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2. Coal tar
Tar does not occur naturally. It results from the pyrolysis of organic matter, sheltered from oxygen (see Box 1).
The vegetable coal is placed in an airtight oven for almost 20 hours. The temperature at the heart of the coke thus prepared rises to 900 to 1,000°C, synthesizing countless chemical substances that are released in gaseous form.
After cooling, the volatile matter is separated into gaseous and liquid products, the latter in turn being separated into substances soluble in ammonia water and total tar.
Fractional distillation of total tar yields several cuts, from the lightest hydrocarbons (benzol, toluol...), through anthracene oils, to the bottom of the column, which may be tar or pitch, depending on its viscosity.
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Coal tar
Types of bitumen
References
Organizations
The bibliographical references relating to bitumens and bituminous binders are extremely numerous and cannot be grouped together in a single work. For this reason, readers are invited to consult the sites listed below:
• Oil Standards Bureau (BNPé)
• French Petroleum Institute (IFP)...
Standards
Specific standards are mentioned in the text. Here, the reader will find a summary of the specification standards and general test methods that apply upstream of the specific methods. The latter must be included in the specification standards which use them.
To keep the text as short as possible, the titles of the standards listed below have been kept to a strict minimum. As a general rule, only the...
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