Engineers use wood pulp to 3D-print stronger concrete for construction

3D printing technology is rapidly evolving and has shown promise in applications spanning from the fabrication of biological tissues to the development of ceramics capable of removing persistent contaminants from water.

Concrete technology is one industry that might benefit significantly from 3D printing.

Concrete production is a major contributor to global carbon emissions, accounting for approximately 8% of the total. This figure highlights the urgent need for sustainable alternatives and improvements in the concrete industry.

3D-printed concrete buildings offer the promise of rapid, eco-friendly construction. However, developing a material that is both printable and exceptionally strong remains a significant challenge.

Researchers from the University of Virginia School of Engineering and Applied Science have presented a novel solution: cellulose nanofibrils (CNF), a plant-based wonder material.

They are exploring how CNF could potentially revolutionize 3D-printed concrete. These plant-based fibers have shown promise as an additive to enhance the flowability and strength of composite materials.

“The improvements we saw on both printability and mechanical measures suggest that incorporating cellulose nanofibrils in commercial printable materials could lead to more resilient and eco-friendly construction practices sooner rather than later,” said Osman E. Ozbulut, a professor in the Department of Civil and Environmental Engineering.

CNF derived from wood pulp

In building construction, specialized printers construct structures layer by layer using a cement-based material and computer-aided designs. However, the range of printable materials is limited, and their long-term performance and environmental impact remain uncertain.

“We’re dealing with contradictory objectives,” Ozbulut said. “The mixture has to flow well for smooth fabrication, but harden into a stable material with critical properties, such as good mechanical strength, interlayer bonding and low thermal conductivity.”

CNF is extracted from wood pulp, making it both renewable and sustainable. When applied to concrete, it increases flowability, allowing for smoother printing. But that is not all. CNF also increases concrete strength and durability, resulting in constructions that can endure the test of time.

Showcase promise in testing

Rigorous testing has shown that concrete with CNF performs exceptionally well under stress, making it a promising material for building resilient structures.

Ozbulut and his team experimented with varying CNF concentrations. They discovered that a minimum of 0.3% CNF greatly enhanced the 3D-printed cement’s flowability. A well-flowed concrete mix helps to expel air bubbles from the concrete, preventing the formation of voids that weaken the structure.

Interestingly, microscopic examinations of the hardened samples indicated improved bonding and overall structural integrity.

Further analysis conducted by Ozbulut’s team revealed that the CNF-enhanced 3D-printed components displayed exceptional strength under pulling, bending, and compression loads.

“Today, a lot of trial and error goes into designing mixtures. We’re addressing the need for more good science to better understand the effects of different additives to improve the performance of 3D-printed structures,” added Ozbulut in the press release .

3D-printed concrete buildings represent a promising development in housing. These structures offer several benefits, including shorter construction timelines, the possibility of using recycled materials, lower labor needs, and minimal waste generation.

Furthermore, this technique could allow the creation of sophisticated designs that are frequently difficult to achieve using standard building methods.

The findings will be detailed in the September 2024 issue of Cement and Concrete Composites.