More C Hence, this test method can be used to develop data to estimate the likelihood of damage due to cyclic freezing and thawing or to explain why it has occurred. The test method can also be used as an adjunct to the development of products or procedures intended to enhance the resistance of concrete to cyclic freezing and thawing. Any such distinction is arbitrary, because the various types of voids intergrade in size, shape, and other characteristics.
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Principle A core is taken from the structure, sliced, ground, and lapped in the laboratory. The resulting surface is plane, smooth, and with sharp edges along the perimeter of air voids. Before final specimen preparation, the lapping quality is checked under a stereomicroscope. The lapped surface is colored black with a hard stamp pad containing black ink.
The zinc paste melts on the surface and flows into the voids. After cooling to room temperature, excess paste is removed from the surface with a straight, sharp steel blade. The quality of the black-white contrast is checked under a stereomicroscope. The voids should be filled totally with white paste and no white regions should be visible on the surface. Finally, voids in aggregates and obvious cracks are colored black under the stereomicroscope using a black marking pen.
The photo on the left shows a properly prepared specimen. The preparation of a well-lapped specimen surface for analysis takes about 30 minutes.
The RapidAir measurement is done within 12 min for linear traverse analysis and within 30 min for modified point count. This should be compared with a time of 4 to 6 hours normally required for manual analysis using a light microscope in accordance with ASTM C or EN Operation: Following contrast enhancement, the prepared specimen is mounted on a moving X-Y-Z stage positioned below a video camera.
The RapidAir control unit automatically moves the stage, and the software determines the portion of the total traverse length that passes through the white air voids, as shown in the magnified view to the right.
The specimen scan is saved automatically in a report file documenting the air content, spacing factor, and specific surface. In addition, graphical presentation of the air-void distribution and the raw data are available. Prepared specimen positioned on the moveable stage ready for image analysis. Overall view of RapidAir system in operation. The study involved thirteen European laboratories. The standard deviations of the air-void parameters determined by RapidAir were as follows: Air content: 0.