This engineer has a concrete plan for recycling plastics

An Australian engineer has devised some novel ideas for turning plastic into concrete, and his findings are already being used in commercial projects.
3D-printed concrete inspired by lobsters and a car park made of recycled plastic are two of the big ideas Dr Jonathan Tran, Senior Lecturer in Structured Materials and Design at RMIT’s School of Engineering has for the circular economy.

“3D concrete printing technology has real potential to revolutionise the construction industry, and our aim is to bring that transformation closer,” he said.

Concrete is second only to water as the most widely used substance on earth. But it comes at a cost — if concrete were a country, it would be behind China and the United States as the largest carbon dioxide emitter in the world.

Digital manufacturing technology such as 3D concrete printing (3DCP) has the potential to save time and materials in construction, as well as push the boundaries of architectural innovation.

The key technical challenge for engineers is making 3DCP strong enough for use in free-form structures. In a new experimental study, Tran and his research team looked at this problem with special 3D-printing patterns, inspired by the natural strength of lobster shells.

“Our study explores how different printing patterns affect the structural integrity of 3D printed concrete, and for the first time reveals the benefits of a bio-inspired approach in 3DCP,” he said.

A 3D concrete printer builds houses or makes structural components by depositing the material layer-by-layer, unlike the traditional approach of casting concrete in a mould.

When the team combined the twisting patterns with a specialised concrete mix enhanced with steel fibres, the resulting material was stronger than traditionally-made concrete. Their bio-mimicking spiral patterns improved the overall durability of the material, as well as enabling the strength to be precisely directed for structural support where needed.

“We know that natural materials like lobster exoskeletons have evolved into high-performance structures over millions of years, so by mimicking their key advantages we can follow where nature has already innovated,” Tran said.

Concrete printing revolution

Engineers around the world are already moving quickly to take advantage of 3DCP technology. Construction on the world’s first 3D-printed community began in 2019 in Mexico, with a house able to be 3D printed in just 24 hours for about half the cost of a traditional build.

Tran and his research team at RMIT have experimented with a range of printing patterns, with the lobster-inspired helicoidal pattern so far the most promising for supporting complex structures.

“As lobster shells are naturally strong and naturally curved, we know this could help us deliver stronger concrete shapes like arches and flowing or twisted structures,” Tran said.

“This work is in early stages so we need further research to test how the concrete performs on a wider range of parameters, but our initial experimental results show we are on the right track.”

Dr Jonathan Tran

RMIT recently acquired a large-scale mobile concrete 3D printer for further research, where the 5×5 metre robotic printer will be used to continue research into structural printing.

Plastic concrete
Tran’s team will use the machine to print concrete made from recycled soft plastic, using it in an Australian-first commercial project made from recycled materials.

They recently worked with industry to include Polyrok — an aggregate made from soft plastics — which was used in the concreting of Coles Horsham’s car park and a footpath in the City of Frankston in Melbourne.

With new legislation phasing out the export of soft plastics, Tran said the breakthrough is part of a new wave of innovation in the circular economy.

“Glass can be easily recycled and turned into things such as sand replacement, but plastic is much harder,” he said.

“Mixing concrete and plastic is difficult, as the two don’t naturally bond.”

The research team was able to identify the best strategy to design the concrete mix by optimising the strength and acoustic energy absorption of the material.

The Coles car park in Horsham alone saw more than 900,000 pieces of plastic packaging saved from landfill and incorporated into the concrete.

“In the future, we’re hoping to explore the production of sustainable concrete structures using a new large-scale concrete 3D printer at RMIT’s Bundoora campus,” he said




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