Pioneering numerical and experimental studies at Victoria University will help urban planners and transport agencies predict the spread of bushfires and make tunnels safer for drivers.
The Victoria University Fire Research Group is working on a series of cutting-edge fire safety engineering projects that include detailed studies of fundamental combustion processes, the application of fire safety engineering in practice and how fires affect the lining of tunnels.
The results are used to verify the fire resistance of materials and the potential for concrete spalling (removing the surface to expose reinforcements) and demonstrate the likely spread of fast-moving bushfires.
The Structural Fire Testing Facility on the university’s Werribee Campus can monitor full-scale tunnel lining concrete tests in real time.
The next-generation fire testing facility is equipped with a large 4x3x3 m furnace, structural test rigs and a room that allows fire tests to be conducted according to ISO 17025 testing standards.
It also tests a range of other fire safety areas, such as the effect of water suppression on lithium-ion battery fires and the containment of blazes in the engine room of a ship or frigate.
Ember transport modelling
Another significant piece of fire safety engineering has been developing superior models for observing the movement of flying bushfire embers and how they impact properties.
The field-scale modelling, spearheaded by Professor Khalid Moinuddin, Executive Director of the university’s Institute for Sustainable Industries and Liveable Cities, can quantify firebrand flux from a range of vegetation fires on different house designs.
“In the past, modelling bushfire behaviours was more simplistic,” Moinuddin said. “They measured how far a blaze would spread in a given time under varying environmental conditions using very basic calculations.
“But our numerical model embodies physics and chemistry to analyse many more factors, particularly how burning pieces of twig or leaf matter fly through the air and ignite buildings.”
Computational fluid dynamics are harnessed to build complex numerical models to track particle movement and assess relative risk.
Understanding how landing patterns combine with heat flux has led to vastly more accurate and reliable risk assessments and helped engineers choose the right construction materials for buildings in bushfire zones.
To validate the numerical model, the team used what it calls an “ember dragon” to “breathe” out 10 mm³ pieces of wood that have been toasted and ignited to represent burning embers. A fan system mimics wind conditions by blowing them up to 10 m.
The experiment is then replicated via a state-of-the-art numerical model optimised for bushfire modelling and also capable of simulating dynamic fire escalations that produce unexpectedly high rates of spread and intensity, often endangering firefighters or civilians. Moinuddin’s team is using the model to investigate the effects of hills, fire breaks and merging blazes on fire propagation.
Tunnel concrete testing
The Structural Fire Testing Facility is run by Professor Maurice Guerrieri, a structural engineer and concrete spalling specialist, and is attracting interest from tier-one companies with major government tunnel contracts.
“There was nothing like this in Australia, so people had to ship these huge, five-tonne, 3.5 m concrete tunnel rigs to Europe to see whether they’d survive a fire,” Guerrieri said. “That was expensive and time-consuming, so we built one here.”
“Its first major project was the Melbourne Metro Tunnel,” Guerrieri said. “Since then, it has undertaken seven infrastructure tunnelling projects and established itself as one of the leading test furnaces in the Southern Hemisphere.”
Watch the furnace in action here.
Superior standards
The concrete testing has already had a seismic impact on the industry, disproving some long-established assumptions and becoming internationally renowned for the sophistication of its results.
“Everyone was testing as if it was still 1960,” Guerrieri said. “The standards hadn’t been updated to take into account new technologies or materials, so they were still saying that the maximum safe moisture content for concrete was three per cent and anything over that was more likely to lead to the concrete undergoing explosive spalling when exposed to fire. This is due to the build of internal pore pressure, believed to increase due to the higher moisture content.”
“My research has shown that’s simply not the case, and that moisture levels can be as high as 10 per cent. All the literature is old and hasn’t been updated, but now I’m writing new international standards.”
He argues that generating reliable data is only possible through live monitoring of tests conducted at full scale to replicate tunnel conditions properly.
“In other labs, they put the specimen inside, press a button and then wait until it’s time to take it out,” he said. “Often there isn’t even a window to look inside, but we have cameras inside the furnace to film the process and we stream the live data on YouTube. It’s like cooking a cake — you need to look through the door to see how it’s going!”
Find out more about the Victoria University Fire Research Group
Supplementary cementitious materials (SCMs) such as slag, a byproduct from the smelting of various ores, and fly ash, from the burning of coal in power plants, were first introduced decades ago. They’re essential in today’s low-carbon concrete, and in the geopolymer concrete of the future.
Sirivivatnanon worked with the CSIRO from 1988 until 2006, using SCMs to improve the durability of concrete.
Engineers who have gone big with low-carbon concrete walk through the challenges, considerations and lessons learned from embracing new forms of concrete.
Key points:
- Supplementary cementitious materials such as slag, essential in modern concrete, may have a limited future.
- Australia leads the world in geopolymer concrete, but there are regulatory and safety concerns.
- Some companies are already adopting low-carbon concrete in major projects – and reaping the sustainability benefits.
In the fast-changing field of concrete, real change is being engineered at a project level to solve the carbon conundrum.
The biggest and most obvious problem is the lack of definition around what “low-carbon concrete” actually means.
