3D printing: carbon fiber reinforced concrete

Still in its developmental years, 3D printing uses layering to manufacture many products in the fields of construction, automobiles, aerospace, and others. In the IDTechEx 3D Printing Composites 2021–2031 report, the forecast is for the overall global 3D composite printing market – including materials reinforced with plastic, carbon or glass fibers – to reach a value of $2-billion in the next nine years. That’s quick growth considering a DesktopMetal estimate that 3D printing today accounts for a fraction – less than 0.10% – of the entire composite manufacturing market. A composite is a combination of two or more materials forming a new material with more desirable properties than its individual parts.  

A 2020 ScienceDirect.com article describes research into the use of high-performance materials (ink) for 3D printing, including composites made of a matrix material, for instance plastic, plus the addition of aluminum powder, wood-based filaments, resins, nylon, polyester, or carbon fibers.

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The construction industry has been working with a composite for thousands of years . . . concrete. And manual placement of reinforcement in concrete has been taking place for a long time (50 years with glass fiber and over 100 years using steel rebar). But researchers are now trying to take concrete reinforcement a step further, adding structural fibers to concrete in one process described as Continuous Fiber 3D Printing (CF3D). Using fibers that range from carbon to fiberglass to Kevlar, the resulting concrete product is stronger but lighter.

Markforged explains that the fibers are thin, brittle and easy to snap if bent, so they are woven into sheets, wrapped into rods or formed into custom molded shapes using a matrix material. When many fibers are bound together to create larger structural elements, forces are distributed along the lengths of all of the fibers. Carbon fiber is stiff and strong and behaves similarly to the aluminum used in 3D printing, so it can enable lightweight components that support heavy loads. A 3Dnatives article states that continuous carbon fiber in 3D printing is strong enough to replace aluminum at half the weight.

Carbon fiber properties include:

• high stiffness,
• high tensile strength,
• high chemical resistance,
• high temperature tolerance,
• low thermal expansion, and
• low weight.

The characteristics of carbon fibers make them ideal as a reinforcement addition to concrete. Zoltek.com describes the strongest carbon fibers as ten-times stronger than steel and eight-times stronger than aluminum – while being lighter. California company Emerging Objects has developed a cement polymer that can be reinforced with fiber to 3D print objects that are stronger than standard concrete. 

Advancements in 3D printing technology are bringing down the cost of automated reinforced concrete. In a November, 2021 scholarly article by Springer Link, the most common form of 3D concrete printing was described as using a robotic arm to extrude a concrete mixture. When chopped carbon fibers were added to the mixture for reinforcement in the one to three percent range by volume, components were “found to be printable without issue.”  

In the manufacturing world, development efforts are creating carbon fiber filaments using high temperature thermo-plastic polymers (HPPs) as base materials (i.e. PEEK or PEKK). The benefits of HPPs include durability with strong mechanical and chemical performance, and the carbon fiber properties give a better ratio of strength to weight.

Methods used for reinforcing 3D printed concrete have not been perfected, but further development is sure to bring about more effective scenarios. New composites are being researched, tested and introduced each year, promising a plethora of component improvements for both the building and manufacturing industries.  

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