Spotlight: Shawn Platt and the Concrete Christmas Tree

🎵Oh concrete tree, Oh concrete tree🎵 How lovely are your layers!

Some people like plastic Christmas trees; others prefer real wood and needles. This year, NIST is printing a tree out of concrete.

The tree is not only festive; it’s also a test of the printing process and the skill of NIST researchers. 3D-printed concrete is a new construction technique that could be used to make everything from park benches to entire houses. But there are no building codes or standards yet for 3D-printed concrete. NIST is doing the basic research to understand the strength of these materials.

As a part of the research team’s training, they occasionally print particularly challenging objects such as this Christmas tree.

At 1.3 meters (4.5 feet), this is the tallest overhanging object ever printed at the lab. The scientists need to constantly tweak the concrete recipe to ensure that it hardens fast enough to stay upright, yet slow enough to flow through the pumps and hoses of the printer. 

The conical shape is particularly challenging because each layer is smaller than the last. This means it has less time to rest before the next layer is pressed on top of it and so it needs to harden slightly faster. The layers also hang a little over the inside edge of the layer below, so it’s possible for the walls to collapse inward if the researchers aren’t careful.

Now that the experiment is done, do you have any ideas on how we should decorate it?