Influence of the mix composition on the thixotropy of 3D printable mortars

Abstract

Digital fabrication of concrete elements requires a better understanding of the rheological behaviour of the cementitious material used. Fresh concrete is known to be a thixotropic material having time-dependent characteristics. Moreover, fresh mortars used in three-dimensional (3D) printing should maintain a sufficient shear stress to avoid any deformation or failure during printing. This paper concentrates on the experimental investigation of the buildability properties of different printable materials, on the basis of shear stress, measured using the Fall cone test. The effect of different constituents such as high-range water reducer, viscosity-modifying agent, limestone filler and water content on the evolution of the yield stress in mortars, derived from the shear stress, are studied experimentally and discussed in detail. Accordingly, the change of variables induces a quasi-linear relationship with the growth of the structuration rate and structural build-up (Athix) of mortars, which corresponds to the variation of the yield stress with time. These findings enable the use of the Athix concept and the proposed curves for designing new printable mixes that better suit the buildability properties of large-scale 3D printed structures.