# Presentation: 535509

## Asphalt Cements

**Background**
**History of Specifications**

**Notes:**
This block of instruction will cover traditional penetration and viscosity grading systems used in the US.  While the Superpave binder specification is quickly replacing these specifications in practice, the vast majority of the literature will refer to these standards.  People in this industry  also commonly ask “So, what AC grade is a PG 64-22?”.  These traditional specifications will remain the baseline against which field experience is translated into an understanding of the new Superpave binder specification.

At the conclusion of this block the student will understand:
*  How to use traditional binder specifications
*  The limitations of these specifications which led to the development of the Superpave binder specification.

This material is covered in detail in Chapter 2 “Asphalt Refining, Uses, and Properties” in the recommended text book.

## Background

**Asphalt**
** ****Soluble in petroleum products**
** ****Generally a by-product of petroleum distillation process**
**Can be naturally occurring**

**Tar**
**Resistant to petroleum products**
**Generally by-product of coke (from coal) production**

**Notes:**
Students commonly use the words “asphalt” and “tar” interchangeably.  However, asphalt is actually a waste product from the refining of petroleum crude oil while tar is a coal by-product.  These chemical distinctions are important in a selecting the appropriate product for a given application.

For example, if protection from oil and fuel spills is desired, then a coating which will not be dissolved by these products is needed.  Since motor oils, fuel, and asphalt are all derived from petroleum, any spills on this pavement can damage the asphalt-based coating as well as the asphalt concrete.  The old chemistry rule-of-thumb applies: Like dissolves like.  Because tar is a coal rather than asphalt-based product, sealers from this material will not be damaged by petroleum  product spills.

## Background

**First US hot mix asphalt (HMA) constructed in 1870’s**
**Pennsylvania Ave.**
**Used naturally occurring asphalt from surface of lake on Island of Trinidad **
**Two sources**
**Island of Trinadad**
**Bermudez, Venezuela**

**Notes:**
The first paved roadway in the United States was Pennsylvania Avenue in front of the White House.  This pavement was constructed with an asphalt product quarried from a naturally occurring “lake” of asphalt on the island of Trinidad off the coast of Venezuela.  A second source of this type of asphalt product can be found in Bermudez, Venezuela.  These asphalts are still used today.  In fact, a Trinidad lake asphalt project was placed near Mobile, Alabama in July, 1998.

Each lake asphalt has consistent but different amounts of bitumen, inorganic material.  Because of these consistent differences, the amount of solvent-insoluble inorganic material is one common method used to identify and specify the lake asphalt source.  This solubility test was used in all subsequent asphalt cement specifications throughout the 20th century.

## Background

**Each lake asphalt source very consistent **
**Used solubility test to determine source **
** ****Insolubles differed substantially between sources**
**Demand for paved roads exceeded the supply of lake asphalts in late 1800’s**
**Led to use of petroleum asphalts**

**Notes:**
During the late 1800's and early 1900's the demand for paved roads increased so fast that the time-intensive processing and shipping of lake asphalt was limiting the miles of paved roads constructed each year.  This led to the increasing use of petroleum refinery-based asphalts.  It is interesting to note that these asphalts were originally considered inferior to lake asphalt because of their crude source-dependent material properties.    

## Petroleum-Based Asphalts

**Asphalt is waste product from refinery processing of crude oil**
**Sometimes called the “bottom of the barrel”**
**Properties depend on:**
**Refinery operations**
**Composition crude source-dependent**

**Gasoline**
**Kerosene**
**Lt. Gas Oil**
**Diesel**
**Motor Oils**
**Asphalt**

**Barrel of Crude Oil**

**Notes:**
A number of products are obtained from one barrel of crude.  Asphalt cement is what is left after the more volatile products are removed and it is commonly referred to as the “bottom of the barrel”.

