Developments in Portland cement/GGBS binders for 3D printing applications: Material calibration and structural testing

The work presented in this paper forms part of a wider research programme being undertaken on the development of low-carbon cementitious mortars for 3D printing applications. Specifically, this paper investigates the potential of ground granulated blast-furnace slag (GGBS) as a partial replacement for Portland cement. Five mortar mixes with varying water/binder (w/b) ratios (0.35 to 0.45) were tested, and to investigate their pumpability and buildability, a series of wall-like specimens were printed using a custom-built 3D printer under a range of speeds of 2 to 4 m/min. Pumpability was found to be directly related to w/b ratio, whereas buildability was found to be dependent upon both test parameters. Mortar mixes with w/b ratios in the range 0.37 to 0.40 demonstrated promising pumpability and buildability characteristics when extruded at the optimum printing speed of 2.5 m/min. Moreover, to demonstrate the application of the optimised mix, an arch truss prototype was printed and subsequently tested to failure to provide insights into the structural behaviour of a 3D printed arch truss member. From the process of crack formation and accompanying analysis, it was found that although the development of tensile stresses in the 3D printed prototype was minimal (a direct result of the arch geometry), it still governed the overall member behaviour due to the presence of internal stresses induced by restrained shrinkage.