specimens due to corrosion.