The Measurement and Analysis of Silica Fume Particle Size Distribution and De-Agglomeration of Different Silica Fume Product Forms
J. Wolsiefer Sr.
Appears on pages(s):
agglomeration; de-agglomeration; densified; dispersability; electrical resistivity; particle size distribution; pozzolanic strength index; product forms; SEM; shotecrete; silica fume; ultrasound; undensified
The research goal of this project was to measure silica fume particle size distribution and conduct dispersion tests, using measured levels of ultrasound as a method to evaluate the relative agglomeration "strength" and de-agglomeration [dispersability] of the undensified and densified product forms of silica fume. Scanning Electron Microscopy (SEM) testing of silica fume samples was performed, showing combinations of individual particles (0.02 to 0.25µm) along with loose agglomerate clusters (25 to 120µm), which could not be quantified in size distribution analysis. A specially modified laser scattering particle size distribution analyzer, with a built in digitally controlled ultrasonic processor, was developed to measure particle size distribution statistics such as mean, medium and standard deviation. Ultrasonic energy levels were determined for complete de-agglomeration of undensified and densified material, which allows the measurement of the primary un-agglomerated material particle size. A test method was developed to evaluate the dispersability or relative agglomerate "strength" of the different silica fume forms by measuring the various particle size distributions, with and without ultrasound. Through the application of ultrasound, at specific energy levels and time periods, the relative agglomerate dispersability at different bulk density levels were determined. Mortar and shotcrete performance tests were conducted to evaluate the dispersability of different silica fume product forms, for different bulk loose density levels. The mortar laboratory evaluation tests included pozzolanic strength activity index ratios and electrical resistivity measurements. The test method’s ability to evaluate product dispersability and quality assurance was further verified through a field shotcrete test program, conducted with various bulk loose densities, measuring rebound percentages, thickness before bond break and compression strength.