The influence of limestone particle size and the type and extent of (partial) cement replacement on the yield stress and plastic viscosity of ternary pastes are studied. Interpretations based on Bingham model indicate: (i) for binary/ternary blends containing coarse limestone, the yield stress and plastic viscosity remain unchanged or decrease with increasing cement replacement, (ii) in ternary blends, plastic viscosity increases with the fine limestone content, and (iii) the yield stress in ternary blends containing fly ash is dependent on the limestone content and fineness whereas in blends containing metakaolin, the yield stress reduces with an increase in limestone content, irrespective of the limestone particle size. These are attributed to: particle packing, water demand, and the interparticle spacing and contacts which are quantified using microstructural simulations. The yield stress and plastic viscosity show strong direct correlations to the specific surface area and inverse correlations to the water film thickness.