INTERFACE BETWEEN CEMENT PASTE AND QUARTZ SAND IN ALKALI-ACTIVATED SLAG MORTARS

Electrical conductivity measurement and scanning electron microscope ( SEM) were used to examine the interfacial zone between cement paste an d quartz sands in Na2SiO3-activated slag mortars. Na2SiO3-activated sl ag mortars exhibited a positive interfacial excess conductance, or a h igher electrical conductivity of the interfacial zone between cement p aste and quartz sands than that of bulk pastes. SEM observation indica ted that no porous transition zone could be observed in Na2SiO3-activa ted slag mortar, but was found in Portland cement mortar. Because elec trical conductivity depends on the pore structure and pore solution ch emistry as well, it is speculated, based on published results, that th e positive interfacial excess conductance was due to the high alkali c oncentration rather than a more porous structure around aggregate. Fin ally, a hypothesis on the formation of dense interface in Na2SiO3-acti vated slag mortars was advanced. (C) 1998 Elsevier Science Ltd.