aggregates aggregates
DESCRIPTION
1TRANSCRIPT
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AGGREGATES
KH4444
ROAD CONSTRUCTION
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1.1 INTRODUCTION
Natural rocks as outcrops near surface or gravel deposits along river streams
Natural igneous, sedimentary, and metamorphic
Other lightweight (heated clay) and slag
Igneous crystalline, cooling of magma, classified based on grain size or acidity
Sedimentary deposition of rock residue or inorganic remains, classification based on predominant mineral calcareous, siliceous, or argillaceous
Metamorphic rocks subjected to heat an/or pressure >> change mineral structure, generally crystalline in nature
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1.1 INTRODUCTION cont..
Gravel breakdown of natural rocks in waterways, smooth, rounded >> need to be crushed B4 use
Sands the most resistant final residue of rocks, predominantly quartz, often contain silt or clay >> maybe need to be washed
Slag byproduct of steel, copper or tin, glassy or honeycombed. Good skid resistance but high absorption
Physical properties important, chemical properties to ensure bonding
Important to sample and test on regular basis to ensure properties consistent and meet the specification
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1.2 AGGREGATE PRODUCTION & SAMPLING
Agg physical characteristic determined by parent rock and production process
The production process in the quarry can significantly improve the quality of the aggregate by eliminating of the weaker rocks and by the
effect of crushing on the particle shape and gradation of the agg.
Inferior rock stripped, wasted tru grizzly
Aggregate processing:
Excavation
Transportation
Crushing
Sizing
Washing*
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1.2.1 Quarry Operations
Basic purpose to remove sound rock from face via blast, then use crushers, pulverizers, screening to separate into diff. size
Desirable to produce cube shaped not flat or elongated
Operation : remove overburden >> blast (danger) >> transport via truck to feeder >> grizzly (waste > jaw >> screen (stockpile) >> cone >> screen
Primary crusher reduce blasted rock to max size ranging from 8 - 1
Secondary & tertiary reduce to desired size
Stockpiled according to size
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1.2.1 Quarry Operations
Four mechanical reduction mechanism impacts, attrition, shearing,
compression (refer figure 3-2 to 3-6)
1. Impact sharp, instantaneous impingement of object against another (most crushers)
harder rocks use of more compression crushers than impact.
1. Attrition rubbing between two hard surfaces (hammermill, gyratory, cone)
2. Shear trimming or cleaving action (single roll crusher combine with other mechanisms)
3. Compression use compressive forces between surfaces (jaw)
Select crusher type based on rock type and production req.
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1.2.2 Aggregate Sampling
B4 test, sample must be obtained from source random (QC) or representative (mix design)
Tests are meaningless if improper sampling
Samples taken from stockpile, belts, bins, or truck
Avoid segregated samples (truck, bin) >> best from conveyor
Representative sample - combine random samples truout time/place
Stockpile coarse (bottom edge), climb to mid, take underneath stockpile, taken at several location >> combine >> representative
Reduce sample prior testing via quartering or splitting
***TEST results depends on technique used
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1.2.2 Aggregate Sampling
Why sampling is important?
1. To evaluate the potential quality of a proposed aggregate source.
Does new source meet aggregate specifications?
2. To determine compliance with project specification requirements.
Do current aggregates meet specifications?
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1.3 AGGREGATE PROPERTIES
Physical properties is primary concern
Physical (density, porosity, strength) and chemical (wetting, adhesion, stripping) are functions of composition and structure of minerals in aggregate
1.3.1 Aggregate Mineralogy Composed of minerals silica, feldspar, ferromagnesian, carbonate
and clay
Mineral composition also affect skid resistance quartz and feldspar
Presence of surface coating and deleterious substance affect bonding and moisture susceptibility
Most important effect of mineralogy its influence on adhesion and moisture damage (carbonate bonds better than siliceous)
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1.4 PHYSICAL PROPERTIES OF AGGREGATES
Classification by size: 1. Coarse Aggregate
Retained on 4.75 mm (No. 4) ASTM D692
Retained on 2.38 mm (No. 8) Asphalt Institute
Retained on 2.00 mm (No. 10) HMA Book
2. Fine Aggregate
Passing on 4.75 mm (No. 4) ASTM D1073
Passing on 2.38 mm (No. 8) Asphalt Institute
3. Mineral Filler
At least 70% passed 75 m ASTM D242
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For HMA need to be hard/tough/strong, durable/sound, properly graded; consist of cubical, low WA; and have
clean, rough, and hydrophobic surfaces
Suitability for HMA determined by evaluating gradation, cleanliness, toughness, soundness, surface texture,
particle shape, WA, and affinity
Characteristics, significant, tests and specification (T 3-6)
JKR/SPJ/1988 toughness, soundness, shape, WA, polishing, cleanliness, gradation, affinity
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1.4.1 Toughness/Abrasion Resistance
Agg transmit wheel load tru internal friction >> must be abrasion, polishing, disintegration and crushing
resistant.
