Innovations to Improve 3D Concrete Printing of Portland Cement-Steel Slag Blended Mortars

This paper identifies typical issues and their remedies during lab-scale 3D printing of Portland cement-steel slag blended mortars. This study used a printer with an accelerator in its feeding system immediately before the extrusion stage. Accelerator dosage can be regulated for such a printer even during printing. However, a higher or lower than optimum dosage may lead to excessive flow or dry surface with a potential risk of cracking in the individual layers. Through the current study, two hollow cylindrical geometry and one hollow square geometry were printed. The print quality was evaluated by investigating various variables, such as considering two superplasticizers with different open times and using constant and variable accelerator dosages during printing. The compatibility of superplasticizers was found to affect the open time and, hence, the print quality with layer shortening and breaking. Changes in accelerator dosage during printing to compensate for the changing rheology were similarly notable, especially in terms of inconsistencies in printed layers. However, the use of a compatible superplasticizer was determined to mitigate both issues. Additionally, shrinkage-reducing admixture was recommended for mortars to avoid cracking due to early-age drying shrinkage.