Block 12 HMA Volumetrics 13

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  • Volumetric calculations are the foundation of any good mix design. By the end of this block the student will understand: * HMA volumetric terms. * Important factors which can influence key mass-volume relationships and calculations.
  • As with aggregates, it is the specific gravities of materials which define the relationships between mass and the volume it occupies. Air voids, VMA, and VFA are the volumetric measurements which are used in mix design calculations.
  • Mass determinations are usually simple: you place a material on a scale and read the mass. In HMA, it is determining key volumes which proves to be difficult. Think of the basic phase diagram outline as an empty bucket. The first thing you add to the bucket is the aggregate. The volume of aggregate has two components: volume of the solid particle and volume of the water-permeable voids. The next thing that is added to the bucket is the asphalt cement. Because the aggregate has surface voids, some of the asphalt fills a portion of these voids. The remainder of the asphalt remains on the surface of the aggregate. This is the asphalt that is available for “sticking” the aggregate together and is referred to as the “effective” asphalt. When the sample is compacted, the total volume will also contain a percentage of air voids. VMA is the sum of the air voids and the volume of effective asphalt (i.e., the asphalt film).
  • This slide provides a review of all of the volumetric variables used in this section.
  • The specific gravity of the compacted sample is defined in this slide.
  • This specific gravity is determined as described in this slide.
  • The mass of the oven dry specimen is being determined in this photograph. The next step is to place the specimen in the water bath directly below the scale (not shown) and determine its mass under water.
  • Calculations are simple.
  • This slide provides a review of all of the volumetric variables used in this section.
  • Maximum specific gravity is the densest configuration that the mix can assume (0% air voids). This value, along with the compacted specific gravity is used to calculate air voids in the compacted specimen.
  • There are three steps in determining the maximum specific gravity.
  • This step removes any air trapped between the asphalt binder-coated aggregate particles. The metal bowl is partially filled with water, a known mass of loose mix is added. More water is added to cover the mix and the lid is placed on top. The bowl is then clamped in the shaker unit. The vacuum is increased until the residual manometer reads 30 mm of mercury and the shaking action is started. The sample is vacuumed for 10 minutes. At the end of the this step, the vacuum is shut off and the pressure released slowly so that air is not pulled back into the mix. The lid is then removed and the bowl with the mix is placed in the bowl holder in the water bath (not shown). The mass of the sample under water is recorded after 10 minutes.
  • The maximum specific gravity calculations are also simple.
  • This slide provides a review of all of the volumetric variables used in this section.
  • Once both test results are obtained, the air voids in the compacted sample are calculated.
  • The effective aggregate specific gravity is the ratio of the mass of the aggregate divided by the volume of the solid aggregate particle and the surface voids not filled with asphalt binder. This property is calculated by testing the asphalt binder-coated aggregate.
  • This aggregate property is calculated using the maximum specific gravity of the mixture, the percent of asphalt (by mass) in the sample used to determine the maximum specific gravity, and the specific gravity of the asphalt. If the asphalt specific gravity is not known, an assumption of 1.000 is usually made.
  • This slide provides a review of all of the volumetric variables used in this section.
  • VMA is calculated using the bulk specific gravity of the compacted sample, the percent of stone (i.e, 100 - the percent asphalt binder), and the bulk specific gravity of the aggregate. Because it is difficult and time consuming to obtain the bulk specific gravity of the aggregate, a number of states are substituting the effective specific gravity of the aggregate. This value is simply a calculation using test results that have to be determined anyway. Altering the VMA calculation this way will result in an increase in the value. If this substitution is made, then either a correction factor is needed or the VMA requirements need to be adjusted for local aggregate properties.
  • This slide shows a simple calculation using the bulk specific gravity of the aggregate.
  • VFA is the volume of the effective asphalt binder and is expressed as the percent of the VMA which is asphalt binder.
  • As stated earlier, mass relationships are simple. Both the mass of asphalt binder and aggregates are expressed as a percentage of the total mass of the mixture.
