# Presentation: 080930

## Aggregate Properties

**Gradation**

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## Types of Gradations

**-  Few points of contact**

**-  Poor interlock (shape dependent)**

**-  High permeability**

***  Well graded**

**-  Good interlock**

**-  Low permeability**

***  Gap graded**

**-  Only limited sizes**

**-  Good interlock**

**-  Low permeability**

**Types of Gradations**

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## Aggregate Gradation

** ****Use 0.45 Power Gradation Chart**
** ****Blend Size Definitions**
**maximum size**
**nominal maximum size**
**Gradation Limits**
**control points**
**restricted zone**

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## 0.45 Power Grading Chart

***Example:  ***
***4.75 mm sieve plots at (4.75)******0.45****** = 2.02***

**Sieve Size (mm) Raised to 0.45 Power**

**0**

**20**

**40**

**60**

**80**

**100**

**0**

**1**

**2**

**3**

**4**

**Percent Passing**

**0.45 Power Grading Chart**

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**Notes:**
To specify gradation the HMA industry uses a .45 power graph.  It is a modification of the Fuller’s curve used by geotechnical engineers - rather than use a power of 0.50 it uses a 0.45 for the exponent in the equation.

## 0.45 Power Grading Chart

** ****0  .075 .3  .6   1.18  2.36      4.75        9.5    12.5      19.0**

**Sieve Size (mm) Raised to 0.45 Power**

**0**

**20**

**40**

**60**

**80**

**100**

***maximum density line***

**Percent Passing**

**max**
**size**

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**Notes:**
The maximum density gradation (line) represents a gradation in which the aggregate particles fit together in their densest possible arrangement.  This is not the most desirable gradation for HMA because there would be very little aggregate space within which to develop sufficiently thick asphalt films for a durable mixture.

## Aggregate Size Definitions

***Nominal Maximum *****Aggregate Size**
**one size larger than the first sieve to retain more than 10%**
***Maximum***** Aggregate Size**
**one size larger than nominal maximum size**

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**Notes:**
For HMA pavements these are the definitions for gradations.

## Percent Passing

**100**

**0**

** ****.075****	****.3****	****   2.36****	****    4.75****	****9.5****	****12.5         19.0**

**Percent Passing**

***control point***

***restricted zone***

**max density line**

**max**
**size**

**nom**
**max**
**size**

**Sieve Size (mm) Raised to 0.45 Power**

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**Notes:**
To specify aggregate gradation, two additional features are added to the 0.45 chart:  control points and a restricted zone.  Control points function as master ranges through which gradations must pass.  They are placed on the nominal maximum size, an intermediate size and the dust size.
The restricted zone resides along the maximum density gradation between the intermediate size (either  4.75 or 2.36 mm) and the 0.3 mm size.  It forms a band through which gradations should not pass.  Gradations that pass through the restricted zone have often been called “humped gradations” because of the characteristic hump in the grading curve that passes through the restricted zone.  In most cases, a humped gradation indicates a mixture that possesses too much fine sand in relation to total sand.  This gradation practically always
 results in tender mix behavior, which is manifested by a mixture that is difficult to compact during construction and offers reduced resistance to permanent deformation during its performance life.  Gradations that violate the restricted zone possess weak  aggregate skeletons that depend too much on asphalt binder stiffness to achieve mixture shear strength.  These mixtures are also very sensitive to asphalt content and can easily become plastic.  

## Superpave Aggregate Gradation

**100**

**0**

** ****.075****	****.3****	****     2.36****	****                  ****12.5  ****    ****19.0**

**Percent Passing**

***Design Aggregate Structure***

**Sieve Size (mm) Raised to 0.45 Power**

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**Notes:**
The term used to describe the cumulative frequency distribution of aggregate particle sizes is the design aggregate structure.  A design aggregate structure that lies between the control points and avoids the restricted zone meets the requirements of Superpave with respect to gradation.  Superpave defines five mixture types as defined by their nominal maximum aggregate size:    

## Superpave Mix Size Designations

**Superpave****	****  ****	****Nom Max Size****	**** ****Max Size**
**Designation****	****          ****	****        (mm)****	****	****     (mm)**
**     ****37.5 mm****	****          ****	****         37.5****	****	****       50**
**     ****25    mm****	****         ****	****         25****	****	****       37.5**
**     ****19    mm****	****          ****	****         19****	****	****       25**
**     ****12.5 mm****	****                     12.5****	****	****       19**
**     ****9.5   mm****	****                       9.5****	****	****       12.5**

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**Notes:**
These are the five gradations developed for Superpave.

## Gradations

***  Considerations:**

**-  Max. size < 1/2 AC lift thickness**

** **

**+  Increases strength**

** **

**+  Improves skid resistance**

** **

**+  Increases volume and surface area of agg which decreases required AC content**

** **

** **

** **

**+  Improves rut resistance**
**+  Increases problem with segregation of particles**

**-  Smaller max size**

** **

**+  Reduces segregation**

** **

**+  Reduces road noise**

** **

**+  Decreases tire wear**

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**Notes:**
Several factors need to be considered in selecting a desirable aggregate gradation.  The maximum size of the aggregate needs to be at a minimum less than one half of the planned lift thickness.  Current construction practices with Superpave gradations indicate that this needs to be changed to less than one-third of the lift thickness.
Larger maximum size aggregate gradations have several advantages such as improved aggregate interlock, improved skid resistance and improved rut resistance.  Local availability of aggregates will usually dictate the largest size aggregate.  Also, the larger maximum size gradations also tend to have more problems with gradation separation (segregation) during construction.

