The flash point of a bitumen that contains a volatile distillate is the temperature at which it begins to give off ignitable vapor. The principal purpose of flash-point testing is to determine maximum safe mixing and applying temperatures; however, these tests are an aid to identification as well. Referring again to table 13-6, you see that RC and MC have flash points below 175F. MC-30 and SC-70 have flash points around 150F, but the other grades of SC have flash points above 175F. Testing for a flash point below 175F is done with the tag open-cup equipment shown in figure 13-31. When testing for flash points above 175F, use the Cleveland open-cup equipment shown in figure 13-32.

When using either of these testers, you need to follow the procedures described in NAVFAC MO-330. While there are important procedural differences, flash-point testing using either equipment is similar in that you use the equipment to heat the test sample at a prescribed rate of temperature increase. Then, when the temperature reading on the thermometer nears the estimated flash

point (table 13-6), you use an alcohol torch to begin passing a flame across the surface of the sample. The flash point is reached when the test flame produces a distinct flicker or flash on the surface of the sample. At this point you read the thermometer and record the temperature.

Figure 13-33 shows an asphalt penetrometer that is used to determine the grade of asphalt cement. In performing the test, the needle is carefully brought to contact with the surface of the sample, then released so as to exert a pressure of 100 grams. The seconds after the needle is released, the distance it penetrated the sample is read, to the nearest 0.01 centimeter, on the penetrometer dial. The reported penetration is the average of at least three tests on the same material whose values do not differ more than four points between maximum and minimum. Detailed procedures can be found in NAVFAC MO-330.

In addition to grade determination, the penetration test is useful for other purposes, such as detecting overheating or prolonged heating of asphalts in storage tanks. Also, when the asphalt is extracted from a pavement, the penetration test is useful in determining how the asphalt has changed with age and weathering.