Ellen Phiddian
Cosmos science journalist
If they’re past re-using, textiles are difficult to recycle – with individual fabrics needing different conditions. Hundreds of thousands of tonnes of textiles end up in Australian landfill every year.
A better destination, according to some engineers, might be concrete.
A team, based at RMIT University in Melbourne, has been trialling ways to add fibres from old clothes and carpets into concrete mixes.
“This is a textile fibre-reinforced concrete,” Dr Chamila Gunasekara tells Cosmos.
The team has found the concrete can have up to 30% fewer initial cracks, as well as being more durable.
“When we place the concrete, maybe an hour or two later the first cracking starts – the water evaporates from the concrete placement, then the concrete starts to shrink,” explains Gunasekara.
“That’s why we call it shrinkage cracking.”
Steel fibres can reduce some of this cracking, but these fibres can still be very rigid.
“Like a rubber band, textile fibres are very flexible,” says Gunasekara.
“Fibres are distributed almost evenly throughout the cement matrix. Then, when a crack is initiated, fibres will go around the crack, [and] absorb the stress in the cement matrix.”
By absorbing pressures from the drying concrete, these textile fibres can stop cracks from getting bigger.
The pre-processing involves extracting fibres from a textile, then chopping them into 12mm lengths with an automated cutter.
“We identified this is the best length that gave the optimum condition, or the maximum crack resistance,” says Gunasekara.
The team initially trialled their concrete at the small scale, using discarded clothes as their source of textile fibre.
“Then we thought: why we can’t use this the same principle for other [wastes], like carpet waste?” says Gunasekara.
“We contacted industries that have a large amount of carpet waste generation.”
And just like the clothes, “it’s working”, says Gunasekara.
In fact, the technique has deliberately been designed to be as unselective as possible when it comes to a source of textiles. Showing the process worked with a single type of fibre would requite a lot of initial sorting and separating.
“That will give additional cost, that will give additional energy,” says Gunasekara.
“The other thing is material supply chain. If we focus on only one single material, then the question is whether we have enough materials to progress the concretes – not only in our research, but in construction prospecting.”
The team has tested a variety of frequently used synthetic fibres in clothes, like polyester, nylon, and polypropylene.
“Up to 70% of textile waste would be suitable for conversion into usable fibres, presenting an opportunity in the materials supply chain,” says Dr Shadi Houshyar, a textile and material scientist at RMIT.
They’ve also got it to work with “almost 100% non-recyclable” fabric used to make firefighting and military uniforms.
These fabrics are designed to be as unreactive and unbreakable as possible, so wearers can survive extreme environments which makes them almost impossible to repurpose at the end of their life – except in concrete.
“We used that material as well,” says Gunasekara.
Now, the team is working with larger samples of concrete and numerical models to test structural performance and long-term durability.
They’re also partnering with councils to test bigger chunks.
“It can be a concrete slab on the ground, or maybe up to a 50-100m footpath,” says Gunasekara.
“We are planning to start those field trials somewhere in the next year.”
