Ductility is the length of a sample of bitumen (in centimeters) that is stretched and elongated in a standard way until it reaches the breaking point. The bitumen that has the appropriate elasticity will not expand or contract against temperature changes.
The elasticity depends on the degree of bitumen hardness, and the bitumen with low elasticity will be hard and brittle. If the bitumen has good elasticity and is used in asphalt, it will rarely crack in the cold season of winter.
Bitumen tensile test
The purpose of the experiment
The purpose of this test is to determine the ductility of bitumen and compare this property in different types of bitumen. By performing this test, a standard for measuring the stretch and adhesion of bitumen is obtained. The bitumens used in road construction must have certain technical specifications so that the constructed pavement is not damaged due to the inappropriate bitumen used. Bitumen used in road construction. It should have high adhesive properties to coat the grains of stone materials well and stick them together. To determine an indication of the adhesion of bitumens, their formability is measured. Because the more sticky the bitumen, the more malleable it will be.
According to the definition, the malleability characteristic of a bitumen is the amount of increase in length that a bitumen sample with a certain shape and dimensions can be stretched so as not to tear.
Test equipment
1- Template:
The mold is made of brass and has the dimensions shown in the figure, which consists of two clamps and two straps. When we assemble the four pieces of the mold together. The dimensions and limits of its permitted changes should be according to the values shown in the figure.
2- Water bath (Ben Marie):
The water bath is used to keep the samples at the test temperature, which should not be more than 0.1 degrees Celsius or 0.18 degrees Fahrenheit. The volume of water in the bathroom should not be less than 10 liters. The location of the samples should be such that the height of the water level from the top is 10 cm and the distance from the bottom of the sample to the floor of the bathroom is at least 5 cm. The important thing about the water bath is that it should not be hit during the test. Because the samples are very sensitive when they are broken and the slightest impact causes the samples to be deformed.
3- Testing machine (bitumen stretching device):
A device that can subject the bitumen sample to tension continuously and at a constant speed can be used. To pull the samples, we use the DOW station. minutes for our test) and are stretched at a constant temperature of 25 ± 0.5 degrees Celsius until they break. During stretching. The samples are in the water. The height of the water above the sample and the distance from the bottom surface of the sample to the bottom of the tank should be at least 2.5 cm. The water inside the device should not be subjected to any kind of slippage or disturbance during the test.
4- Thermometer:
The thermometer used must have the following conditions.
Number of thermometers according to ASTM range of thermometers
63C -8 to 32°C
63F 18 to 89°F
Note: If the test is performed in a standard infiltration bath at a temperature of 25°C 77°F, the D5 standard thermometer in ASTM can replace the high temperature thermometer.
Note: In the device that is used in the pavement laboratory. Under the bottom plate, a heater is placed to regulate the temperature of the bath, as well as a pump and purifier, which by heating and circulating the water, this set causes heat balance in the set.
Test Method
The samples that are used in the test must have been processed under special conditions, but due to the limited time of the test, these steps are already done by the laboratory manager.
First, you should grease the brass plate with a cloth dipped in a mixture of glycerin and dextrin (or paraffin). In the same way, grease the inner surface of the straps. It should be noted that the inner surface of the clamps should not be smeared with oil. Because the clamps must stick to the grave sample or because these clamps are oiled, this operation is incomplete and it is possible that the samples are separated from the clamps even before the samples are torn. We put the parts of the mold on the brass plate after greasing the necessary parts. We heat the bitumen slowly and uniformly, and when it becomes smooth enough, we pass it through sieve No. 50 (300 micrometers).
Then we pour it slowly into the mold. It should be noted that the brass plate must be completely flat and level because otherwise a part of the bottom of the mold may separate from the surface of the plate and cause the bottom of the sample to become uneven. Care should be taken not to separate the different parts of the mold. We pour bitumen back and forth in thin layers.
so that at the end the bitumen level is slightly higher than the mold level. Place the mold at room temperature for about 30 to 40 minutes to dry slowly. Then we put it in a 15C water bath for 30 minutes. Then we cut the existing bitumen with a heated knife so that only the top surface of the mold is filled with bitumen.
We place the brass plate and mold containing bituminous materials in a water bath at a certain temperature for a period of about 85 to 95 minutes inside the water with a temperature of 15°C.
Then we separate the bitumen from the plate and also separate the straps and immediately perform the test.
We place the holes on the clamps on the needles and clamps of the testing machine. And we turn on the device so that the two clamps start moving away from each other at a constant speed. The speed of the two clamps moving away from each other should be equal to 5 cm/min with a difference of ±5% - of course, there are two test methods, in which the samples are tested at a speed of 2.5 cm/min and in the other at a speed of 5 cm. They move away from each other per minute, and in this test, which is according to ASTM D113, the second method is used. We measure the distance between the two clamps in centimeters from the moment they start to stretch until the moment they break.
During the test time, the water inside the tank (water bath) must cover the samples at least 2.5 cm above and below and must continuously maintain the temperature at the test temperature of 25 ± 0.5 degrees Celsius.
If the bituminous material comes in contact with the surface of the liquid or in contact with the bottom of the water bath.
The test cannot be considered a normal test. In this case, we adjust the weight of the water bath by adding methyl alcohol or sodium chloride. In such a way that the bitumen material neither comes to the surface of the water nor is in contact with the floor of the bathroom during the test.
A normal test is a test where the material between two clamps is stretched to a certain point or becomes so thin that tearing occurs at a point where there is practically no contact surface.
They perform this test with 2 to 3 samples and finally note the distance at which the tear occurs and take the average from them and report it as the stigma characteristic of this bitumen.
According to different standards, limitations have been provided for the use of different bitumens based on their corrosive properties. An example of these restrictions, according to the ASTM standard and the regulations of the budget program organization, quoted from the book of road paving by Dr. Amir Mohammad Tabatabai, is as shown in the table below.
In the test we conducted, the samples were stretched to the limit of the device, but no breakage was observed. That is, the samples were stretched to the final limit of the existing device (150 cm) without breaking, and this indicated the high formability of the existing samples. Of course, at the end of the test, the samples were very close to the bottom of the container, which should be solved by adding Materials are removed to the water inside the tank and increase its density.
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