Uses
Polymer-modified bitumen is widely used, not only in traditional and modern hot asphalt mixes, but also in slurry-based systems and tack coats. Traditionally, polymer modification has focused on the pavement wearing course, binder course and on specialist applications such as bridge decks. More recently the application of polymers in the base course has enabled durability improvement and cost savings when combined with an overall thinner road structure.
- The use of bitumen modified with Kraton® D polymer in the asphalt mix helps to:
- Lower permanent deformation
- Increase crack resistance
- Reduce effects from aging
- Increase binder toughness to resist stone losses
- Typical asphalt mixes for pavement are from about 4 to 12% bitumen.
- Porous asphalt mixes consist of a porous wearing layer on top of an impervious base layer.
Stone Mastic Asphalt
A stone mastic asphalt is essentially a stone, skeleton like, porous asphalt with the voids filled with mortar. The traffic loads are carried by the stone skeleton. Slight variations in bitumen content can lead to an incompletely-formed skeleton and hence permanent deformation. The relatively low amount of binder also makes this mix sensitive to cracking despite its somewhat softer base bitumen.
Slurry / Emulsion
Emulsions are widely used for:
- Tack coats
- Chip seal surface dressings
- Slurry seals
Emulsions are small bitumen droplets suspended in water using surfactants. These surfactants prevent the droplets from coagulating. Upon contact with the aggregate, the droplets coalesce and the water separates causing the bitumen to form a layer on the stones surface.
Sealants
Quick repairs using crack sealants ensure the water tightness of the road until major maintenance work can be carried out. The crack sealant fills the crack, but does not reconstitute the mechanical link between the sections. Any movements either through shrinkage or loading will be absorbed by the crack filler. The filler therefore needs to be soft and elastic over the full temperature range. In addition, the crack filler needs to have adhesive properties. Special formulations of selected Kraton polymer grades and specific bitumen give a very good overall performance which can ensure the structure is watertight and elastic over the full temperature range.
Cement Concrete Overlays
Cement concrete used to be widely used during the construction of main roads. Maintenance budgets often do not allow the full replacement of these roads with asphalt roads. If the cement concrete foundation is still in a good condition it can provide a rigid base layer for an asphalt concrete road. Road authorities find that asphalt refurbishment on a cement concrete road enables restoration with the added advantages of the asphalt such as comfort and safety.
The resulting elasticity, toughness and tack can achieve a durable layer, which will resist cracking under deformation and can arrests cracks coming from the cracked cement concrete layers, preventing failure of the water tightness of the asphalt. As a result, the restored structure can retain its watertight nature.
Stress Absorbing Membrane Interlayer (SAMI)
The SAMI is used to reduce reflective cracking when overlaying existing roads. It should not only secure the adhesion between the two layers, but should also have the potential to absorb the movement in the existing pavement without acting as a slip layer.
The SAMI must have:
- Tackiness
- Toughness
- A high cohesive strength
- A high viscosity at service temperature
All these characteristics can be achieved by modifying the bitumen using Kraton polymers.
The use of a SAMI can also be applied in newly constructed roads with rigid, lean cement-concrete base layers.
