# Presentation: 475277

## Aggregates

**Usually refers to a soil that has in some way been processed or sorted.**

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**Notes:**
Soils are materials that are used as-is.  An example would be a finished subgrade surface.  Aggregates are materials that have been specifically sorted or processed to achieve given properties.  This block will present general background information about how aggregates are obtained and processed.

## Aggregate Processing

**Excavation**
**Transportation**
**Crushing**
**Sizing**
**Washing**

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**Notes:**
There are five general steps needed to prepare individual stockpiles of aggregates. Once stockpiles have been prepared, two or more stockpiles are typically blended together to produce a final gradation for a given construction application.

## Excavation

**- Underwater sources**

**+ Rivers & lakes**

**+ Barge-mounted dredges, draglines, **

**   ****scoop, conveyors, or pumps**

**+ Relatively clean**

**-  Land sources**

**+  Gravel or sand pits**

**+  Bucket loader**

**Excavation**

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**Notes:**
Excavation of natural sands and gravels from under water sources requires the use of barge-mounted dredges, draglines, scoops, conveyors, or pumps to bring the material above the water line.  Sand and gravel pits (land sources) are excavated using back hoes and bucket loaders.  The following photos show examples of these procedures.
	Natural sands and gravels have a rounded appearance due to the weathering action of water.  Rounded natural sands are commonly used in portland cement concrete applications but crushing is required to obtain a more angular shape for use in asphalt concrete.

## Excavation

**Excavation**

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**Notes:**
Some aggregate sources are obtained by removing materials from the bottom of lakes and rivers.

## Excavation

**-  Rock depths > 50 ft., remove overburden**

**    ****+  Soil stripped with bulldozers**
**	**** ****and scrapers**

**-  Rock depths < 50 ft., overburden washed out during processing**

**-  Blasting required**

**Excavation**

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**Notes:**
Excavation of rock ledges requires blasting the solid ledges into transportable sizes. However, this can still leave very large blocks of rock to be moved.  One or more crushing operations are needed to further reduce the size of the material.  As a result of the blasting and crushing operations, quarried aggregates always have an angular particle shape.
	The following photographs show examples of these types of operations.

## Excavation

**Excavation**

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**Notes:**
This photograph shows typical operations in a limestone quarry.

## Crushing

**Crushing**

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**Notes:**
The first step in preparing stockpiles for specific uses is the crushing the larger boulders and aggregates  into usable sizes.

## Crushing

**River Gravel****	****	****Partially Crushed **
**	****	****          ****River Gravel**

**Crushing**

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**Notes:**
Crushing of river gravels is used to change the shape of the aggregate particles. 

## Transportation

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**Notes:**
Once materials are obtained,they are usually transported by land, rail, or barge to a centrally located plant for separation into specific sizes.

## Transportation

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## Transportation

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## Sizing

**Sizing**

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**Notes:**
Once the rock has been sufficiently reduced in size, it is separated into individual stockpiles with specific ranges of particle sizes.  Large screening operations have a number of wire mesh screen decks with each deck having progressively smaller openings between the wires.  These screens are slanted and empty the material retained on each screen out onto conveyor belts.  These belts then move the material into individual stockpiles of a particular size.

## Stockpiling

**Stockpiling**

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**Notes:**
Poor stockpiling practices can result in particle size separation even within a pile of limited particle sizes.  Good stockpiling practices limit the drop distance and prepare a number of small stockpiles for a particular gradation of aggregate.  This minimizes the separation of the fine and coarse particles.  Moving stockpiles with trucks and dozers should be minimized in order to prevent excessive degradation of the aggregate (that is, more very fine particles).  The following photographs show examples of good stockpiling practices.

## Stockpiling

**Stockpiling**

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**Notes:**
This photograph shows a typical stockpiling operation.

## Sampling

**To evaluate the potential quality of a proposed aggregate source.**
**Does new source meet aggregate specifications?**
**To determine compliance with project specification requirements.**
**Do current aggregates meet specifications?**

***Sampling***

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**Notes:**
Once stockpiles have been produced, it is necessary to determine the final gradation and aggregate properties of each stockpile.  There are specific guidelines which need to be followed in order to obtain samples of aggregates which represent the entire stockpile.  Samples can be obtained from the stockpiles themselves or from the conveyor belts which move the aggregate from storage bins into the hot mix asphalt (HMA) plant.

## Sampling from Stockpile

**Sampling from Fine Aggregate Stockpile**

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**Notes:**
Samples can be carefully obtained from an individual stockpile.

## Sampling from Conveyor

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**Notes:**
Or they can be obtained by “catching” a sample off of the end of the conveyor belt which feeds into the HMA plant.

