Reaction–structure–strength relationships along coupled formulation trajectories in a high-tailings one-part alkali-activated binder

This study examined coupled formulation effects in a one-part alkali-activated binder containing 65 wt.% untreated lead–zinc tailings. Stage I varied the nominal SiO2/Al2O3 coordinate and Stage II the nominal Na2O/Al2O3 coordinate, while GGBFS, metakaolin, sodium metasilicate and effective water content co-varied. Calorimetry, compressive strength, XRD, FTIR, TG/DTG, O 1s XPS and MIP were evaluated jointly. Along Stage I, 28 d strength increased from 9.66 to 21.22 MPa before decreasing to 12.44 MPa. Along Stage II, the formulation at a nominal Na2O/Al2O3 coordinate of 1.1 reached the highest 28 d strength (26.70 MPa), associated with sustained calorimetric activity, a lower operational FTIR precursor-associated fraction, greater 30–200 °C mass loss and a higher fraction of fine mercury-accessible pore entries. Total intrusion volume and calculated MIP-accessible porosity did not follow strength monotonically. These associations are descriptive, not causal; leaching, durability and life-cycle assessment remain necessary before practical sustainability can be established.