WHEN RENOWNED Italian engineer and architect Pier Luigi Nervi found global fame in the mid-1900s for his work with thin, concrete-shelled structures – including a boat hull – he did it by borrowing from the architecture of the ancient Roman and Renaissance periods.
Many historic cathedrals, for example, had been constructed using light concrete shells and stood for hundreds – and sometimes thousands – of years. When Nervi was working, there were global crises and supply chain issues, with world wars and a boom in building projects.
Certain building materials were difficult to procure. And so he made reinforced concrete his main structural material. To do so, he used knowledge engineers had recently gained about the value of reinforcement, and also what those responsible for the Gothic architecture of the 12th to 16th centuries had discovered about the value of geometry. Today, in a similar environment of supply chain squeeze and global crisis – this time environmental – Dr Philippe, Block, Professor at the Institute of Technology in Architecture at ETH Zurich and co-director of the Block Research Group, is working to achieve parallel success. He, too, is looking into history to find solutions to modern-day
challenges.
Block’s design focus is also on thin concrete structures, but this time without reinforcing materials. Why? For the same reasons that researchers and engineers around the globe are developing concrete alternatives and new concrete recipes: because we need to decarbonise. Pound for pound, concrete is not a major offender. In terms of kilograms of carbon dioxide equivalent per kilogram (kgCO,e/ kg), concrete is equal to straw, at 01 kgCOe/kg. Rebar comes in at 1.2, steel is 2.7, brass is 4.5 and aluminium is 11.5 kgCOe/kg.
The problem comes from the amount of concrete poured. As reported by Architecture 2030, global building floor area is expected to double by 2060, adding about 240 billion square metres. That’s “the equivalent of adding an entire New York City to the world, every month, for 40 years”, the report said. To even come close to current net-zero goals, engineers, researchers and construction professionals must attack the problem on a number of fronts.
GREENING THE JUNGLE
Most of the carbon footprint of concrete comes from the manufacture of limestone-based cement, said Dr Rackel San Nicolas, Senior Lecturer and Academic Leader of the Geopolymer and Minerals Processing Group at the University of Melbourne.
San Nicolas is currently driving research into what she refers to as the “greening of the concrete jungle” by creating better concrete. “Cement represents eight per cent of global carbon emissions,” San Nicolas said. “You can make sustainable concrete in different ways, but at the core it’s about reducing the amount of Portland cement used.
“The main approach I’ve been using is to utilise different waste materials like fly ash or slag, or different processed material like calcined clay, that have a much lower CO, footprint.” A transition to what is known as geopolymer concrete, San Nicolas said, would be relatively simple in Australia, as there is already a stockpile of more than 400 million tonnes of fly ash – waste from the coal industry – 30 per cent of which is appropriate quality for use in concrete. There is also more than 500 years’ supply of clay that can be calcined. Cement-free concrete, and concrete with just 50 per cent cement, is available in the market right now. It might be used for retaining walls or other less structurally important projects. But confidence is yet to be built in products engineers can design with. “It’s a very big hurdle for engineers and project designers to build confidence in these materials,” San Nicolas said. “But more suppliers are saying that by the end of this year they will have concretes we can design with, and we will have more full-scale trials and data around their durability.” Also assisting in the clearance of this hurdle is the SmartCrete Cooperative Research Centre (CRC), which exists to enhance industry-research collaboration.
“We co-invest with industry in research projects that are innovative and generate impact by transitioning concrete for a sustainable Australia,” said Clare Tubolets, SmartCrete CRC’S CEO. “We focus on decarbonising concrete across three research programs, taking a lifecycle carbon approach.
“The first is about sustainability, looking at the concrete mix itself, but also including elements of recyclability. The second is engineered solutions, thinking about how you design structures to optimise concrete use and reduce the carbon load overall. “The third is asset management, focusing on understanding and improving the health of existing concrete infrastructure through sensing and data analytics. “If we can extend concrete lie, we replace it less frequently?
LESS MATERIAL
The primary objective of using concrete in engineering and construction will always be concerned with risk, said Tubolets. “We don’t want our structures falling down,” she said. “If there is a decision between sustainability and durability to be made, durability will always come first.” Here is where Block and his disruption of concrete construction comes in. He believes we can have both sustainability and durability, and he points to ancient cathedrals across Europe, still standing today, as evidence.
“Historically, there was at some stage a shift between cost of labour and material. Material became very cheap and labour very expensive,” Block said. “There was also an aesthetic change with mid-modernism and its straight lines. People no longer liked curved arches and vaults. Then we started to optimise and to look at productivity.
“All the systems around construction and engineering evolved in one direction and we lost the structurally informed geometries that made sense for a certain material, and that also demanded a certain craft. We also lost the tools to design and engineer those.”
