Permeation characteristics and impact factors of geopolymers made of kaolin

Geopolymer was prepared from raw materials that were mixed in various proportions based on design of experiments and permeability tests and statistical analyses are performed to investigate the factor that most strongly affected their hydraulic conductivity. Laboratory results reveal that OH− (M) had the most significant effect on the hydraulic conductivity of geopolymers, followed by SiO2 (mol), Na2O (mol) and the interaction between OH− and Na2O. The measured hydraulic conductivity of 27 groups of geopolymers was in the range 10−9-10−11 m/s and the porosities were 50-61%. Measurements differed considerably from values predicted by the proportionality between the hydraulic conductivity and the cube of porosity for a homogeneous porous medium. The measurement of pore size and distribution by Mercury Intrusion Porosimetry (MIP) revealed that the OH− (M) concentration significantly affected the diameters of pores in geopolymers, and that the variation in the d50 values of the pores varied by a factor of ten. SiO2 (mol) affected only the proportion of pores with small diameters, and insignificantly influenced the overall distribution of diameters of the pores. A linear relationship exists between hydraulic conductivity and d50 of geopolymer, with an r2 as high as 0.98.