Fresh and Hardened Properties of 3D Printable Geopolymer Cured in Ambient Temperature

This paper reports the fresh and hardened properties of an ambient temperature cured 3D printable geopolymer suitable for extrusion-based 3D concrete printing process. Effects of several key geopolymer synthesis parameters including type of alkaline activator (sodium (Na)-based versus potassium (K)-based), mass ratio of silicate to hydroxide solutions, viscosity and SiO₂/M₂O ratio (where M = Na or K) of silicate solution on extrudability, open time, shape retention ability and compressive strength of the 3D printable geopolymers were investigated. The results revealed that the type of alkaline activator solution and SiO₂/Na₂O ratio of the silicate solution had a significant influence on the open time and shape retention ability of the mixtures. The parameters investigated in this study did not have significant effect on the extrudability of the mixtures. The Na-based activators resulted in higher compressive strength of 3D printed geopolymer than the K-based activators. The 3D printable geopolymer mixture made by 8.0 M NaOH solution (25% w/w) and Na₂SiO₃ solution (75% w/w) with a SiO₂/Na₂O ratio = 2.0 exhibited the highest compressive strength of 16.6 MPa when cured for only 3 days in the ambient temperature.