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Test for Solubility

The first procedure in the identification of an unknown bituminous material is to determine whether it is an asphalt, an emulsion, or a tar. Bituminous materials may be differentiated by a volubility test. To perform the test, you simply dissolve an unknown sample (a few drops, if liquid, or enough to cover the head of a nail, if solid) in any petroleum distillate. Kerosene, gasoline, diesel oil, or jet fuel is suitable for this test. One or more of these distillates is usually available to the EA in the field Since asphalt is derived from petroleum, it will dissolve in the petroleum distillate. If the material is an emulsion, it can be detected by the appearance of small black globules, or beads, which fall to the bottom of the container. Road tar will not dissolve. If the sample is an asphalt, the sample-distillate mix will be a dark, uniform liquid If it is a road tar, the sample will be a dark, stringy, undissolved mass in the distillate. You can make a check by spotting a piece of paper or cloth with the mix. If no stain results, the material is a tar; however, if a brown to black stain appears, then it is asphalt. The volubility test provides a positive method of identification.

Tests for Asphalt Cement

When the volubility test determines that the bituminous material is an asphalt you should then perform a pour test to distinguish whether the asphalt material is asphalt cement or asphalt cutback. In this test you place a small sample of asphalt into a container and attempt to pour it at mom temperature (77F). Since asphalt cement is a solid at room temperature, it will not pour. Even the highest penetration grade (200 to 300) will not pour or immediately deform. The thickest asphalt cutback, however, will start to pour in 13 seconds at a temperature of 77F.

The various grades of asphalt cement are distinguished by their hardness, as measured by a field penetration test. For purposes of field identification, the consistency of asphalt cement maybe approximated at room temperature as hard (penetration 40-85), medium (penetration 85- 150), and soft (penetration 150-300. These limitations are flexible, as complete accuracy is not essential. You can make an approximation of the hardness while in the field by attempting to push a sharpened pencil or nail into the asphalt at 77F with a firm pressure of approximately 10 pounds. When the pencil point penetrates with difficulty or breaks, the asphalt cement is hard. When it penetrates slowly with little difficulty, the asphalt cement is medium. If the pencil penetrates easily, the asphalt cement is a high penetration or soft grade.

Tests for Asphalt Cutbacks

In addition to distinguishing asphalt cement from asphalt cutback as discussed above, the pour test will identify the viscosity grade of the cutback at a room temperature of 77F. After the pour test, the approximate viscosity grade of the cutback is known, but the actual type (RC, MC, SC) is not. Asphalt cement is "cut back" with a petroleum distillate to make it more fluid. If the material does not pour, it is an asphalt cement. If it pours, it is a cutback or emulsion. It has been found that the cutbacks of a given viscosity grade will pour like the following substances:

3 0- Water

70- Light syrup

250- syrup

800- Molasses

3000- Barely deform

A smear test is used to distinguish an RC cutback from an MC or SC cutback. The test is based on the fact that RCs are cut back with a highly volatile material (naphtha or gasoline) that evaporates rapidly. To perform the test, you simply apply a thin smear of the material on a nonabsorbent surface, such as a piece of amounts of cutterstock, therefore, you should confirm the identification of the sample by a prolonged smear test.

A prolonged smear test is used to identify the 800 and 3000 grades of MC or SC cutback. In this test, a thin smear of asphalt cutback is placed on a nonabsorbent surface and allowed to cure for at least 2 hours. If at the end of that time, the smear is uncured and still quite tacky, the material is an MC or SC; however, if the smear is hard and only slightly tacky, then the material is not an MC or SC. An RC 3000 cutback will cure completely in 3 hours and an RC 800 in about 6 hours; but, an MC or SC will still be sticky even after 24 hours.

The odor given off from a heated cutback helps differentiate an MC (cutback with kerosene) from an SC (cutback with fuel oil). In the heat-odor test, you heat the unknown sample in a closed container to capture the escaping vapors. (Use MINIMAL heat.) An MC sample will give off a strong kerosene odor. An SC sample will not smell of kerosene, but may have a slight odor of hot motor oil.

Tests for Asphalt Emulsions

You can distinguish asphalt emulsions from other bitumens in various ways as follows:

1. By observing the color of the material. Emulsions are dark brown in color, but other bitumens are black.

2. Emulsions mixed in kerosene or some other petroleum distillate can be detected by the appearance of small black globules, or beads, which fall to the bottom of the container.

3. When an emulsion is mixed with water, the emulsion will accept the extra water and still remain a uniform liquid. Other bitumens will not mix with water.

4. Since an emulsion contains water, a small piece of cloth saturated with it will not burn. Other bitumens will burn or flame.

Once you have established that a bitumen in question is an emulsion, you can then determine whether it is a mixing grade (medium or slow setting) or a nonmixing grade (rapid setting). To do so, attempt to mix a small amount (6 to 8 percent by weight) of the emulsion with damp sand, using a metal spoon. A fast-setting (RS) emulsion will not mix with the sand, but a medium-setting (MS) or slow-setting (SS) emulsion will readily mix and completely coat the sand.

Identifying the emulsion as a mixing or nonmixing type is sufficient for field conditions. Difference in viscosity is unimportant since there are so few grades. No distinction is necessary between MS and SS emulsions because both are mixing types and are used largely for the same purpose.

Tests for Tars

A pour test is used to identify the viscosity grades of tar. Viscosity grades of road tars are comparable to the viscosity grades of asphalt cutbacks and asphalt cement, as shown in figure 13-28. RT-1, the most fluid, is similar in viscosity to the MC-30 asphalt cutback. RT-8 is similar to grade 800 asphalt cutback. RT-12 has the approximate consistency of asphalt cement; that is, 200 to 300 penetration.

Referring again to figure 13-28, you see that road tars RT-4 to RT-7 and road-tar cutbacks RTCB-5 and RTCB-6 have similar viscosities; therefore, if an identified tar has a viscosity range of RT-4 to RT-7, you must perform a smear test to distinguish whether it is a road tar or a road-tar cutback. The test is performed in the manner previously described for cutback asphalt. Like rapid-curing cutback asphalts, road-tar cutbacks are thinned with highly volatile materials, which evaporate quickly, leaving a sticky substance within a 10-minute period. On the other hand, because the fluid coal oil in road tars evaporates slowly, road tars will remain at about the same consistency at the end of an identical period. It is not important to determine whether the road-tar cutback is RTCB-5 or RTCB-6 since both are used under approximately the same conditions.



 


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