Abstract
Density and porosity are fundamental and important physical properties of rocks in various geological problems, and affect the other physical properties. Therefore, measurements of density and porosity of rock samples are important investigation items in both geo-science and geo-engineering areas. Several measurement techniques of the density and porosity are available and being applied currently. To ensure the data quality and to conduct its quality assessment, comparison of measurement results by different measurement techniques is necessary since the techniques are based on different principles and test procedures. In this study, we collected eight types of rock samples including a gabbro, a granite, four sandstones, a welded tuff and a mudstone as study materials, and also prepared several metal specimens for the experimental comparison. The porosities of the eight rocks covered a very wide range from 0.3% to 50% approximately. We employed three methods (caliper, buoyancy and helium-displacement pycnometer) to measure volumes of regularly-shaped specimens and to determine their bulk densities and porosities. As a result, the three techniques yielded almost same bulk densities and porosities for all the specimens. In addition, we also applied mercury intrusion porosimetry to measure density and porosity as well as to determine pore size distribution of the rock samples. Porosity values obtained by the porosimetry method were underestimated in the case of high-porosity (soft) rock samples and overestimated for the very low-porosity rock samples. Ability to determine pore size distribution, however, is a very important advantage of the porosimetry method.
Highlights
Density and porosity are fundamental and important physical properties of rocks in various geological problems, and affect the other physical properties such as elastic wave velocity, permeability, resistivity, strength, Young’s modulus etc. (e.g. Schon 1998) [1]
It is clear that the measurements of bulk volume and pore volume control measurement accuracy of density and porosity of rock specimens rather than mass measurements which can be performed by an electrical balance relatively and accurately
Because the measured volume at dry state is corresponding the volume of solid portion only, the bulk volume can be calculated by adding the measured solid volume to the pore water volume obtained from the difference between wet and dry specimen weights
Summary
Density and porosity are fundamental and important physical properties of rocks in various geological problems, and affect the other physical properties such as elastic wave velocity, permeability, resistivity, strength, Young’s modulus etc. (e.g. Schon 1998) [1]. To ensure the data quality, comparison and examination of the measurement results by the different measurement techniques are necessary since the techniques are based on different principles and test procedures. In this experimental study, for comparison of measurement results we collected eight types of rock samples including a gabbro, a granite, four sandstones, a welded tuff and a mudstone as test materials, and several metal samples and measured the density and porosity of the rock samples by different techniques. We measured the porosities and determined pore size distributions by mercury intrusion porosimetry (American Society for Testing and Materials, 1999) [4]
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