Synergistic Effects and Optimization of Cement Kiln Dust and Glass Powder Incorporation in Self Compacting Mortar Using Central Composite Design

This study investigates the optimization of self-compacting mortar (SCM) properties incorporating cement kiln dust (CKD) and glass powder (GP) as partial replacements for ordinary Portland cement (OPC). Slump, flow, compressive strength, flexural strength, and porosity were studied by central composite design (CDD) to investigate the impact of CKD and GP (0–25% each). Material variability was understood using statistical models developed from SCM property prediction (R² = 0.92–0.95). In the case of CKD, the workability generally increased, whereas the workability decreased in the case of GP, especially at the higher levels. Both materials reduced compressive and flexural strengths, with CKD being the most significant contributor. Higher CKD and GP contents increased porosity, proportional to strength losses. The optimum formulation of 7.22% CKD and 5.26% GP, which showed the highest desirability of 0.97, was identified as the optimum formulation with a balance between fresh and hardened properties through the desirability approach. The optimized mixture resulted in a slump (22.98 cm), flow time (11.55 secs), compressive strength (54.33 MPa), flexural strength (8.4 MPa), and porosity (14.49%). The optimized formulation demonstrates significant environmental and economic benefits, reducing CO₂ emissions by 68.15 kgCO₂/t (12.39%) and decreasing material costs by $5/ton (12.4%) compared to the control SCM. This study demonstrates the possibility of integrating CKD and GP in SCM, offering a sustainable alternative to traditional cement-based mortars without significant performance loss.