Abstract: Pozzolanic tuff powder has a prospect to be used as a new mineral admixture in hydraulic concrete preparation in China's western areas. By using scanning electron microscopic (SEM), X-ray diffraction (XRD) analysis and X-ray fluorometric (XRF) analysis, the influences of grinding process on physical properties, chemical composition and mineral phase components of tuff powder were examined. The relations of activation index of tuff against grinding time and curing age were also investigated. Results manifest that the fineness of tuff powder reduces with the prolongation of grinding period, while density, loss of ignition (LOI) and the ratio of water demand all increase slightly. The grinding process is accompanied by mechanochemical action, which could exert physical activation effect on tuff powder, but has no effect on chemical composition, element distribution and mineral phase component. The activation index of tuff powder is in a notable logarithm relationship with grinding period and curing age. We recommend that tuff powder should be incorporated in concrete accompanied by some other mineral admixtures such as fly ash and slag.

Key words: tuff, activity index, grinding process, physical activation, SEM, XRD, fineness