Observations on microstructure of pumice particles using computed tomography

Pumice occurs widely in New Zealand and is important in infrastructure construction, but is not readily characterized in situ. It is a unique material, the particles of which crush easily under finger pressure, making it arguably the most delicate of the suite of crushable soils found in various locations around the world. In this study, we scanned pumice particles of different sizes using an X-ray computed tomography (CT) scanning machine to investigate particle microstructure. Using image analyses, we were able to determine the solid density of pumice more accurately than the standard method, which showed increasing density as particle size decreased. Results from the CT scanning showed a solid density of about 2.2 g/cm(3), which is similar to the highest value obtained using the standard method. On the other hand, the apparent density from CT scanning was 0.89g/cm(3), which is lower than the density of water, therefore confirming that almost all pumice particles float on water. In addition, the volume of surface voids was observed to be much greater than that of internal voids. Moreover, the particle shape of pumice sand was analyzed and compared to other natural sands. Finally, analyses showed that pumice particles are very fragile not only because they are porous, but also because of their angular nature.