Low-carbon coal fly ash/superfine iron tailings-based three-dimensional printed geopolymer (CS-3DPG) rapid prototyping: The role and impact mechanism of carbonate series accelerator (CSA)

Abstract

The large accumulation of superfine iron tailings (SIT) as solid waste may lead to significant environmental and safety risks, urgently requiring resource utilization. The preparation of geopolymers using SIT is high-valued and environmentally friendly method. Therefore, a low-cost, alkali-containing solid carbonate series accelerator (CSA) was used to accelerate the early geopolymerization process of coal fly ash (CFA)/SIT-based three-dimensional printed geopolymers (CS-3DPG). The optimal addition time and content of CSA were 25 min and 6 %, respectively, which significantly shortened the setting time of CS-3DPG to 9 min and increased its early compressive strength to 24.18 MPa. The addition of CSA enhanced the rheological properties of CS-3DPG, improving its printability and buildability. These results provide assurance for achieving rapid prototyping of CS-3DPG. Combined with microscopic characterization, selective chemical extractions (SCE) and isothermal conduction calorimetry (ICC), CSA effectively promoted the CS-3DPG geopolymerization reaction process, transitioning from interactions at the phase boundary (I) to diffusion (D). Additionally, the CO2 emissions of CS-3DPG were reduced by 76 % compared to Ordinary Portland Cement (OPC). This study successfully reveals the role and impact mechanism of CSA in 3DPG, providing an important theoretical reference for regulating 3DPG buildability.