## Target Gradation

**Acceptable gradation band specified**
**Mix design selects a job mix formula (JMF) which falls within band *****and***** meets design criteria**
**Superpave**
**5 nominal sizes (37.5, 25, 19, 12.5, and 9.5 mm)**
**Four sieve sizes used to set upper and lower limits**
**Staying out of the restricted zone in *****suggested****** *****to minimize problems with natural sands**

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**Notes:**
Target gradations are usually selected to meet an agency-specified gradation band.  The selected gradation needs to meet the agency requirements as well as all other Superpave gradation and aggregate requirements.

At the present time, there are 5 Superpave gradation bands. Each uses 4 sieve sizes to set upper and lower limits on the gradation.

The restricted zone was originally included to help eliminate rounded natural sands. However, with the requirements on fine aggregate angularity, the need to stay out of the restricted zone is evaluated on a case by case basis (historical experience).   

## Blending Stockpiles

**Basic formula for combining stockpiles to achieve a target gradation is:**

**p = Aa + Bb + Cc + ....**

**where:**
**	****p = percent of material passing given sieve size**
**	****A, B, C, .. = percent passing given sieve for each agg.**
**	****a, b, c, ... = decimal fraction of A, B, C, ... to be used**

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**Notes:**
Once a target gradation or gradation band is selected, percentages of the aggregate stockpiles needed to produce an acceptable gradation are determined.

This is usually accomplished using a spreadsheet and a trial and error approach.

## Blending Stockpiles

**Plot individual gradations**
**Plot specification limits**
**Can be used for initial assessment**
**Can blend be made from available materials?**
**Identification of critical sieves**
**Est. trial proportions**

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**Notes:**
The ability of a given set of aggregate stockpiles to meet particular gradation band requirements can be initially assessed by plotting the individual stockpile and gradation band requirements

## All possible combinations fall between A and B

**0.075   0.3       1 .18               4.75              9.5    12.5          19**

**Sieve Size, mm**

**Percent Passing, %**

**Control points for **
**12. 5 nominal max. size**

**Gradation  A**

**Gradation  B**

***All possible combinations fall between A and B***

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**Notes:**
If the individual gradations bracket the gradation band, then it is possible to produce a combined gradation which will be within the gradation band.  Determining the percentages will be a trial and error process.

## No poss. combination of A and B will meet spec.

**0.075   0.3       1 .18               4.75              9.5    12.5          19**

**Sieve Size, mm**

**Percent Passing, %**

**Control points for **
**12. 5 nominal max. size**

**Gradation  A**

**Gradation  B**

***No poss. combination of A and B will meet spec.***

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**Notes:**
If the individual stockpile gradations are both either above or below the target gradation band, then there is no combination of the stockpiles which will produce an acceptable gradation.

## All poss. combinations pass through cross-over point

**0.075   0.3       1 .18               4.75              9.5    12.5          19**

**Sieve Size, mm**

**Percent Passing, %**

**Control points for **
**12. 5 nominal max. size**

**Gradation  A**

**Gradation  B**

***All poss. combinations pass through cross-over point***
***Blends containing more A than B will be closer to A***

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**Notes:**
If the individual stockpile gradations cross, then the any combination of these stockpiles will have that same percentage for that particular sieve size.  

## Trial and Error Steps

**Select critical sieves in blend**
**Determine initial proportions which will meet critical sieves**
**Check calc. blend against specification**
**Adjust if necessary and repeat above steps**

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**Notes:**
Once it has been established that an acceptable gradation can be prepared using the designated stockpiles, these steps need to be followed to determine the desired percentages of each stockpile.

## Blended Aggregate Specific Gravities

**Once the percentages of the stockpiles have been established, the combined aggregate specific gravities can also be calculated**

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**Notes:**
Remember, two specific gravity tests are needed.  The results from these two tests need to be combined to obtain the specific gravity of the composite.

## Combined Specific Gravities

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**Notes:**
This is the equation used for combining aggregate properties.

## Blending of Aggregates

**Reasons for Blending**
**Obtain desirable gradation**
**Single natural or quarried material not enough**
**Economical to combine natural and process materials**

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**Notes:**
We blend aggregates for these reasons.

## Blending of Aggregates

**Numerical Method**
**Trial and Error**
**Basic Formula**

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**Notes:**
There are two methods for blending aggregates.  The most common is trial and error.  The basic formula is not used.

