Behaviour of concrete structures repaired with a novel and sustainable composite jacket

Behaviour of concrete structures repaired with a novel and sustainable composite jacket

Repairing deteriorating structures is a major challenge for many economies around the world. The use of fibre reinforced polymer (FRP) composite jackets has become a preferred solution in repairing bridge piles as they can be easily installed and form a robust single-piece repair system providing structural continuity along the hoop direction. Recently, a novel prefabricated glass-FRP (GFRP) jacket with innovative joining system that comprises two interlocking edges was developed. The actual performance of this jacket however is not fully explored and its structural contribution to the repaired structure is yet to be determined. This study focused on investigating the behaviour of damaged reinforced concrete (RC) structures repaired with the novel jacket and evaluating its effectiveness as prefabricated FRP repair system.

The grout plays a vital role in transferring the stresses between the damaged concrete structure and the FRP jacket, thus the most suitable grout system is determined as the first study. The effects of three types of grout infills, i.e. cementitious- concrete- and epoxy-based grout, on the structural behaviour of prefabricated GFRP tubes were investigated. The considered grouts have compressive strength and modulus of elasticity ranging from 10 MPa to 70 MPa and from 10 GPa to 35 GPa, respectively, which are the experimental parameters of this stage. The results showed that the brittle failure behaviour of the cementitious and epoxy grouts led to localised failure in the FRP repair system while the progressive cracking and crushing of the concrete infill resulted in effective utilisation of the high strength properties of the composite materials. The developed theoretical model accurately predicts the compressive behaviour of the grout-filled GFRP tubes. From this study, it was also determined that a cementitious grout is a suitable grout system due to its relatively high strength and stiffness as well as its ease of handling and installation.

The effectiveness of the novel FRP jacket as a repair system for RC columns with simulated corrosion damage was evaluated as the second study. Large scale circular and square columns were fabricated with 25% and 50% steel corrosion damage, and 50% and 100% concrete cover damage, then repaired with the FRP jacket and tested axially until failure. The results showed that the jacket restored the load-carrying capacity by 99% and 95% for columns with 25% and 50% corrosion damage, respectively, while the repaired columns with 50% and 100% concrete cover damage restored their axial load capacity by 95% and 82%, respectively. Moreover, the FRP jacket was found to be 43% more effective in repairing circular columns than the square columns due to the better confinement provided by the GFRP jacket in the circular than in the square column. Theoretical model predicting the axial strength of repaired columns showed an excellent agreement with the experimental results.

Bridge piers are normally subjected to lateral loads from water, tides and waves which create flexural stresses. Thus, the flexural behaviour of seven RC square members with simulated damage repaired with the novel FRP jacket was investigated as the third study. The FRP jacket was found to be more effective in repairing concrete members under flexural load when the damage is located in the compression zone rather than in the tension zone. This effectiveness could be further increased by placing the joint away from the compression zone. The provision of epoxy and coarse aggregates inside the jacket surface improved the stress distribution and cracks propagation in the jacket with grout. A simplified fibre model analysis which considers the confined tensile and compressive properties of the grout reliably predicted the flexural capacity of the damaged beams repaired with the FRP jacket.

Finally, Finite Element (FE) analysis was conducted to gain a better understanding of the behaviour of the repaired columns and to evaluate the effect of joint strength on the effectiveness of the repair system. ABAQUS software package was utilised to develop the FE model using the information obtained from the experimental stages as inputs for the model. The behaviour of the repaired columns was simulated accurately by considering the damaged plasticity model for concrete, bilinear behaviour for steel and linear elastic behaviour of the FRP composites. The results of the FE analysis revealed that the joint of the jacket should be placed away from the damaged zone to minimise stress concentration and effectively utilise the jacket as a repair system. Moreover, joint with tensile strength of at least 20% of the novel GFRP jacket’s hoop strength can significantly improve the capacity of the repaired column.

The results of this work provided a comprehensive evaluation on the effectiveness of the novel FRP repair system and detailed understanding on the behaviour of the damaged structures where the current system is sufficient for structural repair; however, further improvements are necessary to modify the joint to extend the jacket’s application as a strengthening system. Moreover, this research successfully explored the benefits of this unique system and provided a safe design tools for engineers to effectively utilise the novel FRP jacket in repair applications.