1. Russian Engineers Training March 2011
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 1

2. Russian Engineers Training March 2011
Volumetrics
All matter has mass and occupies space
Volumetrics are the relationships between mass and volume
A basic understanding of weight-volume relationships of compacted HMA is important from both a mixture design standpoint and from a field construction standpoint. It is important to understand that mix design is a volumetric process whose purpose is to determine the volume of asphalt cement and aggregates required to produce a mixture with the desired properties.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 2

3. Russian Engineers Training March 2011
Density
Mass
Volume
This slide presents a simple definition of specific gravity – it is simply mass over volume.
Specific gravity is “the ratio of the mass of a unit volume of a material to the mass of the same volume of water at stated temperatures.” The mass of an object divided by its volume is its density, so another way to describe specific gravity is the density of an object divided by the density of water. Conveniently, at 25°C the density of water is g/cm3. Since the density of water is at 25°C, the specific gravity of any object at 25°C is its weight divided by its volume. By knowing the specific gravity of an object, the volume can be calculated after measuring its mass, or the mass can be calculated after measuring its volume. Although the units for specific gravity and density are not the same, the terms are often used interchangeably. In fact, when using the metric units of g/cm3, the values of density and specific gravity are numerically identical.
In the analysis of HMA, the specific gravities of the specific components of the HMA, as well as the specific gravities of the mixture, are used as “bridges” to go between the mass side of the component diagram and the volume side of the component diagram. Specific gravity is abbreviated using the letter G.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 3

4. Specific Gravity, G = ratio of material density to density of water
Russian Engineers Training March 2011
Specific Gravity, G = ratio of material density to density of water
Massa
Volumea
G =
This slide presents a simple definition of specific gravity – it is simply mass over volume.
Specific gravity is “the ratio of the mass of a unit volume of a material to the mass of the same volume of water at stated temperatures.” The mass of an object divided by its volume is its density, so another way to describe specific gravity is the density of an object divided by the density of water. Conveniently, at 25°C the density of water is g/cm3. Since the density of water is at 25°C, the specific gravity of any object at 25°C is its weight divided by its volume. By knowing the specific gravity of an object, the volume can be calculated after measuring its mass, or the mass can be calculated after measuring its volume. Although the units for specific gravity and density are not the same, the terms are often used interchangeably. In fact, when using the metric units of g/cm3, the values of density and specific gravity are numerically identical.
In the analysis of HMA, the specific gravities of the specific components of the HMA, as well as the specific gravities of the mixture, are used as “bridges” to go between the mass side of the component diagram and the volume side of the component diagram. Specific gravity is abbreviated using the letter G.
Massw
Volumew
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 4

5. Volumetric Relationships
Russian Engineers Training March 2011
Volumetric Relationships
Air
Vair
VMA
Absorbed Binder
Binder
Vfa Vb
Vmm
Vba
Aggregate
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).
Vsb
Vse
Vmb
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 5

6. Russian Engineers Training March 2011
Basic Terms
Specific Gravity (G): Gxy
x: b = binder
s = stone (i.e., aggregate)
m = mixture
y: b = bulk
e = effective
a = apparent
m = maximum
Example:
Gmm = gravity, mixture, maximum
(i.e., maximum gravity of the mixture)
Standard definitions used.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 6

7. Russian Engineers Training March 2011
Basic Terms (cont.)
Mass (P) or Volume (V) Concentration: Pxy or Vxy
x: b = binder
s = stone (i.e., aggregate)
a = air
y: e = effective
a = absorbed
Example:
Pb = percent binder
Definitions cont.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 7

8. Russian Engineers Training March 2011
HMA Volumetric Terms
Bulk specific gravity (BSG) of compacted HMA
Maximum specific gravity (Gmm)
Air voids or voids total mix (Va)
Effective specific gravity of aggregate (Gse)
Voids in mineral aggregate, VMA
Voids filled with asphalt, VFA
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.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 8

9. Russian Engineers Training March 2011
BSG of Compacted HMA
AC mixed with agg. and compacted into sample
Mass agg. and AC
Vol. agg., AC, air voids
Gmb =
Bulk Specific Gravity, Gmb - the ratio of the mass in air of a unit volume of the compacted asphalt and aggregate mixture at a stated temperature to the mass in air of equal density of an equal volume of gas-free distilled water at a stated temperature. In other words, the bulk specific gravity, Gmb, is the mass of the asphalt and aggregate mixture divided by the volume, including the air voids.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 9

