Investigation on working properties and microstructural characteristics of activated geopolymer matrix composites for 3D printing

Abstract

To address the critical industry challenges of high carbon emissions and the inherent trade-off between printability and fast-setting performance of cement-based materials for 3D printed construction, this study developed a cement-free alkali activated composite tailored for 3D printing applications. It utilizes S95-grade ground granulated blast furnace slag (GGBS) and Grade I fly ash as the primary cementitious precursors, together with multi-grade quartz sand, polyvinyl alcohol (PVA) fibers, and tailored functional additives. Based on a printability evaluation system specifically developed for 3D printing materials, the effects of the mass replacement ratio of slag for fly ash on extrudability, buildability, and setting time were systematically investigated, and the corresponding hydration products and underlying micromechanism were characterized via X-ray diffraction (XRD). The results indicate that increasing the slag replacement ratio simultaneously enhances extrudability and buildability, and the initial setting time decreases linearly to within one hour at 100% slag replacement. XRD characterization reveals that the main hydration products are predominantly amorphous C-S-H and N-A-S-H gels, and the increased slag content significantly promotes the formation of these gel phases, which is the fundamental mechanism underlying the enhanced macroscopic printability.