What is the role of water in the geopolymerization of metakaolin?

Despite the significant advances in understanding the structure of geopolymers in the last decades, the role of water in the geopolymerization of aluminosilicates and within the structure of geopolymers remains elusive. The present paper investigates the role of water in the geopolymerization of metakaolin, a low calcium aluminosilicate. We differentiate between different states of water in these materials and discuss the nature and the origin of non-evaporable (chemically bound) water, and evaporable water. We propose a conceptual model for the microstructure of metakaolin based geopolymers that accounts for different states of water within their structure and discuss the implications of their composition on pore size distribution.