Optimization of mechanical performance, shrinkage, and environmental impact of slag-based geopolymer mortars with CKD and glass powder using response surface methodology

The development of low-carbon binders requires optimized formulations that balance mechanical performance, durability, and environmental impact. This study investigates the multi-criteria optimization of slag-based geopolymer mortars incorporating ground granulated blast furnace slag (GBFS), cement kiln dust (CKD), and glass powder (GP) as ternary precursors. A multifactorial Central Composite Design (CCD) coupled with Response Surface Methodology (RSM) was employed to evaluate the individual and interactive effects of CKD and GP (0–30%) on fresh, mechanical, dimensional, microstructural, and environmental properties. Nine formulations were produced and tested for flow spread, compressive strength (7 and 28 days), open porosity, drying shrinkage (56 days), mass loss, and carbon footprint. The developed statistical models showed high reliability (R² = 0.94–0.97; p < 0.01). Incorporation of 15% GP reduced open porosity from 14.23% to 11.1% and increased 28-day compressive strength by 20.3%. In contrast, 30% CKD increased porosity to 17.85% and drying shrinkage above 1.10‰. GP at 30% minimized shrinkage to 0.82‰ and reduced mass loss to 3.2%. Multi-response optimization identified an optimal composition of 17.91% CKD and 25.34% GP, achieving 47.67 MPa at 28 days, 185.26 mm flow spread, 13.86% porosity, 962 µm/m shrinkage, and a carbon footprint of 143.8 kg CO 2 /m 3 . Microstructural analyses (XRD, DTG, SEM–EDX) confirmed the formation of hybrid C-(N)-A-S-H gels responsible for matrix densification. The novelty of this work lies in the integrated mechanical–microstructural–dimensional–environmental optimization of a ternary geopolymer system through a statistically validated multi-response framework, providing a comprehensive methodology for sustainable construction materials design. • Ternary geopolymer mortars based on GBFS, CKD, and GP were optimized using CCD. • Synergistic CKD–GP interactions improved strength and matrix densification. • ∼15% GP increased compressive strength and reduced porosity and shrinkage. • Alkaline activators dominated the environmental footprint.