10. Russian Engineers Training March 2011
Testing
Mixing of asphalt and aggregate
Compaction of sample
Mass of dry sample
Mass under water
Mass saturated surface dry (SSD)
This specific gravity is determined as described in this slide.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 10

11. Russian Engineers Training March 2011
Testing
Obtain mass of dry compacted sample
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.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 11

12. Testing Obtain mass of specimen at SSD
Volumetric Analysis of HMA Mixtures

13. Calculations Gmb = A / ( B - C ) Where: A = mass of dry sample
B = mass of SSD sample
C = mass of sample under water
Volumetric Analysis of HMA Mixtures

14. Maximum Specific Gravity T 209
Russian Engineers Training March 2011
Maximum Specific Gravity T 209
Loose (uncompacted) mixture
Mass agg. and AC
Vol. agg. and AC
Gmm =
Maximum Theoretical Specific Gravity, Gmm - the ratio of the mass in air of a unit volume of the asphalt and aggregate in the mixture at a stated temperature to the mass in air of equal density of an equal volume of gas-free distilled water at a stated temperature. In other words, the maximum theoretical specific gravity, Gmm, is the mass of the asphalt and aggregate mixture divided by the volume, not including the air voids
The test is covered in detail in the CTQP course Plant Level I. The first step is to break the sample into separate particles of less than ¼ inch.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 14

15. Testing Mixing of asphalt and aggregate Mass in air Mass under water
Volumetric Analysis of HMA Mixtures

16. Testing Loose Mix at Room Temperature
Volumetric Analysis of HMA Mixtures

17. Testing Residual Manometer Metal Bowl with Lid Vacuum Pump
Shaker Table
Volumetric Analysis of HMA Mixtures

18. Calculations Gmm = A / ( A - C ) Where: A = mass of dry sample
C = mass of sample under water
Volumetric Analysis of HMA Mixtures

19. Russian Engineers Training March 2011
Air Voids
Calculated using both specific gravities
Gmm – Gmb
Gmm
Air voids (Va) = 100 * Or
Gmb
Gmm
1 -
Air voids (Va) = 100 *
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 19

20. Russian Engineers Training March 2011
Example Calculations
Air voids Va :
Gmb = 2.456
Gmm = 2.535
2.535 – 2.456
2.535
Air voids (Va) = 100 *
Air voids (Va) = 3.1 %
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 20

21. Why Are Air Voids Important?
Russian Engineers Training March 2011
Why Are Air Voids Important?
Related to Rut Resistance
Related to Durability
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 21

22. Effective Specific Gravity
Russian Engineers Training March 2011
Effective Specific Gravity
Surface Voids
Solid Agg.
Particle
Mass, dry
Gse =
Effective Volume
Vol. of water-perm. voids
not filled with asphalt
Effective Specific Gravity, Gse - the ratio of the mass in air of a unit volume of a permeable material (excluding voids permeable to asphalt) at a stated temperature to the mass in air of equal density of an equal volume of gas-free distilled water at a stated temperature. In other words, the effective specific gravity includes the volume of the water permeable voids in the aggregate that cannot be reached by the asphalt
Absorbed asphalt
Effective volume = volume of solid aggregate particle + volume of surface voids not filled with asphalt
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 22

23. Russian Engineers Training March 2011
Effective Specific Gravity
Gse =
100 - Pb Pb
Gmm Gb
This is the equation for calculating the effective specific gravity of an aggregate.
Gse is an aggregate property
Measured With the Mix
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 23

24. Russian Engineers Training March 2011
Example Calculations
Mixed with 5 % asphalt cement
Gmm = 2.535
Gb = 1.03
Gse = =
Example calculation.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 24

25. Russian Engineers Training March 2011
Voids in Mineral Aggregate
VMA =
100 -
Gmb Ps
Gsb
VMA is an indication of film thickness on the surface of the aggregate
Voids in the Mineral Aggregate, VMA - the volume of intergranular void space between the aggregate particles of a compacted paving mixture that includes the air voids and the effective asphalt content, expressed as a percent of the total volume of the compacted paving mixture.
This is the equation for VMA. Gmb is the bulk specific gravity of the mix, Ps is the percent stone (it is the total percent (100) minus the percent asphalt – for a mix with 6.3% asphalt the Ps = 93.7) and Gsb is the bulk specific gravity of the aggregate.
Note: Some states use Gse rather than Gsb to calculate VMA
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 25

