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Sieving

Sieving is a simple and widely used method of classifying powders according to their physical size alone, independent of other physical or chemical properties, by using a series of woven wire or punch plate sieves arranged in decreasing order of aperture size [14]. The sieve method covers a wide particle size range, from roughly 37 µm to 125 mm using woven wire sieves [15]. Micromesh sieves extend the lower size range to about 5 µm, but as the aperture decreases in size, the time required to sieve an equivalent mass of powder increases. Sieves are identified according to their ASTM mesh size, where a 400 mesh sieve corresponds to a minimum square aperture of 37 µm. A variety of sieve aperture ranges are available. Sieving can be performed either dry or wet, with manual or machine agitation, and for a set time or until a sufficiently low and constant powder flow rate is observed through the sieves. Key variables that influence sieving results include particle shape, presence of very fine particles, initial sieve loading, time and method of agitation, and cohesiveness of the powder (in dry sieving only). Repeatability can be high, although reproducibility is often poor due to the many variables that provide sources for user error [11].

Because of size limitations at the lower end, sieving, by itself, is not a suitable method for characterizing the complete PSD of cement powders. In conjunction with other methods, however, it can serve as a means for pre-classification of powders. Overall, sieving is better suited for analyzing the large size fraction contained in cement powders, i.e., larger than 50 µm.


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