Effect of chitosan on the carbonation behavior of γ-C2S

gamma-dicalcium silicate (gamma-C2S) exhibits limited hydraulicity but high carbonation reactivity, and thus has been utilized in the production of low carbon concrete. In this study, chitosan, an essential component in the structure of shells, is introduced in the carbonated compacts of gamma-C2S. Its effect on the carbonation behavior, mechanical and microstructural characteristics is investigated. Results indicate both the compressive and flexural strengths of the carbonated compacts are significantly improved with the addition of chitosan, and the increasing percentages are 66.3% and 298.9%, respectively, at 0.6% chitosan content. The mechanical enhancement is found to be associated with the formation of coordinate covalent bonds by the complexation between calcium ions and the polar groups in chitosan (C=O), which in turns facilitates the further dissolution of calcium ions and increases the carbonation reactivity. In addition, the addition of chitosan induces the preferential formation of calcite in the crystalline carbonation products of gamma-C2S, which may be beneficial to the densification of the carbonated matrix.