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An introduction to polymer blending systems

WHAT A POLYMER BLENDING SYSTEM DOES

  • It mixes virgin AC (asphalt cement) with a polymer.
  • Mixture is known as PMAC (Polymer Modified Asphalt Cement).
  • Mixture is used to make the road paving material known as HMA (hot mix asphalt).
  • HMA is a mixture of aggregates bound together with asphalt cement.
  • Using polymer to make HMA is a relatively new development of the past two decades.

WHY MIX POLYMER WITH ASPHALT?

  • Polymer enhances the properties of asphalt cement.
  • Increases the service life of highway surfaces.
  • The surface is more stable at warmer temperatures and more flexible at colder temperatures.
  • Reduces costs for road repair and replacement.
  • Motorists enjoy smoother ride and their vehicles last longer.
  • Usage has increased dramatically in last few years.
  • Now mandated for most state and federal highways throughout the U.S.

WHAT IS POLYMER?

Polymer pellets

  • A polymer is simply two or more monomers linked together.
  • Examples are rubber, rayon, polyethylene, nylon, vinyl, Styrofoam, polystyrene.
  • Not all are suitable for mixing with asphalt cement for road building.
  • The polymer most commonly used for road building is SBS.
  • It is usually comes in the form of small pellets or granules (shown here).

WHAT IS SBS?

Ground Tire Rubber

  • It is the monomer styrene linked with the monomer butadiene to form a new giant molecule: styrene-butadiene-styrene or SBS.
  • It withstands high temperatures and extreme tearing forces.
  • These are ideal characteristics for a polymer that is to be added to AC.
  • Another polymer often used to make PMAC is GTR (ground tire rubber) shown here.
  • It has characteristics similar to SBS.

POLYMER SYSTEM COMPONENTS

  • Storage tanks for virgin AC used for blending.
  • Mixing tanks where polymer pellets are added to the AC.
  • Box dumper for loading boxed polymer pellets into the hopper.
  • Hoisting system for loading bagged polymer into the hopper.
  • Hopper for polymer pellets.
  • Augur that transports pellets to a mix tank.
  • A mill that grinds the pellets while mixing into fine particles for a more uniform mixture.
  • Let-down tanks that store and stir the mixture as additional virgin AC is added.
  • A thermal-fluid heating system that heats the tanks.
  • Electrical power panel with operator controls.

SYSTEM VARIATIONS

  • Heatec has built a wide variety of polymer and rubber blending systems over almost two decades.
  • Used primarily at asphalt terminals throughout the U.S. and at a several overseas locations.
  • Also used at facilities that make roofing shingles.
  • Most use stationary polymer blending systems.
  • Fully portable system are also available.
  • Also available are compact skid mounted systems suitable for delivery in an overseas shipping container.
  • The latest systems offer both automated and manually operated controls.