Researchers demonstrate viability of 3D printed concrete

“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,” explained Osman E. Ozbulut, a professor in the Department of Civil and Environmental Engineering.

Concrete is arguably one of the most widely used materials worldwide, predominantly for building construction, but it carries a significant environmental impact: cement, the key ingredient of concrete, generates approximately between 5% and 8% of global carbon emissions.

The potential to change how concrete is made is seeing methods such as the investigation of 3D printing by the researchers. The team’s findings will be featured in the September 2024 issue of Cement and Concrete Composites.

3D-printed concrete buildings are an emerging trend in the housing sector, offering numerous benefits: rapid, precise construction, potential use of recycled materials, reduced labour costs, and minimal waste. Additionally, this technology allows for intricate designs that are challenging to achieve with traditional building methods.

The process employs a specialised printer that layers a cement-like mixture to construct structures based on computer-aided design software. However, the current range of printable materials is limited, and there are ongoing concerns about their sustainability and durability.

“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.”

Cellulose nanofibrils are derived from wood pulp, offering a renewable and low-impact material. Known in the industry as CNF, this plant-fibre derivative has shown strong potential as an additive to enhance the rheology (flow properties) and mechanical strength of these composites.

Until the UVA team’s detailed study in Ozbulut’s Resilient and Advanced Infrastructure Lab, the effects of CNF on conventional 3D-printed composites were not well understood.

“Today, a lot of trial and error goes into designing mixtures,” Ozbulut noted. “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.”

Through experiments with varying amounts of CNF additive, the team, led by Ozbulut and Ugur Kilic, now a Ph.D. alumnus of UVA, discovered that adding at least 0.3% CNF significantly enhanced flow performance. Microscopic analysis of the hardened samples revealed improved material bonding and structural integrity.

Further tests in Ozbulut’s lab demonstrated that CNF-enhanced 3D-printed components withstood pulling, bending, and compression. The paper, titled "Effects of Cellulose Nanofibrils on Rheological and Mechanical Properties of 3D Printable Cement Composites," is currently available online. Co-authors include Nancy Soliman, an assistant professor at Texas A&M University – Corpus Christi, and Ahmed Omran, a professor of practice at the Massachusetts Institute of Technology.