Assessing lightweight foamed concrete multi-property with alkaline, calcium, and iron-rich cement kiln dust variants

Cement production accounts for nearly 8% of global CO₂ emissions, driving the search for sustainable alternatives in concrete manufacturing. Lightweight foamed concrete (LFC) offers benefits in insulation and reduced structural weight but relies heavily on ordinary Portland cement (OPC). This study evaluates the incorporation of three cement kiln dust (CKD) variants, alkaline-rich (AR), calcium-rich (CR), and iron-rich (IR), as 40% partial replacements for OPC in LFC with a target density of 1000 kg/m³. The experimental program included fresh-state tests (slump flow, setting time, density), mechanical tests (compressive, flexural, and splitting tensile strength at 7, 14, 28, 56, 90, and 180 days; modulus of elasticity), transport properties (water absorption, permeable porosity), thermal properties (conductivity, diffusivity, specific heat), and microstructural analysis (SEM at 200× magnification). All tests followed relevant BS EN and ASTM standards. Three replicate specimens were tested per mix per age; error bars in figures represent standard deviation. CR-CKD LFC achieved the highest mechanical performance: compressive strength of 4.32 ± 0.21 MPa at 180 days (18% higher than control), flexural strength of 0.92 ± 0.05 MPa (20% higher), and splitting tensile strength of 0.64 ± 0.03 MPa (23% higher). Water absorption decreased from 21.50% (control) to 19.90%, and porosity from 43.80% to 42.21%. AR-CKD showed inferior performance due to high alkali content (Na₂O + K₂O = 16.32%), which increased porosity (45.45%) and reduced strength. IR-CKD gave moderate improvements but did not outperform CR-CKD. Thermal properties were not enhanced by any CKD variant. These findings are applicable to non-structural LFC components such as partition walls, floor toppings, insulation panels, and void filling, where moderate strength and reduced weight are required.