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Plain concrete cylinders and beams externally strengthened with natural flax fabric reinforced epoxy composites

: Yan, L.


Materials and structures 49 (2016), No.6, pp.2083-2095
ISSN: 0025-5432
ISSN: 1359-5997
Journal Article
Fraunhofer WKI ()
flax FRP; external strengthening; interfacial bond; flexural behaviour; compressive behaviour

The use of bio-composites as construction and building materials will be beneficial for the development of sustainable construction industry. This study evaluated the performance of natural flax fabric reinforced epoxy polymer (FFRP) composites as external strengthening materials for concrete elements. A total of 24 plain concrete cylinders and beams with and without FFRP reinforcement were tested under uni-axial compression and four-point bending. The considered FFRP thicknesses were 2, 4 and 6 layers of the fabric. Microstructures of flax/epoxy and FFRP/concrete interfaces were analysed by scanning electronic microscope (SEM). Test results indicate that in axial compression, FFRP as external strengthening material enhanced peak strength, strain, fracture energy and ductility of the concrete cylinders remarkably, i.e. the increase in strength and fracture energy by 6-layer FFRP is 134 and 2570 %, respectively. Experimental peak strength of the strengthened specimens were compared with the predictions by existing strength equations. A strength equation was proposed to predict the ultimate compressive strength accurately. In flexure, FFRP strengthening increased lateral load, deflection, flexural strength and fracture energy of the concrete beams significantly, i.e. the increase in peak load and fracture energy by 6-layer FFRP is 374 and 4660 %, respectively. SEM studies showed the good interfacial bond between FFRP and concrete because of the epoxy adhesive. The study therefore concluded that the woven FFRP composite is a suitable material for external strengthening of concrete structures.