Main factors affecting mechanical characteristics of geopolymer revealed by experimental design and associated statistical analysis

• We clarify factors dominating mechanical characteristics of geopolymers via DOE and statistics.
• The OH−(M) affects mechanical parameters of a geopolymer mostly.
• Ratio of OH−(M) and SiO2(mol) affects polymerization process and developed microstructure.
• Q4(4Al) and Q4(3Al) are main coordination of a geopolymer, and dominate its mechanical parameters.

This manuscript adopts experimental design and statistical analysis to quantify the influence of componential factors and associated interactions on mechanical characteristics for a geopolymer. Microstructural analyses are performed for geopolymers with contrasting mechanical parameters to interrelate with mechanical characteristics. Results show that the impact factor of uniaxial compressive strength (UCS) of the geopolymer is primarily OH−(M), which has an interactive effect with SiO2 (mol), followed by Na2O (mol). On the Fourier transform infrared spectroscopy spectrum, the geopolymer has an obvious peak in the Si–O–Si (Al), Si–OH, and AlO2 groups at wavelengths of 980, 862, and 680 cm−1, respectively. The 29Si and 27Al nuclear magnetic resonance analyses demonstrate that the main structure of the Si ion in the geopolymer present in a form of Q4(3Al) and Al(4) signal appears generally. The percentage of the Q4(4Al) and Q4(3Al) in the structure is the major factor impacting the mechanical characteristics of the geopolymer.