Agg undergo all this during manufacturing, placing, construction and service life.
Tests involved ACV, LAAV
ACV 30, LAAV < 40
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1.4.2 Durability and Soundness
Estimates resistance to weathering (breakdown and
disintegration) Soundness Test
* Simulates freeze/thaw action by successively wetting and
drying aggregate in sodium sulfate or magnesium
sulfate solution
+ One immersion and drying is considered one cycle
* Result is total percent loss over various sieve intervals for
a prescribed number of cycles
+ Max. loss values typically range from 10 to 20% per
5 cycles (depends on aggregate)
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1.4.3 Particle Shape & Surface Texture
Cubical not flat or elongated shape (angular better interlock and internal friction), rough texture increase bond with AC.
Tests particle index (ms 106 - time consuming), fractured face, EI & FI
JKR/SPJ/1988 specifies material shall be crushed rock, or crushed gravel, or mixture of crushed and natural
aggregates, which is hard, durable
Flaky 30, Fracture face 80%
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1.4.4 Cleanliness & Deleterious Materials
Absence of foreign or deleterious material.
Tests sand equivalent, clay lumps, PI
JKR/SPJ/1988 aggregate shall be . clean and essentially free from clay and any deleterious materials
PI 6
Clean?, deleterious?
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1.4.5 Specific Gravity
Ratio weight of mat. to water of equal volume at 23C, useful in making weight-vol conversion
In metric units, G simply:
G = weight / vol
Four Gs apparent, bulk, effective, bulk impregnated: (F 3-9)
1. Apparent weight / vol solid Dry
2. Bulk weight / overall vol SSD
3. Effective weight / (overall vol asp asorb. pores)
4. Bulk impregnated eff. but immerse in asphalt
Gsb < Gse < Gsa
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1.4.5 Specific Gravity, cont
G and absorption of coarse & fine
Weighted G, aggregate of various sizes/stockpiles
P1 + P2 + + Pn
G = P1 + P2 + + Pn
G1 + G2 + + Gn
Example 3 -1 and 3 2, pages 114 -117
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1.4.6 Gradation
Distribution of particle sizes expressed as a percentage of total weight (total % passing various sieve sizes)
Determined by sieve analysis
Graphically presented on semi-log graph
3 gradations : well (dense), uniform (single), gap graded (F 3-10)
Gradation affect stiffness, stability, durability, permeability, workability,
fatigue, skid, and moisture damage resistance >> limits on the agg
gradation to be used in HMA
HMA need to have sufficient air voids in grading mix for durability (permits
enough AC to be incorporated) and avoid bleeding and rutting (yet
still have enough air space in mixture)
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1.4.8 Gradation, cont
Two designation for max size
1. Max size smallest sieve tru which 100% particles pass
2. Nominal max size largest sieve retain some agg (
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Sieve Analysis
To determine gradation dry sieve and washed-sieve
Washed more accurate but dry faster and often used (measured amount passing 75 m lower)
Example 3-3 pg 122
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Aggregate Blending
Two or more stockpile need to be blended to get max density and desired void for HMA (or meet spec envelope)
Reasons for blending:
1. Obtain desired gradation
2. Single natural or quarried material not enough
3. Economical to combine natural and processed materials
Normally three or more stockpiles plus mineral filler
Most common method for determining proportion trial & error
Example 3-4 and 3-5
Blended aggregate specific gravity
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Questions?
