Long-term durability and microstructure of advanced high-performance concrete with cement kiln dust, boiler slag and PP fibers: flexural response and sustainability assessment

Abstract This study presents a comprehensive long-term investigation (up to 730 days) of advanced high-performance concrete (HPC, w / b = 0.25) incorporating a combined system of cement kiln dust (CKD, 5–10 %), boiler slag (BS, 5–10 %), and 0.06 % polypropylene fibers (PPF). Such a multi-component hybrid design has not been previously examined for long-term mechanical and durability performance. Mechanical, non-destructive, and durability tests were supported by SEM/EDX microstructural analysis. The combined incorporation of CKD and BS increased open porosity and water absorption, reducing compressive strength and stiffness, while flexural strength benefited from fiber bridging (22 % at 56 days for 10 % CKD + 10 % BS). Despite lower compressive performance, resistance to salt crystallization improved, particularly for 10 % BS + 5 % CKD. SEM/EDX confirmed higher portlandite content, elevated Ca/Si ratios, and a more porous ITZ at higher CKD/BS levels, explaining macroscale strength losses. A simplified cradle-to-gate CO 2 assessment indicated 80–90 kg CO 2 /m 3 reduction for 10 % cement replacement with CKD and an additional 0.5 kg CO 2 /m 3 benefit from granite substitution by BS. The results demonstrate the long-term performance–sustainability balance and define practical dosage limits for durable, low-carbon HPC containing multiple industrial by-products and fibers.