Harnessing Iron Industrial Wastes to High-Performance Geopolymer Concrete: Studies on Hot Mixing of One-Part Geopolymer Cement

The current study investigates the potential for valorizing iron-rich industrial waste streams through their integration into high-performance geopolymer cement and concrete formulations. Specifically, the performance of a one-part geopolymer cement paste (GP), produced via alkaline activation of blast furnace slag using a synthetic solid activator, was examined. The influence of the activator-to-slag mass ratio (A/S) at values of 0.16, 0.23, and 0.31 on hydration kinetics, setting times, and mechanical strength development was evaluated under two curing regimes: humid curing (HC) at 25°C and oven curing (OC) at 80°C for 7 hours. The results indicated that increasing the A/S ratio led to accelerated setting and a reduction in compressive strength. The highest early-age strength was observed in OC specimens at 1 day, whereas HC specimens exhibited superior strength at later ages. The mixture demonstrating the optimal mechanical performance was selected for further investigation into the effect of mixing water temperature (MWT), ranging from 25°C to 80°C, on the properties of GP cured under humid conditions. Geopolymerization progress and microstructural evolution were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) mapping, and transmission electron microscopy (TEM). Elevating the MWT to 80°C resulted in reduced setting times and enhanced compressive strength, achieving 23.5 MPa at 1 day and 45.6 MPa at 28 days, compared to values obtained at 25°C (13.3 MPa at 1 day and 40.5 MPa at 28 days). The microstructure of hydrated GP was predominantly amorphous and dense, although increased crystallinity and the formation of aggregated nano-grains were observed under elevated MWT or heat curing. Based on these findings, a geopolymer concrete (GC) was formulated using electric arc furnace slag as a full aggregate replacement, with the incorporation of either glass or basalt fibers. Under optimized curing conditions, the concrete achieved a maximum compressive strength of 47.5 MPa.