## Source Aggregate Properties

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***Source Aggregate Properties***

**Toughness**
**Soundness**
**Deleterious Materials**
**Gradation**

**Notes:**
Source aggregate properties are those properties which are measured for the aggregate as-stockpiled and are commonly used for aggregate source acceptance control.  These properties are toughness, soundness, and deleterious materials.  In addition, the gradations of individual stockpiles may be evaluated.

## Definitions

***  Coarse Aggregate**

**-  Retained on 4.75 mm (No. 4)**

**ASTM D692**

**-  Retained on 2.38 mm (No. 8) **

**Asphalt Institute**

**-  Retained on 2.00 mm (No. 10)**

**HMA Book**

***  Fine Aggregate.**

**-  Passing 4.75 mm (No. 4)**

**ASTM D1073**

**-  Passing 2.38 mm (No. 8)**

**Asphalt Institute**

***  Mineral Filler**

**-  At least 70% Pass. 0.075 mm**

**ASTM D242**

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**Notes:**
Source aggregate property tests evaluate specific fractions of each stockpile.  Toughness evaluates the percent change in coarse aggregate particle size while aggregate soundness and the amount of deleterious material (clay lumps and friable particles) can be assessed for both fine and coarse aggregate.  For Superpave testing, coarse aggregate is usually that which would be retained on a 4.75 mm sieve and fine aggregate the fraction which would pass this sieve.  However, each test method needs to be checked to determine which definition is being used.  Depending upon the test requirements, the very fine aggregate, called mineral filler, may or may not be included in the fine aggregate.

## Toughness

***  Los Angeles Abrasion (AASHTO T96, ASTM C131):**

** **

**Resistance of coarse agg to abrasion and mechanical degradation during handling, construction and use**

***  Aggregate at standard gradation subjected to damage by rolling with prescribed number of steel balls in large drum for a given number of rotations**
***  Result expressed as % changes in original weight**

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**Notes:**
This test subjects the coarse aggregate (in this case, retained on the 2.36 mm sieve) to impact and grinding by steel spheres.  Each sphere has a mass between 390 and 445 g.  The number of spheres introduced into the drum depends on the gradation of the aggregate to be tested.  The number of spheres increases with increasing size of aggregate.

Once the aggregate and spheres are placed in the steel drum, the machine is rotated at between 30 and 33 rpm’s for 500 revolutions.  The aggregates are then removed from the drum and sieved to determine the degradation as a percent loss.  The percent loss is the difference between the original mass at the required gradation and the final mass of the test sample)

## LA Abrasion Test

**-  Approx. 10% loss for extremely hard igneous rocks**

**-  Approx. 60% loss for soft limestones and sandstones**

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**Notes:**
This photo shows the equipment needed for the Los Angeles abrasion test.  The panel on theside of the drum is removed and the aggregate and steel balls are placed inside.  The panel is replaced and the drum rotated the prescribed number of cycles.

Examples of typical values are noted at the bottom of this photo.

## Soundness

*** Estimates resistance to weathering .**
*** Simulates freeze/thaw action by successively wetting and drying aggregate in sodium sulfate or magnesium sulfate solution**
**	****+  One immersion and drying is considered one ****	****    cycle**
*** Result is total percent loss over various sieve intervals for a prescribed number of cycles**
**	****+  Max. loss values typically range from **
**	****    ****10 to 20%per 5 cycles**

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**Notes:**
Weathering of aggregates is simulated by repeated immersion in saturated solutions of either sodium or magnesium sulfate followed by oven drying.  The internal expansive force from the expansion of the rehydration of the soluble salts upon re-immersion simulates freeze-thaw damage.  The difference between the original and final mass, expressed as a percent of the original mass is the percent loss.  A weighted percentage is used when several fractions are tested.  The soundness of both fine (passing the 4.75 mm sieve) and coarse aggregate can be determined using this test.

## Soundness

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**Notes:**
Minimal supplies are needed for this test.  Either sodium or magnesium sulfate can be used by dissolving the appropriate amount in water.  Aggregates are placed in a wire mesh basket and then submerged in the solution (not shown). 

## Soundness

- Before

-    After

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**Notes:**
Damage to the aggregate after a number of wet-dry cycles can be seen by visual examination as well as in the change in gradation.

## Clay Lumps and Friable Particles

***ASTM C 142***

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**Notes:**
Deleterious material is the mass percent of contaminants such as clay lumps, shale, wood, mica, and coal in the blended aggregate.  This test can also be performed for both fine and coarse aggregates.  The mass percentage of the material lost during a wet sieve is reported as the percent of clay lumps and friable particles.

## Gradations

**The distribution of particle sizes expressed as a percent of total weight.**
**Determined by sieve analysis**

**Gradations**

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## Steps in Gradation Analysis

**Part 1 - Washed sieve analysis**
**Dry aggregate and determine mass**
**Wash and decant water through 0.075 mm sieve until water is clear**
**Dry aggregate to a constant mass**

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**Notes:**
For this test (ASTM C117), a portion of aggregate is dried and the original mass of the sample is recorded.  The aggregate is then placed in a bowl, gently washed with water, and the water decanted over a 0.075 sieve.  When the water being decanted is reasonably clear, the aggregate is removed container.  Any aggregate retained on the sieve used for decanting is returned to this sample and then dried to a constant mass.  Once the dry mass is recorded, it is used for the mechanical particle size analysis.

