Road Construction Bitumen. Bitumen, as a road construction material, must meet certain requirements to ensure long service life of the structures.
There are three types of road construction bitumen: I, II and III.
The behaviour of type I bitumen is defined by the coagulation structure of asphaltenes, which enlarge in aromatic hydrocarbons and interact through the thin membranes of the dispersion phase.
At higher temperatures, this material does not possess oxidation stability and is prone to aging.
Type I bitumen does not adhere well to minerals which contain less than 30% heavy and alkaline earth metal oxides. Satisfactory results can only be achieved when this parameter is 50% or higher. This bitumen should also not be used with minerals which have porous surface.
The advantages of type I bitumen are:
- good elasticity and plasticity at low temperature;
- wide flexibility temperature range;
- high heat resistance;
- strong adhesion to carbonate and basic materials.
Type II bitumen can be in one of the three rheological states: real viscosity, elastic viscosity and elastic brittleness. The transition to elastic brittleness occurs at -8…-12ºС, the risk of cracks and breaks in roads built with this bitumen is high. The advantages of type II bitumen are high cohesion and deformation stability. Strong and stable adhesion is only possible with mineral materials, containing over 50% heavy and alkaline earth metal oxides. IN other cases, surfactants are required. Type II bitumen is also resistant to oxidation factors at elevated temperatures.
The limitations are:
- lack of elastic and flexible elastic rheological states;
- no elasticity in elastic viscous state;
- llow heat resistance;
- lack of strong adhesion to most materials used in road construction;
- low water resistance.
Type II bitumen properties depend on the presence of asphaltene coagulation structure, and supermolecular thin film resin formation. The binder of this type has all properties necessary for road construction. They do not feature the high parameters of certain rheological and strength indications, characteristic of other types, but they are also free from strong disadvantages, also common for the other types.
Type III bitumen has the following properties:
- flexible-plastic state in a wide temperature range;
- flexible and elastic deformation with low shear loads;
- high strength and deformation stability;
- satisfactory heat resistance;
- satisfactory aging resistance;
- satisfactory adhesion to carbonate and basic minerals.
