Researchers patent bendable concrete for 3D printing

According to The University of New Mexico (UNM), researchers in the Gerald May Department of Civil, Construction, and Environmental Engineering have officially patented a bendable concrete material design for 3D construction printing.

Traditional construction relies on people operating heavy machinery to place steel or wood beams to create a building frame, but the process can be dangerous and expensive. This is just one of the material and manufacturing problems Maryam Hojati, assistant professor in the Gerald May Department of Civil, Construction, and Environmental Engineering, hopes to solve.

Another problem is infrastructure maintenance. Even concrete reinforced with steel requires ongoing repair, which means regular maintenance on everything from buildings and bridges to sidewalks. A more resilient material could make public infrastructure longer-lasting and less expensive to maintain.

“Concrete by itself does not show any tensile properties, meaning if you have a piece of concrete and start pulling it apart, it can easily break. It’s a very brittle material,” said Hojati. Concrete’s tendency to fracture under stress is especially problematic when it comes to natural disasters and weather events like earthquakes and winds that put lateral stress, or tension, on buildings. “The material should hold and resist both tension and compression. Concrete is a great material for compression, but when it comes to tension, it’s a weak material.”

Researchers worldwide have explored what materials and processes might solve these problems. Some structures have been built in part with 3D printers, but so far, most processes rely on the placement of key materials like beams or rebars – limiting the automation that 3D printing should offer. To print something without those supports, the material must be strong enough to hold itself up.

Muhammad Saeed Zafar, who received his Ph.D. in the summer of 2024 and worked as a graduate research assistant for Hojati, created a substance that might solve this. “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,” he said. “If we can successfully design ultrahigh ductile material without using conventional steel bars, which will solve the problem of the incompatibility of reinforcement with the 3D printing process.”

The resulting substance, known as self-reinforced ultra-ductile cementitious material, was patented last August by UNM Rainforest Innovations on behalf of Hojati, Zafar, and Amir Bakhshi, who worked on the project as a research assistant and master’s degree student early in its development. Zafar published his research on substances in construction and building materials last year.

“The basic purpose of doing this work was to address the problem of reinforcement in 3D concrete printing,” said Zafar. “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 fiber 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 fiber is in the mix, and the printed shapes might cave in on themselves. Too much fiber and the material won’t make it very far in the printing process. To test the viability of the materials, they must be precisely mixed, measured, and printed.

Even after designs are printed in several different shapes and designs, including small structures, prisms, and dog bones, they must be tested for their bending and direct tensile strength. The researchers repeated this process and explored mixes made of many materials and fibers, like polyvinyl alcohol, fly ash, silica fume, and ultra-high molecular weight polyethylene fibers.

The resulting patent offers four different mixes with up to 11.9% higher strain capacity.

“Because of the incorporation of large quantities of short polymeric fibers in this material, it could hold all of the concrete together when subjected to any bending or tension load,” said Hojati. “If we use this material at a larger scale, we can minimize the requirement of external reinforcement to the printed concrete structure.”

The development of a bendable, printable concrete-like substance was funded by grants from the Transportation Consortium of South-Central States (Tran-SET), Region Six’s University Transportation Center. The grants funded three research projects: developing a 3D printable engineered cementitious material, evaluating the material’s properties in both fresh and hardened states, and developing a 3D printable eco-concrete.

After the first two project phases and many designs, researchers successfully designed the material the team submitted for a patent.