Portland cement high specific surface area

HIGH SPECIFIC SURFACE AREA PORTLAND CEMENT... 

The specific gravity of microsilica is around 2.20. Because of its very small particle size and high specific surface area, the bulk unit weight of the loose material is very low, and ranges typically between 240 and 300 kg/m. To lower the transportation costs, it is common to ship the material in a predensified form, by which the unit weight may be increased to 540-600 kg/m. It is even more convenient to transport and handle the material in the form of a slurry with a high solid content. Blended cements, in which microsihca is combined with Portland clinker and calcium sulfate, are also commercially available. A comparison of different forms of microsilica indicates that densification of this material decreases its chemical reactivity (Sanches de Rojas et al, 1999). 

The fineness of cement may be conveniently characterized by the Blaine method, even though the values obtained by this procedure are systematically lower than those found by the more accurate, but also more complicated, BET method. The specific surface area of ordinary Portland cement typically ranges between 280 and 350 m /kg (Blaine), whereas high early strength cement may be groimd up to a specific surface area of 450-500 m /kg (Blaine). This higher smface area contributes to an accelerated hydration of the cement, but also increases its water requirement. 

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