ABSTRACT:

Traditional medical X-ray imaging, CT scanning, and cross-specimen acoustic tomography (CSAT) were used to visualize the internal structure of macroporous plaster specimens and calculate the total volume of the macropores. The traditional medical imaging and CT scanning produced highly detailed images that could be used to assess the size and shape of the macropores. The CSAT imaging could be used to approximately locate macropores but shapes could not be distinguished. Only CT scanning and CSAT imaging could be used to determine the volume of the macropores. A rigorous procedure which provided very detailed measurements was used to calculate the macropore volume using the CT scans. The volume of the macropores using CSAT imaging depended upon a compression wave velocity cut-off velocity which varied from specimen to specimen. Future plans are already in-place to further develop the CSAT imaging technique to hopefully provide better macoopre shape identification and macropore volume calculation abilities.

1. INTRODUCTION

It is well established that the presence of pores of any size, either micropores or macropores, within a rock specimen will have a negative effect on both strength and stiffness. Within microporous rock, the pore space is assumed to be evenly distributed throughout the rock specimen. For the special case of macroporous rock, the macropores may not be evenly distributed throughout the specimen. The properties of macroporous rock are highly dependent on not only the volume of macropores but also the size, shape, and distribution of the macropores (for example [1 and 2]). It is highly desirable to image the internal structure macroporous rock specimens prior to destructive testing to quantify the size, shape, location, and any number of other parameters that could be used to describe the macropores. If this information is known a-priori it would be possible to develop various relationships between macropore parameters and strength and/or stiffness. This paper presents a comparison of twodimensional imaging techniques for both qualifying and quantifying macropore location and volume within plaster of Paris specimens containing regularly shaped Styrofoam inclusions meant to represent macropores.

2. SPECIMENS

Seven specimens were produced for this study. The specimens were made from plaster of Paris and contained regularly shaped Styrofoam inclusions. The inclusions were meant to represent macropores. The specimens were designed to include a variety of simple macropore shapes (specimen 1 and 7), a variety of similarly shaped macropores (specimen 2 and specimen 6), a variety of similarly sized macropores (specimen 4 and specimen 5), and a variety macropores with the same shape but different sizes (specimen 6). The one notable exception to this list is specimen 3. This specimen was meant to be the test case; the specimen contains a number of the same sized simple shape of inclusions. The macropore volumes presented in Table 1 should be considered approximate volumes. The cone shaped macropores were really not true cones but were truncated cones; the top ends of the cones did not come to a point but were cut-off so they had a flat top.

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