The increased UK investments in the wind energy sector will result in an upsurge in the fabrication of wind turbines. Fibre Reinforced Polymer (FRP) wind turbines have a design life of approximately 20 years due to fatigue limitations [1] and a high volume of construction waste is expected from the offshore wind farms by 2050. FRP reuse strategies, such as the pyrolysis, focus on fibre retention with a particular interest in carbon due to the high value of the material [2]. Yet, these methods are more energy intensive and can often lead to damage and degradation of the fibres [2]. Mechanical recycling and use of FRP material as aggregate replacement or fibre reinforcement in concrete is an alternative method (downcycling) [3]. The mechanical properties of concrete with recycled FRP (FRPcrete) depends on the aspect ratio of the FRP needles with low aspect ratios leading to considerable decrease in both compressive and tensile properties [3] and high aspect ratios resulting in superior tensile performance [4]. However, high aspect ratios of FRP needles can lead to agglomeration and porous concrete when a dense steel reinforcement cage is used on site in concrete structural elements. Fibre alignment in FRP needles plays a significant role in the tensile performance of FRPcrete and pultruded recycled FRP rods result in higher toughness via the crack bridging effect [4]. However, in FRP blades the fibre orientation changes within the same laminate (through thickness variation) and across the blade. Despite the majority of FRP blades being made of Glass Fibre Reinforced Polymers (GFRPs), Carbon Fibre Reinforced Polymer (CFRP) laminates can also be found inhibiting standardisation in the recycling process. To provide FRPcrete with reliable mechanical performance, other key aspects that need to be addressed are the durability of GFRP within the concrete alkaline environment and the structural integrity of the interfacial transition zone (ITZ) between the FRP needle and cement matrix that affects the concrete failure process.

The aim of the project is to assess both the short-term and long-term mechanical performance of FRPcrete for structural applications considering different variables (e.g. optimised geometry of FRP needles and aggregate replacement ratio). Both experimental and numerical work will be conducted using a validation and integration design approach. The end goal is to develop concrete that can effectively take advantage of the FRP wind blade waste.

Objectives

1) Find the optimum geometry (aspect ratio) of FRP needles and aggregate replacement ratio considering manufacturing limitations (steel reinforcement, concrete segregation and FRP needles agglomeration).
2) Find the optimum surface deformation of FRP needles (e.g. sand blasting and grooves) to increase the bond at the FRP/concrete interface.
3) Build an analytical model to predict the mechanical performance of FRPcrete considering variations in FRP needle geometry, fibre orientation, type of fibre (carbon and glass) and aggregate replacement ratio.
4) Assess the long-term performance of FRPcrete by conducting both permeability and mechanical tests.
5) Address size effects and the mechanical performance of large-scale beams