Concrete Reinforcement Structure of the Future

The challenge

The current rebar manufacturing and assembly process can be imprecise and highly variable due to the heavy reliance on worker skill and experience. This makes it difficult to achieve reliable and repeatable quality, particularly as the quality is directly linked to the capability of the worker. Furthermore the reliance on skilled workers can be time-consuming and costly when scheduling of labour and materials goes wrong.

Rebar also presents significant health and safety concerns – OSHA (Occupational Safety and Health Administration) reviewed their incident database to reveal that 61% of construction accidents are related to rebar impalement.

Project Approach

As part of the Construction Innovation Hub, the MTC wanted to find a better way of doing things and conducted a state of the art review to assess the effectiveness of traditional rebar, evaluate recent research, and identify opportunities for innovation.

The MTC then realised an opportunity of using laser cutting to produce steel reinforcement through a different method of manufacture. MetLase, who specialise in highly accurate, fast-make laser-cut tooling and fixturing, took MTC’s findings and produced a demonstration of a future state concrete reinforcing structure, tackling issues identified in the current state review.

The MTC compared the assembly of the current state and future state rebar cages, analysing adherence to the original design. To provide a fair comparison the workers utilised had no prior skills or experience in assembling either design and were instructed to work from the drawings without additional guidance.

Project Outcomes

Traditional and future state rebar cages were assembled, taking 26 and 4 man hours respectively. The cages weighed in at 105kg (traditional) and 155kg (future state), however the traditional design has had decades to be optimised compared to the future state design which has only had 2 weeks.

Time-lapse footage was taken of these assemblies, showing the disparity in effort to assemble the two cages.

Using photogrammetry analysis, the geometric adherence to the design was shown to be at least an order of magnitude better in the future state assembly than in the traditional assembly. Flatness, perpendicularity (below), and lengths/widths were all assessed.

The results of the comparison were presented to over 60 industry professionals at the MTC - including representatives from Laing O’Rourke, Kier, HS2 and Heathrow Expansion - as part of a CIH Open Call event on the 29th July 2019. Quotes following the event

“This ingenious proof of concept is exactly the reason the Hub was set up. Placing rebar traditionally can be difficult and physically demanding; showing an alternative solution that uses existing precision manufacturing techniques to create components that can be installed quickly, accurately and consistently by untrained operatives has the potential to be transformative.”
“…the solution has a long way to go before it can be considered as a viable alternative to conventional rebar and the conventional systems that have evolved such as our mesh bender that can create complex cages in seconds. If you are going to make the new solution effective you need to consider other areas where your solution is better than normal solutions and I suspect there are some good structural aspects in it that have not been explored.”

Benefits Identified

The MTC and MetLase demonstrated a new approach to rebar producing more accurate and higher performing reinforcement which could, based on rebar usage in the UK, save £1.35bn on labour time and 54,000,000 hours for the construction industry each year.

#	Target Area	Benefit
1	Reduction in whole life costs	The known/assured quality of the future state manufacture and assembly lends itself to reduced whole life costs. Particularly as the amount of cover can be more accurately controlled.
2	Reduction in delivery time	The future state cage took 4 hours to deliver compared to 26 hours for the traditional cage, a reduction of 85%.
3	Reduction in greenhouse gas emissions	The plate metal enables flat packing, therefore more efficient transport, but at a lower material utilisation than traditional rebar.
4	Reduction in productivity gap	The assembly times show a productivity increase of over 500%, and a part count assessment shows a reduction of 85% (450 down to 65). 374 of the 450 parts are wires that had to be tied.
6	Higher levels of lifetime build asset performance	The quality assurance of the future state manufacture and assembly means that the lifetime performance can be better known.
7	Improved assurance of buildings	Manufacture and assembly of the future state design is far more repeatable and less reliant on skilled workers than the traditional design, therefore the quality assurance is much better. The photogrammetry analysis showed the future state cage to be within 4mm of the design for flatness and perpendicularity, and within <1mm of the design for length and width. This is in comparison to the traditional cage which deviated from the design by 6 to 112mm.
8	Ethical impact	Rebar assembly requires workers to adopt unnatural and repetitive postures which can result in musculoskeletal injuries over time. The rebar demonstrator used much more ergonomic fasteners and less time was spent in uncomfortable positions. As part of duty of care this has a postitive ethical impact on those working in the industry.
9	Improved Health and Safety in construction projects	Removed the need for use of sharp wire and rebar ends, significantly reducing the risk of cuts and impalement. According to OSHA this has previously accounted for 61% of all construction incidents. Furthermore workers will spend up to 85% less time in a compromised (stooped) working position due to the reduced assembly time. The reconfigurable fixturing used as a platform also helped with ergonomics, bringing the cages to a more comfortable working height. Quotes from the technicians who built the traditional cage: “Tying knots in the wire is difficult and painful, I’ve got cuts and blisters all over my hands.” “Everything is dirty, the rust gets everywhere – your face, clothes, hands, eyes, nose.” “Everything about this is wrong apart from the cost.” “Constantly bending over to place the bars and tie the wires has given me backache.” Compared to quotes from the same technicians who built the future state cage: “Much, much easier to assemble.” “Quicker by far, and a very simple design. Didn’t even need the drawings!”
10	Reduce the skills gap in construction workforce	The future state design is less reliant on skilled workers to complete the assembly due to the on-part instructions and patented MetLase twist dowels.

Next steps

Test future state design i.e. cage concrete adherence, scalability of manufacture.
Investigate use of knowledge-based engineering to design rebar cages.
Financial viability study to prove out use of plate metal and laser cutting.
Loughborough University have a PhD project, supported by both MTC and MetLase, to develop the concept of the Manufactured Rebar approach.
Further work within the Construction Innovation Hub to further this research.