Geopolymer mortars for use in construction 3D printing: Effect of LSS, graphene oxide and nanoclay at different environmental conditions

The environmental impact of concrete 3D printing (C3DP) has become a concern due to its large cement con-sumption and over-exploitation of natural resources. This study investigates the viability of using geopolymer mixtures in C3DP prepared with fly ash (FA)/ground granulated blast furnace slag (GGBS) and underutilised aggregate as substitutes for ordinary Portland cement (OPC) and natural aggregate, respectively. This paper focuses on the rheological, mechanical, and shrinkage properties of FA/GGBS-based geopolymer mortar with lead smelter slag (LSS) as natural sand (NS) substitute and the impact of adding nanoclay (NC) and graphene oxide (GO), as thixotropy agents, on the yield stress development and viscosity recovery properties of the mixtures. The effect of various outdoor environmental conditions of 24 degrees C-50 %RH, 35 degrees C-90 %RH and 35 degrees C-50 %RH on pore water evaporation and 28-day drying shrinkage of 3D printable geopolymer mortar was studied, considering the effect of NS, LSS, NC and GO in free-formed and control conditions. LSS GO-modified mortars exhibited superior viscosity recovery capacity and yield stress evolution compared to their NC -modified counterparts. Moreover, using LSS instead of NS resulted in increased 28-day compressive strength under various environmental conditions, and LSS mortars exhibited lower drying shrinkage in both conventional casting and free-formed conditions. The findings of this paper will serve as a benchmark for further studies on the effect of different curing techniques (internal or external) on the hardened state dimensional stability of 3D printed products using alkali-activated binder systems to improve the structural integrity by controlling the water evaporation and drying shrinkage development.

Automated summary

This study investigates the use of geopolymer mixtures in concrete 3D printing to reduce cement consumption and natural resource exploitation. By adding alternative materials and thixotropic agents, the performance of the geopolymer mixtures was improved. The results show that replacing natural sand with lead smelter slag can increase compressive strength and decrease drying shrinkage. These findings are significant for improving the structural integrity of 3D printed products.