Transportation bitumen

• Asphalt is the material of choice for heavy traffic roads due to its strength, durability and ease of maintenance and rehabilitation. It is also ideal for urban roads due to speed of construction, noise reduction, better surface drainage and ease of cleaning.
• Asphalt composition


  Bitumen and aggregates in a definite proportions
• Bitumen


  A fluid binder produced by distillation of crude oil. Its chemical composition consists of Carbon and Hydrogen, parked in three parts of oil, resin and asphaltenes.

  
• Common types of Bitumen

  • Penetration grade bitumen
  • Cutback Bitumen
  • Bitumen Emulsions

  
• Penetration grade bitumen


  Specified by the penetration and softening point tests. Designation is by penetration range only, e.g. 40/60 pen bitumen has a penetration that ranges from 40 to 60 inclusive and a softening point of 48 to 56ºC.

  
• The unit of penetration is given as deci-millimetre (dmm). This is the unit that is measured in the penetration test.

  
• Notwithstanding, penetration grade bitumens are usually referred to without stating units.

  
• Specifications for paving grade bitumens with penetrations from 20 to 330 dmm

  • 20/30
  • 30/45
  • 35/50
  • 40/60
  • 50/70
  • 70/100

  
• Cutback bitumens


  Manufactured by blending either 70/100 pen or 160/220 pen bitumen with kerosene to comply with a viscosity specification.

  
• Types of Cutback bitumens

  • Rapid Curing (RC)
  • Medium Curing (MC)
  • Slow Curing (SC)
• Bitumen Emulsion


  Liquid bitumen obtained by diluting semi-solid bitumen with water and emulsifying agents (the agents disperse bitumen in small droplets that later on combine again after evaporation of water).

  
• Main types of Bitumen Emulsion

  • Ionic emulsion
  • Cationic emulsion

  
• Satisfactory performance of a bitumen on the road

  • Rheology
  • Cohesion
  • Adhesion
  • Durability

  
• Rheology


  Adequately characterized by the values of penetration and penetration Index.
• Cohesion


  Characterized by its ductility at low temperature, as shown in the ductility test.
• In the ductility test, three 'dumb-bells' of bitumen are immersed in a water bath and stretched at a constant rate of 50 mm per minute until fracture occurs. The distance the specimen is stretched before failure is reported as the ductility.
• Adhesion


  Assessed by a retained Marshall test.
• Durability factors


  • Oxidative hardening
  • Evaporative hardening
  • Exudative hardening
• Exudative hardening


  If the constitution of a bitumen is unbalanced, it may, when in contact with a porous aggregate, exude an oily component into the surface pores of the aggregate. This may result in a hardening of the bitumen film remaining on the surface of the aggregate.

  
• Penetration Test


  Used to measure consistency of bituminous materials expressed as the distance in tenths of a millimeter that a standard needle vertically penetrates a sample of the material under known conditions of loading, loading time and temperature.

  
• Softening Point Test


  Used to measure and specify the temperature at which bituminous binders begin to show fluidity. The softening point is also an indicative of the tendency of the material to flow at elevated temperatures encountered in service.

  
• Ductility Test


  Used to describe the ductile and tensile behavior of bituminous binders. The test, which is normally performed at ambient temperatures, is believed to reflect the homogeneity of the binder and its ability to flow.

  
• Viscosity Test


  Measures consistence (fluidity) of cutback bitumen at specific temperature (preferably, 60ºC).