Performance-Based Evaluation of Cement Kiln Dust Incorporation in Alkali-Activated Slag Concrete: Mechanical Strength, Durability and Composition-Controlled Performance

• CKD-modified AASC tested with 0–100% CKD range and benchmarked against OPC concrete. • Optimal CKD content (20–30%) delivers superior properties due to ideal oxide ratios. • High CKD contents (≥50%) caused sharp drops in strength and durability. The increasing accumulation of cement kiln dust and the demand for low-carbon binders highlight the need to define its safe and effective incorporation into alkali-activated slag concrete. Existing studies rarely determine the optimum replacement level while simultaneously evaluating mechanical performance, durability, and the interaction between slag and cement kiln dust. This study examines mixtures containing 0–100% cement kiln dust and assesses workability, compressive, tensile and flexural strength, water absorption, penetration depth, carbonation resistance and freeze–thaw scaling with and without salt. Mechanical tests results showed a clear optimum at 20–30% replacement, where compressive strength increased to 52–53 MPa (compared with ∼50 MPa at 0%), and tensile and flexural strengths improved by 8–15%. Water absorption and penetration depth reached minimum values in this range, while mixtures with 50% and 100% cement kiln dust exhibited greater permeability and significantly lower strength (<43 MPa and <3 MPa). Freeze–thaw testing without salt produced negligible mass loss (<0.15 kg/m²), but salt scaling severely deteriorated mixtures containing ≥50% cement kiln dust, whereas those with 20–30% performed best. Overall, 20–30% cement kiln dust is identified as the optimum range (with full respect to recognizing optimum ranges of Si, Al, Ca and Na contents and their ratios), balancing mechanical and durability criteria and defining practical limits for high replacement levels.