BITUMEN
Introduction
Bitumen is a pasty black substance known for its high viscosity. This industrial product has no specific chemical formulation. In other words, it is a mixture of hydrocarbons. Most importantly, carbon’s number in the hydrocarbon chain provides different features and grades. For example, its mixture affects its form and stickiness.
It contains four main components; naphthalene (naphthalene aromatics), polar aromatics, saturated hydrocarbons, and asphaltenes.
Two different kinds of primary sources provide it. The first is petroleum bitumen. Its main source is crude oil. The second is natural bitumen. This kind arises naturally and under the influence of atmospheric conditions over time and its main source is gilsonite.
Production methods
There are three ways to manufacture this viscous product from petroleum:
- Straight run: vacuum distillation tower residue (VB) is the main source of petroleum bitumen. When the features of VB are close to bitumen, it is considered the final product and the name of this process is straight run.
- Air blowing: when the features of VB aren’t the same, it should undergo some processes such as oxidization, polymerization and dehydrogenation with air blowing to the reactor to meet the needed features.
- Blending: blending is mixing different cuts of petroleum products (with optimal formulation). As a result, this process causes achieving standard specifications.
Bitumen vs asphalt
You may be one of those who use asphalt and bitumen interchangeably. Let’s clarify the differences. Bitumen is used as a binder in the asphalt combination. The combination of gravel and other aggregate particles with this pasty black substance is called asphalt concrete or asphalt. To clarify the asphalt type and avoid misunderstanding, there are names such as liquid asphalt, asphalt binder and asphalt cement.
Different modification
In refineries, they modify this useful substance by mixing and performing processes. Furthermore, each of the items mentioned below is divided into different grades.
- Emulsion Bitumen: It is a mixture of water, emulsifier and bitumen. It’s appropriate for producing cold asphalt which works in humid areas.
- Polymer Modified Bitumen (PMB): This type has elastomeric thermoplastic resin. So, they have high elasticity and adhesion. Because of these features, it’s a suitable choice for coatings and polymer-modified asphalts.
- Cutback Bitumen: when it comes to lower viscosity, this one is the most suitable. This type is obtained by combining it with organic solvents such as kerosene or gasoline. Due to its lower viscosity, it is liquid at room temperature. Its application is in covering asphalt.
- Oxidized Bitumen: this type has lower penetration levels and softer texture than others. It’s also less sensitive to temperature changes. As a result, it finds applications in waterproofing and plating.
In addition, this industrial substance is available in different grades. Each grade has its properties and is suitable for a specific application. According to the ASTM penetration test these grades are: 40/50, 60/70, 85/100, 120/150, 200/300
Features
Bitumen is a mixture of dense hydrocarbons. Its two outstanding features are water permeability and stickiness. Its stickiness comes from its high viscosity. It contains lots of nitrogen and asphaltene. This product is non-polar, so it dissolves in organic solvents. Moreover, It’s a hydrophobic and resistant substance. Moreover, combining it with other additives reduces its cost and improves properties.
Applications
- it is primarily used as a binder in asphalt construction. About 70% of this product in the world finds application in the asphalt industry; road surfacing, road construction and paving are examples of this product.
- Bituminous waterproofing is another application. About 10% is for roofing felt and roof sealant.
- Sealing and insulating are important purposes that this pasty viscous product offers. Pipe coatings and paint are good examples.
Bitumen Different Grades
The ASTM penetration test is a standard test that determines petroleum products’ characteristics. This test measures the penetration levels of solid or semi-solid products like bitumen. The amount of the needle penetration into the bitumen measures the penetration level. The needle weighs 100 grams and the duration of its penetration into the bitumen is 5 seconds. The penetration unit is 0.1 mm. As a result, this test classifies bitumen into different grades. The ASTM standard grades are 40/50, 60/70, 85/100, 120/150 and 200/300. The softer the bitumen, the higher its penetration levels.
Processes like vacuum bottom oxidation produce penetration-grade bitumen. The hot air-blowing process occurs continuously during the bitumen production in distillation towers to obtain stable and homogeneous material.
The choice of grades depends on factors such as the type of road, climate, and traffic volume.
