The fineness of cement directly influences the rate of hydration, as the hydration begins at the surface of the cement particles. In addition to hydration, the fineness of cement is vital for various properties of concrete including workability, gypsum requirement, and long-term behavior. The fineness of cement is represented in terms of the specific surface of cement which is typically measured in square meters per kilogram, with several methods available for this determination.
Direct measurement of a specific surface can be done through sedimentation or elutriation, utilizing Stokes' law to find the terminal velocity of spherical particles in a fluid. Another method involves the Wagner turbidimeter, which estimates particle concentration in a suspension and measures the surface area of particles through light transmission.
Additionally, air permeability methods like the Lea and Nurse method and the Blaine method are used. The Lea and Nurse method measures the pressure drop of air flowing through a cement bed, relating it to the bed's permeability, which indirectly gives the specific surface area per unit mass of cement. The Blaine method records the time it takes for a known volume of air to pass through the cement bed at a constant rate, also allowing for the calculation of the specific surface area.