## Asphalt Cement Components

**Asphaltenes**
**Large, discrete solid inclusions (black)**
**High viscosity component**
**Resins**
**Semi-solid or solid at room temperature**
**Fluid when heated**
**Brittle when cold**
**Oils**
**Colorless liquid**
**Soluble in most solvents**
**Allows asphalt to flow**

**Notes:**
The simplest general compositional model considers asphalt cements to be made up of asphaltenes, resins, and oils.  The combination of the resins and oils is also referred to as the maltenes.

Asphaltene contents vary considerably from asphalt to asphalt.  Low concentrations have been linked to tenderness in the HMA by some researchers.

Resins are credited with dispersing the solid asphaltene particles in the asphalt.  Oxidation of resins produce asphaltene-type molecules.

Oils are soluble in most solvents.   Upon oxidation, they produce both resin and asphaltene-type molecules.

## Refinery Operation

***Refinery Operation***

**FIELD STORAGE**

**PUMPING****STATION**

**LIGHT DISTILLATE**

**HEAVY DISTILLATE**

**PROCESS**
**UNIT**

**ASPHALT**
**CEMENTS**

**FOR PROCESSING INTO**
**EMULSIFIED AND**
**CUTBACK ASPHALTS**

**STILL**

**AIR**

**AIR**
**BLOWN**
**ASPHALT**

**STORAGE**

**TOWER**
**DISTILLATION**
**REFINERY**

**RESIDUUM**

**OR**

**GAS**

**PETROLEUM**

**SAND AND WATER**

**CONDENSERS **
**AND**
** ****COOLERS**

**TUBE**
**HEATER**

**MEDIUM DISTILLATE**

**Notes:**
Distillation is used to separate the various crude fractions by boiling point ranges.  The crude oil is heated in a large furnace to about 343 oC and partially vaporized.  The remaining material is transferred to a distillation tower.  Different fractions reach their boiling point ranges at various heights in the tower.  When the temperature is reduced, each material condenses on a tray and is drawn off at each level.

## Types

**Asphalt cements**
**Generally refinery produced material**
**Air blown asphalt cements **
**Cutbacks**
**Asphalt cements “cut” with petroleum solvents**
**Emulsions**
**Mixture of asphalt cement, water, and emulsifying agent**

**Notes:**
The residuum or “resid” from the distillation process is used to make various asphalt cement products.

## Air Blown Asphalt Cement

**Notes:**
This process is used to increase the viscosity of the resid to produce products such as roofing asphalts.  Oxidation hardening of the asphalt cement  due to air being continually injected results in a large increase in viscosity.  This process can also be used to reduce the temperature susceptibility of a paving-grade asphalt cement. 

## Cutbacks

**Rapid cure (RC) (Naphtha or Gasoline)**
**High volatility of solvent**
**Tack coats, surface treatments**
**Medium cure (MC) (Kerosene)**
**Moderate volatility**
**Stockpile patching mix**
**Slow cure (SC) (Low viscosity oil)**
**Low volatility**
**Prime coat, dust control**

**Notes:**
Cutbacks are liquid at room temperature and are manufactured by adding or “cutting” asphalt cements with petroleum solvents.  The volatility of the solvent dictates the rate at which the solvent evaporates.  How fast the solvent escapes into the atmosphere regulates how fast a mixture of cutback and aggregate will set.  Environmental regulations are increasingly limiting the use of these products.

## Emulsions

**Emulsifier gives surface charge to asphalt droplets suspended in water medium**
**Anionic**
**Negative charge**
**Alkaline**
**Good with limestones (positive charge)**
**Cationic **
**Positive charge**
**Acid**
**Good with silica gravels (negative charge)**

**Notes:**
Emulsions are produced by blending asphalt cements, water and an emulsifier (e.g. soap)  in a high shear colloid mill.  The resulting asphalt droplet suspended in the water has a charge which reflects the chemistry of the emusifier.  The charge of the emulsion is usually selected so that it is opposite that of the aggregate to promote adhesion of the asphalt to the aggregate surface.

Emulsions are an asphalt-based product which is also liquid at room temperature.  