And so we reached a status quo, Block said – one that has been difficult to challenge. But today, that is fast changing. Block and his team have been working on the design and production of a concrete floorplate system that reduces the amount of concrete required by up to 70 per cent, and the amount of reinforcing steel by up to 90 per cent. It’s a system that turns concrete floor pieces into a sort of concrete masonry – reusable, replaceable and removable many times over. “This is nothing new,” he said. “It’s just reintroducing the same principles behind why Gothic cathedrals are still standing. We started a spin-off called Vaulted to commercialise these floorplates that are now built into a couple of projects. We have reduced materials so much, embodied emissions are reduced by 85 per cent.”
Interestingly, there’s no green premium in terms of cost for the floorplate system. Most of the benefit comes from getting the geometry right. The rib-stiffened floorplates are designed essentially as a thin funicular vault of unreinforced concrete supported by a series of spandrel walls, which act as vertical stiffeners.
They handle weight the same way the roof of a cathedral does. With the correct geometries, and the materials savings across all floors of a building, specifically in the foundations, the system can be cost-neutral while hitting high sustainability targets, Block said The concept of concrete masonry also creates an inherently flexible building system. Flexibility for future use, said Paul Easingwood, Director, Structures and Facades at Bligh Tanner, is now an essential ingredient in construction.
“You can make a relatively small investment to lift a building one or two grades in terms of yield and rental income, breathing another 30 or 40 years of life into a concrete frame,” he said. “You don’t have to go through that financial and environmental expense of demolishing 40 storeys of concrete, then pouring another 40 storeys of fresh concrete. What’s really important is making sure that core building can change its purpose.”
DIFFERENT MATERIALS
There are various options that can be added to the materials mix, Easingwood said. While none will ever replace concrete, they can be used to reduce our reliance. Timber in its various forms is becoming a more frequent selection, as is steel framing, particularly with the potential modularity they can offer. “We’re doing a number of schools projects in New South Wales, which are modular,” Easingwood said. “It’s a mandate from School Infrastructure NSW.
A lot of those systems are using timber, timber framing or cross-laminated timber.
“Ten years ago, that wouldn’t have been a conversation. Every day of the week it would have been a two-storey concrete frame. But now, there’s a heavy momentum to steer the construction industry toward different paths.” New engineering challenges also arise with new materials, around construction methodologies, tolerances, procurement and accuracy. “With long delivery times for some materials, it requires a different mindset to fix a lot of the design elements early and make sure everyone understands they cannot change those elements,” Easingwood said.
“Then there are new problems to solve. How does this timber work? How does it shrink? How do we connect it? How do we build earthquake design into it?” While different and new materials are a welcome addition, Tubolets said, it’s important not to lose focus on the improvement of concrete and reinforcement.
“Concrete is always going to play a vital role in the built environment, so we need to consider more sustainable ways of using it. Research in engineered solutions is considering new generations of reinforcement to help reduce or remove the steel component and move to carbon or plastic fibres,” she said. “At the same time we’re looking at recycling other industrial waste products into concrete as aggregate, including crushed glass, crumbed rubber and recycled concrete.”
REUSE AND RECYCLING
Speaking of recycling, Tubolets said, the first stage of a successful circular economy framework is the most simple: do nothing. A Bligh Tanner project in Hanlon Park, in Brisbane’s Stones Corner, attracted much positive attention for doing almost that.
When a 600 m concrete drain was dug up and turned into a natural waterway, the concrete pieces taken out of the ground were used elsewhere in the park, as retaining walls, as seating areas and to armour parts of the new creek. Very little of the concrete went to landfill. A great deal of work is now being done around recycling concrete itself, and on using those materials to create concrete that is just as durable as the virgin mix.
Professor Vivian Tam from Western Sydney University, Director of the Centre for Infrastructure Engineering, is a leader in this field, having developed a product known as CO, Concrete. Tam has spent many years perfecting CO, Concrete, produced by injecting carbon dioxide into recycled aggregates to accelerate the carbonation process. It improves binding and boosts the durability and strength of the recycled concrete.
Not only does the final product match performance of virgin concrete, she said, it also costs less, reduces carbon emissions, sequesters carbon permanently and is compatible with carbon capture technologies. “We have been working with a lot of companies, including Holcim, Sika, AW Edwards, Mott McDonald and Bouygues via the Holcim Accelerator Program Season 3,” Tam said.
“I’m now looking into other waste, such as brick waste, that can be recycled into concrete.” There is change in the air, Tam said. Having dealt with an industry that was previously reluctant to transform, her work is now receiving a great deal of attention.
“I have some partners saying that even if CO, Concrete was more expensive than virgin concrete, they would still use it because of the great benefits,” she said.
While this acceptance of change is a positive, what is required now is cross-sectoral collaboration, Tubolets said. “To certify a building for 50 years, we’ll need to work together to gather a lot of data on the products that are used.” she said
“We are risk-averse in this sector for very good reason. But we’re moving in an excellent direction toward the future of concrete.”
– by Chris Sheedy, published In Engineers Australia August Newsletter 2023