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Ce 4650 Lec 10 Aggregates

Terms in this set (40)

Materials used in asphalt mix
-Asphalt cement
Aggregate" coarse and fine
Materials must meet spec requirements
Aggregates
Predominant construction material in volume of use
Aggregates used alone
Alone: used as road base and various types of fill
Aggregates used as/in binder
Binder: asphalt cement or portland cement

AC: asphalt cement concrete
PC: Portland cement concrete
Mineral aggregate responsibility for asphalt mixtues
- % of mixture: -93-95% by weight or 73-85% by volume
- responsible for load supporting capacity of pavent ( aggregate caries the load)
-pavement performance influenced by aggregate
Mineral Aggregate for HMA Definition
-any hard, inert mineral materials used for mixing in graduated particles or fragments. It includes sand, gravel crushed stone, slag, and rock dust or powder
- usually refers to soil that has in some way been processed or sorted
Mineral Aggregate for HMA
Local supplies of natural rock or imported

-Natural rock classification based on geological origin
>igneous
>sedimentary
>metamorphic

-Artificial
artificial aggregates
-lightweight aggregate: (heating clay to very high temp)

-Slag: (produced in blast furnace during steel production)
Rock classifications by igneous sedimentary metamorphic
Igneous:
-granite, syenite, deorite
-basalt (trap rock)
- diabase (trap rock)
-gabbro (trap rock)

Sedimentary
-limestone, sandstone, chert, shale

metamorphic
-gneiss, schist, slate, quartzite, marble, serpentine
Aggregate production
-Produced in quarry or mine
>convert in situ rock into aggregate w/ specified characteristics
-rock is blasted or dug from quarry walls then reduced in size using series of screens and crushers
>quarries capable of washing the finished aggregate
largest sieve and smallest sieve
3/4 inch (19 mm)

No. 200 (75 um)
Aggregate classification by size
Coarse aggregate
fine aggregate
filler
coarse aggregate
-retained on No 4 sieve
-opening: .187 inch, 4.75 mm
fine aggregate
Passing No. 4 Sieve
-Opening: .187 inch, 4.75 mm
Filler
- Greater than or equal to >/= 70% passing No.200 sieve
- opening: .0029 inch, .075 mm
Type of aggregates desired for ashpalt - Trafficking
Cubical, rough texure aggregate is desire

- provides more strength than smooth textured aggregate
Shearing behavior of aggregate: internal friction
-Cubical is better becase it has a higher angle of repose = higher internal friction
cohesion
- comes from binder
Suitability characteristics used to define aggregates for use in asphalt mixtures
- Toughness and Abrasion resistance

-Durability and Soundness

-Particle shape & Surface texture

-Cleanliness and Deleterious materials

- Size and Gradation
Cleanliness and Deleterious materials
-sand equivalent test
-Clay lumps & Friable particles
-Plasticity index
Los Angeles Abrasion test
Toughness

-degradation during handling, construction, and use
-resistance of coarse agg to abrasion by mechanical force
-% passing no 12 sieve is a measure of degradation

-sample of coarse agg placed in tumbler with steel balls. tumbling causes abrasion b/w particles and b/w steel balls and particles
LA abrasion results
-%change in original wt
-LA abrasion = [wt passing no 12/total wt]*100

Ex. 5000 gm of blend, 1500 gm passing no 12 sieve
-LA abrasion= [1500/5000]*100= 30%
L.A. Abrasion values
hard, igneous: 10
soft limestones and sandstones: 60
basalt: 10-17
dolomite: 18-30
gneiss: 33-57
granite: 27-49
limestone: 19-30
quartzite: 20-35
Micro Deval
Toughness
-resistance of coarse aggregate to abrasion
- abrasion loss in presence of water and damage through abrasion
Micro deval procedure/ results
-conducted on coarse agg
-obtain wt initial: retained on no 4: 1500 gm
-obtain wt final: retained on no 16: 1400 gm

-%loss=[wt no 4- wt no 16/wt no 4]*100= 6.7
Soundness Test
-estimates resistance to weathering
-simulates freeze-thaw process
-repeated submerging an agg sample in saturated solution of sodium or magnesium sulfate
-salt crystals will form in agg pores which simulates ice crystal formation
Soundness tets procedure
-immerse sample in solution and sit at constant temp for 18 hrs
-dry sample to constant weight at 110C +/- 5C (230F+/- 9F)
-repeat 5 times, wash sample to remove salt
-determine weight loss for each sieve
- max loss values range between 10-20% for evry 5 cycles
Particle shape and surface texture: Shape
-workability and strength
-cubical vs flat, thin or elongated
Shape: Desired aggregate
-Cubical
-not flat, thin or elongated
Round aggregate
-provides better workability
-requires less compaction
-lower structural capacity
-natural gravel and sands
Surface Texture
-Workablility and strength
-rough vs smooth
Rough texture
-sand paper like
-increases mixture strength: high degree of internal friction
-requires additional AC to overcome loss of workability
-higher voids space in compacted mass: this provides extra space for AC
>the increase in amount of AC provides a stronger mechanical bond
Particle shape and texture test
- Ia=1.25(V10)-.25(V50)-32---(in-lb)
-Each layer:
10 tamps :V10=% voids in agg compacted w/ 10 blows per layer
50 tamps+V50
shape and texture test procedure
measures change in voids as the agg sample is compacted in mold
agg sample divided up in to specific size fractions
-each size fraction goes in container in 3 layers, repeat process twice
-first time, each layer tamp 10 blows, second 50
shape and texture test results
Ia is computed as a weighted avg of the individual size fraction Ia based on the size fraction weights
-Ia=6-7 for round, smooth
Ia=15-20 for cubical, rough
-Higher Ia is better
Deleterious Material: Clay lumps and friable particles
-Deleterious material is the mass percent of contaminants in the blended agg
--soak for 24 hr, each particle rubbed
-wash sieve over several scrrens
-percent loss is reported as the % clay or friable particles
Performance
Performance grade of HMA's is influenced by agg properties
Increase in agg angularity and texture
-increase in strength and stability of HMAs
-rutting: agg properties
Angularity influence on HMA performance
-fine aggregates: greater influence
binder affects
low temperature cracking
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