The present study aimed primarily to determine the effect of particle size distribution and the chemical and mineralogical composition of different types of Chinese fly ash on the nature of the reaction products resulting from the alkaline activation of those materials and on mechanical strength development in the hardened pastes.Three type F (ASTM C618) fly ash materials were studied, with SiO2/Al2O3 ratios ranging from 2.4 to 3.8.The activator used in all cases was an 8-M NaOH solution.Selective chemical attacks were applied to determine potential ash reactivity.Paste mechanical strength was determined on lxlx6-cm prismatic specimens.Both the starting ash and the reaction products were characterised with XRD and 29Si and 27A1 MAS-NMR.The findings showed that the vitreous phase content, reactive silica/alumina ratio and particle size distribution play an important role in both mechanical strength development and the composition and microstructure of the reaction products.