Predictive Strain Debonding in RC Beams Externally Strengthened with S-FRCM
Francesco Bencardino and Mattia Nisticò
Appears on pages(s):
debonding, externally bonded, fabric-reinforced cementitious matrix, inorganic matrix, reinforced concrete, repair, strengthening
Composite materials that employ modified cement-based mortars are usually named Fabric-Reinforced Cementitious Matrix (FRCM). The two main components are the cementitious matrix and the reinforcement fabric. The matrix can contain silica fume, blast furnace slag, fly ash and in some cases chemical property that can act as corrosion inhibitor. Some types of fabrics commonly used for the strengthening of existing Reinforced Concrete (RC) structures include nets with carbon or polyparaphenylene benzobisoxazole fibers disposed along one or two orthogonal directions, and unidirectional steel ropes (S-FRCM).
The S-FRCM system can be applied according to the traditional Externally Bonded (EB) or the innovative Inhibiting-Repairing-Strengthening (IRS) technique. The latter is a sustainable strengthening method and it is a useful solution for existing RC structures with deteriorated or damaged cover concrete.
Experimental tests show that for S-FRCM systems, applied with EB or IRS technique, the debonding occurs at fiber-matrix interface without significant damage at concrete substrate. Consequently, the debonding strain depends mainly by geometric and mechanical properties of external reinforcement and elastic/fracture properties of fiber-matrix interface.
Considering experimental data available in literature, related to RC beams strengthened in flexure using S-FRCM systems, a predictive strain debonding relationship is defined and its reliability is evaluated through comparison between experimental and theoretical ultimate load.