Asphalt Concrete Aggregates

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Asphalt Concrete Aggregates

• Soil Definition (Engineering)
• refers to all unconsolidated material in the
  earths crust, all material above the bedrock
• mineral particles (gravel, sand, silt, clay)
• organic material (top soil, marshes)
• Aggregates
• mineral particles of a soil
• specifically, granular soil group
• gravel, sand, silt

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Asphalt Concrete Aggregates

• Granular Soil Group (Aggregates)
• Physical weathering
• action of frost, water, wind, glaciers,
  plant/animals ..
• particles transported by wind, water, ice
• soils formed are called granular soil type
• grains are similar to the original bedrock
• Larger grain sizes than clays
• Particles tend to be more or less spheres/cubes
• Bound water is small compared to overall mass

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Asphalt Concrete Aggregates

• Granular Soil Group (Aggregates)
• ability to achieve greater densities
• well graded granular material
• increased soil strength
• lower permeability
• reduced future settlement
• These improvements dictate the use of aggregates
  in pavement layers where wheel loads are greater

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Asphalt Concrete Aggregates

• Aggregates for asphalt concrete include
• coarse aggregates
• aggregate particles larger than the 4.75 mm sieve
• fine aggregates
• aggregate particles smaller than the 4.75 mm
  sieve
• mineral filler
• aggregate particles smaller than the 75 um sieve

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Asphalt Concrete Aggregates

• Mineral Filler
• provides the fines that are important in
  producing a dense-graded strong material
• however the amount of mineral filler must be
  limited
• covering them would require excess asphalt cement
• strength of the concrete mix would be reduced as
  the mixture would depend on friction between
  smaller particles, which is less than between
  larger particles
• limestone dust is the most common material

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Asphalt Concrete Aggregates

• Aggregate Properties
• Well graded-dense including mineral filler
• Hard-resistance to wear and traffic polishing
• Sound-resistance to breakdown due to freeze/thaw
  cycles
• Rough Surfaced-crushed rough surfaces
• higher friction strength
• better adhesion to asphalt cement
• Avoid cubical-thin elongated particles that break
  easier

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Asphalt Concrete Aggregates

• Aggregate Properties (contd)
• Free from Deleterious Substances
• clay, dust, dirt, lightweight pieces
• lower quality of asphalt film on the particle
• breaking of some particles
• Hydrophobic water hating
• siliceous aggregates such as quartz are
  hydrophilic
• greater affinity for water than asphalt cement
  due to surface charges
• stripping, asphalt coating comes away from the
  particle in the presence of water

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Asphalt Concrete Aggregates

• Stripping Tests
• Visual tests (Saskatchewan Highways)
• samples saturated under vacuum / stripped
• Strength Tests
• ASTM D1075, Effect of water on Compressive
  Strength of Compacted Bituminous Mixtures
• samples are submerged for 4 days
• ASTM D4876, Effect of Moisture on Asphalt
  Concrete Paving Mixtures
• samples are submerged under vacuum 80 saturation
• AASHTO T 283, Modified Lottman Test
• 80 saturation / freeze thaw

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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates

• Superpave Aggregate Properties
• three critical distress mechanisms
• rutting
• fatigue cracking
• low temperature cracking
• central role in overcoming permanent deformation
  ie. Rutting
• lesser role in pavement fatigue and low
  temperature cracking

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Asphalt Concrete Aggregates

• Consensus Aggregate Properties
• pavement experts agreed that these aggregate
  properties were critical to well performing mixes
  and wide agreement in their use and specified
  values
• criteria are based on traffic levels and position
  within pavement structure

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Asphalt Concrete Aggregates

• Source Aggregate Properties
• pavement experts agreed that there were other
  critical aggregate properties that were dependant
  on local sources and experience and were left to
  local agencies to specify

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Asphalt Concrete Aggregates

• Superpave consensus aggregate properties
• Coarse aggregate angularity
• ensures a high degree of internal friction and
  rutting resistance
• percent by weight of aggregates larger than 4.75
  mm with one or more fractured faces
• Fine aggregate angularity
• ensures a high degree of fine aggregate internal
  friction and rutting resistance
• percent air voids in loosely compacted aggregates
  smaller than 2.36 mm

