Printability, accuracy and strength of geopolymer made using powder-based 3D printing for construction applications

The authors of this study have recently succeeded to develop geopolymer materials using slag only formulations for the requirements and demands of commercially available powder-based 3D printers. In this study, the formulation is extended to fly ash and slag combinations so that to expand the scope of geopolymer materials that can be used in the commercially available powder-based 3D printers for construction applications. The quantitative influence of fly ash content on the printability characteristics (i.e., depositability and wettability) of the geopolymer powder, as well as the linear dimensional accuracy and compressive strength of the printed specimens were investigated. The effect of type of alkaline solution used for post-processing on the linear dimensional accuracy and compressive strength of the post-processed specimens were also evaluated. The results indicated that the increase in fly ash content had no effect on the powder depositability, but adversely affected the powder wettability, linear dimensional accuracy and compressive strength of the printed specimens. The minimum slag content required to prepare fly ash/slag blended geopolymer powder for powder-based 3D concrete printing process is 50 wt%. The post-processing significantly increased the compressive strength. The post-processed specimens printed with 50 wt% slag/50 wt% fly ash powder exhibited a 7-day compressive strength of up to 25 MPa, which is sufficiently high for many construction applications.