30a. Aggregate Flashcards
Natural rock types
Igneous (granite), sedimentary (limestone), metamorphic (shale/slate)
Aggregate processing
Excavation, transportation, crushing, sizing, washing
Crushing
Crushing of large boulders and aggregates to usable sizes
Sizing
Separating into stockpiles with specific size ranges
Stockpiling
Two or more stockpiles are blended together
Poor stockpiling
Results in separation and segregation in sizes
Aggregate sampling
Small amount of aggregate blend taken to evaluate quality
Aggregate selection
Based on economics of suitable aggregates
Cleanliness
Limits on foreign or harmful substances in the aggregate
Surface texture
Rough surface increases mixture strength, and influence workability
Particle shape
Influences workability and compaction
Particle lock (higher produces higher mix strength) is higher with cubical shapes and lower for rounded particles
Toughness and abrasion resistance
Resistance to crushing and wear during their life cycle
Poor abrasion will cause premature structural failure and loss of skid resistance
Durability and soundness
Resistance to breakdown from wetting and drying (freezing/thawing)
Poor resistance causes premature distress
Angular particles
Greater interlocking and internal friction so greater HMA stability
Best particles to use
Rounded particles
Better workability, require less compactive effort, easier to coat with asphalt
Flat/Elongated particles
Tend to impede or break during construction, so may decrease strength
Smooth-surfaced particles
Easier to coat with binder due to surface-to-volume ratio
Stripping of aggregates
One of main failure modes, results in loss of adhesion between particles and bitumen
