Use of geopolymers for composite external reinforcement of RC members

Nowadays fiber reinforced polymers represent a well-established technique for structural retrofit of reinforced concrete structural members. However, the severe degradation of mechanical properties with temperature and fire conditions represents one of the weakest point of these systems. The use of a fire resistant inorganic resin, as geopolymers, instead of polymeric resins, would be highly desirable to overcome this issue. The present work is aimed at investigating the effectiveness of two different fiber reinforced geopolymer-based systems in strengthening of reinforced concrete beams. In particular, this paper presents the main outcomes of experimental flexural tests on shallow reinforced concrete beams strengthened with high strength steel cord and carbon fiber reinforced geopolymers, cured at room temperature. No mechanical anchorage was employed to fix the composite to the concrete substrate. The mechanical behavior of the strengthened beams was evaluated by means of four-points bending tests. Two beam specimens for each system (i.e. steel cord and carbon fiber reinforcement) and one unstrengthened control beam were tested. A significant increase in the failure strength of the reinforced concrete beams was experienced, in case of steel cord reinforcement. The adhesion of geopolymer to the concrete substrate and to steel cords and carbon fibers was also evaluated by means of scanning electron microscopy.