Penetration Test of Bitumen
EXPERIMENT NO. 8
PENETRATION TEST ON BITUMINOUS MATERIALS.
ASTM DESIGNATION: D 5-97
Consistency of a bituminous material expressed as the distance in tenths of a millimeter that a standard needle vertically penetrates a sample of the material under known conditions of loading, time, and temperature.
SOURCES OF BITUMEN
Bitumen is generally obtained from the following three sources;
- Naturally occurring (in West Indies)
- Extracted from Limestone and Sandstone (procedure adopted in USA).
- From Oil Refineries (this is the major source of bitumen in Pakistan).
GRADES OF BITUMEN:
Bitumen is usually characterized in the following three types of grades;
- Viscosity grades
- Penetration grades
- Density grades
SCOPE & SIGNIFICANCE
- The penetration test is used as a measure of consistency. Higher values of penetration indicate softer consistency.
- The test is widely used all over the world for classifying bituminous materials into different grades.
- Depending upon the climatic conditions and type of construction, bitumen of different penetration grade are used. Commonly used grades are 30/40, 60/70 and 80/100.
- In warmer regions, lower penetration grades are preferred and in colder regions bitumen with higher penetration values are used.
- The test is not intended to estimate consistency of softer materials like cut back which are usually graded by viscosity test.
- Penetration Apparatus — Any apparatus that permits the needle holder (spindle) to move vertically without measurable friction and is capable of indicating the depth of penetration to the nearest 0.1 mm, will be acceptable. The weight of the spindle shall be 47.5 ± 0.05 gram. The total weight of the needle and spindle assembly shall be 50.0 ±0.05 grams. Weights of 50 ± 0.05 grams and 100 ± 0.05 grams shall also be provided for total loads of 100 gram and 200 gram, as required for some conditions of the test. The surface on which the sample container rests shall be flat and the axis of the plunger shall be at approximately 90° to this surface. The spindle shall be easily detached for checking its weight.
- Penetration Needle — The needle shall be made from fully hardened and tapered stainless steel. The standard needle shall be approximately 50 mm in length. The diameter of needle shall be 1.00 to 1.02 mm. It shall be symmetrically tapered at one end by grinding to a cone having an angle between 8.7° and 9.7° over the entire cone length. The cone should be coaxial with the straight body of the needle. The truncated tip of the cone shall be within the diameter limits of 0.14 and 0.16 mm and square to the needle axis within 2°. The needle shall he mounted in a non-corroding metal ferrule. The exposed length of the standard needle shall be within the limits of 40 and 45 mm and the exposed length of the long needle shall be 50 to 55 mm. The needle shall be rigidly mounted in the ferrule. The weight of the ferrule needle assembly should be 2.50 ± 0.05 grams.
- Sample Container — A metal or glass cylindrical, flat-bottom container of the following dimensions shall be used.
- Water Bath — A bath having a capacity of at least 10 Liter and capable of maintaining a temperature of 25 ± 0.1 °C or other temperature of test within 0.1 °C.
- Timing Device — For hand operated Penetrometers any convenient timing device such as an electric timer, a stop watch, or other spring activated device may be used provided it is graduated in 0.1 second or less and is accurate to within ± 0.1 second for a 60 second interval.
- Thermometers — Calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.1 °C or any other thermometric device of equal accuracy, precision and sensitivity shall be used.
PREPARATION OF TEST SPECIMEN
Heat the sample with care, stirring when possible to prevent local overheating, until it has become sufficiently fluid to pour. In no case should the temperature be raised to more than 90 °C above expected softening point for petroleum asphalt (bitumen). Do not heat samples for more than 30 minutes. Avoid incorporating bubbles into the sample.
Pour the sample into the sample container to a depth such that, when cooled to the temperature of test, the depth of the sample is at least 10 mm greater than the depth to which the needle is expected to penetrate. Pour two separate portions for each variation in test conditions.
Loosely cover each container as a protection against dust (covering with a lipped beaker) and allow cooling in air at a temperature between 15° and 30 °C for 1 to 1.5 hours for the small container and 1.5 to 2 hours for the taller.
Where the conditions of test are not specifically mentioned, the temperature, load, and time are understood to be 25 °C, 100 gram, and 5 seconds, respectively. Other conditions may be used for special testing, such as the following:
In such cases the specific conditions of test shall be reported.
Report to nearest whole unit the average of three penetrations whose values do not differ by more than the following:
Examine the needle holder and guide to establish the absence of water and other extraneous materials. Clean a penetration needle with toluene or other suitable solvent, dry with a clean cloth, and insert the needle into the penetrometer. Unless otherwise specified place the 50 gram weight above the needle, making the total weight 100 ± 0.1 gram. Place the sample container in the transfer dish, cover the container completely with water with the constant temperature bath and place the transfer dish on the stand of the penetrometer.
Position the needle by slowly lowering it until its tip just makes contact with the surface of the sample. This is accomplished by bringing the actual needle tip into contact with its image reflected on the surface of the sample from a properly placed source of light. Either note the reading of the penetrometer dial or bring the pointer to zero. Quickly release the needle holder for the specified period of time and adjust the instrument to measure the distance penetrated in tenths of a millimeter. If the container moves, ignore the result.
Make at least three determinations at points on the surface of the sample not less than 10 mm from the side of the container and not less than 10 mm apart. If the transfer dish is used, return the sample and transfer dish to the constant temperature bath between determinations. Use a clean needle for each determination. If the penetration is greater than 200, use at least three needles leaving them in the sample until the three determinations have been completed.
The experiment has been performed successfully and the mean penetration value came out to be 79.33. According to the tables the values ranging from 50 to 149 should have difference of maximum 4. In our case the difference is = 80-79 = 1 which is lesser then 4 so our performed experiment and the penetration value is correct. We performed the experiment at room temperature.
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