Recycling of FRP wind blade waste material in concrete

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

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.