PSI - Issue 68

Aseel Salameh et al. / Procedia Structural Integrity 68 (2025) 166–172 A. Salameh et al. / Structural Integrity Procedia 00 (2025) 000–000

168

3

2. Experimental testing and bond-slip calculations 2.1 Material Properties & testing

For the experimental investigation, Mape Wrap C UNI-AX unidirectional CFRP sheets (MAPEI, 2016) were used for concrete strengthening. The CFRP sheets exhibited a density of 1800 kg/m³, a nominal thickness of 0.164 mm, an elastic modulus of 252 GPa, and an ultimate tensile strength of 4900 MPa. The sheets were bonded to concrete using a two-component epoxy adhesive (Mape Wrap 31 SP) with a density of 1.16 kg/dm³, elastic modulus of 1000 GPa, and tensile strength of 28 MPa. The concrete substrate was designed to achieve a characteristic compressive strength ( f'c ) of 60 MPa at 28 days. Three specimens (CB-01, CB-02, CB-03) with identical dimensions of 100×100×500 mm were reinforced using CFRP. The size and arrangement of the CFRP reinforcement are described in Fig.1.

(a)

(b)

Fig.1. Specimens details: (a) side view; (b) cross-section.

Before testing, four strain gauges were properly attached to CFRP laminates. The specimens were subjected to a three point bending test set up at room temperature, as shown in Fig. 2. The load was applied at a constant rate of 0.08 kN/s until failure.

Fig. 2. Testing set-up.

2.2 Calculating bond-slip models from experimental testing Bond forces generate the change in the tensile force of the CFRP laminate to the interface layer between the laminate and the concrete substrate. The bond shear stress between two strain gauge positions can be obtained by equilibrium and compatibility equations (Eqs.1-3) (Pellegrino et al., 2008). By the assumption of linear elastic behavior, the equilibrium of bond/shear stress considers the normal stresses and + and shear stresses τ(x) along a segment length of the CFRP laminate and could be written as shown in Eq.1: