PG bitumen is new technolgy of modifiying bitumen by mix of SBS and use of PG grades help asphalt in summer time to have thoughness and in winter time elasticity which the normal asphalt in summer time become soft and in wintertime hard cold weather make it crack.
85 % of bitumen production (on the average about 90 mln tons of bitumen per year) is used as a binder in road construction. However oxidized and residual bitumen does not have the necessary properties to meet modern requirements to the pavement.
The most common way to increase the performance properties of oil bitumen (primarily, oxidized bitumen) is the use of various polymers as modifiers. Polymer modified bitumen compared to conventional bitumen has a number of significant advantages. They are more elastic, flexible and durable, less sensitive to the temperature changes and aging, have better adhesive and cohesive properties.
SBS mixing with bitumen to make PG grade
Thermoplastic elastomers, particularly SBS, are most widely used as bitumen modifiers due to their complex action. They provide bitumen with high strength (the same as thermoplastics and thermosetting plastics), elasticity (as elastomers), heat resistance, adhesion, and improved low-temperature characteristics. But the main reason that restrains thermoplastic elastomers prevalence is their high cost. An effective solution of this problem is their partial or complete replacement by cheaper polymers. A promising direction is the production of modifiers from by-products of fossil fuels thermo destruction, which contain a sufficiently large amount of unsaturated compounds. Among mentioned by-products are “heavy” benzene and/or coal tar light fractions, obtained at coke plants and used for the production of indene coumarone resin. The latter one can be used to produce modified bitumen, which meets regulatory requirements and has extremely high adhesion (till 100 %).
Benefit of using bitumen PG grade
As mentioned above, due to its natural properties petroleum bitumen is not able to create the conditions for long-term operation of pavement under modern heavy duty traffic and adverse weather factors. Therefore, in addition to providing the required quality and durability it is necessary to radically improve the physical and mechanical characteristics of these materials by complex modification with additives from a technical point of view, to create a bitumen based composite materials with a given set of properties only those substances may be applied, which meet the following requirements:
Use of bitumen PG grade
- They are not destroyed at the temperature of asphalt-concrete mixture preparation.
- They are compatible with bitumen during the mixing process on conventional equipment at the
- Temperatures usual for preparation of asphalt-concrete mixtures.
- In summer they increase the stability of bitumen (which is a part of the roadway) to the deformation impact loads without increasing its viscosity at the temperatures of mixing and laying and do not impart brittleness to bitumen at low temperatures.
- They are chemically and physically stable and do not change their properties during transport, storage, processing and operating conditions of pavement.
Bitumen performance grade PG 46 52 58 64 70 76 82 – 10 16 22 28 34 40 46
The bitumen performance grade (PG) asphalt composition is effective across a wide range of temperatures. An ideal PG modifier would be one which lowers the low end of this temperature range while raising the upper end of the temperature range. It has been found that the addition of a high viscosity base oil or finished lubricant to the asphalt will decrease the lower and upper ends of the temperature range by about a one to one (1:1) ratio.
These modifiers, although not ideal, eliminate or significantly reduce the need to add polymers to the asphalt composition. This is due primarily to the fact that lubricants already contain polymeric compounds. However, these high viscosity base oils and finished lubricants are typically hydrotreated during their manufacture in order to purify them for use as lubricants. As a result, the hydrotreating process is extremely costly and requires a great deal of specialized equipment. What is needed are more cost-effective ways to modify the asphalt with alternative PG modifiers which would be able to lower the low end of the temperature range while raising the upper end of the temperature range.The working temperature range determines whether a given grade of bitumen requires special manufacture or addition of a modifier. For example, a bitumen PG 64-28 has a working range of 92° (64 + 28 =92). Usually, binders with a temperature difference of 92° or more would generally require some sort of modification (Table 5).
PG grades for different bitumen blends