26. Russian Engineers Training March 2011
Example Calculations
Given that Gmb = 2.455, Ps = 95%, and Gsb = 2.703
VMA =
(2.455) (95)
2.703
= 13.7
Example calculation.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 26

27. Russian Engineers Training March 2011
Voids Filled with Asphalt
VFA =
100 x
VMA - Va
VMA
Voids Filled with Asphalt, VFA - the percentage portion of the volume of intergranular void space between the aggregate particles that is occupied by the effective asphalt. It is expressed as the ratio of (VMA - Va) to VMA.
VFA is the percent of VMA that is filled with asphalt cement
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 27

28. Russian Engineers Training March 2011
Example Calculations
Given that Va = 3.1 , VMA = 15.8
VFA = X
15.8
= 80.4 %
Example calculation.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 28

29. Russian Engineers Training March 2011
Percent Binder Absorbed
Pba =
100 (
Gse - Gsb
Gsb Gse
) Gb
Pba is the percent of absorbed asphalt by wt. of aggregate
Absorbed Asphalt Content, Pba - the portion of asphalt absorbed into the aggregate particles.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 29

30. Russian Engineers Training March 2011
Percent Binder Absorbed
Example Calculation
Pba =
100 (
2.746*2.703
) 1.03
Example calculation.
Pba = 0.60 %
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 30

31. Russian Engineers Training March 2011
Effective Asphalt Content
Pbe =
Pb -
Pba
100 Ps
The effective asphalt content is the total asphalt content minus the percent lost to absorption.
Effective Asphalt Content, Pbe - the total asphalt content of a paving mixture minus the portion of asphalt absorbed into the aggregate particles.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 31

32. Russian Engineers Training March 2011
Effective Asphalt Content
0.60
100
Pbe =
5 -
x 95
Example calculation.
Pbe
= = 4.43 %
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 32

33. Factors That Influence Volumetric of HMA
Russian Engineers Training March 2011
Factors That Influence Volumetric of HMA
Asphalt viscosity
Mix temperature
Time held at elevated temperature
The volumetric properties of the compacted mixture are dependent on the viscosity of the asphalt cement at the time of the compaction. The viscosity of the asphalt cement is dependent of the temperature of the mixture. If the temperature is high-the viscosity of the asphalt is low and if it is low the viscosity is high. If the viscosity of the asphalt cement is high (or the temperature at time of compaction) the mixture will be difficult to compact in the mold and the air voids will be high. As the temperature of the mixture is held at elevated temperature the lighter ends of the asphalt cement will absorb into the aggregate and the asphalt cement will oxidize. The result will be a stiffer or higher viscosity asphalt. Therefore for Superpave mix designs the criteria of two hours of oven aging for the loose mix has been established. This simulates the absorption and oxidation that will occur in the mix at the hot mix production facility.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 33

34. Factors That Influence Volumetrics
Russian Engineers Training March 2011
Factors That Influence Volumetrics
When Vmm decreases, Gmm increases
Affects calculations:
Gse
Percent binder absorbed
Calculated maximum specific gravity
Air voids
As the asphalt is absorbed into the mix the volume of asphat and aggregates will decrease. If the volume decreases (Vmm), the maximum specific gravity will increase.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 34

35. Important Considerations
Russian Engineers Training March 2011
Important Considerations
Consistent laboratory procedures
Equiviscous mixing temperatures
Mixing times
Curing time to simulate field conditions
It is essential that consistent laboratory procedures are followed and that the curing time in the laboratory simulates what is happening in the field.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 35

36. Russian Engineers Training March 2011
Example Problem
The next series of slides presents an example problem.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 36

37. Russian Engineers Training March 2011
- Example Problem -
Let’s assume we have a compacted HMA mixture with the following properties.
Bulk Specific Gravity of the Mixture - Gmb = 2.425
Theoretical Maximum Specific Gravity - Gmm = 2.521
Asphalt Binder Specific Gravity - Gb = 1.015
Asphalt Content - Pb = 5.0 % (by mass of total mix)
Given this mix data we want to compute the various volumetric properties of the mix.
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 37

38. Russian Engineers Training March 2011
- Example Problem -
Let’s also assume that three stockpiled aggregates were used to manufacture this HMA mixture. The percent of each aggregate and the Bulk Specific Gravity (Gsb) for each is as follows:
Aggregate % of Total Aggregate G sb
Example problem data. A B C
50 %
25 %
2.695
2.711
2.721
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 38

