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Bitumen Specifications

Bitumen Specifications. Agenda. 1. What is Bitumen?. 2. Modes of Failure of Pavement. 3. Methods of Classification. 4. Test Methods. What is Bitumen?. What is Bitumen?. Last residue obtained from fractional distillation of Crude Oil Is black or dark brown in colour

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Bitumen Specifications

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  1. Bitumen Specifications

  2. Agenda 1. What is Bitumen? 2. Modes of Failure of Pavement 3. Methods of Classification 4. Test Methods

  3. What is Bitumen?

  4. What is Bitumen? • Last residue obtained from fractional distillation of Crude Oil • Is black or dark brown in colour • Is a visco-elastic material • Does not have a distinct melting point • Gradually softens when heated • More solid at low temperatures and more liquid at high temperatures • Has adhesive properties • Has water proofing properties • Forms good bond with a variety of aggregates

  5. What are Performance Parameters? • Mix and form a good bond with aggregate (at high temperature) • Not melt on the road at highest atmospheric temperature • Not crack at extreme low atmospheric temperature • Be able to withstand repeated cycles of loading and unloading • Be able to withstand repeated cycles of temperature change • Not be inflammable • Be free from impurities

  6. What type of tests do we develop? • Tests should be simple • Tests should replicate the actual field conditions as accurately as possible • Rate of change of properties with time, temperature and load should be measurable or predictable

  7. Modes of Failure

  8. Rutting/ Permanent Deformation

  9. Fatigue Cracking

  10. Low Temperature Cracking

  11. Low Temperature Cracking

  12. Methods of Classification

  13. Methods of Classification Viscosity of TFOT Performance Penetration Viscosity

  14. Penetration Based System • More than 100 years old • Has stood the test of time • Based on Penetration at 25 OC • Penetration 30 to 100 are suitable for road construction • Harder grades suitable for heavier traffic loads • Softer grades suitable for light traffic loads

  15. Viscosity Based System • Viscosity is considered to be the primary property • Most tests over lap with that of Penetration based classification • Classified as VG 10, 20, 30 and 40 based on viscosity at 60OC

  16. Viscosity of TFOT Residue Based System • Simulates aging of Bitumen • Viscosity ranging from 40 to 700 pascal seconds at 60OC are suitable for road construction • Most tests overlap with that of Penetration based classification • Higher viscosity for higher traffic and low viscosity for lower traffic

  17. Performance Based System • Radically different from Penetration & Viscosity based system • New set of tests developed for better simulation of field conditions • Long term & short term aging taken into consideration • Classification is based on the maximum and minimum pavement temperature that the Bitumen can withstand (PG 58 -22)

  18. Test methods

  19. Penetration Test • Arbitrary Empirical Number • Depth of penetration of a standard size needle under standard test conditions • Very easy to perform at field level • Helps in classification and traceability

  20. Softening Point Test • Arbitrary test to indicate the temperature at which bitumen is more of a liquid and less of a solid • Higher softening points indicate higher resistance to melting on road • Higher resistance to melting indicates higher rutting resistance

  21. Ductility Test • Arbitrary empirical test to measure the cohesive strength • Cohesive strength is loosely related to the fatigue strength • Testing temperatures may vary from country to country and from grade to grade also

  22. Fraass Breaking Point • Tests low temperature properties • This mode of failure likely to take place only when temperatures are less than 0OC

  23. Viscosity Test • Viscosity at 135OC is a fair indicator of the coating ability of Bitumen • Viscosity at 65OC is a replacement for Softening Point test and is an indicator of the ability of Bitumen to resist rutting.

  24. Thin Film Oven Test • This test simulates the process of aging of Bitumen during mixing and laying • Sample is kept in an oven at 163OC for 5 hours • TFOT aged bitumen can be tested for Penetration, Softening Point, Ductility, Viscosity, etc.

  25. Other Tests • Penetration ratio or penetration index • Wax content • Specific gravity • Water content • Matter soluble in organic solvents • Flash Point

  26. Performance Grade Tests

  27. Mixing and Laying • Tested in rotational viscometer • Max. viscosity of 3 Pa-s at 135oC

  28. Aging of Bitumen • During Construction • Early in Pavement’s life • Post construction upto two years • Late in pavement’s life • Seven plus years of life Rolling thin film oven test (RTFOT) RTFOT + Pressure Ageing Vessel (PAV)

  29. Rutting • Due to melting of bitumen on the road • Always occurs at max. pavement temp. • Test to be conducted at max. pavement temp. • Tested in Dynamic Shear Rheometer • Complex Shear Modulus G*/Sind min. 1 kPa, @ 10 rad/s for unaged bitumen • G*/Sind min. 2.2 kPa, @ 10 rad/s for RTFOT aged bitumen

  30. Fatigue • Due to repeated loading,unloading cycles • Always occurs near the average pavement temp. • Test to be conducted at average + 4OC pavement temp. • Tested in Dynamic Shear Rheometer • Fatigue Strength G*Sind max. 5000 kPa, @ 10 rad/s for RTFOT + PAV aged bitumen