## Purchasing of Asphalt Cements

**Need to be able to specify desirable characteristics**
**“****Desirable characteristics” have evolved over time and with increasing technological advances**
**Purchasing requires *****specifications***

**Notes:**
In order to purchase a product, the desirable characteristics and important material properties must be known.  When these parameters are presented in written form, they are called specifications.

## Early Specifications

**Lake Asphalts**
**Appearance****	**
**Solubility in carbon disulfide**
**Petroleum asphalts (early 1900’s)**
**Consistency**
**Chewing**
**Penetration machine**
**Measure  consistency**

**Notes:**
The first approach to characterizing the stiffness of an asphalt cement was to chew on it.  An engineer would take a small sample of asphalt, roll it into a ball, and place it between his teeth.  The pressure required to deform the ball was considered an indication of the stiffness of the asphalt.  However, this method was very subjective and could not be used to routinely specify the particular requirements of an asphalt cement for a given construction project.  These drawbacks eventually led to the development of the penetration test.

## Penetration Testing

**Sewing machine needle**
**Specified load, time, temperature**

**Notes:**
The penetration test started out using a No. 2 sewing machine needle mounted on a shaft for a total mass of 100 g.  This needle was allowed to sink into (penetrate) a container of asphalt cement at room temperature (25 oC) for 5 seconds.  The consistency (stiffness) of a given asphalt was reported as the depth in tenths of a millimeter (dmm) that the needle penetrated the asphalt.

## Penetration Specification

**  ****Five Grades**
** ****40 - 50**
** ****60 - 70**
** ****85 - 100**
** ****120 - 150**
** ****200 - 300**

**Notes:**
This test was used to standardize the penetration grading system approach for specifying asphalt cements.   This specification uses the penetration of the original asphalt cement in the grade names.  That is, a 120-150 penetration grade asphalt will have a penetration value for the original asphalt of between 120 and 150 tenths of a millimeter.

## Penetration Gradation Specification

**Uses penetration results to specify**
**Adds**
**Flash point test**
**Ductility**
**Solubility**
**Thin film oven aging**
**Penetration**
**Ductility**

**Notes:**
Other tests have been added to address safety issues (the flash point test), the ability of the asphalt to deform without breaking (ductility test), and the influence of heat hardening on asphalt cement properties (thin film oven test).

## Flash Point (Safety)

**Thermometer**

**Cup filled with asphalt**

**Wand attached to gas line**

**Notes:**
If an asphalt cement is heated to a high enough temperature, it gives off sufficient vapors to flash (ignite) in the presence of a spark or open flame.  The Cleveland Open Cup test determines the temperature at which this flash occurs.

In this test, a small sample of asphalt is poured into the brass cup which is placed over an electric heater.  A thermometer is submerged to a prescribed depth into the asphalt and used to monitor the temperature rise.  When the temperature gets close to the suspected flash point, the gas line is turned on and a small flame lit at the end of the wand.  The  flash point is the temperature at which a small blue flicker around the inside of the cup is seen as the wand is passed horizontally  over the surface of the cup.

## Ductility

**Notes:**
This test evaluates the ability of an asphalt sample to stretch at a rate of 5 cm/min at 25oC.  The distance the samples can be pulled is measured directly from the centimeter scale mounted to the top of the tank.

The significance of the ductility test to indicate performance-related properties has been debated for a number of years due to its empirical nature and poor reproducibility of test results.

In general, asphalts with lower ductility have a greater tendency to produce pavements which have excessive cracking

## Solubility (Purity)

**Notes:**
A sample of asphalt is dissolved in a solvent then filtered through a Gooch crucible mounted in the top of a vacuum flask.  The amount of insoluble material retained on the filter represents the impurities in the asphalt cement.

## Thin Film Oven

**Outside of Oven**

**Rotating Shelf**

**Pan**

**Thermometer**

**Notes:**
Thin film oven aging is a laboratory procedure for simulating the change in asphalt cement properties which occur during tank storage, mixing and construction processes.  This test can also be used to measure the loss of volatiles in the asphalt cement by determining the percent difference in the mass before and after aging. 

