Influence of carbonation initiation timing on CO2 uptake and mechanical performance of geopolymer made from ternary solid wastes

The utilization of concrete slurry waste (CSW), fly ash (FA), and ground granulated blast-furnace slag (GGBS) for geopolymer production, integrated with CO₂ sequestration, represents a crucial pathway towards sustainable construction materials. However, the regulatory mechanism of carbonation initiation timing on the performance of ternary solid waste-based geopolymers (TSWGs) remains unclear. This study systematically investigates the evolution of CO₂ uptake and mechanical properties in TSWGs with varying GGBS contents (30–50 %) under different carbonation initiation timings (0–28 days). Multi-scale characterization reveals a critical threshold of 55 % sub-10 nm pores, governing the transition from complete to incomplete carbonation. As GGBS content and initiation timing increase, CO₂ uptake initially rises then declines, while compressive strength progressively increases, indicating a performance trade-off: earlier carbonation enhances CO₂ sequestration (max: 12.7 %), whereas later timing improves strength (max: 78.9 MPa under standard curing). A net CO₂ uptake of 4.68 % was achieved. The findings demonstrate that carbonation initiation timing is a decisive parameter for microstructural control and balancing carbon sequestration with mechanical performance in TSWGs, providing a theoretical basis for designing high-performance, carbon-negative binders.