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Igneous Rock
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Sedimentary Rock
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Metamorphic Rock
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Gravel, Sand, Slag
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Simplified Crusher Set-up
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Blasting
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Impact (F3-2)
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Impact and Attrition (F3-4)
Hammermill
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Shear, Impact and Compression (F3-5)
Single-roll Crusher
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Compression and Impact (F3-6)
Jaw
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Natural sands and gravels 2 sources, underwater and land
1. Underwater sources lakes and river Use barge-mounted dredges, draglines,
scoops, conveyors or pumps
Relatively clean 2. Land sources gravel or sand pits
Use bucket loaders and back hoes
Excavation
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Excavation
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Crushed stone and rock 1. Rock depths < 50, overburden washed out during
processing
2. Rock depths > 50, remove overburden (soil stripped with bulldozers and scrapers
Blasting required
Excavation
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Excavation
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Crushing
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Partially Crushed
River Gravel
River Gravel
Crushed Rock
Crushing
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Land Transportation
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Rail Transportation
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Barge / Water
Transportation
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Sizing
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* Prevent segregation and contamination * Good stockpiling = uniform gradations
- Short drop distances - Minimize moving - Don't use "single cone" method - Separate stockpiles
Stockpiling
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Stockpiling
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Sampling from Fine
Aggregate Stockpile
Sampling from Stockpile
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Sampling from Conveyor
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Splitter
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Classification based on Surface Charges
F3-7
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Characteristics & Tests of Aggregate for HMA
Characteristics Test Malaysian Requirement
Hardness/Toughness MS-30, ASTM C131 ACV < 30, LAAV < 40
Soundness AASHTO T104 Loss < 12%
Shape & Texture MS-30 FI < 30, > 80% fracture
Polishing resistance MS-30 PSV > 40
Stripping resistance AASHTO T182 Coated > 95%
SG and WA MS-30 WA < 2%
Gradation and size BS 1377 Minimum & maximum
depends on use & mix
Cleanliness &
deleterious material
BS 1377 Free from dust, clay,
vegetative and organic, and
deleterious substances
PI < 6%
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Toughness
* Aggregate Crushing Value (MS 30: Part 8: 1995)
Relative measure of the resistance of an aggregate to
crushing under a gradually applied compressive load
Test specimen compacted into steel cylinder
subjected to load applied tru plunger.
Degree of crushing assessed by sieving test and
taken as a measure of aggregate crushing value
(ACV)
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ACV
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* Los Angeles Abrasion (AASHTO T96, ASTM C131):
Resistance of coarse agg to abrasion and
mechanical degradation during handling,
construction and use
* Aggregate at standard gradation subjected to
damage by rolling with prescribed number of steel
balls in large drum for a given number of rotations
* Result expressed as % changes in original weight
Abrasion Resistance
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LA Abrasion Test
- Approx. 10% loss for extremely hard igneous rocks - Approx. 60% loss for soft limestones and sandstones
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Soundness
(AASHTO T 104)
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Soundness
Before After
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Flakiness & Elongation
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Flakiness & Elongation (MS 30)
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* ASHTO T176, ASTM D2419
- Used to estimate the relative proportions of fine agg. and clay-like or plastic fines and dust.
SE = Sand Reading Clay Reading
Sand
Reading
Clay Reading
Flocculating
Solution
Suspended
Clay
Sedimented
Aggregate
x 100
Clay Content
(Sand Equivalent Test)
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Bottle of Solution on Shelf
Above Top of Cylinder
Hose and
Irrigation Tube
Measurement Rod
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Marker on Measurement Rod
Top of Suspended Material
Top of Sand Layer
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Clay Lumps and Friable Particles
ASTM C 142
Clay and friable particles may cause stripping, pitting and affect durability
Normally removed during crushing operation at grizzly or washing
1. Washed and dried a given mass of aggregate
2. Soaks for 24 hrs
3. Rubs each particle
4. Performs washed sieve over several screens
5. Dries the aggregate
6. Report percent loss as % of clay and friable
particles
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Plasticity Index
ASTM D4318
Difference between LL and PL of material passing 42 m
PI is measure of degree of plasticity of fines, can indirectly indicate amount and type of plastic fines
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Ratio of the mass to volume of an object to that of water at the same
temperature
G =
Mass Solid
Volume
Mass Water
Volume
Specific Gravity, G
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Density is the unit weight of a material
lb/ft3 or kg/m3
Unit weight = g w G
gw = 1.000 g/cm3
gw = 1000 kg/m3
gw = 62.4 lb/ft3
Bulk density means sample contains
more than one mass and/or volume
Densities
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Gsa =
Mass of oven dry agg
Vol of agg
Apparent Specific Gravity
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Gsb =
Vol of agg, + perm. pores
Vol. of water-perm. pores
Surface Voids
Bulk Specific Gravity
Mass of oven dry agg
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Gs, eff = Mass oven dry agg
Vol of agg, + perm. pores not absorb. asphalt
Effective Specific Gravity
Surface Voids
Solid Agg.
