Chemical deformation of metakaolin based geopolymer

Chemical deformation (chemical shrinkage/expansion), the absolute volume change during reactions, is a key parameter influencing the volume stability, especially the autogenous deformation of a binder material. This work, for the first time, reports an in-depth investigation on the chemical deformation of metakaolin based geopolymer (MKG). Unlike ordinary Portland cement-based binders with monotonic chemical shrinkage, MKG experiences three stages of chemical deformations: chemical shrinkage in the first stage, chemical expansion afterward and chemical shrinkage again in the final stage. Various experimental techniques (XRD, FTIR and NMR) plus theoretical calculations are applied to explore the mechanisms behind the chemical deformation of MKG. Clear correlations are found between the chemical deformations and the reaction processes during geopolymerization. A conceptual chemical deformation model for geopolymer is summarised. The insights into the chemical deformation provided by this study will play a fundamental role in further understanding, controlling and even utilizing the deformation behaviours of geopolymers.