Debonding of Vegetal FRCM from Concrete Beams Subjected to Bending Loads

Abstract

The increasing need of society to develop more sustainable and renewable materials has made vegetal fibers an interesting potential substitute for synthetic fibers in strengthening systems, due to their considerable strength and deformation capacity. This paper aims to increase the knowledge on how the materials interact between them in vegetal FRCM composites to strengthen concrete structures. To do it, two fibers were selected: cotton (CO), due to its good deformation capacity, and hemp (HE), due to its high strength. A low-viscosity and high adherence epoxy resin was used to coat the yarns to protect them from the alkali environment of the cementitious matrix. To study the FRCM-substrate interaction, an adaptation of the test methodology described in ISO 10080:2005 was developed and performed. Three different lengths (30, 40, and 50 cm) were used to obtain the optimal bonding length for hemp case. A single case (50 cm) for cotton was tested to compare its behaviour against hemp. In the FRCM-substrate interaction, it is noticed that hemp-FRCM shows complete bonding as all except one specimen failed by mesh failure. In the case of cotton-FRCM, its deformation capacity (at least 4 times hemp-FRCM) made all specimens deform until the geometric end of the testing set up without the mesh breakage, bearing a lower load but keeping it constant through fiber-matrix friction. In terms of load, hemp-FRCM reached the highest load, 10% higher than cotton-FRCM’s peak load. To conclude, the testing method for assessing steel reinforcement bonding in reinforced concrete was proved to be satisfactory at assessing FRCM-concrete interaction, being able to transmit the load from the substrate to the composite without the slippage of the vegetal-FRCM.