  31. Low Temp. Cracking • Due to loss of elasticity at very low temp. • Always occurs at lowest pavement temp. • Testing done at min. temp. + 10OC • Bending Beam Rheometer • Creep Stiffness of max. 300,000 kPa, Rate of Change of Creep with load (m-value) min. 0.30 • Direct Tension Test - For Modified Bitumens • Failure strain min. 1%

  32. Performance Vs Tests Low Temperature Cracking Mixing and Laying Fatigue Cracking Rutting Fraass Breaking Point Creep Stiffness Rate of change of Creep Failure Strain Softening Point Viscosity Penetration Complex Shear Modulus Ductility Fatigue Strength Softening Point, Viscosity & Penetration after Aging Viscosity at 135OC

  33. Types of Binders • Tar • Natural Asphalt / Rock Asphalt / Lake Asphalt • Bitumen

  34. Tar • COKE OVEN TAR • Produced at temperatures above 1200OC during manufacturing of coke. • High aromatic content. • Pitch content - 50 %. • LOW AROMATIC TAR • Produced at temperatures 600OC to 700OC. • Less viscous. • Paraffinic in nature. • Pitch content - 35 %.

  35. Natural Asphalt / Rock Asphalt / Lake Asphalt • Naturally occurring Bituminous binder. • Biggest deposits in Trinidad • 100 Acres, • 90 meter deep • 10 to 15 Million MT • Pen - 5 max • Asphalt found in France, Italy & Switzerland - Rock Asphalt.

  36. Bitumen • Conventional Bitumen • Paving Grade Bitumen • Industrial Grade Bitumen • Cutback • Bitumen Emulsions • Modified Bitumen • Modified Bitumen Emulsions

  37. B I T U M E N A VISCO - ELASTIC MATERIAL

  38. Engineering Properties of Bitumen • Bitumen is a visco-elastic material & it’s deformation under stress is a function of both temperature & loading time • At higher temperature &/or longer loading time • Behave as viscous liquids • At low temperature &/or short loading time • Behave as elastic solids • The intermediate range of temperatures, more typical of the conditions in service, result in visco-elastic behaviour.

  39. The Stiffness Concept In solids : E = s e where E = Elastic modulus s = Stress e = Strain

  40. The Stiffness Concept In visco-elastic material : St,T = s et,T Where St,T = Stiffness modulus at specific time t & Temp. T. s =Stress et,T=Strain at specific time t & temp. T.

  41. COMPOSITION B I T U M E N

  42. Elemental Analysis Carbon 82 - 88 % Hydrogen 8 - 11 % Sulphur 0 - 6 % Oxygen 0 - 1.5 % Nitrogen 0 - 1 %

  43. Chemical Composition Decreases Penetration Increases Penetration Increases Softening Point, reduces Penetration Index, increases Viscosity Reduces Shear Susceptibility

  44. BITUMEN PRODUTION PROCESSES

  45. Bitumen Production Process • Atmospheric Distillation • Vacuum Distillation • Air Blowing of Short Residue • Propane Deasphalting

  46. Atmospheric Distillation • Only very heavy Crudes like Boscan Crudes can be processed • The atmospheric unit can be adjusted in such a manner that the residue of the atmospheric unit meets the bitumen specifications without any alteration and can be directly used as bitumen • Very little scope to control Bitumen properties

  47. Vacuum Distillation • Heavy Crudes like Arab Heavy can be processed • Vacuum Distillation Unit (Vacuum Tower Bottoms) may meet the specifications of paving grade bitumen without any further processing • Depending on origin of the crude, bitumen with penetration ranging form 35 to 300 can be produced directly from the Vacuum Distillation Unit • Still little scope for controlling the properties of Bitumen

  48. Air Blowing of Short Residue • Relatively lighter Crudes can be used • The VTB is rectified by blowing hot air into it • The process is controlled by regulating the temperature, rate of blowing, duration of blowing and usage of catalyst • When hot air is blown into VTB the process of oxidation takes place resulting in increase in molecular weight. The increase in molecular weight is due increase in Asphaltenes and Resins accompanied by reduction in Aromatics and Saturates • Catalyst like Ferric Chloride, Phosphorus Pentoxide, Sulphuric Acid or Hydrochloric Acid can also be used to reduce the blowing time. However, the catalyst is consumed in the process of blowing and therefore strictly speaking it is not really catalytic reaction • Catalytic blowing results in bitumen with higher penetration for the same softening point

  49. Propane Deasphalting • This process takes advantage of the complex internal solubility parameters of bitumen • In the Propane Deasphalting process Propane or mixture of Propane and Butane in liquid state is introduced at the bottom of the column • Under controlled conditions the Aromatics get dissolved in Propane and the resultant material left at the bottom is Propane Deasphalted Asphalt • This has very high concentration of Asphaltenes and Resins and confirms to specifications of harder grades of Bitumen • This can be blended with VTB to get a wide variety of bitumen

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