Strengthening of existing reinforced concrete beams by self compacting fiber reinforced concrete jackets

This paper focuses on the structural strengthening of existing Reinforced Concrete (RC) beams. Different traditional and new techniques can be found in the literature for improving RC beams structural capacity, among which, some are related with the strengthening by application of jackets made of concrete and, in particular, of different types of High Performance Concrete. However, for the multiple cases where standard building structures need interventions, some special concretes may not be suitable regarding its costs and concrete technology. The aim of this work is to analyze the performance of Self Compacting Fiber Reinforced Concrete (SCFRC) jackets for strengthening RC beams. The results of an experimental campaign consisting on the design, elaboration and testing under Three Point Bending of strengthened medium scale beams are presented. Three different jacket cases are considered: 60 mm thick made of plain concrete with steel bars, i.e. traditional RC jackets, and 60 and 30 mm thick, respectively, made of SCFRC. Besides, two different substrate conditionings are considered. A simplified numerical approach is also addressed. The results showed that although the highest increase in flexural strength was achieved for the jacket with reinforcing bars, for the same thickness, SCFRC permitted to achieve almost the same initial stiffness and a considerably higher ductility similar to that of a RC beam designed for a tension controlled failure. Moreover, comparing the two SCFRC cases, by reducing the jacket thickness to the half, a reduction in flexural strength of only 13.3% was observed, without any decrease in ductility. It was concluded that SCFRC is an efficient and competitive material for beam strengthening, particularly for reducing final cross sections and for improving ductility.