Bitumen is a non-crystalline viscous material, black or dark brown that is substantially soluble in carbon disulfide(CS2) possessing adhesive and waterproofing qualities. It consists essentially of hydrocarbons and would typically compose of at least 80% carbon and 15% hydrogen by mass, the remainder being oxygen, sulfur, nitrogen and traces of various metals.
Although bitumen does occur naturally, the world relies on petroleum refinement for it’s supplies of bitumen. The bitumen content of crude oil can vary between 15% and 80% but the normal range is 25-40%. Depending on the type of crude oil, bitumen is present either in the form of colloidally dispersed particles or in a true solution.
Bitumen’s main property is that of a very strong and durable adhesive that will bind together a very wide variety of other materials without affecting their properties. It’s durability is essential to major engineering projects such as roads and waterways where it must last for 20 years or more.
As it is highly waterproof, it can also act as an effective sealant. It also resists action by most acids, alkalis and salts, and because it does not contaminate water it can be used to line watercourses. These properties have also made it a very popular roofing material. It is a thermoplastic material; it softens and becomes liquid when heated and harden as it cools. As it can readily be liquefied it can be spread relatively easily where it is required.