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Bitumen has been used in construction since ancient times, thanks to its key waterproofing properties. Unmodified bitumen is a highly viscous liquid, and its tendency to become brittle at low temperatures and soft at high temperatures has limited its use.
For many decades, bitumen has been successfully used in asphalt concrete to pave roads. Despite continuous improvements to bitumen production processes, mix design and pavement design, there are limits to the extent that bitumen can surmount the challenge. Accelerating wear and tear caused by heavy traffic and harsh climates are taking a toll. In addition there are increasing demands for quieter and safer roads.
Polymer modification of bitumen is helping to overcome the challenges. Today, millions of tons of polymer modified bitumen is used by the global roads industry
Photo: Use of soft unmodified bitumen on a dyke to bind the stones and provide waterproofing. The flow patterns result from the non-elastic viscous characteristics of bitumen.
Bitumen is a complex mixture of hydrocarbons. It can be derived from a straight distillation of a single crude oil. However, it is usually a combination of the heavier products from different processes in a refinery, blended to obtain the right specification. Because of its complexity, the composition is expressed by determining the relative amounts of classes of molecules, asphaltenes and maltenes.
Asphaltenes - these are polar aromatics which associate in large structures to give solidity at ambient temperatures.
Maltenes consist of:
- Saturates - segregated into paraffins and naphthenes. Regarded as carrier or solvent for the asphaltenes.
- Aromatics - also regarded as carrier or solvent for the asphaltenes.
- Resins - act as dispersion agents
Blending with Bitumen
Highly Modified Asphalt, or HiMA, is a new SBS polymer technology developed by Kraton Polymers for asphalt paving. The SBS polymer loading is more than twice that of ordinary modified asphalt, yet mixes are readily workable and easy to lay in the field. The high polymer loading makes the asphalt more like an asphalt-modified rubber than a rubber-modified asphalt so it has many times the fatigue and deformation resistance of ordinary modified asphalt.
The primary function of a roof is to present a waterproof barrier of lasting effectiveness. Flat or slightly inclined roofs have proven to be highly space economical and have therefore been applied in commercial buildings over many years. Flat roofs have now also gained acceptance in the housing market, although perception is influenced by the bad performance of early flat roofs.
The modification of roofing material with Kraton® D polymers has been a major factor in improving the quality and performance of roofing materials for flat roofs to become reputable and inspire public confidence for waterproofing of flat or slightly inclined roofs.
While these modified roofing materials have become the standard in Europe and North America in regions with hot and cold climates, the use of modification has not developed throughout the world. This section of Kraton Performance Polymers' website aims to inform anyone on the merits of polymer-modification of roofing materials, and also focuses on recent developments related to bituminous roofing materials.