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Aggregate Specific Gravity
• If SG of coarse and fine are same – Little difference in volumetrics
• If SG of coarse significantly different
– Slight changes in proportions can cause great differences
– Air void content variations
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Aggregate Specific Gravity
• If SG changes due to source (new supplier, new ledge in quarry,
different part of gravel pit) – Plant values won’t match lab – Can occur with assumed SG from
past experience – Should verify SG on regular basis
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Aggregate Moisture Content
• Moisture in mix at production may contribute to stripping
• Moisture in mix is measured as asphalt content by plant unless correction is done
124 Stockpile Management
125
Stockpile Management
• Reduce moisture content – 1% M.C. = 13% increase in fuel cost
• Also 13% reduction in production – 2% grade for stockpile – Pave if possible – Face the sun
126
N
127
Stockpile Management
• Reduce moisture content – Work sides & middle for consistency – Don’t feed material just delivered – Don’t take material from subgrade – Monitor moisture content
128
129
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Aggregate Stockpiles
Aggregate v. Asphalt Mix Specs Example: ASTM Size 8 Aggregate • #4 sieve
– 10 to 30% • Typical tolerance for Asphalt on #4 sieve
– + 5 • Much tighter tolerance for Asphalt
Plant Production
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Aggregate Stockpiles • If aggregate always coarse
– Plant produces consistent mix • If aggregate always fine
– Plant produces consistent mix • If aggregate variable with tolerance
– Almost impossible to control mix production
• Uniformity of gradation critical to plant
Plant Production
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Aggregate Stockpiles • Segregation of aggregate at plant
– Building stockpile – Retrieving from stockpile – Less of a problem with single-sized
agg • Contamination
– Improper handling – Commingling of different products
Plant Production
134
Hot Bins cannot
fix all
problems!
136
Factors Affecting Volumetric Properties
Assuming mix is close to JMF
VMA Adjustments
+ Reduce P200 + Reduce natural sand + Adjust gradation relative to
maximum density line These all assume mix is reasonably
close to JMF
VMA Adjustments - Aggregate
• Re-screening stockpile • Re-blend at different % • Split into additional stockpiles
– May be helpful for size with high percentage in blend
• Change aggregate source
VMA Adjustments – Particle Shape
+ Increase cubical particles + Reduce flat and elongated particles + Add intermediate coarse aggregate Review Crushing Operations
Air Void Adjustments
+ Reduce asphalt + Reduce P200
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Waste Materials in Asphalt Mixes
Asphalt Industry
• Long supporter of recycling • Recycling cannot be at the expense
of product performance • +70 million tons RAP used annually • Asphalt 100% recyclable
Recycling Advantages
• Reduced Cost of Construction • Conservation of Aggregate & Binders • Preservation of Existing Geometrics • Preservation of Environment • Conservation of Energy • Less User Delay
Asphalt Recycling
• Used Routinely, No Longer Experimental
• Tens of millions of tons used/yr
• Has Performed as Well as Conventional Pavements
RAP use has been evolutionary
Asphalt Recycling
“Overly conservative specifications may be the greatest obstacle limiting the use of RAP.” John Sullivan FHWA