  • Volumetric terms which use P with a subscript indicate percent by mass of a particular component. In this case, the percent of asphalt binder absorbed by the aggregate is expressed as a percent of the mass of aggregate. Both aggregate and mixture specific gravities are needed to get this value.
  • This slide provides a review of all of the volumetric variables used in this section.
  • The percent effective asphalt binder is expressed as a percent of the total mass of the mix rather than just the aggregate.
  • This slide provides a review of all of the volumetric variables used in this section.
  • A predetermined mass of the dry loose mix is placed in the metal bowl and covered with water. A vacuum lid is fitted and secured to the bowl and placed on a vibratory shaker table. The vacuum pump is started and the manometer reading used to determine the proper vacuum adjustment. Once the proper pressure is obtained, the shaker table is started. This provides gentle agitation to help in the removal of any air voids between particles. This is continued for 5 to 15 minutes. All of this effort is to ensure that the air voids are as close as possible to zero. At the end of this time, the vacuum pump and shaker are turned off and the pressure gradually released. The container is removed from the shaker, the lid removed and the bowl with the sample is suspended under water for 10 minutes. At the end of this time and the mass under water is determined (the tare of the bowl is factored out).
  • The loose mix is warmed and separated into loose, individually coated aggregates.
  • There are three basic steps in determining the maximum specific gravity.
  • The maximum specific gravity determines the mass and volume that would be occupied by the mix if there were no air voids present.
  • As with the specific gravity equations for aggregates, this equation is also the relationship between the mass of the specimen to the mass (volume) of water it displaces.
  • The last step is to determine the mass of saturated surface dry specimen (SSD). SSD is obtained by quickly blotting the sample so that the surface is still wet but not shiny.
  • Air voids are calculated from the bulk and maximum specific gravities. The ratio of these two specific gravities is actually the volume percent of solids (in decimal form).
  • This slide provides a simple example of how to use the laboratory data to calculate air voids.
  • The effective specific gravity of the aggregate is determined after the aggregate is coated with asphalt binder. The mass is the dry mass of the aggregate without asphalt binder but the volume is the volume of the dry particle plus only the surface.
  • This slide shows a simple example of this calculation.
  • Block 12 HMA Volumetrics 13

    1. 1. Senior/Graduate HMA Course Hot Mix Asphalt (HMA) Volumetric PropertiesHMA Volumetrics 1
    2. 2. HMA Volumetric Terms• Bulk specific gravity (BSG) of compacted HMA• Maximum specific gravity• Air voids• Effective specific gravity of aggregate• Voids in mineral aggregate, VMA• Voids filled with asphalt, VFAHMA Volumetrics 2
    3. 3. Volumetric Relationships Va VMA Vb V ba Vse Vmm Vmb VsbHMA Volumetrics 3
    4. 4. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 4
    5. 5. BSG of Compacted HMA • Asphalt binder mixed with aggregate and compacted into a sample Mass agg. and AC Gmb = Vol. agg., AC, air voidsHMA Volumetrics 5
    6. 6. Testing • Mixing of asphalt and aggregate • Compaction of sample • Mass of dry sample • Mass under water • Mass saturated surface dry (SSD)HMA Volumetrics 6
