The morphology of inner product region derived from alite or belite is identical to those present in neat OPC paste. In mature pastes, fully hydrated small grains of both alite and GGBFS often display a coarse morphology.
Similar to Portland cement, microstructure of slag hydrate could also be classified as inner product, which formed within the boundaries of the original anhydrous grains, and outer product that formed in the originally water-filled spaces.
Though the chemical reaction of the fine particles of limestone in cement paste is limited to a low extent due to its inert property, the addition of limestone particles has significant effect on the microstructure development. Research conducted by Sellevold et al. using mercury intrusion method showed that specimens containing 12% CaCO3, which have the main body of the particles smaller than 0.1 µm had finer pore structure and somewhat reduced total pore volume.