Aggregates

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AAPA training

Aggregates

Topics

  Aggregate sources and rock types   Aggregate Production   Aggregate Properties   Coarse and fine aggregates in Asphalt Mixes   Aggregates in Sprayed Seals   Filler in asphalt mixes

Australian Continent Aggregate (Rock) Types   Igneous rocks

– Basalt – Granite / rhyolite / diorite

  Metamorphic rocks – Hornfels / Greywacke/ Greenstone – Quartzite / Argillite

  Sedimentary rocks – Limestone – Sandstone

Aggregate Types

Aggregate Sources

  Crushed and screened quarry products

  Naturally occurring sands and gravels

  Manufactured aggregates (e.g. Blast furnace slag)

  Recycled material - RAP

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Aggregate Production Aggregate Production

  Primary Crushing

  Secondary Crushing

  Screening

  Washing / dust extraction systems

  Stockpiling

Crusher Types

Jaw Crusher Cone Crusher

Impact Crusher / Hammer Mill Vertical Shaft Impactor

Typical crushing and screening plant

Bins

Primary Crushing

  A Jaw Crusher is one of the main types of primary crushers   A fixed jaw is the stationary breaking surface, while the movable jaw exerts force on the rock by forcing it against the stationary plate (impact)   The rock remains in the jaws until it is small enough to pass through the gap at the bottom of the jaws

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Secondary Crusher

  Gyratory cone crushers can be used for primary or secondary crushing   The crushing action is caused by the closing of the gap between the mantle line (movable) mounted on the central vertical spindle and the concave liners (fixed) mounted on the main frame of the crusher

Aggregate Properties

  Properties dependent on type (source) of material (acidic / intermediate/ basic)

  Properties controlled by processing suitability of bituminous activities

Mechanical Sieve

Stack in Mechanical

Shaker

Properties controlled by processing

  Shape   Particle size distribution (grading)   Cleanliness (silt, clay and organic matter)

Face sampling – shielding ( AS 1141.3.1)

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Sampling

Sampling Rock Spalls AS 1141.3.2

Sampling Product AS 1141.3.1

The sample needs to be representative of the material!

Evaluation – General

  Aggregates for use in asphalt mixes or sprayed seals should be: – sound and durable – well shaped – cubical, not elongated – clean and consistently graded –  resistant to polishing – resistance depends

on the particular application e.g. lower resistance can be tolerated on lightly trafficked roads subjected to slow moving traffic

Properties Dependant on Source

  Toughness (strength, hardness and resistance to wear)   Soundness   Density   Porosity (water absorption)   Resistance to polishing   Affinity for bitumen

Toughness

  Aggregate Crushing Value (Wet-Dry Strength Variation)   Los Angeles Test

Typical Wet & Dry Strengths AS 1141.22 – 1996 Table 2

ROCK TYPE DRY STRENGTH (kN)

WET STRENGTH (kN)

AVERAGE RANGE AVERAGE RANGE

GRANITE 299 190-460 244 144-440

DIORITE 255 230-280 225 210-240

BASALT 340 210-520 280 150-470

DOLERITE 233 170-350 145 80-300

LIMESTONE 145 130-150 97 85-110

SANDSTONE – 150 – 45

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LA Abrasion Test

- Approx. 10% loss for extremely hard igneous rocks - Approx. 60% loss for soft limestones and sandstones

Typical Los Angeles Abrasion Loss Values

LA (% max)Rock typeClass A Class B

Granite 25 35Basalt 20 25Hornfels 20 25River gravel 25 30Sedimentary 25 25Blast furnace slag 20 25

Evaluation – Coarse Aggregate Evaluation – Coarse Aggregate

  Test methods in AS 1141 –  Particle density –  Particle size distribution –  Particle shape –  Flakiness Index –  Aggregate Crushing Value –  Wet-dry Strength Variation –  Los Angeles Abrasion Loss –  Sodium Sulphate Soundness –  Polished Aggregate Friction Value

  Adhesion with bitumen –  Plate stripping test for sealing aggregate –  Modified-Lottman Test for asphalt – loss of Marshall Stability or

stiffness after soaking

Classification

Applies only to aggregate for use in asphalt mixes

  Coarse > 4.75mm   Fine < 4.75mm   Filler < 75µm, i.e. 0.075mm

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AGGREGATE SPECIFICATIONS Functions in Asphalt Mixes   Coarse aggregate

–  Major contribution to the stability and strength of the mix –  Macro- and micro-texture which determine skid resistance –  Abrasion resistance

  Fine aggregate –  Stability –  Reduction of voids in the coarse aggregate structure –  Contribution to the micro-texture and hence skid resistance –  Improves mix durability – increases surface area and binder

effectiveness

  Filler –  Reduction in air voids –  Increase the stiffness of the binder – depends on the fineness of the

filler –  Improves mix durability – increases surface area and binder

effectiveness

Evaluation – Fine Aggregate

  Quality controlled by –  the selection of the source – particle size distribution – particularly the

percentage passing 75µm – Plasticity Index (LL/PL)

  For crushed fines acceptance also based on testing of the coarse aggregate

Evaluation – Fillers Depends on the type of filler Types of filler

Baghouse dust – Hydrated lime Cement – Cement works flue dust Fly Ash – Ground Limestone

Tests applied to all fillers Particle size distribution Dry compacted voids – measure of fineness Moisture Content

Tests applied to some fillers Loss on Ignition – applied to fly ash Clay Index (rock source / baghouse) Water soluble fraction – applied to cement works flue dust

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Functions of Aggregates in Asphalt Surfacing

  Provides a safe road surface for the public to use.

  Provides surface texture and skid resistance

  Provides the increased resistance to the traffic loads and tyre pressures

  Spreads wheel loads to lower pavement layers

Wheel Tracking

  wheel tracking device as per TRL design   test at 60 C   42 passes per

minute   load with 700 N   terminate at 15 mm

rut or 10,000 passes

Sand Patch Test

SCRIM

Sideway-force Coefficient Routine Investigation Machine

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Functions of Aggregates in Sprayed Seals

  Provides a safe road surface for the public to use.

  Provides the resistance to the traffic loads and tyre pressures

  Provides surface texture and skid resistance

Aggregates in asphalt

Fine Aggregate50%

Coarse Aggregate

34%

Air Voids 5%

Binder6%

Filler5%

Coarse Aggregate

34 %

Fine Aggregate

50 %

Air Voids 5 % Binder

6 % Filler 5 %

Aggregate Sizes Used in Sprayed Seals

  5 & 7 mm –  Lightly trafficked pavements, second application in

multiple application seals, temporary treatments, corrective treatments

  10 & 14 mm –  Common sizes for single/single seals

  16 & 20 mm –  Generally only as first application in double/double

seals, e.g 16/7, 20/7 or 20/10

Australian Standards The following Australian Standards apply to aggregate and fillers

AS 2758 Aggregates and rock for engineering purposes Part 2: Aggregate for sprayed bituminous surfacing

Part 5: Asphalt aggregates

AS 1141 Methods for sampling and testing aggregates

AS1289 Methods of testing soils for engineering purposes

AS 2357 Mineral filler for asphalt has been withdrawn and requirements incorporated in AS 2150 Hot Mix Asphalt

Other Reference Material

  AUSTROADS Asphalt Guide   AAPA National Asphalt Specification   State Road Authority Specifications   Queensland TMR Technical Standards

MRTS11 – Spray (Bituminous) Surfacing MRTS22 – Aggregate Coverings MRTS30 – Dense & Open Graded Asphalt