Experimental Evaluation and Model-Assisted Multi-Objective Optimization of Semi-Dry Alkali-Activated Paving Units Containing Tailings and EAF Steel Slag

Iron-ore tailings (IOT) were evaluated as a fine solid constituent in semi-dry alkali-activated paving mixtures containing electric arc furnace (EAF) steel slag. Seventeen unique mixture formulations were evaluated through 19 experimental batches, including three independent center-condition batches, with 50–80% IOT in a fixed 500 kg/m3 IOT/EAF-steel-slag precursor, nominal NaOH molarity of 8–14 mol/L, and dry sodium-metasilicate-to-NaOH (SMS/NaOH) ratios of 1.50–3.00. For each batch, the reported compressive and flexural strengths were the arithmetic means of three specimens tested for each response. The units were formed by vibration and pressure, sealed at 23 ± 2 °C, and tested after three days. Measured compressive and flexural strengths ranged from 15.17 to 25.66 MPa and 2.41 to 3.14 MPa, respectively. A quadratic response surface fitted to the 19 batch-level compressive-strength responses gave R2 = 0.9997 and RMSE = 0.054 MPa; because no independent validation data were available, the stationary-point prediction of 26.36 MPa is treated as model-based rather than experimentally confirmed. Discrete Pareto screening using measured strength and provisional cost/GWP indicators identified M11, M13, M15, and M17 as non-dominated experimental cases. M11 is reported as a representative compromise solution within the tested cases. The results apply to the tested materials and three-day conditions and do not establish paving-product conformity.