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Bitumen and asphalt
Bitumen or asphalt?
Bitumen and asphalt history
Bitumen’s structure
Main test
   Bitumen content
   Consistency
   Softening Point
   Viscosity
   Marshall Test




Bitumen and asphalt
The asphalt, also named bituminous conglomerate, is the main material used in the road construction field. The asphalt is a material mainly composed by aggregates and binder, with an infinite variation of mixtures. The binder of the asphalt is called bitumen.

Nowadays the asphalt is under higher and higher stress degree, due to the road traffic more and more intense. That’s the reason why asphalts have to grant higher and higher performances. Actually road pavements, made of asphalt, have to face different kinds of stress: compression and flexural stress as well as tangential stress. The internal friction (guaranteed by the presence of aggregates) and the cohesion (guaranteed by the bitumen’s composition) are the two main properties which allow asphalt to face the everyday stresses. For that reason, working on asphalt composition as well as on bitumen composition is the valuable way to improve asphalt properties in order to get high performances. Actually, modified bitumen are now studied and an accurate attention is paid to the binder proportion (bitumen proportion), according to the requirements each specific road pavement is planned to meet.

Low and high temperatures, as well as water and humidity, being considered the main bitumen “enemies”, are the special features to pay attention to.

For all the above mentioned reasons and for all the details we still ignore about bitumen, the bitumen might be defined as one of the worse materials in the world of the testing equipment.

It is therefore necessary to get suitable equipment to perform different test methods on bitumen and on asphalt in general, in order to determine bitumen content, consistency, softening point, viscosity, Marshall test results and many other parameters. We invite you to enter the “Bitumen-Asphalt” section to discover the complete list of Matest equipment for testing on bitumen and asphalt.

Bitumen or asphalt?
Worldwide there is a lot of confusion concerning bitumen and asphalt.
Actually bitumen and asphalt are often used as synonyms but those terms define two different materials.
The term “bitumen” defines the brown or black material, solid or partially solid, derived from the refining of crude oil. The bitumen is mainly composed by organic compounds with high molecular weight, mainly by hydrocarbons. The thermoplastic behaviour is proper of bitumen. Bitumen is involatile at ambient temperature and not water-soluble. It is also present in the natural environment and in such a case it is defined as natural bitumen.

The term “asphalt” defines a mixture of bitumen and aggregates (filler, sand and crushed stones).
In the U.S.A., the term “asphalt” defines bitumen, whilst to define the asphalt (that means the bituminous conglomerate) the term “asphalt mix” is used.

Bitumen and asphalt history
Nowadays asphalt and bitumen are studied in order to know and improve their properties. However it could be interesting to discover when humane civilization start to deal with such useful materials.
It could be surprising to learn that human beings have always dealt with asphalt and bitumen. Since more than 6.000 years ago, Sumers and Akkadians used asphalt as a binder and waterproofing material. Actually Babylonian wall is said to be built with bricks and asphalt and Babylonia’s famous hanging gardens risen on terraces waterproofed with bitumen.
Because of several different asphalt’s outcrops in the wide region from Nile to Indo, Egyptian civilization and old Indian civilization used asphalt a lot.

Roman and Greek historians relate how Egyptians used to use asphalt from Dead Sea to maintain their mummies. The term “mummy” is even said to originally mean bitumen.
Bitumen and asphalt were so really wide spread, but obviously the bitumen was different in comparison to the bitumen we know. It was a sort of natural bitumen: actually bitumen has a biological origin (as well as oil has), being originated in oceanic or lake sediments.
Concerning the bitumen as a derived material from the refining of crude oil, it was produced for the first time at the end of 19th century.

Concerning asphalt used for road pavements, we have no reliable information. Presumably, due to the successful applications of bitumen in the construction field, some civilizations might have used natural bitumen as a binder material among stones. Starting from 1830-1850, the natural bitumen becomes to be largely used in the big European cities for the sidewalk pavements. The first road to be asphalted is said to be in Paris, but in the USA’s biggest cities too the main roads were asphalted due to the wide spread of the asphalt coming from Trinidad and Bermudez. Anyway, asphalt was not so widespread until the beginning of 20th century, considering that mud and dust did not represent such a big problem until car’s spread.
Starting from 20th century, the bitumen derived from the oil replaced the natural bitumen. Actually the bitumen derived from oil was more convenient, granting also a higher level of workability and flexibility.

Bitumen’s structure
From a chemical point of view, bitumen is composed by asphaltenes, resins and malthenes. Among them, the most important bitumen’s components are asphaltenes, being the most specific bitumen components, due to their properties and structures which can be rarely found in other natural substances.

From a physical point of view, the presence of asphaltenes characterizes the bitumen as a material extremely viscous, plastic and elastic. The bitumen, thanks to the presence of asphaltenes in its composition, can take mechanical stresses and grant adhesiveness and a certain cohesion degree.

Resins are important to grant the colloidal equilibrium which characterizes the general bitumen behaviour, especially according to the fatigue life bitumen is subjected to. Bitumen’s flexibility property is also due to resins. Bitumen is so flexible that it reacts like an elastic material when subjected to very rapid stresses of mechanical nature, like shearing stresses and compression stresses. Always due to resins, the bitumen shows to be a ductile material with a higher binder property. Bitumen’s flowability, when melted, is granted by malthenes instead.

Bitumen’s properties are strictly linked to the environment temperature. Actually bitumen grants properties similar to the properties of a viscous fluid when exposed to high temperatures, whilst it grants the features proper of an elastic material when exposed to normal or low temperatures.

Main test

 Bitumen content Consistency Softening Point Viscosity Marshall Test
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