Knitting bespoke reinforcement for new concrete structures

Lead Research Organisation: University of Bath
Department Name: Architecture and Civil Engineering


Emissions data suggests that 30-50% of all carbon emissions arise from activities in the built environment. The global population is expected to reach 9bn by 2050, with 67% living in urban areas. Meeting strict emissions reductions targets (in the UK - an 80% reduction by 2050) and facilitating global low-carbon design is therefore a major challenge for structural engineering.

Concrete is the world's most widely used man-made material. The manufacture of cement accounts for a large proportion of global raw material expenditure and at least 5% of global CO2 emissions. Recent research has made it possible to cast geometrically complex concrete structures, capitalising on a key advantage of this fluid material. These developments allow new architectural expression, and the new geometries allow us to save considerable amounts of material through design optimisation.

This new potential is being held back by current methods for reinforcing concrete. Although the steel rods that we use can be bent into standardised shapes, any further complexity adds considerable cost to the construction process.

With the goal of achieving low carbon concrete design, two major challenges exist: 1) to reinforce structures with complex geometries and 2) to provide durable and resilient structures. Meeting both challenges would allow us to capitalise on the fluidity of concrete to meet long-term emissions reductions targets. This will require a completely new approach to design and construction of concrete structures.

This proposal will completely replace internal steel reinforcement with a knitted composite reinforcement cage made from carbon fibre tows. By fabricating this reinforcement in exactly the right geometry, we will provide exactly the right strength exactly where it is needed. This will be transformative for concrete construction, and will greatly simplify the reinforcing of more efficient concrete structures to help the UK meet its ambitious targets for emissions reductions.

Planned Impact

This proposal will provide new technical and practical methods for the reinforcement of low-carbon concrete structures with novel geometries, with its outcomes and long term impacts potentially affecting all users of the built environment. The ambition of the proposal is to provide a prototype design and construction method to act as the founding blocks of a longer-term research effort to fully realise the potential of the woven cage system. These impacts will be seen in the order of years after this initial project is complete.

Researchers in concrete formwork technology will benefit through the provision of a feasible construction process for the all-important internal reinforcement. This research will help those engineers and architects working on novel geometries of concrete structures to understand how they may be reinforced with materials other than steel - a step that may be important to provide alternative, commercially viable, construction processes. This will help to enhance the UK's economic competitiveness in the construction industry and will provide a new avenue of both academic research and industrial development.

This proposal will provide initial steps towards a design method for the distributed woven carbon fibre internal reinforcement. Verification by structural testing will provide initial evidence for the method's efficacy - but much more research will be required before codified approaches are made available. This will impact colleagues working in structural engineering, and advanced composite design processes.

The societal impacts of this proposal will be seen in the medium-long term, and are found in its provision of an alternative method for the reinforcement of geometrically complex concrete structures. In this way it has the potential to reduce the contribution of the built environment to carbon emissions, which in turn will positively impact our quality of life. These steps will be crucial if we are to meet government targets for an 80% reduction in carbon emissions by 2050.

This project will provide design and construction guidance for the woven carbon fibre cage, which will be a trigger for additional research in the process that will in turn lead to a more widespread use of optimised concrete structures. This will be a significant impact in the race to reduce the carbon emissions of the built environment.

In the longer term the initial research completed here will be developed into a completely automated system for the fabrication of entirely bespoke reinforcement cages for concrete structures of any geometry. This will bring new potential for architectural, engineering, and construction industries.


10 25 50
Description It is feasible to 'knit' or 'wind' carbon fibre filaments into reinforcement cages for concrete beams. These beams can be optimised to minimise their embodied energy.
A novel gripping method for performing tensile tests on a straight portion of wound reinforcement was developed.
The results obtained on bent reinforcement show that the use of wound CFRP in lieu of conventional circular CFRP stirrups not only offers advantages in terms of construction flexibility at more affordable costs, but can also help to mitigate the reduction of the strength due to bent corners.
It is possible to provide shear reinforcement in concrete beams by winding CFRP reinforcement around the longitudinal bars.
The existing FRP provisions can be used to predict the shear strength of W-FRP prismatic beams, provided the actual strength of FRP at bent corners and a good estimate of the angle of inclined concrete struts is known. The value of strains observed on different shear links intersecting the same cracked section appears substantially uniform and in agreement with values that can be predicted.
The winding patterns are a crucial to the capacity and failure mode of the beams.
Journal papers have been published and additional papers are in preparation. All planned experimental work was completed on time. Further research is required to develop 1) Analytical methods (linking with research appropriate for brittle materials, such as peridynamics) 2) construction methods that improve productivity, building on automated winding developed here; 3) formwork methods that enable complex geometries, such as fabric formwork; and 4) full scale prototypes do demonstrate feasibility to industry and clients
Exploitation Route FRP reinforced concrete structures have significant durability benefits. This work has demonstrated how FRP can be used effectively in non-prismatic structures. The work could be taken forwards in full scale manufacturing of components for construction, and there are also impacts for design methods.
There is a key link to the use of lignin-FRP, a topic that is the subject of €100M in funding from the EU.
Journal papers are available on the project website and further papers are in preparation.

The grant has fed directly into the EPSRC funded research project ACORN (EP/S031316/1)
Sectors Aerospace, Defence and Marine,Construction,Energy,Transport

Description The winding process developed in this project has been expanded on in EPSRC funded "ACORN" EP/S031316/1 and subsequently has led to discussions with manufacturers in the UK and overseas about commercialisation of some of the ideas - principally to allow the reinforcement of complex panel geometries (either as facades or floor panels). The work has also led to discussions about the use of bio-based FRP materials to further reduce embodied carbon of such a system
First Year Of Impact 2018
Sector Construction
Impact Types Societal,Economic

Description Automating Concrete Construction (ACORN)
Amount £1,243,062 (GBP)
Funding ID EP/S031316/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2019 
End 03/2022
Title Data supporting research paper Shear behaviour of fabric formed T beams reinforced using W-FRP 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Title Dataset for "Wound Fibre Reinforced Polymer shear reinforcement for non-prismatic concrete beams" 
Description The dataset includes: 1. experimental data measuring the strain of W-FRP (Wound Fibre Reinforced Polymer) reinforced tapered beams under different load conditions; 2. MATLAB files of the prediction-making following the revised ACI 440, CSA S806 and MCFT model; 3. a spreadsheet to summarise the predictions. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Description Extending the service life of new reinforced concrete structures by using advanced composite materials workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Workshop in July aimed to build a bridge across the ocean to stimulate the communication and exchange of knowledge on the use of fibre-reinforced polymer (FRP) composite materials for construction. The event was held on campus and online to allow international speakers and attendees to take part in the debate.
Year(s) Of Engagement Activity 2016
Description ISE 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact IStructE evening lecture describe results of an EPSRC funded research project which aimed to completely replace internal steel reinforcement with a knitted composite reinforcement cage made from carbon fibre.
Year(s) Of Engagement Activity 2018
Description University visit, Missouri University of Science and Technology 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Dr Saverio Spadea gave a short course lecture on 'Bespoke FRP Reinforcement for Optimised Concrete Structures' on Feb 10 2016. A Q&A session and discussion followed. The presentation was streamed online as a webinar.
Year(s) Of Engagement Activity 2016
Description Webinar hosted by Trimble, on the topic of embodied carbon 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Webinar hosted by Trimble "why embodied carbon matters and why structural engineers play a crucial role in achieving reductions". Panel discussion covering many outputs from research grants, and how they relate to professional practice.
Year(s) Of Engagement Activity 2021