A 50 g sample of asphalt is poured into each of three flat-bottomed pans.  This results in a layer of asphalt of about 3.2 mm deep.  Three pans are placed on a rotating shelf in a 163 oC oven for 5 hours.  The aged samples are then combined into one container, mixed, and used to determine the aged asphalt cement properties.

## Typical Penetration Specifications

**Penetration****	****	****    40 - 50****	****200 - 300**

**Flash Point, C****	****      450+****	****	****    350+**

**Ductility, cm****	****	****     100+****	****	****   100+**

**Solubility, %****	****	****     99.0+****	****	****   99.0+**

**Retained Pen., %       55+****	****	****     37+**

**Ductility, cm****	****	****      NA****	****	****   100+**

**Notes:**
There are five penetration grades of asphalt cements with discrete ranges.  That is, there is no overlap in penetration values between grades.  It is possible to have an asphalt which will not meet any penetration grading requirement.  This table presents two of these grades.

Note the flash point decreases with increasing penetration.  This is because softer asphalts usually have a higher percentage of lighter ends which will “flash” at lower temperatures.  The specification allows for this difference.

Since these  fractions of the asphalt are also easily removed by heating, this means that there will be a higher percentage mass loss on aging.  This greater loss of the softer asphalt components is reflected in the differences in requirements on the percent of the original penetration retained after aging.  That is, the more light ends lost during aging, the greater the stiffening affect due to aging.  This loss of the softer asphalt components is also reflected the ductility requirements.

## Temperature

**Temperature**

**25C (77F)**

**Penetration, 0.1 mm**

**Notes:**
Temperature susceptibility (i.e., the rate of change in material properties with a change in temperature) can be estimated by determining the penetration at two (or more) temperatures.  The most commonly used temperatures are 4 and 25 oC with a 100 g load for 5 seconds.  This figure highlights one of the major problems with the penetration grading system.  For example, three sources of asphalt can have the same penetration at 25 oC but decidedly different properties above and below this temperature.  This helps explain the differences in observed pavement performances even though the same penetration grade of asphalt is specified.

## Advantages

**Grades asphalt near average in-service temp.**
**Fast**
**Can be used in field labs**
**Low capital costs**
**Precision well established**
**Temp. susceptibility can be determined                        **

**Notes:**
Several advantages are responsible for the penetration specifications being widely used throughout the 20th century.  For instance, as late as 1995 the Minnesota Department of Transportation was still using this specification to purchase asphalt cements.  These advantages include an estimate of material properties at the average in-service temperature (i.e, the average between summer highs and winter lows), low cost of the equipment, simplicity, and short testing times needed to obtain results.

## Disadvantages

**Empirical test**
**Shear rate **
**High**
**Variable**
**Mixing and compaction temp. information not available**
**Similar penetrations at 25C (77F) do not reflect wide differences in asphalts**

**Notes:**
However, there are several disadvantages associated with penetration specifications. These include allowing a wide range of material properties at high and low temperatures for a given penetration grade, variable shear rates (i.e., the needle will penetrate the asphalt faster for softer as compared to harder asphalts), lack of fundamental measurements needed for mechanistic pavement performance prediction models (i.e., no stress or strain measurements), their inability to evaluate shear rate dependent materials (e.g., polymer modified asphalts), and lack of information for selecting appropriate mixing and compaction temperatures (necessary information for preparing mixtures in the laboratory and plant).

## Viscosity Graded Specifications

**Notes:**
These disadvantages led to the development of the viscosity grading system in the 1970's which is detailed in ASTM D3381.  This one ASTM standard actually contains three separate specifications designated as: Table 1, Table 2, and Table 3.  The first two specifications are based on the original properties of the asphalt while the last table is based on the properties of the asphalt after rolling thin film oven aging.  Each of these tables and differences between them will be discussed in the following slides.

## Definition

***Definition***

**Notes:**
Viscosity is shear stress divided by the shear strain rate.  These units of measurement provide at least a limited estimate of fundamental material properties.  

