Textiles, materials made from fibres, yarns, or threads that can be woven, knitted, or felted into fabric, are very difficult to recycle. Before we can really start effectively recycling it, we need to separate all the different fabrics and dyes. This is pretty hard to do by hand and even mechanically. Because of this, hundreds of thousands of tons of textiles end up in Australian landfill every year, but some engineers say that there’s a better destination for the textiles: concrete.

A team, based at RMIT University in Melbourne, has been trialling different ways to add fibres from old clothes and carpets into concrete mixes. The team has found that the modified 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 Dr. Chamila Gunaseka, “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 pressure from drying concrete, these textiles can stop cracks from growing any bigger.

The pre-processing involves extracting fibres from a textile, then cutting them into 12mm lengths with an automated cutter. “We identified this as the best length that gave the optimum condition, or the maximum crack resistance,” explains Gunasekara.

The team initially trialled their concrete on a small scale, using discarded clothes as their source of textile fibre. “Then we thought: why can’t we use this 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.

Gunasekara’s team has deliberately designed the technique to be as unselecting as possible when it comes to a source of textiles, showing the process worked with a single type of fibre would require 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 process the concretes – not only in our research, but in construction prospecting.” The team has tested a variety of regularly-used synthetic fibres in clothes, like polyester, nylon, and polypropylene.

The team has worked 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.

Now, the team is working with larger scales of concrete to test the structural performance and long- term durability. They’re also partnering with city councils to test bigger chunks of their modified concrete. “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 next year.”