W/C Ratio Profile in ITZ of Mortar

摘要

In mortar and concrete, the microstructure of the cement paste is affected by the presence of the aggregate and sand particles and this is most significant in the interfacial transition zone (ITZ). The durability of concrete is affected by the inferior proportion of constituents in ITZ compared with bulk paste, i.e. higher porosity, higher calcium hydroxide (CH), lower calcium silicate hydroxide (C-S-H), and almost no anhydrous in ITZ. This work for the first time investigates the effect of sand size on the proportion of different constituents in ITZ and mortar as a whole. It shows that, as sand size reduces, the shearing force exerted on the paste during mixing increases leading to an increase in C-S-H/CH ratio. Also the effective w/c ratios in the ITZs are calculated for different sand sizes. It is shown that water/cement (w/c) ratio increases with sand size and decreases with distance from the sand surface.