In this paper, PARC software was used to determine the spatial distribution of the dominant reaction products, their chemical composition and area/volume percentage in alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes. The pastes reacted at different rates and dominant compositional domains were Mg rich gel around GBFS particles, i.e. Ca-(Na-)Al-Si+Mg, while the domains further form the GBFS and FA particles consisted mainly of Ca-(Na-)Al-Si. The reaction degree of GBFS and FA was calculated. Alkali-activated GBFS reacted faster in the studied alkaline conditions, reaching 66 % reaction at 28 days as GBFS contains 99 vol.-% of highly-reactive calcium and magnesium-rich aluminosilicates. The reaction degree in alkali-activated FA and GBFS paste was lower, as FA contains 31 vol.-% of nonreactive phases (quartz, mullite, hematite). The results obtained from PARC were compared with independent bulk analytical techniques X-ray fluorescence (XRF) and X-ray diffraction (XRD).