    7. 7. Testing Obtain mass of dry compacted sampleHMA Volumetrics 7
    8. 8. Testing Obtain mass of specimen at SSDHMA Volumetrics 8
    9. 9. Calculations• Gmb = A / ( B - C ) Where: A = mass of dry sample B = mass of SSD sample C = mass of sample under waterHMA Volumetrics 9
    10. 10. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 10
    11. 11. Maximum Specific Gravity Loose (uncompacted) mixture Mass agg. and AC Gmm = Vol. agg. and ACHMA Volumetrics 11
    12. 12. Testing • Mixing of asphalt and aggregate • Cool to room temperature • Mass in air • Mass under waterHMA Volumetrics 12
    13. 13. Testing Loose Mix at Room TemperatureHMA Volumetrics 13
    14. 14. Testing Residual Manometer Metal Bowl with Lid Vacuum PumpShaker Table HMA Volumetrics 14
    15. 15. Calculations• Gmm = A / ( A - C ) Where: A = mass of dry sample C = mass of sample under waterHMA Volumetrics 15
    16. 16. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 16
    17. 17. Percent Air Voids Calculated using both specific gravities Gmb Air voids = ( 1 - ) 100 Gmm Mass agg + AC Vol. agg, AC, Air Voids Vol. agg, AC Mass agg + AC = Vol. agg, AC, Air Voids Vol. agg, ACHMA Volumetrics 17
    18. 18. Example Calculations • Air voids: • Gmb = 2.222 • Gmm = 2.423 ( 1 - 2.222 / 2.423 ) 100 = 8.3 %HMA Volumetrics 18
    19. 19. Effective Specific GravitySurface Voids Mass, dry Gse = Effective Volume Solid Agg. Vol. of water-perm. voids Particle not filled with asphalt Absorbed asphalt Effective volume = volume of solid aggregate particle + volume of surface voids not filled with asphaltHMA Volumetrics 19
    20. 20. Effective Specific Gravity 100 - Pb Gse = 100 - Pb Gmm Gb Gse is an aggregate propertyHMA Volumetrics 20
    21. 21. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 21
    22. 22. Example Calculations • Mixed with 5 % asphalt cement • Gmm = 2.535 • Gb = 1.03 100 - 5 Gse = = 2. 770 100 - 5 2.535 1.03HMA Volumetrics 22
    23. 23. Voids in Mineral Aggregate VMA = 100 - Gmb Ps Gsb VMA is an indication of film thickness on the surface of the aggregateHMA Volumetrics 23
    24. 24. Example Calculations • Given that Gmb = 2.455, Ps = 95%, and Gsb = 2.703 (2.455) (95)VMA = 100 - = 13.7 2.703 HMA Volumetrics 24
    25. 25. Voids Filled with Asphalt VFA = VMA - Va 100 x VMA VFA is the percent of VMA that is filled with asphalt cementHMA Volumetrics 25
    26. 26. Mass Relationships Air Ma = 0 Mb = P b MT Asphalt MT = Mb + Ms Aggregate Ms = Ps MTHMA Volumetrics 26
    27. 27. Percent Binder Absorbed Pba = Gse - Gsb 100 ( ) Gb Gsb Gse Pba is the percent of absorbed asphalt by mass of aggregateHMA Volumetrics 27
    28. 28. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 28
    29. 29. Effective Asphalt Content Pba Pbe = Pb - Ps 100 The effective asphalt content is the total asphalt content minus the percent lost to absorption (based on mass of total mix).HMA Volumetrics 29
    30. 30. Summary of Terms • VMA = Voids in mineral aggregates • Va = Air voids • VFA = Voids filled with asphalt binder • Gb = Specific gravity, asphalt binder • Gse = Effective specific gravity of aggregate • Gsb = Bulk specific gravity of aggregate • Pbe = % by mass of effective asphalt binder • Pb = % by mass of total asphalt binder • Pba = % by mass of absorbed asphalt binder • MT = Total mass • Ms = Mass of solids • Mb = Mass of asphalt binder • Gmb = Specific gravity of compacted HMA • Gmm = Maximum specific gravity of loose HMAHMA Volumetrics 30