## Washed Sieve

**Washed Sieve**

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**Notes:**
This photograph shows a mechanical  washing system.  The aggregate is placed in the large bucket and a gentle stream of water is started.  Once the bucket is full of water, the excess water pours out the side and over a nest of two sieves. The larger sieve on top is there to protect the 0.075 mm sieve below in case larger aggregate particles are washed out of the bucket. The bucket is slowly rotating during this process. 

Once the water pouring over the sieves is clear, the aggregate in the bucket is emptied into a pan.  Any material retained on either of the two wash screeens is also added to the pan.  The aggregate is then dried to a constant mass.  The amount of 0.075 mm material lost during washing is the difference between the original mass and the dry mass after washing.

## Steps in Gradation Analysis

**Part 2 - Mechanical sieve analysis**
**Place dry aggregate in standard stack of sieves**
**Place sieve stack in mechanical shaker**
**Determine mass of aggregate retained on each sieve**

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**Notes:**
In the second step, the oven dry aggregate is placed in a stack of increasing smaller sieves, placed in a shaker and agitated for about 5 to 10 minutes.  Gently separate the sieves and determine the mass of the sieve and aggregate.  Dump aggregate out of sieve, thoroughly clean the sieve, and determine the mass of the sieve without the aggregate.

## Mechanical Sieve

- Individual Sieve

- Stack of Sieves

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**Notes:**
Each sieve has wire mesh in the bottom.  The sieve size (4.75 mm, 2.36, mm etc.) denote the distance between each wire.  Sieves are stacked from largest openings  on the top to smallest openings on the bottom.  There is always a pan (no openings) at the bottom of the stack. 

## Mechanical Sieve

**Stack in Mechanical Shaker**

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**Notes:**
Once the stack is assembled and the oven dry aggregate added to the top, it is placed in a mechanical shaker.  This is run from 5 to 15 minutes.  Care needs to be taken to ensure that any given sieve is not overloaded.   That is, that there is so much material on the screen that material cannot be efficiently separated.

## Gradations - Computation

**Sieve****	****  Mass ****	****  **_**                     Cumulative                         **_
**	**** ****Retained****	****Mass Retained  %  Retained    % Passing**

**9.5**
**4.75**
**2.36**
**1.18**
**0.60**
**0.30**
**0.15**
**0.075**
**Pan**

**0.0**
**6.5**
**127.4**
**103.4**
**72.8**
**64.2**
**60.0**
**83.0**
**22.4**

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**Notes:**
Once the shaker stops, the stack is removed and the mass of aggregate retained on each screen is determined.  These masses are recorded and used in subsquent calculations (next slides).

## [

**% Passing =**

_**Cum. Wt Retained**_
**Original Dry Wt.**

*** 100**

**% Retained =**

_**Cum. Wt Retained**_
**Original Dry Wt.**

*** 100**

**[**

**1 -**

**]**

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**Notes:**
The percent retained on each sieve is a ratio of the mass of aggregate on each sieve divided by the original mass (before washing).  The cumulative percent retained is simply the sum of the percent retained on each sieve above the one of interest.  The cumulative percent passing, commonly referred to as “percent passing”, is 1 minus the cumulative percent retained.

## Gradations - Computation

**Sieve****	****  Mass ****	****  **_**                     Cumulative                         **_
**	**** ****Retained****	****Mass Retained  %  Retained    % Passing**

**9.5**
**4.75**
**2.36**
**1.18**
**0.60**
**0.30**
**0.15**
**0.075**
**Pan**

**0.0**
**6.5**
**127.4**
**103.4**
**72.8**
**64.2**
**60.0**
**83.0**
**22.4**

**0.0**
**6.5**
**133.9**
**237.3**
**310.1**
**374.3**
**434.3**
**517.3**
**539.7**

**0.0**
**1.2**
**24.8**
**44.0**
**57.5**
**69.4**
**80.5**
**95.8**
**100.0**

**100.0**
**98.9**
**75.2**
**56.0**
**42.6**
**30.6**
**19.5**
**4.2**
**0.0**

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**Notes:**
This is an example of the calculations necessary for a sieve analysis.  What is not shown is that the 22.4 g of material in the pan is the sum of the mass which was washed past the0.075 mm sieve in the first part and the mass of the aggregate retained in the pan after the mechanical sieve analysis.  This is an important point as the final gradation reported needs to reflect the true percentage of fractions in the stockpile which will be used during construction.

## Questions - ?

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