1 EFFECTIVENESS OF PRESTRESSED NSM CFRP LAMINATES FOR THE FLEXURAL STRENGTHENING OF RC SLABS M. R. Mostakhdemin Hosseini 1 , S. J. E. Dias 2 and J. A. O. Barros 3 1 Phd Student, ISISE, Dep. of Civil Eng., Univ. of Minho, Azurém, 4810-058 Guimarães, Portugal, hoseini_engineer@yahoo.com 2 Assistant Prof., ISISE, Dep. of Civil Eng., Univ. of Minho, Azurém, 4810-058 Guimarães, Portugal, sdias@civil.uminho.pt 3 Full Prof., ISISE, Dep. of Civil Eng., Univ. of Minho, Azurém, 4810-058 Guimarães, Portugal, barros@civil.uminho.pt ABSTRACT An experimental program was carried out to investigate the effect of the prestressed Near Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) laminates on the behavior of reinforced concrete (RC) slabs. Four RC slabs were tested, a reference slab (without CFRP), and three slabs flexurally strengthened using NSM CFRP laminates with different prestress level of the ultimate tensile strength of the CFRP: 0%, 20% and 40%. The experimental program is described and the main results are presented and analyzed in terms of the structural behavior of the RC slabs, failure modes and performance of the NSM technique with prestressed CFRP laminates. The results show that prestressing CFRP laminates with NSM technique is an effective solution to increase cracking, service, yielding and maximum loads of RC slabs failing in bending. By applying 20% of prestressed NSM CFRP laminates, the service and ultimate loads have increased, respectively, 55% and 136%, when the corresponding values of the reference slab are taken for comparison purposes, while 119% and 152% were the increase when applying 40% of prestressed laminates. A numerical strategy was used to evaluate the load-deflection of the tested RC slabs, and a good agreement between experimental and numerical results was obtained. KEYWORDS: CFRP laminates, NSM technique, Flexural strengthening, RC slabs, Experimental results, Numerical simulation 1. INTRODUCTION Carbon fiber reinforced polymer (CFRP) materials have high potential for an effective strengthening of reinforced concrete (RC) structural elements, since they are lightweight, have high durability (non corrodible), exhibit high tensile strength and their availability are practically unlimited in size, geometry and dimensions [1-3]. The possibility of making relative fast interventions without interfering with the normal functionality of the RC structures and minor level of interference that this technique introduces in terms of architectural and aesthetic point-of-views are important advantages of the CFRP-based strengthening solutions.