Roofing and paving bitumen grades produced in Bitumen Production Unit have different specifications. Roofing bitumen must be highly viscous and resistant to flow at high temperatures encountered on the roof. Recently, this type of bitumen is most popular in production of shingles and different types of adhesive roofing applications. Bitumen is generally used as raw material in manufacture of various end use bituminous roofing products rather than in its as refined state.
Paving grade bitumen is subject to stringent performance requirements. A major form of deterioration in bitumen pavements built in cold climates is low temperature cracking which results in transversely oriented surface-initiated cracks of various lengths and width. Therefore resistance to embrittlement is crucial for bitumen used in such climates as in Lithuania. Here not so much the lowest temperature reached but the number of thermal fatigue cycles bituminous paving can withstand matters. Differently from cold climate zones where high and frequent variations in temperature do not exist, coastal area is exposed to over 200 of freeze - thaw cycles per year. Such frequent changes in temperature accelerate degradation of paving as thermal expansion-contraction results in thermal
fatigue cracks which in contact to water further erode the paving.
In summer asphalt paving is exposed to high temperatures and becomes less viscous. Under heavy traffic road becomes rutted. Therefore it is crucial for bitumen to retain its properties, in particular viscosity, at elevated temperatures as much as possible. For this purpose special additives are used however they not only improve the quality but also significantly add to the price.
The main quality parameters of bitumen are penetration, ductility and softening point. Bitumen with high ductility, high softening point and good adhesive properties is considered as the best. Other quality parameters of bitumen are flash point, viscosity, brittleness temperature, density, cohesive and adhesive properties.
Penetration of bituminous material is the distance in tenths of millimeter that
standard needle will penetrate vertically into a sample under standard conditions
of temperature (25°C), load (1N) and time (5 s). The lower penetration, the higher bitumen thermal stability is.
Adhesion between bitumen and mineral aggregates is an important criterion which describes the quality of bitumen binder, pavement performance and resistance to distress as lack of bonding can lead to a significant paving damage.
At low temperatures bitumen becomes rigid and brittle. The quality of paving bitumen depends on its brittleness temperature - the lower the better. It is the temperature at which bitumen becomes brittle as indicated by the appearance of crack when a thin-film of bitumen on steel plaque is cooled and flexed in accordance with specified conditions.
Ductility test on bitumen measures the distance in centimeters to which it elongates before breaking. Ductility of bitumen is its property to elongate under traffic load without getting cracked. It decreases with the decrease of temperature.
To determine softening point, i.e. temperature at which bitumen achieves a specified degree of viscosity, steel ball is placed on a disc of binder that is slowly heated. Softening point is defined as temperature at which bitumen sample can no longer support the weight of steel ball. This test is usually called the ring-and-ball test. Higher softening point means lower susceptibility of bitumen to temperature.
Density in blown bitumen increases with the elongation of time it is exposed to air. According to standard, bitumen density should be over 1 g/cm3 @25°C.
Viscosity characterizes the consistency of bitumen at different temperatures of application. Dynamic viscosity is typically measured @60° and kinematic viscosity @135°C. With all other parameters being the same at maximum temperature maximum viscosity is preferred.