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

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

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 1.000 g/cm3. Since the density of water is 1.000 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

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 1.000 g/cm3. Since the density of water is 1.000 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

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

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

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

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

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

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

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

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

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

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

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

Testing Loose Mix at Room Temperature Volumetric Analysis of HMA Mixtures

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

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

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

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

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

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

Russian Engineers Training March 2011 Effective Specific Gravity Gse = 100 - Pb 100 - 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

Russian Engineers Training March 2011 Example Calculations Mixed with 5 % asphalt cement Gmm = 2.535 Gb = 1.03 100 - 5 100 - 5 2.535 1.03 Gse = = 2. 746 Example calculation. Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 24

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

Russian Engineers Training March 2011 Example Calculations Given that Gmb = 2.455, Ps = 95%, and Gsb = 2.703 VMA = 100 - (2.455) (95) 2.703 = 13.7 Example calculation. Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 26

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

Russian Engineers Training March 2011 Example Calculations Given that Va = 3.1 , VMA = 15.8 VFA = 100 X 15.8 - 3.1 15.8 = 80.4 % Example calculation. Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 28

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

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

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

Russian Engineers Training March 2011 Effective Asphalt Content 0.60 100 Pbe = 5 - x 95 Example calculation. Pbe = 5 - 0.57 = 4.43 % Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 32

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

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

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

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

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

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

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

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 ( 50+ 25 + 25 ) Gsb = = 2.705 50 25 25 + + + + 2.695 2.711 2.721 Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 40

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 = 100 Pb - Gmm Gb Based on the information given: Pb = 5.0 % Gmm = 2.521 Gb = 1.015 100- 5.0 Gse = = 2.735 100 5.0 - 2.521 1.015 Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 41

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 * 1.015 ) (2.735 - 2.705 ) Pba = = 0.41 % ( 2.735 * 2.705 ) Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 42

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

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 (2.521 - 2.425 ) Va = 100 * = 3. 8 % 2.521 Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 44

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 ( 2.425 * 95.0 ) VMA = 100 - VMA = 100 - VMA = 100 - = 14.8 2.705 Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 45

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 % ( 14.8 - 3.8 ) VFA = 100 * VFA = 100 * = 74.3 % 14.8 Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 46

Example Problem - Volumetric Equations Russian Engineers Training March 2011 Example Problem - Volumetric Equations Summary Gsb = 2.705 Gse = 2.735 Pba , % = 0.41 % Pbe , % = 4.61 % Va, % = 3.8 % VMA , % = 14.8 % VFA, % = 74.3 % Volumetric Analysis of HMA Mixtures Volumetric Analysis of HMA Mixtures 47

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