Using mechanical activation of quartz to enhance the compressive strength of metakaolin based geopolymers

The present work synthesized geopolymer with quartz mechanical activated at different time, and the strengthening mechanism of geopolymer by activated quartz was investigated. The changes of quartz before and after activation and the microstructure of geopolymer was explained by the determinations of particle size, specific surface area and the concentration of reactive Si, as well as XRD, XPS and NMR measurement. With the activation time of quartz increasing from 0 to 60 min, the compressive strength of geopolymer increased from 31.5 to 55.2 MPa. The results showed that increase of quartz reactivity is mainly due to the formation of the Si-centered radicals and non-bridging oxygen on the surface rather than the changes in physical property or crystal structure of quartz. The high activity tetrahedra Si with non-bridge oxygen on the surface of quartz replace the tetrahedra Al in geopolymer gel, which lead to a Si-rich gel formed around quartz and the improvement of compressive strength.