How can the concrete and steel industries come together to create prefabricated, net-zero, reusable structures?
Dr Sarah Connolly MIMMM at Innovate UK reports for Institute of Materials Magazine.
Concrete underpins the construction industry. It is versatile, durable, and ideal for large, strong structures. Every year, ten billion tonnes of concrete is used globally.
However, the impact on our natural environment needs to be considered, with that of large construction projects increasingly coming under the spotlight. Indeed, scrutiny of sustainability credentials has led to significant delays or rejection of applications.
Over the past decade, the concrete industry has been slowly improving, and has moved away from a time when one tonne of cement emitted one tonne of CO2, but there is a long way to go. Despite advances in manufactured approaches to construction, most buildings are still delivered through a traditional approach to steel-framed construction and the majority of emissions come from the use of Ordinary Portland Cement (OPC).
If the cement industry were a country, it would be the world’s third largest CO2 emitter. Predictions for the industry suggest this will only increase by 2050 with population growth and further urbanisation worldwide.
This could be negated by using more sustainable concrete alternatives that are already available. There are alternatives to OPC, but its price and availability, the amount of data and confidence the industry has in this material, and its aversion to change, means there is often pressure to fall back on what is well accepted.
The sustainable options are subject to misconceptions by some in the industry that functionality and performance is sacrificed for sustainability. But by replacing OPC with an alternative binder, it is possible to create a high-quality concrete while emitting less CO2. With technology advances, contractors no longer have to sacrifice the compressive strength, versatility, thermal mass, low cost and well-established supply chain once unique to OPC.
Removing the barriers
Cemfree is a proprietary alkali-activated cementitious material developed by DB Group in Cambridge, UK.
It uses materials including ground granulated blast-furnace slag from steel mills or pulverised fly ash from power stations to create a cement-free binder that leads to a product with similar properties to concrete and uses 80% less CO2. But how can DB Group challenge misconceptions of such products if no construction projects are willing to partner with them?
Global consultancy and construction company Mace aims to facilitate an environment where Cemfree can be trialled in real construction projects to extract data and learnings. It is working with DB Group on a project partially funded by the Transforming Foundation Industries Challenge of Innovate UK, part of UK Research & Innovation, to develop prefabricated
net-zero carbon structures.
Not only is the project looking at energy usage and emissions from cement production, but also the steel used in the structural framing. Within steel production, energy constitutes 20-40% of the costs. Improvements in energy efficiency not only mean better sustainability, but also a reduction in production costs and improvements in competitiveness. Collaborative efforts between the concrete and steel industries are necessary to develop impactful low-energy solutions to meet the needs of future generations.
This is the key driver behind the Transforming Foundation Industries Challenge – to collaboratively develop innovative technology to reduce energy and resource use within the foundation industries.
The vision of this project is to make energy-efficient structures for buildings that can be dismantled and reused, ultimately enabling zero-carbon buildings.
Out of site
The proposal is an offsite method of construction that makes use of recycled steel in the structural beams from project partners, Hare, and cement-free concrete from DB Group. Targeting commercial offices and infrastructure applications, the components will be manufactured offsite and delivered to the project as sub-assemblies and installed as a single operation,
reducing traffic to site.
Compared to traditional construction, this will reduce:
• Weight of the structural frame by 10%
• Structural steel content by 15-20%
• Deliveries to site by 40%
• Labour resources for steel frame erection and
following trades by 60%
• Reduced embodied energy (and therefore carbon
reduction) of 80%
• Cement content in floors by 100%
Structural cassettes are being designed by project partners AKT II specifically for prefabrication, meaning 80% of the work can be offsite (managed by project partners Oranmore Precast), and installation is a single operation, allowing for social distancing.
The more efficient design and material choice, combined with offsite construction methodology, will enable a predicted productivity gain of 25% and reduction of carbon by 80%. The cassettes are also demountable and the project is researching flexibility and reuse in other projects to incorporate circular economy principles.
Working in a controlled prefabrication environment enables greater understanding of Cemfree’s curing behaviour and optimisation of pour parameters. It also allows all relevant checks to be carried out prior to installation, resulting in increased appetite for innovation risk as in situ projects have large cost and programme installations if anything goes wrong.
