Hydrolysis kinetics of aluminates in geopolymers synthesis

The mechanisms of Al speciation and hydrolysis in geopolymers were investigated based on the partial charge model together with preliminary experimental validation. The study essentially concludes that aluminate species generally promote the condensation reactions in aluminosilicate systems owing to such factors as their partial charge, atomic size and the number of hydroxyl groups. Consequently, the solubility of aluminate sources, like metakaolin, has important influence on the properties of geopolymers. Experimental results further show that the duration of milling metakaolin, which results in different particle sizes and different dissolution rates of metakaolin, has an important effect on geopolymer properties such as setting time, microstructure and compressive strength. The samples from the larger specific surface area of metakaolin give quicker setting time, higher compressive strength, and a more homogeneous microstructure. The compressive strength is 54 MPa for the samples produced from coarse metakaolin, up to 74 MPa for those from fine metakaolin