It is vital to understand the two most common types of low-carbon concrete, according to Professor Vute Sirivivatnanon, Research Director at SmartCrete CRC and Professor of Concrete Engineering at the University of Technology Sydney.
“One is basically concrete with supplementary cementitious materials, which also has some Portland cement in it,” Sirivivatnanon explained. “That’s the type of low-carbon concrete that is being used to a large extent right now.”
“The second type is generally called geopolymer concrete. This type basically has zero, or a very low amount of, Portland cement. So, it has much lower embodied carbon than the first one.”
The future of concrete
Today, engineers recognise that cement production causes a large portion – up to eight per cent – of carbon emissions globally. The use of waste material from another sector brings certain circular economy values into play, and more efficient use of Portland cement helps reduce the embodied carbon count.
But what if that waste material comes from a sector that is going through its own sustainability transformation, meaning some of the material will no longer be available?
“The reality is that, as we look towards 2050, SCMs like the fly ash we use today may be extinct if there is no more coal-fired power generation,” Hollie Hynes, General Manager of Environment and Sustainability at Laing O’Rourke Australia, told create.
It’s not the end of the road, however. There are stores of fly ash, also called dam ash when stored in dams, that can be used, according to Hynes.
As steel manufacture is likely to be transformed, slag as the by-product we know today will change.
“We have to do this all over again with the next generations of low carbon concrete,” Hynes explained. “We need really progressive thinking along the whole value chain. Do we leapfrog and start looking at what the future will hold, and just do it now?”
According to a paper on geopolymer cement and concrete, “any waste material containing aluminosilicate mineral such as fly ash, granulated blast furnace slag, rice husk ash, calcined clay … when treated with alkali solutions, give geopolymer cement”.
Australia is a global leader in the geopolymer space, Sirivivatnanon said.
“Dr Kwesi Sagoe-Crentsil started working on geopolymer concretes at the CSIRO in the mid-1990s, and this was followed by a lot of work at many universities,” he said.
“On a worldwide scale, in my opinion, Australia is probably leading in the development of geopolymer concrete.”
If a move away from slag and fly ash becomes necessary, it might lead towards calcined clay, which Dr Rackel San Nicolas, engineer and Senior Lecturer and Academic Leader of the Geopolymer and Minerals Processing Group at the University of Melbourne, said is in plentiful supply in Australia – over 500 years’ worth.
What’s the problem with geopolymer concrete?
There are four main issues with geopolymer concrete that Sirivivatnanon and his colleagues at SmartCrete CRC, and the CRC’s industry and academic partners, are racing to solve:
- Regulation
- Safety
- Early strength and long-term durability performance
- Product propriety
As far as regulation is concerned, Australia is part-way to enabling greater use of geopolymer concrete, he said, particularly since the 2023 release of the technical specifications.
Safety concerns primarily stemmed from the highly alkaline nature of the liquid activator used in some geopolymer formulation. This issue has been resolved by the use of solid activator, and safety protocols for workers.
The third challenge is around our need for certainty about the product’s durability in certain exposure situations. This is important from the design life viewpoint, Sirivivatnanon said.
For above ground structures, durability with respect to carbonation-induced corrosion has been addressed in TS199 with performance-based specifications.
“In sub-structures, in the soil, carbonation is not a problem,” he said. “Instead, it’s the sulfate and acid sulfate in the soil. With respect to geopolymers, [Australia needs] a bit more work.
“But the area that is the weakest is in the area of concrete exposed to marine environments, where there are chloride-induced corrosion issues of the steel reinforcement.”
Until we have certainty in each of these areas, the use of geopolymer concrete, in Australian construction at least, will remain subdued.
Where to from here?
Laing O’Rourke Australia is the first construction company to develop and publish limits on the embodied emissions allowed in the concrete used in projects.
The company made a conscious decision to leave out any specifications about how concrete suppliers should make concrete. Instead, the limits are based on a specified embodied carbon limit for the different strength grades. These limits are expressed in kilograms of carbon dioxide per cubic metre of concrete.
“Concrete is a big area of focus,” chemical engineer Dr Monica Hanus-Smith, Low Carbon Materials Lead at Laing O’Rourke, told create. “Everyone is talking about it. But when we dug into it, there was no definition.
“We wanted to set a target and policy in our own organisation around how we reduce emissions associated with concrete, so we worked with our supply chain and came up with a set of concrete carbon limits.
“We published it so others knew what we were doing, and we welcome them to adopt it … a rising tide lifts all boats.”
In the meantime, low-carbon concrete is being adopted across numerous major projects.
Holcim and the University of Melbourne developed a low-carbon mix that also used processed glass waste instead of sand, for use in Melbourne’s Metro Tunnel project, saving a claimed 150,000 t of carbon emissions.
For the famous spaces and spires of Punchbowl mosque in Sydney, a high-fly ash concrete helped reduce carbon output.
For more from create digital, check out the below:
- Winning green concrete formula stands the test of time
- Behind the scenes of the Bruce Highway upgrade project
- Tyres literally make the world go around, so how do we decarbonise?
