A new research paper suggests a simple method to overcome one of the biggest issues in 3DCP.
3DCP, or 3D Concrete Printing, is rapidly growing in industry. It’s similar to FFF 3D printing, except that the build volumes are enormous, and the material being extruded is concrete. 3DCP today is used to rapidly build the concrete portions of exterior structures, sometimes several stories tall.
But there’s a common problem.
Unlike conventional concrete techniques where the material is deposited in a continuous pour and cures simultaneously, 3DCP deposits the concrete in layers as it extrudes. By the time the printhead comes around for the next layer, some curing has already taken place on the prior layer.
This results in poorer layer adhesion, as compared to the traditional simultaneous cure approach. That’s definitely not a welcome issue in the construction world where building strength is a critical factor.
The new research has found what could be a simple solution to the issue: apply a lithium silicate solution to the surface of printed concrete layers before the next layer is deposited.
The lithium silicate solution used was able to penetrate layers by up to 6mm, which is significant. They also note that this material is non-hazardous and VOC-compliant: it’s environmentally friendly.
What does this do? The lithium silicate reacts with calcium hydroxide (CH), forming calcium silicate hydrate (C-S-H), densifying the interlayer region.
The researchers undertook a series of tests of the resulting structures, including compression, tensile, and microstructural for pore analysis.
They found that the interlayer bond strength and compressive strength improved notably. They also found that the specimens printed have lowered porosity and were more homogeneous. They found the frequency of large pores (greater than 1mm) was reduced to only 0.3% from two percent.
The best part of this approach is that lithium silicate is widely available and is quite inexpensive, near US$1 per square metre of application. That would be a very small percentage of a building cost.
However, there are currently no 3DCP devices that can automatically apply lithium silicate as they print. It should be a relatively simple hardware modification to do so, so we should see this approach appear in good time.
The ability to print concrete structures with increased strength and reliability will certainly open more possibilities for applications; more complex geometries could be attempted. The technology could also speed up print jobs, as there could be less time waiting between layers.
The added layer strength might also mean decreased water ingress, as the layers would be tight.
Another possibility is a way around the “cold joint” issue that is encountered when 3D printing concrete in cold weather. If the layer adhesion is made stronger, it is possible that cold weather 3DCP operations might become possible.
Finally, the idea of painting liquid additives on layers is fascinating, and could potentially be applied to FFF 3D printing as well. Is there a simple material that could increase layer adhesion the same way?
Via Science Direct
