Ambient temperature cured ‘just-add-water’ geopolymer for 3D concrete printing applications

Abstract This paper aims to enhance the printability performance (namely open time and buildability) and mechanical properties (namely compressive strength) of a recently developed ‘one-part’ (just-add-water) geopolymer for 3D-concrete-printing (3DCP) applications. A combination of slag and fly ash was activated with two different grades of sodium silicate powders with different combinations. The influences of type and dosage of solid activators and the retarder content on the resultant geopolymers in fresh and hardened states were investigated using several mixtures to identify an optimum mixture. Subsequently, the printability performance (including open time, extrudability, buildability and shape-retention-ability), along with the rheological properties (including static yield stress evolution, dynamic yield stress, plastic viscosity and thixotropy) of the optimum mixture were evaluated. In addition, the printed specimens made of the optimum mixture were tested in compression and flexure in different directions. Based on the results, the optimum mixture exhibited a combination of long open time, and excellent extrudability, buildability, shape-retention-ability and thixotropic behavior, all of which are desirable for large-scale 3DCP applications. In addition, the high mechanical properties of the printed specimens ascertained the optimum mixture can be used for 3DCP of structural members. Moreover, the material sustainability indicators showed production of the optimum 3D-printable geopolymer mixture requires 14% less energy and emits 61% less CO2 than those of a 3D-printable Portland cement-based mixture with comparable compressive strength. It is anticipated that development of such 3D-printable ‘one-part’ geopolymers considerably promote large-scale applications and commercial viability of geopolymers in the context of 3DCP.