Evaluation for design parameters of cementitious mixtures for 3DCP printing with constant humidity
3DCP, printability, squeezze-flow tests, constitutive ratios of mix, hardened state.
3D concrete printing (3DCP) has gained prominence in several recent researches, however there are still gaps in the parameters required for the design of printable cementitious mixtures. 3DCP printability depends on intrinsic properties of cementitious mixtures, such as materials particle size, cement types and mineral additions, water/binder volumetric ratios (Vw/Vb), paste/aggregate volume (Vp/Vs), paste volume (Vp), water volume (Vw) and sand/total solids ratio (S/solids) correlated with the printing system (printer type, pumping, extrusion, printing speed, etc). 3DCP buildability depends on intrinsic properties of the cementitious mixtures, such as materials granulometry, cement types and mineral additions, water/binder volume ratio (Vw/Vb), paste/aggregate volume (Vp/Vs), paste volume (Vp), water volume (Vw) and sand/total solids ratio (S/solids) correlated with the printing system (printer type, pumping, extrusion, printing speed, etc). This paper analyzes six mixtures for 3DCP printing with variations in the cement:sand ratios (by mass), keeping the mixture's humidity constant, in relation to the mass of the dry materials (Vw/Md), evaluating the printing capacity of these mixtures in a low-cost gantry-type 3D printer with mechanized movement in its axes, having an extruder nozzle for material deposition. The hardened state properties, flexural and compressive strength, specific gravity, and voids content of the printed mixtures were also determined. The results showed that for the printing system used there is an ideal range for these constitutive relations, and that the mixtures, even if they have different viscosity flow, measured according to squeeze flow, can have printability, as long as they meet the ideal ranges for the constitutive relations.