CLA 5 - Preventing Bitumen Surface Skin

ASTM D92 Appendix X1 describes a technique to prevent the surface skin formation when testing the flash point of asphalts with an open cup flash point tester like Anton Paar’s CLA 5.

The automatic Cleveland open-cup (COC) measures and describes the properties of a sample in response to heat and a test flame under controlled conditions. The flash point measures the tendency to form a flammable mixture with air while the fire point indicates the tendency of sustained burning.

The CLA 5 is suitable for flash and fire point applications of lubricants or bituminous material. It is an open-cup determination for expected flash and fire points in the range of 79 °C to 400 °C (175 °F to 752 °F).

Asphalt and bitumen tend to form a surface skin when heated up. When a surface skin is present, the flash point detection will fail, because the flammable vapors cannot evaporate from the sample and therefore cannot be ignited by the test flame.

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