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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates Superpave consensus
aggregate properties
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Asphalt Concrete Aggregates
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Asphalt Concrete Aggregates

• Superpave consensus aggregate properties
• Flat and Elongated Particles
• percentage by mass of coarse aggregates that have
  a maximum to minimum dimension ratio greater than
  five
• particles are undesirable because of their
  tendency to break during construction and under
  traffic
• procedure uses a proportional caliper device to
  measure the dimensional ratio of a representative
  sample of aggregate particles
• percentage of flat percentage of elongated
  particles

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Asphalt Concrete Aggregates Flat and Elongated
Particles
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Asphalt Concrete Aggregates Flat and Elongated
Particles
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Asphalt Concrete Aggregates

• Superpave consensus aggregate properties
• Clay content
• percentage of clay material contained in the
  aggregate fraction that is finer than the 4.75 mm
  sieve
• sand equivalency test is used in which a sample
  is mixes with a flocculating solution forcing
  clay particles into suspension
• after a settling period the height of suspended
  clay and sedimented sand is measured
• sand equivalent is the ratio of sand to clay
  readings

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Asphalt Concrete Aggregates
Clay Content
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Asphalt Concrete AggregatesClay Content
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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Toughness
• percent loss of material from an aggregate blend
  larger than 2.36 mm using a Los Angeles Abrasion
  Test
• estimates the resistance of coarse aggregate to
  abrasion and mechanical degradation during
  handling, construction and in service
• maximum loss values typically range from 35 to 45
  percent

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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Soundness
• percent loss of material from from an aggregate
  blend during the sodium or magnesium sulfate
  soundness test
• can be used on both coarse and fine aggregates
• resembles freeze/thaw in the field
• test result is total percent loss over various
  sieve intervals for a required number of cycles
• maximum loss values typically range from 10 to 20
  percent for five cycles

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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Deleterious materials
• defined as mass percentage of contaminants such
  as clay lumps, shale, wood, mica, and coal in a
  blended aggregate
• performed on both coarse and fine aggregates
• mass percentage of material lost as a result of
  wet sieving is reported as the percent of clay
  lumps and friable particles
• values range as low as 0.2 percent to 10 percent
  depending on the exact composition of the
  contaminant

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Asphalt Concrete Aggregates

• Superpave aggregate properties
• Gradation Chart
• the 0.45 power gradation chart is used in which
  sieve sizes are raised to the power 0.45 on the
  horizontal axis (normal sieve gradation graph
  already in use)
• maximum density gradation is a straight line from
  the maximum aggregate size to the origin
• maximum size is defined as one sieve size larger
  that the nominal maximum size
• nominal maximum size is defined as one sieve size
  larger than the first sieve to retain more than
  10

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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Gradation Chart (contd)
• specifies two new features to the gradation chart
• Control Points placed on the nominal maximum
  sieve, an intermediate sieve (2.36 mm), and the
  smallest sieve (75 um) through which the
  gradation must pass
• Restricted Zone placed on the maximum density
  line between an intermediate sieve and the 0.3 mm
  sieve through which the gradation cannot pass.
  Gradations that pass through the restricted zone
  are called humped gradations

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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Gradation Chart (contd)
• Humped gradations indicate an
• oversanded mixture and/or a mixture that contains
  too much fine sand in relation to total sand
• restriction zone discourages the use of fine
  natural sand and encourages the use of a clean
  manufactured sand

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Asphalt Concrete Aggregates

• Superpave source aggregate properties
• Gradation Chart (contd)
• Results
• mixtures that poses compaction problems during
  construction tender mixes
• offers reduced resistance to rutting
• gradations that follow to close to the maximum
  density line for fine aggregates often have
  inadequate VMA to allow enough asphalt for
  adequate durability

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Asphalt Concrete Aggregates Gradation Chart
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Asphalt Concrete Aggregates Gradation Chart