Synthesis and characterization of one-part geopolymers for extrusion based 3D concrete printing

Interest in innovative construction processes such as 3D concrete printing (i.e. digital construction), is growing rapidly both in academia and industry. Processing conventional geopolymer mixes, in which alkaline solutions are used for activation, could be troublesome in concrete printing due to the high viscosity of the alkaline solution. One-part geopolymers offer one possible solution to this challenge as they involve the use of a solid activator with solid aluminosilicates precursors. In this work, a printable one-part geopolymer mix was developed, which could be extruded through the nozzle of a 3D printer and stacked together without deforming the bottom layers. Flow properties such as yield stress, viscosity and thixotropy of the developed geopolymer were assessed along with its strength development curve. Printed specimen showed anisotropic behaviour in mechanical properties when compared to the mould casted samples. Microstructural characterization revealed the formation of alumino-silicate gel with high tetrahedrally coordinated Al and interlayer K ions in its structure. When compared to OPC-based mixes, the developed geopolymer mixes revealed a lower environmental impact, which could be even further reduced with the use of alternative activators. (C) 2019 Elsevier Ltd. All rights reserved.