Mix design optimization of metakaolin-slag-based geopolymer concrete synthesis using RSM

Abstract

Geopolymers have attracted considerable attention recently due to their promising environmental and economic benefits. This study used alkali activation to create an environmentally friendly material with good workability and high mechanical qualities from metakaolin from Oulmès, Morocco, and SONASID-Jorf steel factory slag (BFS). The authors optimized geopolymer synthesis using mixture design and Response Surface Methodology. The results demonstrate the importance of components in ANOVA modelling. This is evidenced by the high experimental Fisher factor (FCv = 16.8916 and FSt = 20.5902), which exceeds the critical value of the Fisher factor (Fc = 15.52) according to the F-test. In addition, the high values of the coefficient of determination (R2) and the adjusted coefficient of determination (R2Adj) indicate strong correlations between the experimental and calculated values (R2Cs = 95.48 % and R2Adj-Cs = 89.83 %, and R2St = 96.26 % and R2Adj-St = 91.58 %). Furthermore, the response surface analysis in the range of variables suggests that metakolin, blast furnace slags, and alkaline activation solution are best for the synthesis of a 35.31 MPa geopolymer. Under ideal conditions, Fourier transform infrared spectroscopy (FTIR) revealed bands associated with the asymmetric strain modes Si–O–Si and Al–O–Si in the metakaolin-BFS-based geopolymer. Similarly, X-ray diffraction (XRD) analysis shows a remarkable peak between 15° and 40° in 2Ɵ, indicating a significant growth rate of the amorphous phase corresponding to geopolymer formation. This study shows that design of experiments and response surface methods can optimize geopolymer synthesis, producing a material with high mechanical characteristics and good workability.