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Particle Size Analysis by Laser Diffraction Spectrometry: Application to Cementitious Powders.


pdf icon Particle Size Analysis by Laser Diffraction Spectrometry: Application to Cementitious Powders. (2301 K)
Hackley, V. A.; Lum, L. S.; Gintautas, V.; Ferraris, C. F.

NISTIR 7097; 70 p. March 2004.

Keywords:

laer diffraction spectrometry; cementitious powders; particle size

Abstract:

Particle size distribution (PSD) measurements are now routinely employed to characterize cement powders. A variety of techniques are available for this purpose. However, at present, an industry standard does not exist for PSD analysis, nor do uniform methods exist for sample preparation. Two recent international round-robin tests sponsored by ASTM committee CO 1.25.01 revealed high variability in reported PSDs, even among participants using similar instruments. The round-robin studies also identified laser diffraction spectrometry (LDS) as the most common technique used by the cement community for routine determination ofPSD. Therefore, studies were conducted to identify and examine the factors that significantly influence the determination of the PSD in cement powder by LDS. Potentially, the single most significant influence on measurement of the PSD arises from the requirement that powders be dispersed prior to analysis by LDS; dispersion efficiency will depend on factors such as solids concentration, choice of dispersion medium, and the application of chemical and/or mechanical deagglomeration methods. Another potentially significant source of error originates from the conversion of the measured optjcal spectrum to a PSD, a process that requires application of an appropriate optical model. The Mie model requires input of optical constants (real and imaginary refractive index) for the solid phase. The choice of optical constants can greatly influence the PSD, especially the ultrafme fraction (below about 1 ~m djameter). The current work was undertaken with the objective of improving the precision, and therefore the degree of confidence, associated with the LDS technique in its application to cement characterization, and to assess the overall measurement precision of LDS under controlled conditions. We report all relevant experimental data gathered in the course of these studies, and briefly summarize each set of results pertajning to a specific influence or parameter.