The easiest way to picture shear is to visualize a deck of cards which have a vertical line marked on the side.  As pressure is applied to the top of the deck, the cards slide over one another and the marked dots on the individual cards start to separate.  The shear rate is the rate at which these dots separate.

## Types of Viscosity Tubes

**Asphalt Institute Tube**

**Zietfuchs Cross-Arm Tube**

**Notes:**
Two viscosity measurements are used in this specification: Absolute viscosity (60 oC) and kinematic viscosity (135 oC).  Both use the principle of the rate of flow through a known area to measure viscosity.  Because asphalt is still very thick (stiff) at 60 oC, a vacuum is needed to move the asphalt through the tube in a reasonable time.  At 135 oC, gravity and a falling head pressure is sufficient to get the asphalt to flow.

## Testing

**Absolute viscosity**
**U-shaped tube with timing marks & filled with asphalt**
**Placed in 60C bath**
**Vacuum used to pull asphalt through tube**
**Time to pass marks**
**Visc. in Pa s  (Poise)**

**Notes:**
At the 60 oC test temperature, the tube is charged at 135 oC and then placed in the test temperature bath.  The tube temperature is allowed to equalize  with the bath temperature, a vacuum line is attached to the top of the small diameter tube, and the flow is started.  The time it takes the asphalt to flow past the timing marks times the tube calibration constant gives the viscosity of the asphalt in Poise.

## Testing

**Kinematic viscosity**
**Cross arm tube with timing marks & filled with asphalt**
**Placed in 135C bath**
**Once started gravity moves asphalt through tube**
**Time to pass marks  **
**Visc. in mm****2**** / s (centistoke)**

**Notes:**
The tube is charged in the 135 oC  bath and left for about 20 minutes.  A vacuum  line is touched briefly to the top of the small diameter tube until the asphalt moves over the upper hump in the tube.  The time it takes the asphalt to flow past the timing marks times the tube calibration constant gives the viscosity of the asphalt in centistoke.  Centistokes are converted to centipoise by mulitplying centistokes by the specific gravity of the asphalt.

## Viscosity Grade Specifications

**ASTM D3381**
**Three specifications**
**Table 1**
**Original properties**
**Table 2**
**Original properties**
**Table 3**
**Rolling thin film oven aging**

**Notes:**
All three of the viscosity graded asphalt specifications are listed in ASTM D3381.  The first two specifications are based on the viscosity of the original asphalt at 60 oC.  The third specification is based on the viscosity of the rolling thin film oven aged residue at 60 oC. 

## Table 1 & 2 Tests

**Viscosities at 60 and 135****o****C**
**Penetrations at 25****o****C**
**Flash point**
**Solubility**
**TFO aged  residue**
**Viscosity at 60****o****C**
**Ductility at 25****o****C**

**Notes:**
Requirements on both the absolute and kinematic viscosities are set in these specifications.  The grading system is based on the absolute viscosity (60 oC).

A minimum viscosity at 135 oC is included to help define the maximum rate of change of material properties with temperature. A minimum penetration value is also included in these specifications as a means limiting temperature susceptibility.

The penetration values decreases with increasing viscosity.  In other words, the stiffer the asphalt, the less distance the needle will penetrate into the asphalt.

As with the penetration specifications, requirements for safety and limits on aging of the binder during construction are included.  The flash point temperature requirements increase with increasing viscosity (less volatiles with increasing viscosity).  Maximum limits on viscosity after thin film oven aging limit the amount of acceptable aging during mixing and construction.

## Table 1 & 2 Grades

**Table 1 **
**AC 2.5, AC 5, AC 10, AC 20, AC 40**
**Table 2**
**AC 2.5, AC 5, AC 10, AC 20, **_**AC 30**_**, AC 40**

**Notes:**
Table 2 viscosity specifications are very similar to Table 1 specifications with two exceptions:  Table 2 specifications allow for an AC 30 grade, and Table 2 asphalts are required to be less temperature susceptible.

