Concrete doesn’t burn but it does split when exposed to extreme heat. New research from the UK claims adding tyre fibres to a concrete mix can stop this occurrence. Not all agree. Roads and Infrastructure investigates.
Concrete does not burn and does not emit toxic fumes when affected by fire. The is largely due to concretes constituent materials – cement and aggregates – that, when chemically combined, form an inert and therefore non-combustible material.
When concrete is exposed to fire it chips and flakes in a process known as spalling. This happens when water is trapped within the concrete element, vaporising in high temperature. As more water vapour is produced, the pressure within concrete structures increases.
According to researchers at The University of Sheffield in the UK, the modern high-performance concrete commonly used in public infrastructure projects, is susceptible to explosive, fire-induced spalling.
More technically, spalling occurs through a combination of differential thermal stresses, and excessive pore pressure. This pressure leads to a reduction of the cross-sectional areas of structural elements, which causes the structure to weaken. When exposed to extreme heat, the weakened structure is susceptible to explosion.
The University of Sheffield Engineering School claims to have found a solution by adding fibres extracted from tyres to concrete mixes. Results show, when tyre fibres are added to a concrete mix, there is a reduction in the materials tendency to spall when exposed to intense fire heat.
Lead researcher, Dr. Shan-Shan Huang, says because the fibres are small, they don’t affect the strength of the concrete.
Dr. Huang explains that the fibres only job is to melt when heat becomes intense, leaving networks of tiny channels that allow moisture trapped within the concrete to escape, thereby reducing the potential for concrete to break out explosively.
Using man-made polypropylene fibres to protect concrete from spalling and damage has been happening for a number of years. Research suggests that the resistance of conventional concrete to heat can be enhanced by adding a few kilograms of polypropylene fibre per cubic metre of concrete mixture.
What makes the Sheffield research significant is that it’s the first to show these fibres don’t have to be made from virgin material but can rather be reclaimed — a step in the direction of the circular economy.
A circular economy is an alternative to the traditional linear economy, which sees products made, used and then disposed. A circular economy prioritises keeping resources in the economic loop for as long as possible, providing maximum value and sustainable outcomes.
According to Liam O’Keefe, Senior Strategy Manager at Tyre Stewardship’s Senior, who runs Australia’s Tyre Product Stewardship Scheme to promote the development of viable markets for end-of-life tyres, tyre rubber waste is one of the most significant environmental hazards in the world.
Mr. O’Keefe says his organisation is looking into similar concrete research here in Australia. Highlighting Tyre Stewardship’s commitment to finding real world outcomes for end-of-life tyres
“We’re focussed on measuring consumption and the use of research for practical outcomes. It’s great to see this research,” Mr. O’Keefe says. “More and more people are realising the specific benefits crumbed rubber can have on safety and structural integrity.”
According to Tyre Stewardship Chief Executive Office, Lina Goodman, a recent audit found a significant amount of end-of-life Australian tyres are sent overseas, where they are stockpiled in unsafe conditions or offloaded outside the known supply chain.
This audit suggests, if implemented in Australia, the Sheffield research could have a big impact on the sustainable usage of end-of-life tyres.
Similar research has also been conducted in New Zealand, which is looking into how recycled tyres could be reused to earthquake-proof structures.
Laura Banasiak, who works for the Institute of Environmental Science and Research, says she has undertaken preliminary testing into the use of shredded rubber from old tyres for seismic isolation foundations.
Spalling is an issue for the concrete industry and public safety at large. However, with a spate of high-profile fires involving concrete structures over the last few years being deemed to be caused by cladding, one has to question cause and effect.
National Precast Concrete Association (NPCA) CEO, Sarah Bachmann, said while she finds the Sheffield research interesting as a means to reduce spalling, NPCA have no plans to conduct similar research in Australia.
When asked about the research, Ms Bachmann stated National Precast will be watching the results with interest. She reiterated that concrete itself is non-combustible, nor does it emit toxic fumes when exposed to fire, which cannot necessarily be said for other building materials, including those which have been at the centre of recent fires. Professor Jay Sanjayan of Swinburne University expressed similar sentiments, arguing while tyres and spalling reduction it is a good research topic, it’s not very practical.
Some think cladding could be the issue. Cladding is the application of one material over another, like a skin. Reports suggest it is this outer layer that generally causes a concrete structure to catch on fire.
Dr. Sanjayan says if concrete were used for cladding, rather the combustible material often used, the community wouldn’t have the problem of concrete fires.
Earlier this year, industry bodies called on the Federal Government to review the National Construction Code (NCC) and restrict the use of combustible materials in construction.
Cement Concrete and Aggregates Australia, Think Brick Australia, and the Concrete Masonry Association of Australia came together to urge politicians to tighten the standards expressed in the NCC to keep the community safe.
Similarly, at the Building Minister’s Forum in Hobart this year Victorian Minister for Planning, Richard Wynne, called on the states, territories and Federal Government to support a ban on combustible cladding.
“We’ve seen how quickly fires spread up buildings fitted with combustible cladding and we have a responsibility to stamp out these sub-standard building materials.”
“Victoria has pushed for a national response to flammable cladding ever since the 2014 Lacrosse fire but has been met with resistance from the Federal Government,” Mr. Wynne said.
“Given the fire risk and the cost to apartment owners to fix cladded buildings, the most common-sense approach is to stop this material from coming in to the country all together – and we need Federal Government support to make that happen.”
While the cause of concrete fires might not be spalling induced, the Sheffield research still offers valuable insights into how structural integrity can be improved — while simultaneously assisting in the creation of a more circular infrastructure economy.