Geopolymer Materials for Extrusion-Based 3D-Printing: A Review

Abstract

This paper examines how extrusion-based 3D-printing technology is evolving, utilising geopolymers (GPs) as sustainable inorganic aluminosilicate materials. Particularly, the current state of 3D-printing geopolymers is critically examined in this study from the perspectives of the production process, printability need, mix design, early-age material features, and sustainability, with an emphasis on the effects of various elements including the examination of the fresh and hardened properties of 3D-printed geopolymers, depending on the matrix composition, reinforcement type, curing process, and printing configuration. The differences and potential of two-part and one-part geopolymers are also analysed. The applications of advanced printable geopolymer materials and products are highlighted, along with some specific examples. The primary issues, outlooks, and paths for future efforts necessary to advance this technology are identified.

Thermokinetic and Chemorheology of the Geopolymerization of an Alumina-Rich Alkaline-Activated Metakaolin in Isothermal and Dynamic Thermal Scans

“…The growing interest in understanding the science and technology relationships behind geopolymerization chemo-physical properties [ 1 , 2 , 3 ] is related to the potential use of geopolymers as greener materials for greener production technologies [ 4 , 5 , 6 , 7 ].…”

“…The most widely used additive manufacturing technique in the construction sector is extrusion-based 3D printing, in which the object is built by depositing material extruded layer-by-layer from a moving nozzle [ 4 , 12 ]. The knowledge of the reacting geopolymeric slurry viscoelasticity evolution during the processing is a critical parameter to control in extrusion-based additive manufacturing [ 4 , 5 , 12 ].…”

“…The most widely used additive manufacturing technique in the construction sector is extrusion-based 3D printing, in which the object is built by depositing material extruded layer-by-layer from a moving nozzle [ 4 , 12 ]. The knowledge of the reacting geopolymeric slurry viscoelasticity evolution during the processing is a critical parameter to control in extrusion-based additive manufacturing [ 4 , 5 , 12 ]. The proposed chemorheological approach relating the chemical evolution and the associated changes of the slurry viscoelastic characteristics could help define the correct 3D-printing process parameters.…”

“…In particular, the tetrahedral hydrate silicate [O[Si(OH) 3 ]] − and [Al(OH) 4 ] − ionic precursors (reported in the upper right side of Figure 1 ) reassemble themselves in linear and branched macromolecules [ 2 , 3 ], generating the initial inorganic monomeric molecules [ 3 , 18 ]. However, the relatively slow dissolution rate of metakaolin compared to the formation rate of the oligomeric species, which are characterized by rates of the order of milliseconds [ 4 , 19 ], is the parameter controlling the sialate oligomers actual availability rate. Both dissolution and low Mw oligomer formation occur in the very early stages, and they could be comprised in the first oligomeric species formation.…”

“…The concurrent presence of activated silica and alumina units is mandatory for geopolymerization reactions to occur [ 16 ] since, although Al 3+ as a modifier ion cannot independently participate in the formation of a polymeric network, it can replace Si 4+ in the [SiO 4 ] 4− tetrahedron when presenting four-oxygen coordination [ 20 , 21 , 22 ]. In the forming polymeric network, the excess negative charge of Al in tetrahedron monomeric ions [AlO 4 ] 5− (compared to the [SiO 4 ] 4− ) is balanced by a positive alkali ion such as Na + and K + [ 4 , 18 ].…”