## Table 1 Example

**	****	****	****       ****AC 2.5****	****	****AC 40**

**Visc, 60C****	****     250 **_**+**_** 50    4,000 **_**+**_** 800**

**Visc, 135C****	****          80+****	****	****  300+**

**Penetration****	****	**** 200+****	****	****   20+**

**Visc, 60C****	****	****<1,250****	****    <20,000**

**Ductility****	****	****	**** 100+ ****	****	****   10+**

**Notes:**
This table compares two of the viscosity graded Table 1 specifications. The viscosity grading system provides immediate information as to the mean anticipated viscosity at 60 oC.  For example, an AC 25 will have a mean viscosity of 250 Poise (2.5 times 100).  Because of the limited allowable range (coefficient of variance of 20 percent), there is no overlap between the AC grades. 

## Table 2 Example

**	****	****	****       ****AC 2.5****	****	****AC 40**

**Visc, 60C****	****     250 **_**+**_** 50    4,000 **_**+**_** 800**

**Visc, 135C****	****         125+****	****	****  400+**

**Penetration****	****	**** 220+****	****	****    40+**

**Visc, 60C****	****	****<1,250****	****    <20,000**

**Ductility****	****	****	**** 100+ ****	****	****   ****25+**

**Notes:**
All of the same tests are used to specific Table 1 and Table 2 specifications.  The differences between the two specifications are highlighted in this example.  While the original and maximum aged viscosities at 60 oC remain the same for both tables, the minimum requirements for the 135 oC viscosity and penetrations are increased.  There is also an increase in the required ductility after aging for the harder (higher viscosity) asphalts.

## Temperature

**Temperature**

**25C (77F)**

**60C (140F)**

**135C (275F)**

**Ave. **
**Service **
**Temp.**

**Mixing **
**& **
**Compaction**

**Table 2**

**2400**

**1600**

**Viscosity (Stiffness)**

**Notes:**
This figure demonstrates the differences between a Table 1 and a Table 2 AC 20.  Both asphalts can have similar viscosities at 60 oC.  The minimum 135 oC for the Table 1 AC 20 is 210 centistokes.  This minimum limits the steepness of the viscosity temperature line (i.e., puts a maximum on the temperature susceptibility.  The higher minimum requirement (300 centistokes) for the Table 2 AC 20 further limits this slope.  

The minimum penetration value places a limit on maximum stiffness of the asphalt at  25 oC.  Remember that higher penetration numbers represent lower asphalt stiffness.  The higher minimum requirement for the Table 2 AC 20 also results in a shallower maximum slope.

Neither Table 1 or Table 2 specifications place any lower limit on the rate of change in properties with temperature.  This means that the pavement performance of a given AC 20 can still vary widely.

## Mixing/Compaction Temps

- .1

- .2

- .3

- .5

- 1

- 10

- 5

- 100

- 110

- 120

- 130

- 140

- 150

- 160

- 170

- 180

- 190

- 200

**Temperature, C**

**Viscosity, Pa s**

***Compaction Range***

***Mixing Range***

***Mixing/Compaction Temps***

**Notes:**
Information from this testing can be used to  estimate appropriate mixing and compaction temperatures.  This is accomplished by graphing viscosity in  Poise (on a log scale of the y-axis) versus temperature (arithmetic scale on the x-axis).  The mixing temperature is selected so that an equal viscosity is achieved.  Based on historical experience, a viscosity of   1.7 + 0.2 Poise is used.  The temperature at which the viscosity is 2.8 + 0.3 is used to select the compaction temperature.

## Advantages (Original AC Visc. Grade)

**Fundamental property**
**Wide range of temperatures**
**Based on max. pavement surface temp.**
**Wide range of instruments**
**Test method precision established**
**Temperature susceptibility is controlled**
**Limits aging**
**Information on mixing & compaction temps.**

**Notes:**
Advantages to using viscosity specifications include measurements with engineering units, limits on maximum temperature susceptibility and changes in properties due to aging, and information can be obtained on appropriate mixing and compaction temperatures.

