1- Penetration Test
The penetration test is used to measure the hardness and softness of bitumen. Penetration bitumen obtained from the refinery is classified based on this test. The degree of penetration of bitumen is directly related to its ductility and shows that asphalt has a higher loading capacity.
High penetration bitumen is suitable for cold climates and low penetration bitumen is suitable for hot climates.
To perform this test, a needle is penetrated into the bitumen surface with a load of 100 grams for 5 seconds. The degree of penetration is equal to the amount of needle penetrating. Its unit of measurement is 0.1mm.
2- Viscosity Test
Viscosity test is used to determine the adhesion of bitumen to asphalt aggregates. Bitumen must have an optimal viscosity value. This means that very viscous or very low viscosity bitumen are not suitable for road construction. In addition, viscosity is highly sensitive to temperature increase, and with increasing temperature, the amount of viscosity decreases as a result, its cohesion is lost. For this reason, viscosity is measured at temperatures of 60 °C and 135 °C. By measuring these two viscosity we can have sufficient information about the best temperature we should mix and compact bitumen with aggregates.
To measure the viscosity, by the viscometer apparatus, the time required to remove a certain amount of bitumen from the viscometer is measured and multiplied by the correction factor of the device. The number obtained is equal to the viscosity of the bitumen.
3- Softening Point Test
Bitumen as a combination of different hydrocarbon materials such as asphaltene and resin does not have a specific melting point. By heating the bitumen, it becomes soft and melts slowly.
The temperature at bitumen starts to melt/softer is called the softening point. This point is important for engineers because it indicates at what temperature the bitumen loosens and its adhesive decreases.
The laboratory method of measuring the softening point is the ring and ball method.
To perform the test, the bitumen sample is taken in two brass rings. Two steel balls are placed on the bitumen samples. Then the assembly is placed in a water bath and heated.
The softening point is the temperature at which the steel ball coated with bitumen hits the bottom of the glass beaker.
4- Ductility Test
As long as the bitumen has good ductility, it will be resistant to road traffic as well as expansion and contraction of bitumen due to temperature changes, and the possibility of asphalt cracking will decrease and asphalt life will increase.
To measure this property, bitumen is poured into a special mold and the mold is pulled from both sides at a constant speed of 5 cm per minute. The amount of bitumen stretched to the moment of rupture is reported as ductility. The longer the length, the greater the ductility.
5- Specific Gravity Test
Specific gravity is the ratio of the mass of bitumen to the mass of water, while both of which have the same volume.
Each bitumen has a certain amount of specific gravity. As a result, this property is used to measure the amount of impurities in the bitumen. It is also used for calculations.
We use a pycnometer to measure this property. First, weigh the pycnometer, then fill it with bitumen and weigh it again. In the same way, fill the pycnometer with water and weigh it. We subtract the weight of the pycnometer from the readings of the pycnometer filled with water and bitumen. The ratio of bitumen weight to water weight is equal to the specific gravity of bitumen.
6- Solubility in TCE
This test is performed to measure the purity of bitumen. This test detects non-oil impurities. For this purpose, 2 grams of bitumen is dissolved in 125 ml of trichloroethylene. The solution is weighed and then filtered through Whatman paper. Impurities are washed and dried and finally weighed. The percentage of impurities should not be more than 1% because it indicates the low quality of bitumen. High impurity in bitumen will have low adhesion strength.
Insoluble matter (%) = mass of insoluble materials / mass of bitumen sample
7- Flash and Fire Point Test
There are also risks in transporting and storing flammable materials. As a result, it is more important to notice the flash and fire point of bitumen.
Heat causes liquid materials to evaporate. If the liquid is flammable, it will catch fire if there is an ignition source like a flame.
Two devices are used to obtain the flash point and fire point:
Pensky-martens
Cleveland open cup tester
The procedure of the test is that bitumen is poured into the cup of the apparatus and then it is heated.
During heating, the flame passes over the liquid surface and through the vapors once every 2 seconds.
The temperature at which an instant flame appears on the surface of bitumen is called a flash point.
To obtain the fire point, heat is continued and the flame continues to pass over the surface of the liquid until an instant flame reappears on the liquid surface for a moment.
Compared to the previous flame, this one lasts longer. Its temperature is reported as the fire point.
8- Loss on Heating Test
The amount of volatiles in the bitumen is measured by the loss on heating test. Volatiles are compounds that have a lower boiling point than water and evaporate at a lower temperature.
The higher the percentage of volatile materials in the bitumen, the harder it becomes for the asphalt during the heating process and it loses its elasticity. A suitable bitumen binder should contain less than 1% volatiles.
To perform this test 50 g of bitumen sample is heated in the oven at 163 °C for 5 hours. After that, the bitumen sample is weighed.
The percentage of loss on heating is calculated as follows:
Loss on heating (%) = [(Initial weight – Final weight)/Initial weight]*100
9- Spot Test of Bitumen
The spot test of bitumen is used to indicate that the bitumen is not damaged during the refinery’s overheating.
In a refinery, if the heating was so high the cracking occurs in bitumen. Cracked bitumen is not sticky enough to hold aggregates together. Moreover, it can not tolerate the preheated process for road construction.
To perform the test 10 ml of a solvent is put in a flask containing 2 grams of bitumen sample. The solution is rotated and placed in boiling water until it is dissolved completely.
After it cools at room temperature, put a drop on filter paper.
If the trace of the drop is brown the test is negative. Inversely if the drop is brown with a black center the test is positive and the bitumen is damaged.
10- Drop in Penetration after Heating Test of Bitumen
Drop in penetration tests measure the hardness and volatile content of bitumen.
When bitumen is heated for construction the volatile component evaporates and causes the material to harden. When bitumen has more volatile content, its hardness increases after heating.
To perform the drop in penetration after the heating test, apply the needle with a load of 100 grams for 5 seconds on the bitumen surface. Note the amount of penetration in 0.1 mm.
Then the bitumen sample is placed in the oven at 163 ͐degrees celsius for 5 hours.
After removing the sample, it is allowed to cool. In the next step, the penetration test is repeated.
Drop in penetration value (%) =
[ difference between 2 amount of peneration/initial amount ] * 100
