ASPHALTS AND BITUMENS.
Asphalt and bitumens form an inter-related group or materials that have wide application in construction engineering. You’ll know different types of Asphalt here.
The term asphalt is used somewhat differently in different countries. Thus in the USA, by Asphalt it is understood a solid or semisolid product in which the dominating constituents are the bitumens.
This definition covers both the natural asphalt rock and the byproduct of a similar composition obtained during refining of crude petroleum.
In Europe and elsewhere, however, the term asphalt is generally restricted to a naturally occurring rock which contains bitumens in good abundance.
It is not used for artificial mixtures or products.
The term bitumen, however, is universally regarded a complex mixture of hydrocarbons.
Types of Asphalt.
1. Native Asphalt.
Pure asphalts occur in nature in the form of solid or semi-solid deposits in certain parts of the world.
The best known are the Lake Asphalt deposits of Venezuela. Sometime the asphalt rock may contain other mineral impurities.
2. Asphalt Rock.
It is a type of limestone converted to asphalt rock. This has happened at places where natural bitumens have entered the crevices of limestone rock and changed it to an asphaltic composition.
The asphalt rock is used at places of occurrence for road paving and road making.
3. Asphaltites.
These are actually asphalt like in composition and have low softening points (200° F or so).
Some asphaltites are used considerably in electrical storage batteries, thermo-plastic molded goods, mastic flooring and pipeline coatings.
Countries producing natural asphalt and asphalt rock are: Trinidad, Albama, France, Germany, Italy, United States of America, Iraq and Syria.
Uses of Asphalts.
Asphalts are used, generally in combination with other materials, in many engineering fields. Some examples are given below:
1. ELECTRICAL USES.
High-grade asphalts are used in electrical industry on mixing with wood tar, pitch, rubber, and resin. The battery containers are its best examples.
2. ROADWAY CONSTRUCTION.
Asphaltic bitumens are characterized by a set of useful properties such as: resistance to weather, water proofness, binding capacity and ability to provide a flexible surface.
For these qualities, they are used extensively in highway construction both in the road foundations and as surface materials.
Types of Asphalt Mixture used in Roads.
Three types of the asphaltic mixture used in roads are:
- Rolled Asphalt,
- Mastic Asphalt,
- Compressed Rock Asphalt .
The rolled asphalt is used for paving only. The mastic asphalt is rich in bitumens. It is used mixed with aggregates when it forms a water proof and plastic material which can be given any desired shape while in hot condition.
3. ASPHALTIC PAINTS.
Bituminous asphalts are used as essential ingredients in certain paints. Such paints are especially useful for damp walls and over concrete structures.
4. ASPHALT CONCRETE.
Some asphalt is refined to specifications that give it excellent binding properties. It is called asphalt cement, and when mixed with fine and coarse aggregates, it gives asphalt concrete.
It is in this form that the asphalt is generally used in highway and airport paving, where it gives the pavement desired flexibility and strength at the same time.
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