39. Russian Engineers Training March 2011
Example Problem –
Based on the information given for this problem, the following steps should be followed:
Calculate the bulk specific gravity of the combined aggregate
Calculate the effective specific gravity of the aggregate
Calculate the percent absorbed asphalt for the mixture
Calculate the percent effective asphalt for the mixture
Calculate the percent voids in total mix for the mixture
Calculate the percent voids in mineral aggregate for the mixture
Calculate the percent voids filled with asphalt for the mixture
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 39

40. Russian Engineers Training March 2011
Example Problem –
Bulk Specific Gravity of the Combined Aggregate - Gsb
( PA + PB + PC )
Where: PA, PB & PC = Percent by Mass of Each Aggregate in Blend GA,
GB & GC = Bulk Specific Gravity of Each Aggregate
Gsb =
PA PB PC + +
GA GB GC
Based on the information given:
PA = 50%
PB = 25%
PC = 25%
GA = 2.695
GB = 2.711
GC = 2.721
( )
Gsb =
= 2.705 + + + +
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 40

41. Russian Engineers Training March 2011
Example Problem –
Effective Specific Gravity of Aggregate - Gse
100 - Pb
Where: Pb = Percent Asphalt Binder by Total
Mass of Mixture
Gmm = Theoretical Maximum Specific
Gravity of Mixture
Gb = Specific Gravity of Asphalt Binder
Gse = Pb -
Gmm Gb
Based on the information given:
Pb = 5.0 %
Gmm = 2.521
Gb = 1.015
Gse =
= 2.735 -
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 41

42. Russian Engineers Training March 2011
Example Problem –
Percent Absorbed Asphalt Binder - Pba
(100 * Gb) (Gse - Gsb)
Pba =
Gse * Gsb
Where: Gb = Specific Gravity of Asphalt Binder
Gse = Effective Specific Gravity of Aggregate
Gsb = Bulk Specific Gravity of Aggregate
Based on the information given:
Gb = 1.015
Gse = 2.735
Gsb = 2.705
( 100 * ) ( )
Pba =
= 0.41 %
( * )
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 42

43. Russian Engineers Training March 2011
Example Problem –
Percent Effective Asphalt Binder - Pbe
( Pba * Ps )
Where: Pb = Percent Asphalt Binder in Total Mix
Pba = Percent Absorbed Asphalt Binder
in Total Mix
Ps = Percent Aggregate in Total Mix
Pbe =
Pb -
100
Based on the information given:
Pb = 5.0 %
Pba = 0.41 %
Ps = 95.0 %
= 4.61 %
( 0.41 * 95.0 )
100
5.0 -
Pbe =
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 43

44. Russian Engineers Training March 2011
Example Problem –
Percent Voids in Total Mix - Va
( Gmm - Gmb )
Where: Gmm = Theoretical Maximum
Specific Gravity of Mix
Gmb = Bulk Specific Gravity of Mix
Va, % = 100 *
Gmm
Based on the information given:
Gmm = 2.521
Gmb = 2.425
( )
Va = 100 *
= 3. 8 %
2.521
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 44

45. Russian Engineers Training March 2011
Example Problem –
Percent Voids in Mineral Aggregate - VMA
( Gmb * Ps )
Where: Gmb = Bulk Specific Gravity of Mix
Ps = Percent Aggregate in Total Mix
Gsb = Bulk Specific Gravity of
Aggregate
VMA, % = 100 -
Gsb
Based on the information given:
Gmb = 2.425
Ps = 95.0 %
Gsb = 2.705
( * 95.0 )
VMA = 100 -
VMA = 100 -
VMA = 100 -
= 14.8
2.705
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 45

46. Russian Engineers Training March 2011
Example Problem –
Percent Voids Filled with Asphalt - VFA
( VMA - Va)
Where: VMA = percent Voids in Mineral
Aggregate
Va = percent Voids in Total Mix
VFA, % = 100 *
VMA
Based on the information given:
VMA = 14.8 %
Va = 3.8 %
( )
VFA = 100 *
VFA = 100 *
= 74.3 %
14.8
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 46

47. Example Problem - Volumetric Equations
Russian Engineers Training March 2011
Example Problem - Volumetric Equations
Summary
Gsb = 2.705
Gse =
Pba , % = %
Pbe , % = %
Va, % = 3.8 %
VMA , % = %
VFA, % = %
Volumetric Analysis of HMA Mixtures
Volumetric Analysis of HMA Mixtures 47

48. Questions – does it all make sense?
Volumetric Analysis of HMA Mixtures