## Disadvantages (Original  AC Visc. Grade)

**More expensive **
**Longer testing time**
**More technician skill needed**
**Not applicable for Non-Newtonian materials**
**Wide range of properties for same grade**

**Notes:**
Disadvantages include the higher cost of the more sophisticated equipment and glassware required for viscosity tests, longer testing times, increased training needed for technicians, the lack of lower limits for temperature susceptibility, and the inability of these viscosity measurements for assessing non-Newtonian (shear rate dependent) properties.

## Table 3

**AR Grades**
** ****AR 1000, AR 2000, AR 4000,  AR 8000, AR 16000**

**Tests on RTFO aged residue**
**Viscosities at 60 and 135****o****C**
**Penetrations at 25****o****C**
**% of Original Penetration**
**Ductility**
**Properties of unaged asphalt**
**Flash point and solubility**

**Notes:**
Table 3 viscosity specifications are based on rolling thin film oven (RTFO) aging.  This method of aging was developed by the California Department of Transportation to simulate both the oxidation and heat aging of asphalts which occurs during mixing and construction and uses an AR (asphalt residue) designation.  As with the AC designations, the numbers are directly related to the viscosity at 60 oC.  For example, the RTFO aged viscosity of an AR 4000 is 4,000 Poise. 

Both penetration and ductility of the residue are also included.  Two tests are conducted on the original asphalt:  penetration (to get percent of original penetration value) and the flash point (safety) test.

## Rolling Thin Film Oven

**Notes:**
The rolling thin film oven places 35 g of asphalt in glass jars which are then anchored in a rotating carriage.  As the carriage rotates, the asphalt cement rolls around the inside of jar and air is blown over the surface each time the jar passes the air nozzle at the bottom of the oven. This continually exposes a new surface of asphalt to the effects of air and heat.  This test is run at 163 oC for 80 minutes.

At the end of this time, the asphalt is scraped out of the jars and combined into one container, stirred, and used to determine the effects of oxidation and heat aging on viscosity, penetration, and ductility. 

## Table 3 Specification

**	****	****       ****AR 1000****	****          AR 16,000**

**Visc, 60C     1,000 **_**+**_** 250    16,000 **_**+**_** 4,000**

**Visc, 135C****	****     140+****	****	****         550+**

**Pen.****	****	****       65+****	****	****           20+**

**% Orig. Pen****	****       NS****	****  ****	****	****   52+**

**Notes:**
The allowable range of RTFO aged viscosities is greater than those for the AC viscosity designations.  The coefficient of variation is 25 percent. 

The only tests which are conducted on the original asphalt are flash point and penetration (so that the percent of original penetration can be calculated).

## Advantages (AR Visc. Grade)

**Represents asphalt properties after mixing**
**Fundamental properties**
**Covers wide range of temperatures**
**Limits aging**

**Notes:**
The main advantage to this specification is that it is based on the properties of the asphalt  behind the paver.  That is, it is based on the in-place asphalt properrties at the time the roadway is opened to traffic.

Other advantages to using the AR specification are similar to those for the first two viscosity specifications. 

## Disadvantages (AR Visc. Grade)

**Highly regional**
**Requires different testing equipment **
**Longer testing time**
**No consistency test on original AC**
**Not applicable for Non-Newtonian materials**
**Wide range of properties for same grade**

**Notes:**
Disadvantages include a problem with a lack of wide-spread experience in determining desirable properties, longer times before results can be reported because the material has to be aged prior to testing, and other disadvantages as seen  in the previous viscosity grading specifications.

## Viscosity, 60C (140F)

**100**

**50**

**10**

**5**

**Viscosity, 60C (140F)**

**Notes:**
This figure provides a general comparison of the various traditional specifications.  While there is no direct relationship between the specifications, there is a general relationship between stiffness and viscosity.  Higher penetration numbers correspond with lower viscosities.

## Questions - ?