    31. 31. Hot Mix Asphalt (HMA) Volumetric Properties Using Phase DiagramsHMA Volumetrics 31
    32. 32. VOL (cm3 ) Gmb = 2.329 MASS (g) air effective asphalt Gb = 1.015 Pb = 5% by mix absorbed asphalt1.000 aggregate Gsb = 2.705 Gse = 2.731 HMA Volumetrics 32
    33. 33. VOL (cm3 ) Gmb = 2.329 MASS (g) air Ma = 0 effective asphalt Gb = 1.015 Pb = 5% by mix absorbed asphalt1.000 Mm = 1.0 x 2.329 x 1.0 = 2.329 aggregate Gsb = 2.705 Gse = 2.731 M= V x G x 1.000 HMA Volumetrics 33
    34. 34. VOL (cm3 ) Gmb = 2.329 MASS (g) air 0 effective asphalt Gb = 1.015 Mb = 0.05 x 2.329 =0.116 Pb = 5% by mix absorbed asphalt1.000 2.329 aggregate Gsb = 2.705 Gse = 2.731 Ms = 2.329 - 0.116 = 2.213 HMA Volumetrics 34
    35. 35. VOL (cm3 ) MASS (g) air 0 effective asphalt Gb = 1.015 0.116 absorbed asphalt1.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Vse = 2.213 = 0.810 M 2.731x 1.0 Vsb = 2.213 = 0.818 V= G x 1.000 2.705x 1.0 HMA Volumetrics 35
    36. 36. VOL (cm3 ) MASS (g) air 0 effective asphalt 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt1.000 2.329 aggregate 0.818 0.810 Gsb = 2.705 2.213 Gse = 2.731 M Vb = 0.116 = 0.114 1.015 x 1.0 V= G x 1.000 Vba = 0.818 - 0.810 = 0.008 HMA Volumetrics 36
    37. 37. VOL (cm3 ) MASS (g) 0.076 air 0 effective asphalt 0.106 Gb = 1.015 0.114 0.116 0.008 absorbed asphalt1.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Vbe = 0.114 - 0.008 = 0.106 Va = 1.000 - 0.114 - 0.810 = 0.076 HMA Volumetrics 37
    38. 38. VOL (cm3 ) MASS (g) 0.076 air 0 0.106 effective asphalt 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 0.810 Gsb = 2.705 2.213 Gse = 2.731 M= V x G x 1.000 Mbe = 0.106 x 1.015 x 1.000 = 0.108 Mba = 0.116 - 0.108 = 0.008 HMA Volumetrics 38
    39. 39. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 effective asphalt 0.106 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Air Voids = 0.076 x 100 = 7.6 % VMA = Vbe + Va = ( 0.106 + 0.076 ) x 100 = 18.2 % HMA Volumetrics 39
    40. 40. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 0.106 effective 0.108 0.114 asphalt 0.116 Gb = 1.015 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 0.810 Gsb = 2.705 2.213 Gse = 2.731 Air Voids = 7.6 % VMA = 18.2 % VFA = ( 0.106 / 0.182 ) x 100 = 58.2 % HMA Volumetrics 40
    41. 41. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 effective asphalt 0.106 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Air Voids = 7.6 % Eff. Asp. Cont. = ( 0.108 / 2.329 ) x 100 = 4.6 % VMA = 18.2 % VFA = 58.2 % HMA Volumetrics 41
    42. 42. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 effective asphalt 0.106 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 0.810 Gsb = 2.705 2.213 Gse = 2.731Air Voids = 7.6% Effective Asphalt Content = 4.6%VMA = 18.2 % Abs. Asph. Cont. = ( 0.008 / 2.213 ) x 100 = 0.4%VFA = 58.2 % HMA Volumetrics 42
    43. 43. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 effective asphalt 0.106 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Air Voids = 7.6% Max Theo Sp Grav = 2.329 = 2.521 VMA = 18.2 % 1.000 - 0.076 VFA = 58.2 % 1.000 HMA Volumetrics 43
    44. 44. VOL (cm3 ) MASS (g) 0.076 air 0 0.182 effective asphalt 0.106 0.108 0.114 Gb = 1.015 0.116 0.008 absorbed asphalt 0.0081.000 2.329 aggregate 0.818 Gsb = 2.705 0.810 2.213 Gse = 2.731 Air Voids = 7.6% Effective Asphalt Content = 4.6% VMA = 18.2 % Absorbed Asphalt Content = 0.4% VFA = 58.2 % Max Theo Sp Grav = 2.521 HMA Volumetrics 44
    45. 45. QUESTIONS ?HMA Volumetrics 45

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