2.bituminous mix

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1. Bituminous Mix Design Archana M R Assistant Professor, Department of Civil Engineering, RV College of Engineering, Bangalore 28th January 2016 2. Bituminous Mix Design…
  • 1. Bituminous Mix Design Archana M R Assistant Professor, Department of Civil Engineering, RV College of Engineering, Bangalore 28th January 2016
  • 2. Bituminous Mix Design • Objective: – Develop an economical blend of aggregates and asphalt that meet design requirements Requirements: • Sufficient asphalt to ensure a durable pavement • Sufficient stability under traffic loads • Sufficient air voids – Upper limit to prevent excessive environmental damage – Lower limit to allow room for initial densification due to traffic • Sufficient workability
  • 3. Marshall mix design • Developed by Bruce Marshall for the Mississippi Highway Department Steps involved: • Select and test aggregate • Select and test asphalt cement – Establish mixing and compaction temperatures • Develop trial blends – Heat and mix asphalt cement and aggregates – Compact specimen (100 mm diameter)
  • 4. Marshall mix design - Procedure Video
  • 5. Marshall mix design criteria Sl. No. Parameter Test Method Specifications as per MoRT&H – V Revision 1 Compaction Level 75 Blows on each side of the sample 2 Marshall stability at 600C, kN AASHTO T 245 9, 12*, 10** 3 Marshall flow, mm AASHTO T 245 2-4, 2.5-4*, 3.5-5** 4 % Air voids 3-5 5 % Voids filled with Asphalt 65-75 Tensile strength ratio AASHTO T 283 80% minimum *Modified Asphalt under hot climate ** Modified asphalt under cold climate Source: Table 500.11, MoRT&H – V Revision
  • 6. Mix design - Calculations 1. Theoretical Maximum Density 2. Bulk Specific Gravity of the mix 3. Percent Air voids 4. Voids in Mineral aggregate 5. Voids filled with bitumen
  • 7. Marshall Properties – for OBC
  • 8. Marshall properties – at OBC Marshall Stability •Laboratory and field results – cannot be matched •If stability is a problem, it necessitates comprehensive study •Helps in determining the consistency of plant produced HMA Flow value •High flow value – Indicates plastic mix •Low Flow value – Indicates mix with higher than normal voids/ insufficient asphalt
  • 9. Marshall properties Unit weight •Magnitude of density achieved in lab – not very important •Field density requirement – expressed as a percent of theoretical density – so that the density is achieved by increased compaction, asphalt content, filler content or any other methods •Satisfactory compaction effort on properly designed mixture – produces high shear strength and reduces permanent deformation Percent Air voids •Higher air voids – must ensure air and water permeability are quite low •Air voids – isolated and not inter- connected •Low air voids – minimize aging of asphalt •Ultimate density in situ – should be 3- 5% air voids
  • 10. Marshall properties Voids filled with bitumen •Maximum aggregate size increases – VMA reduces •Large VFB – Permanent deformation •Low VFB – Inadequate film thickness – oxidation faster, tensile strength greatly affected
  • 11. Thank you
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