## Blending of Aggregates

**P = Aa + Bb + Cc + ....**
**Where****:**
**P = % of material passing a given sieve for the ****	****blended aggregates A, B, C, ...**
**A, B, C, ... = % material passing a given sieve ****	****for each aggregate A, B, C, .....**
**a, b, c, .... = Proportions (decimal fractions) ****	****	****of aggregates A, B, C, ... to be used in ****	****Blend**

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**Notes:**
This is the basic formula for blending.

## Blending of Aggregates

- Agg. #2

- Agg. #1

- Blend

- Target

- Material

- %
- Passing

- %
- Passing

- % Used

- U.S. Sieve

- %
- Batch

- %
- Batch

- No. 4

- No. 8

- No. 16

- No. 30

- No. 50

- No. 100

- No. 200

- 3/8 “

- 90

- 30

- 7

- 3

- 1

- 0

- 0

- 100

- 100

- 100

- 88

- 47

- 32

- 24

- 10

- 100

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**Notes:**
Example.  Starting with two aggregates.

## Blending of Aggregates

- Agg. #2

- Agg. #1

- Blend

- Target

- Material

- %
- Passing

- %
- Passing

- % Used

- U.S. Sieve

- %
- Batch

- %
- Batch

- No. 4

- No. 8

- No. 16

- No. 30

- No. 50

- No. 100

- No. 200

- 3/8 “

- 45

- 15

- 3.5

- 1.5

- 0.5

- 0

- 0

- 100

- 100

- 100

- 88

- 47

- 32

- 24

- 10

- 100

- 50 %

- 50 %

- First Try
- (remember trial & error)

- 90

- 30

- 7

- 3

- 1

- 0

- 0

- 50

- 90   * 0.5 = 45

- 30   * 0.5 = 15

- 7     * 0.5 = 3.5

- 3     * 0.5 = 1.5

- 1     * 0.5 = 0.5

- 0     * 0.5 = 50

- 0     * 0.5 = 0

- 100 * 0.5 = 50

- 80 - 100

- 65 - 100

- 40 - 80

- 20 - 65

- 7 - 40

- 3 - 20

- 2 - 10

- 100

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**Notes:**
The first trial we will use 50% of each pile.

## Blending of Aggregates

- Agg. #2

- Agg. #1

- Blend

- Target

- Material

- %
- Passing

- %
- Passing

- % Used

- U.S. Sieve

- %
- Batch

- %
- Batch

- No. 4

- No. 8

- No. 16

- No. 30

- No. 50

- No. 100

- No. 200

- 3/8 “

- 80 - 100

- 65 - 100

- 40 - 80

- 20 - 65

- 7 - 40

- 3 - 20

- 2 - 10

- 100

- 45

- 15

- 3.5

- 1.5

- 0.5

- 0

- 0

- 100

- 50

- 50

- 44

- 23.5

- 16

- 12

- 5

- 50

- 50 %

- 50 %

- 90

- 30

- 7

- 3

- 1

- 0

- 0

- 50

- 95

- 65

- 47.5

- 25

- 16.5

- 12

- 5

- 100

- 100

- 100

- 88

- 47

- 32

- 24

- 10

- 100

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**Notes:**
This worked but the No. 50 sieve and the No 100 sieve are low.

## Blending of Aggregates

- Agg. #2

- Agg. #1

- Blend

- Target

- Material

- %
- Passing

- %
- Passing

- % Used

- U.S. Sieve

- %
- Batch

- %
- Batch

- No. 4

- No. 8

- No. 16

- No. 30

- No. 50

- No. 100

- No. 200

- 3/8 “

- 80 - 100

- 65 - 100

- 40 - 80

- 20 - 65

- 7 - 40

- 3 - 20

- 2 - 10

- 100

- 45

- 15

- 3.5

- 1.5

- 0.5

- 0

- 0

- 100

- 50

- 50

- 44

- 23.5

- 16

- 12

- 5

- 50

- 50 %

- 50 %

- 90

- 30

- 7

- 3

- 1

- 0

- 0

- 50

- 95

- 65

- 47.5

- 25

- 16.5

- 12

- 5

- 100

- 100

- 100

- 88

- 47

- 32

- 24

- 10

- 100

- Let’s Try
- and get
- a little closer
- to the middle of
- the target values.

- NCAT

## Blending of Aggregates

- Agg. #2

- Agg. #1

- Blend

- Target

- Material

- %
- Passing

- %
- Passing

- % Used

- U.S. Sieve

- %
- Batch

- %
- Batch

- No. 4

- No. 8

- No. 16

- No. 30

- No. 50

- No. 100

- No. 200

- 3/8 “

- 80 - 100

- 65 - 100

- 40 - 80

- 20 - 65

- 7 - 40

- 3 - 20

- 2 - 10

- 100

- 27

- 9

- 2.1

- 0.9

- 0.3

- 0

- 0

- 100

- 70

- 70

- 61.6

- 32.9

- 22.4

- 16.8

- 7

- 70

- 70 %

- 30 %

- 90

- 30

- 7

- 3

- 1

- 0

- 0

- 30

- 97

- 79

- 63.7

- 33.8

- 22.7

- 16.8

- 7

- 100

- 100

- 100

- 88

- 47

- 32

- 24

- 10

- 100

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## Questions - ?

- NCAT