The influence of material temperature on the in-print strength and stability of a 3D print mortar

Due to the lack of formwork, a key issue in the novel technology of filament-based 3D concrete printing (3DCP) is the ‘buildability’: the capacity of the deposited dormant material to support itself during the print process. Since the strength and stiffness development of fresh concrete is determined by chemical and physical processes, it may be expected that the temperature of the material that is being printed influences the buildability. This paper presents the results of several experiments that have been performed to study this effect. First, fresh material specimens were cooled or heated to different temperatures and subjected to unconfined uniaxial compression tests at ages of 30, 75 and 200 minutes (relating to material setting time as well as common print durations). A clear effect on both compressive strength and stiffness was noted at an age of 75 minutes. Subsequently, a print trial was performed on a rectangular shape partially heated by heat lamps. The results supported the experiment on material samples: the buildability of the smaller object (with a shorter printing time) was not influenced by externally applied heat, whereas the larger object was. In a third experiment, a print trial was performed on two shapes for which the water was pre-cooled or pre-heated before mixing with the dry mortar. Warm water resulted in higher buildability of the objects, but also in reduced interlayer strength and an increased risk of system overheating, which instigates the need for further research in the relations between temperature and 3DCP.