Stainless steel-FRCM system for strengthening of RC beams: towards a sustainable strengthening technique

Abstract

Fabric-Reinforced Cementitious Matrix (FRCM) systems for strengthening concrete structures are an alternative to traditional techniques. The FRCM system is a composite material consisting of two or more layers of cement-based matrix reinforced with dry fibres in the form of open mesh or fabric. When adhered to concrete structural members the FRCM system acts as supplemental external reinforcement. Many existing Reinforced Concrete (RC) members exhibit degradation due to the carbonation of concrete and/or corrosion of internal reinforcing steel bars. These RC members can be strengthened using stainless steel, in strip format (unidirectional fibres), embedded in a cementitious based matrix. The system, named Stainless Steel-FRCM, can be applied according to the Externally Bonded (EB) technique. In order to reduce times and costs of intervention, number of used materials, as well as the amount of chemical compounds, a novel Inhibiting-Repairing-Strengthening (IRS) technique is proposed and experimentally tested. Using a suitable matrix (thixotropic mortar with passivation properties) the main three operations of steel bars corrosion  inhibition/protection, restoring of deteriorated concrete, and installation of the external strengthening can be carried out in one-step. For evaluating the effectiveness of both new strengthening system and installation technique an extensive experimental investigation was planned and developed. A part of the experimental research includes two groups of three RC beams (3.00 m and 4.80 m long): one strengthened withIRS technique, one strengthened with EB technique and one control beam. These beams were tested  under monotonic loading. Further two beams, one beam for each group, strengthened according to IRS technique, were also tested under cyclic loading. The experimental results show the validity of the proposed solution in terms of structural performance and environmental sustainability.