The Effect of the P/Si Ratio on the Preparation and Properties of Phosphoric Acid-Metakaolin Geopolymers

The present research deals with the production and characterization of geopolymers prepared by mixing metakaolin, different amounts of phosphoric acid solution and water. Hardening was performed by aging the geopolymeric pastes in a climatic chamber. The workability of the pastes has been improved while the H2O/total solid content has been kept constant and the P/Si ratio increased. However, such a benefit implies considerable heat output, which must be controlled in order to limit the formation of extended fractures. The compressive strength of the hardened materials increases with increasing P/Si ratio at a constant H2O/total solid content, whereas their strength decreases with increasing H2O/ total solid content at a constant P/Si ratio. The open macroporosity, which is directly dependent on the total amount of water added to the geopolymeric pastes, may explain the above results better than the nano/microporosity and/or chemical bonds that contribute to building up the materials’ textural features.