Can We 3D Print with Construction and Demolition Waste? A Look at Recycled Concrete in 3D Construction Printing
This study set out with a question: “can we take old, broken-up concrete from roads and buildings and use it to 3D print new ones?”
Funded by the Department of Environment, Climate and Communications (DECC) under the Circular Economy Innovation Grant Scheme, the team at the Future Cast Materials Testing Laboratory (MTL) in Collooney, Co. Sligo, put that idea to the test.
We used crushed pavement slabs taken during the redevelopment of a local village — including concrete, unconsolidated aggregate fill, trace bitumen and metal — and ran a suite of chemical, physical, and geological tests to see how it compared to the regular gravel used for 3D printing. After characterisation, we tested how this material behaved when mixed into concrete used in 3D printing. Finally, the 3D printed samples were re-crushed and tested for strength to evaluate the potential for circularity.
Findings
- Recycled C+D waste can work! It’s not perfect, but it has similar characteristics to natural aggregate. There are some issues — higher sulphate content, some contaminants, and lower concrete strength if you use too much.
- Concrete Compressive Strength increased with small blends of recycled material. Adding up to 20% recycled aggregate actually made concrete stronger. When adding 100% recycled aggregate, the strength dropped — possibly due to chemical reactions between the cement paste and the recycled cement in the aggregate.
- Testing 3D printed Samples. Using the COBOD Bod2 printer, we created 3D printed samples with various mixes of recycled aggregates. While the cube samples (cast in moulds) were strong, the printed versions were a bit weaker, maybe because of trapped air during printing.
- Recycling printed concrete again? When we crushed the printed concrete and tested it again, it was weaker than the original recycled aggregate.
Innovative Compressive Strength Test proxy. We developed a non-destructive proxy to estimate strength using sonic velocity and density. With some more development this could become a fast and practical way to check compressive strength of concrete on-site.
This study shows it’s totally possible to mix recycled concrete waste into new 3D printed structures — especially if you blend it with traditional, natural aggregate. When using recycled aggregate there are some trade-offs in strength and durability if you use too much! Any recycled aggregate will need to meet applicable standards and legislation as defined by the National Standards Authority of Ireland, and the Irish Environmental Protection Agency.
The link to the full report can be found here
