Researchers in the Gerald May Department of Civil, Construction and Environmental Engineering at the University of New Mexico (UNM) in Albuquerque have been awarded a patent for their design for a bendable concrete material that can be used in concrete 3D printing. The self-reinforced, ultra-ductile cementitious material combines tensile strength with the necessary viscosity to be extruded by a concrete 3D printer without clogging the nozzle.
The use of concrete 3D printing in construction promises to reduce the time it takes to build a structure and could help to reduce waste. However, structures still require the placement of key materials such as beams or rebar, limiting the automation that 3D printing should offer. To print something without those supports, the material must be strong enough to hold itself up without getting stuck in the printer.
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‘If we talk about 3D printing or additive manufacturing in the field of metals and plastics, it’s at a very advanced stage, but concrete printing is still developing,’ said graduate research assistant Muhammad Saeed Zafar. ‘If we can successfully design ultra-high-ductile material without using conventional steel bars, which will solve the problem of the incompatibility of reinforcement with the 3D-printing process.’
The new substance developed by the UNM team, known as self-reinforced ultra-ductile cementitious material, was patented by UNM Rainforest Innovations on behalf of assistant professor Maryam Hojati, Zafar and research assistant Amir Bakhshi.
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‘The basic purpose of doing this work was to address the problem of reinforcement in 3D concrete printing,’ Zafar said. ‘We claim that 3D concrete printing is an automated process,’ but the conventional reinforcing methods are compromising the automation in this process.
The ultra-ductile cementitious material must contain enough fibre to stand firmly on its own while maintaining a viscosity that allows it to pass through the printing nozzle without getting stuck. While it might sound simple, finding the right balance is a complex research challenge. Too little fibre is in the mix, and the printed shapes might cave in on themselves; too much fibre and the material won’t make it very far in the printing process.
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The researchers explored mixes made of many materials and fibres, including polyvinyl alcohol, fly ash, silica fume and ultra-high molecular weight polyethylene fibres. The resulting patent offers four different mixes with up to 11.9 per cent higher strain capacity.
‘Because of the incorporation of large quantities of short polymeric fibres in this material, it could hold all of the concrete together when subjected to any bending or tension load,’ Hojati said. ‘If we use this material at a larger scale, we can minimise the requirement of external reinforcement to the printed concrete structure.’
New materials such as that developed at UNM could eventually offer benefits such as greater resilience to natural disasters, less frequent maintenance and more automation in the construction process.
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‘This was very successful research. This material has 3D printing property and very high structural viability that could be used in the construction industry,’ Hojati said.