Al-Rafidain Engineering Journal (AREJ) ISSN (Print) 1813-0526; Vol. 25, No.1, June2020, pp. 17-24 ISSN (Online) 2220-1720 Al-Rafidain Engineering Journal (AREJ) Vol. 25, No.1, June2020, pp. 17-24 Strengthening and Rehabilitation of Concrete Prisms Using GFRP Sheets Ashtar S. Al-Luhybi Bayar J. Al- Sulayfani aziztaher@uomosul.edu.iq dr.bayar.alsulayvani@umosul.edu.iq Civil Engineering Department, Collage of Engineering, University of Mosul Received: 10/1/2020 Accepted: 16/5/2020 ABSTRACT The use of external strengthening by fiber reinforced polymer (FRP) technology has significantly increased in recent decades. This is because (FRP) has the properties that make it the most suitable option for strengthening and rehabilitation of damaged concrete structures instead of using traditional materials such as steel plates.In this paper, the behaviour of non-reinforced concrete beams externally wrapped with Glass Fiber Reinforced Polymer (GFRP) sheets has been examined. Fourteen unreinforced concrete prisms were cast with a rectangular section of (150 × 125 mm) and a length of (760mm), these specimens were divided into five group. First group was not externally wrapped with GFRP sheets (control specimens), and the remaining groups were GFRP wrapped with a variable number of GFRP layers (thickness of wrapping). In the first stage of study, the prisms have been tested and the effect of external wrapping and increasing the wrapping thickness on the behaviour of prisms was observed. In the second stage, the unwrapped concrete prisms that were tested and failed (control specimens) were rehabilitated by externally wrapping them with one layer of GFRP sheets. The results have shown that wrapping with GFRP sheets increased the capacity of the prisms and failure load had reached to (342.5%) for prisms wrapped with three layers when compared to the control specimens. It was also noticed that there was an increase in the toughness of the prisms by increasing the number of GFRP layers. The results have shown that there was a decrease in the failure load of the four layer wrapped prisms, and this was due to the early failure of the prisms due to the debonding of the GFRP sheets from the prism surface. The damaged specimens which were later rehabilitated have shown an increase in load carrying capacity compared to the control specimen. Keywords: Enhancement; Externally bonding; Flexure strength; Glass fiber reinforced polymer; Retrofitting. Copyright © 201x College of Engineering, University of Mosul, Mosul, Iraq. All rights reserved. https://rengj.mosuljournals.com Email: alrafidain_engjournal1@uomosul.edu.iq ============================================================================= 1. INTRODUCTION The use of fiber reinforced polymer (FRP) to strengthen reinforced concrete structures has grown and become a known technique. The lightweight and formability of these fibers have made them non-corrosive and resistant to chemicals, so they are the right choice for external reinforcement[1]. Many of the practical investigations conducted in the past have shown that the use of polymer fiber in the strengthening has several benefits compared to conventional methods, this is because of their high strength, low weight and improved durability [2]. There are three known types of polymer fiber used in the civil structures namely glass, aramid, and carbon fiber. The physical and chemical properties of these fibers vary not only from one type to another but also differ for the same fiber type [3]. Al-Luhybi[4] investigated the effect of wrapping standard cylinders(150×300 mm) by GFRP sheets on its compressive strength, where it was observed from the results that wrapping using fiberglass sheets increased the capacity of cylinders. Meisam et al.[5] Conducted experimental study to investigate the effect of FRP strengthening on