Effectiveness of S-FRCM Strengthening System Applied with Two Different Techniques

The work aims to investigate the structural performance of Reinforced Concrete (RC) beams strengthened with an innovative system made of stainless steel fibre strips embedded into an inorganic matrix (S-FRCM: Steel –Fibre Reinforced Cementitious Matrix). To simulate existing RC structures and investigate the potential application of S-FRCM system on a poor concrete substrate, the beams were built with low concrete strength. Two different strengthening procedures were used: traditional Externally Bonded (EB) technique and innovative Inhibiting-Repairing Strengthening (IRS) technique. The IRS solution consists in the installation of stainless steel strips in the cover concrete, restoring the latter with a polymer-based inorganic matrix that contains property of protection against further corrosion. This inorganic matrix, as well as similar matrices available on the market labeled as “geopolymeric matrices”, contains fly-ash and/or slags and it is suitable for retrofitting of RC structures with deteriorated cover concrete and/or corroded steel bars. A set of RC beams strengthened according to the two different techniques (EB and IRS) were monotonically tested under four-points bending. Test results show that the S-FRCM system provides an average increment on load carrying capacity of about 25% compared with unstrengthened beam. On the basis of experimental data available in literature, a simple analytical formula for prediction of S-FRCM debonding strain is proposed.