Sensing a change
The project is also advancing state-of-the-art digital engineering and sensor technology. This is focusing on three areas – interrogating design and construction elements to ease manufacture and assembly; reduce complexity and improve safety and logistics; optimising the design-life of the product and improving long-term performance; and creating an end-of-life deconstruction strategy to make products reusable.
Project partners, Converge, are using their ConcreteDNA monitoring to accurately track the strength gain of the pre-cast Cemfree concrete. This allows the manufacturing process to be optimised, enabling pre-cast units to be lifted as soon as they reach the necessary strength, and the moulds to be re-used as efficiently as possible.
The firm is also deploying a technology that measures strain development within pre-cast units during assembly, lifting, installation, as well as in-service. This will generate a rich dataset on the units’ performance, allowing a digital twin of the process to be created to further optimise manufacturing and handling, or even the structure’s design.
Converge has looked at historical data to identify how the installation process is normally conducted, combining this with plans on how installation will be improved in the future to identify where sensors should be placed for maximum insight.
A dress rehearsal
The team is nine months into a 12-month project to deliver a full factory trial of a two-storey, 9m x 12m demountable, mock-up assembly. This will not only be produced through an energy efficient process but will be reusable and scalable. This full-scale mock-up will demonstrate the potential for use of a clinker-free concrete in a structural module, generating that vital data needed for integration into future contracts and a route to market.
“Innovation is a non-linear process, but DB Group together with Mace and the other consortium partners have demonstrated with this reusable, ultra-low carbon structural cassette that for those who understand the value of an idea, barriers will be overcome and the journey from concept to commercialisation will happen. It’s been a fantastic experience working at the forefront of construction design and we’re excited to help deliver a solution that can bring efficiency and significant
environmental benefits to commercial projects,” says Adam Gittins, Cemfree Commercial Manager, DB Group.
Modelling has shown that the areas in greatest need of monitoring in the mock-up will be joins between the individual cassettes. Measured data through the sensors will provide good insight into their behaviour. This will be combined with lab testing at University College London, UK, using numerical modelling from Converge data and physical testing of assemblies this summer.
The project team has also been able to balance the research alongside maintaining business operations during a pandemic.
“The challenges of a project like this are that they are beyond everyone’s day job. It has been something that all parties have had to not only shuffle around their own commitments (and all parties have very senior people involved) but with the backdrop of the pandemic. It has meant that we’ve been workshopping design details over [Microsoft] Teams and in some cases have developed relationships having never met the other parties face to-face. All challenges which were not visible from our
application a year ago,” explains Martin Pike, Senior Construction Engineer at Mace.
Making the case
This project has been vital in demonstrating the potential of innovative technologies for large-scale construction projects. It is only through partnerships and early-stage trials, that innovative players can progress in their scale-up and commercialisation
journeys. Tier 1s are integral to the development of new techniques and processes by providing the platform for validation.
But this is by no means a charity mission – by leading on the development projects, construction companies can tailor technologies to meet their requirements through demand-driven innovation. For the UK processing industries, who are often baseline price driven and have little incentivisation to invest in making their processes more energy efficient, collaboration
through the supply chains to drive innovation is essential to provide the business case for investment.
We need big players to start making moves to drive others to respond competitively and initiate a market for sustainable solutions. There are also business wins for construction firms, as shown by this work. Mace is already including the cassettes developed within live tenders. Pike says, “We’ve bullishly used the mock-up and the concept design to gain live design feedback from potential future clients through working the cassettes into proposals – the feedback was cycled back into
alterations of our mock-up design. It slowed the Innovate UK programme but increased the viability of the product.
Through varying details across the mock-up, we have therefore effectively developed several assembly solutions which could open up multiple sectors for exploitation when we stand back and evaluate the result.”
Looking ahead, being energy efficient may mean a change from the current processes, but it can also mean profitability for the whole supply chain and an upper hand in tendering in the future.
To read the actual Institute of Materials article, follow this link https://dbgholdings.com/wp-content/uploads/2021/05/49-51-Net-zero-structures-LC.pdf
