Monotonic and fatigue performance of RC beams strengthened with a polyurea coating system

• The polyurea coating system increases the flexural capacity of reinforced concrete beams.
• Based on degradation of concrete, a theoretical model is proposed for deformation of RC beams under fatigue loading.
• The correspondence principle is used for damage growth and fracture healing of the external polyurea coating system.
• The influence of the polyurea coating thickness is considered for the strengthening system.

This paper has been conducted to evaluate fatigue and monotonic behavior of concrete beams strengthened with a polyurea coating system. Ease of application and multi-hazard benefits of polyurea has made it useful in retrofit–repair situations. Rather than blast or impact mitigation, polyurea has the capability of flexural and shear reinforcement for structural members. In this research, parametric study has been done to describe the flexural capacity of coated beams. Moreover, theoretical model was developed to predict the maximum deflection of strengthened beams under cyclic service loads. In order to validate the models, large size reinforced concrete beams were fabricated and externally strengthened in two levels of polyurea thickness. Beams were tested under four-point monotonic and fatigue loading. The relationship between deflection, coating thickness and number of cycles was studied and analyzed. In addition, the elastic–viscoelastic correspondence principle was used to evaluate the damage mechanism of the coating system in repetitive load condition. Results indicated that application of polyurea, improves the flexural capacity as well as ductility of RC beams, additionally, the correspondence principle represented an acceptable model for damage growth and fracture healing of the external polyurea coating under complex cyclic loading.