Natural asphalt is formed gradually in the natural condition and open environment resulting from evaporation and transformation of crude oil in nature with the passage of a long time (millions of years). This type of bitumen is called natural asphalt or mineral bitumen, which has a variety of applications.
As already mentioned, evaporation of crude oils from natural bitumen within a long period of time is one of the causes of the formation of natural asphalt. Natural asphalt is a natural resinous hydrocarbon and it is also called uintaite or asphaltum. Its durability is more than the petroleum asphalts, which is also called lake
asphalt such as asphalt of Behbahan Lake or Lake Asphalt of Trinidad in the US.
Natural asphalt in our country is usually known as Gilsonite, which actually originates from the solidification of crude oil under pressure. To determine the characteristics of natural asphalt, its odor and softening point, moisture, level of ash and carbon, and solubility are measured.
There are many natural asphalt mines under exploitation in Iran, especially in the west of the country such as Kermanshah, Ilam, and Kordestan. The level of ash in the natural asphalt is of great importance. The lower the level of ash, the higher the quality of bitumen. The softening point of bitumen is another significant parameter in measuring the quality of the natural asphalt.
Bitumen’s level of sulfur and natural asphalt’s oxygen are crucial as well.
In comparison to petroleum asphalts, the natural asphalts include more sulfur and some level of ash, while petroleum asphalt contains no ash at all. Natural asphalt is used in the drilling mud to control well walls and to aggregate in the asphalt and the walls of the casting molds or printer ink.
Considering that natural asphalt is hydrophobic and both acid resistance and base resistance, it is used in the production of rooftop asphalt, bituminous waterproofing, and moisture insulations.
Natural asphalt is in lump form, a shiny and black substance, and in powder form, it is a dark brown micronized powder, which can be collected using an excavator and compressor. It is highly soluble in organic solvents.
Even though coal and natural asphalt are similar in appearance, coal is formed from the decomposition of plants and trees through the passage of time and natural asphalt originates from the evaporation of crude oil, which is produced from the remains of planktons.
Natural asphalt is mostly used in bituminous waterproofing, in which by adding petroleum asphalt the level of penetration is decreased, and its viscosity and the softening point are increased, which can result in reducing bitumen’s thermal sensitivity and enhancing its function in the higher degrees and reducing the damages caused by the low temperature.
Using natural asphalt in warm mix asphalt can result in enhancing the strength and resistance of pavements against traffic load and prevents the asphalt from cracking in the lower temperature. However, considering that natural asphalt contains ash, it is recommended to add it to petroleum asphalt for the purposes of asphalt production and road construction.