3D printing of cement-based materials with adapted buildability

Abstract

This paper investigates the thixotropic behavior of cement-based materials used in large-scale 3D printing. Five different mortar mixtures containing optimized admixtures, including a polycarboxylate ether-based high-range water reducing agent (PCE-based HRWR), attapulgite nanoclay, a viscosity modifying agent (VMA), fly ash, and silica fume, were subjected to rheological measurements to quantify their thixotropic behavior. The process-induced variations in the static yield stress and the storage modulus of the investigated mixtures were estimated by testing disturbed and undisturbed samples. Uniaxial compression tests were also conducted to simulate the layer-wise pressure increments in extrusion-based 3D printing. Large-scale 3D printing tests were then performed to evaluate and quantify the buildability of the investigated mixtures and validate the scalability of the obtained results during the laboratory tests. The rheological measurements and the large-scale printed elements indicated that incorporating attapulgite nanoclay and a modified starch-based VMA enhanced the thixotropic behavior of the investigated printing mixtures. Moreover, the proposed thixotropy evaluation methods were found to effectively capture the thixotropic evolution of the mixtures and accurately evaluate the impacts of admixtures. Furthermore, the uniaxial compression test method permitted study of the influence of the extrusion pressure (the pressure induced by the 3D-printed layers’ deposition) on the buildability of the deposited layers. This was validated using large-scale printing trials.