Additive manufacturing : 3D printing of low impact concrete

Abstract

3D concrete printing, although a relatively new technology, is not yet a common construction method. This technology also reduces a lot of waste generated and leads to lower demand for resources such as formwork. Additive manufacturing also leads to reduced demands on the number of workers required and construct time required, all of which contribute to lower embodied carbon of the final product. However, the concrete required for 3D concrete printing requires about 2 to 3 times the cement content of conventional concrete construction methods. Yet the technology can lead to a more optimised design with lower volume consumed. The research refers to the development and use of a prototype Frame System 3D printer for Concrete designed and constructed at the University of Malta. This research provides insight into the possibilities of creating a concrete mix design with the intention of minimizing embodied carbon. This was done by replacing the cement content with fine globigerina limestone powder. Replacement of the coralline limestone sand with recycled globigerina limestone sand was also assessed to confirm the viability of 3D concrete printing with such a mix design. All constituents were locally sourced to further reduce the concrete mix designs’ embodied carbon. Testing was set into 3 phases which included: the investigation of the effects of different dosages of the constituents, the identification of optimised mix designs for 3D concrete printing, and lastly, the uses of the identified mixes using the prototype 3D concrete printer to confirm the printability of said mixes. Finally, the printed concrete was analysed in the fresh state and the hardened state with respect to specific parameters including compressive strength and porosity. As there was no prior literature for 3D printed concrete based on local coralline limestone and globigerina limestone as the main aggregates, this research also provides insight into how these local constituents affect the mix design for the purposes of 3D printing.