Investigation of surface modification and volume content of glass and carbon fibres from fibre reinforced polymer waste for reinforcing concrete.

The proportion of composites, mainly glass and carbon fibre-reinforced polymers (FRP) in the material cycle have been increasing for years in many sectors. Landfilling of FRP waste is forbidden and recycling is still an unsolved issue. Aim of this paper is the investigation of a feasible reuse of FRP as reinforcement in concrete as shredded material or as thermally recovered plain carbon fibres. A huge amount of glass fibre polymer waste is generated in the wind energy sector and shows low alkaline resistance which is not directly applicable as a reinforcement in alkaline concrete without any surface protection. Therefore, different surface treatments were conducted: on the one hand the aim is to protect FRP fragments in concrete and on the other hand to improve the adhesion. The results of pull-out tests show that a sanded surface of glass fibre polymers increases the averaged maximum shear strength by 16 %. Investigation of the influence of different volume contents (0.25, 0.5, 1 and 2 Vol.-%) of recycled, pyrolized carbon fibres with a varying fibre length show a maximum flexural strength at 1 Vol.-% in bending tests on fibre reinforced concrete. Compared to plain concrete an increase of +111 % can be observed.