New research from RMIT University shows that patterns inspired by lobster shells can make 3D printed concrete stronger, to support more complex and creative architectural structures.

Digital manufacturing technologies like 3D concrete printing (3DCP) have immense potential to save time, effort and material in construction. They also promise to push the boundaries of architectural innovation, yet technical challenges remain in making 3D-printed concrete strong enough for use in more free-form structures.

In a new experimental study, researchers at RMIT looked to the natural strength of lobster shells to design special 3D printing patterns. Their bio-mimicking spiral patterns improved the overall durability of the 3D printed concrete, as well as enabling the strength to be precisely directed for structural support where needed. 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.

Lead researcher Dr Jonathan Tran, a senior lecturer in structured materials and design at RMIT, said 3D printing and additive manufacturing opened up opportunities in construction for boosting both efficiency and creativity.

“3D concrete printing technology has real potential to revolutionise the construction industry, and our aim is to bring that transformation closer,” says Tran. “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. We know that natural materials like lobster exoskeletons have evolved into high-performance structures, so by mimicking their key advantages we can follow where nature has already innovated.”

The automation of concrete construction is set to transform how we build, with construction emerging as the next frontier in the automation and data-driven revolution known as Industry 4.0. 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.

The research team in RMIT’s School of Engineering focuses on 3D printing concrete, exploring ways to enhance the finished product through different combinations of printing pattern design, material choices, modelling, design optimisation and reinforcement options. The most conventional pattern used in 3D printing is unidirectional, where layers are laid down on top of each other in parallel lines. The new study investigated the effect of different printing patterns on the strength of steel fibre-enhanced concrete.

Previous research by the RMIT team found that including 1%-2% steel fibres in the concrete mix reduces defects and porosity, increasing strength. The fibres also help the concrete harden early without deformation, enabling higher structures to be built.

The team tested the impact of printing the concrete in helicoidal patterns (inspired by the internal structure of lobster shells), cross-ply and quasi-isotropic patterns (similar to those used for laminated composite structures and layer-by-layer deposited composites) and standard unidirectional patterns. The results showed strength improvement from each of the patterns, compared with unidirectional printing, but Tran said the spiral patterns hold the most promise for supporting complex 3D printed concrete 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,” he explains. “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.”

Further studies will be supported through a new large-scale mobile concrete 3D printer recently acquired by RMIT – making it the first research institution in the southern hemisphere to commission a machine of this kind. The 5m x 5m robotic printer will be used by the team to research the 3D printing of houses, buildings and large structural components. The team will also use the machine to explore the potential for 3D printing with concrete made with recycled waste materials such as soft plastic aggregate.

New tech improves sustainable concrete

RMIT researchers have developed a new technology to manufacture concrete made from recycled materials that is stronger and more durable than the traditional product. Recycled concrete aggregates made with everything from coffee cups to building rubble offer huge environmental benefits, from reducing landfill and carbon dioxide emissions, to saving natural resources and boosting the circular economy. Despite ongoing improvements, however, challenges with matching the strength and durability of traditional concrete have hindered the practical application of these sustainable alternatives.

Now researchers from RMIT have developed a new method for casting prefabricated concrete products made with rubber tyres and construction and demolition waste that are up to 35% stronger than traditional concrete. Professor Yufei Wu from the School of Engineering led the development of the Rubberised Concrete Processing Technology (RCP-Tech) and said it offered an efficient and inexpensive solution.

“This technology can be used to significantly improve the strength, hardness and durability of any type of concrete material, such as rubber concrete, recycled aggregate concrete, and even ordinary concrete,” says Wu.

The method involves combining a mix of course and fine aggregates with rubber tyre waste, cement and water, which is then compressed to its minimum volume using pressure in a customised mould.

“By enhancing the properties of the recycled waste without the use of any additional materials, we have developed a feasible and practical solution that addresses the performance issues affiliated with waste recycling in concrete,” Wu adds.

Rubber from waste tyres is the cause of significant health, environmental and landfill problems worldwide owing to its chemical, flammable and non-decomposable nature. From 2015-16 Australia generated around 450,000 tonnes of waste rubber, 63% of which was sent to stockpiles or landfills and Victoria alone produces the equivalent volume of the Eureka Tower every four years.

PhD researcher and RCP-Tech co-creator Syed Kazmi says the team was now looking to partner with the precast concrete industry to manufacture and test prototypes of products like blocks and roadside barriers, wall panels, beams and slabs.

“The technology can be easily applied in the precast concrete industry and requires very little change to existing manufacturing processes with the addition of just one extra step in the final stage of production,” says Kazmi.

Kazmi and fellow PhD researcher Muhammad Munir presented the technology at the City of Melbourne Open Innovation Competition 2020 where they were finalists. They were also awarded the RMIT LaunchHUB prize for their work.

www.rmit.edu.au