Particle
Vol. of water-perm. voids
not filled with asphalt
Absorbed asphalt
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Phase: a change in state (e.g. solid, liquid, gas) Oven dry weight of agg = Ws Unit weight of water, gw = 1 g/cm3
Water
permeable
pores
Aggregate
Solids Vs
Vpp
Vpp - Vap
Vap
Phase Diagram (F 3-9)
Gsa = Ws / (Vs x gw )
Gsb = Ws / (Vs + Vpp) gw
Gse = Ws / (Vs + Vpp -Vap) gw
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Specific Gravity Tests for
Aggregates
Two tests are needed:
1. Coarse aggregate (retained on the 4.75
mm sieve)
2. Fine aggregate (passing the 4.75 mm
sieve)
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Coarse Aggregate Specific Gravity
ASTM C127
1. Dry aggregate
2. Soak in water for 24 hours
3. Decant water
4. Use pre-dampened towel to get SSD condition
5. Determine mass of SSD aggregate
6. Determine mass under water
7. Dry to constant mass
8. Determine oven dry mass
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Coarse Aggregate Specific Gravity
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Coarse Aggregate Specific Gravity
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Coarse Aggregate Specific Gravity Calculations
Gsb = A / (B - C)
A = mass oven dry
B = mass SSD
C = mass under water
Gsa = A / (A - C)
Water absorption, %
Absorption % = [(B - A) / A] * 100
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Fine Aggregate Specific Gravity
ASTM C128 1. Dry aggregate
2. Soak in water for 24 hours
3. Spread out and dry to SSD
4. Add 500 g of SSD aggregate to pycnometer of known volume
Pre-filled with some water
5. Add more water and agitate until air bubble have been removed
6. Fill to line and determine the mass of the pycnometer, aggregate and water
7. Empty aggregate into pan and dry to constant mass
8. Determine oven dry mass
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Fine Aggregate Specific
Gravity
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Fine Aggregate Specific
Gravity
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Fine Aggregate Specific
Gravity
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Fine Aggregate Specific Gravity Calculations
Gsb = A / (B + D - C)
A = mass oven dry
B = mass of pycnometer filled with water
C = mass pycnometer, SSD aggregate and water
D = mass SSD aggregate
Gsa = A / (B + A - C)
Water absorption, %
Absorption % = [(D - A) / A] * 100
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2. Uniformly graded (single size)
Few points of contact Poor interlock (shape dependent) High permeability
1. Well graded (dense) Good interlock Low permeability
3. Gap graded Only limited sizes Good interlock Low permeability
Types of Gradations
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Aggregate Gradations
0
10
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10 100
Gap-graded
(open)
Well-graded
(dense)
Uniformly graded
(single-size)
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Aggregate Gradation
Use 0.45 Power Gradation Chart
Blend Size Definitions maximum size
nominal maximum size
Gradation Limits control points
restricted zone
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Example:
5.00 mm sieve plots at (5.00)0.45 = 2.25
Sieve Size (mm) Raised to 0.45 Power
0
20
40
60
80
100
0 1 2 3 4
Percent Passing
0.45 Power Grading Chart
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0.45 Power Grading Chart Percent Passing
0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0
Sieve Size (mm) Raised to 0.45 Power
0
20
40
60
80
100
maximum density line
max
size
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Aggregate Size Definitions
Nominal Maximum Aggregate Size one size larger than the first sieve
to retain more than 10%
Maximum Aggregate Size one size larger than nominal
maximum size
100 100 90 72 65 48 36 22 15 9 4
100 99 89 72 65 48 36 22 15 9 4
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Gradations Considerations
Considerations: Max. size < 1/2 lift thickness
Larger max size:-
1. Increase strength
2. Improve skid resistance
3. Increase volume and surface area of agg which decreases required AC content
4. Improve rut resistance
5. Increase problem with segregation of particles
Smaller max size:-
1. Reduces segregation
2. Reduces road noise
3. Decreases tire wear
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Expected Problems
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T 4.11 Tolerances for Asphaltic Concrete Mixes
JKR/SPJ/1988
Parameter Permissible Variation
(% by weight of total mix)
Bitumen 0.2 %
Fraction of combined agg.
passing 5 mm and larger sieves
5.0 %
Fraction of combined agg.
passing 3.35 mm and 1.18 mm
4.0 %
Fraction of combined agg.
passing 425 m and 150 m
3.0 %
Fraction of combined agg.
passing 75 m sieve
2.0 %
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100
0 .075 .3 2.36 4.75 9.5 12.5 19.0
Percent Passing
control point
restricted zone
max density line
max
size
nom
max
size
Sieve Size (mm) Raised to 0.45 Power
Restricted Zone
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Superpave Aggregate Gradation
100
0 .075 .3 2.36 12.5 19.0
Percent Passing
Design Aggregate Structure
Sieve Size (mm) Raised to 0.45 Power
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Superpave Mix Size
Designations
Superpave Nom Max Size Max Size
Designation (mm) (mm)
37.5 mm 37.5 50
25 mm 25 37.5
19 mm 19 25
12.5 mm 12.5 19
9.5 mm 9.5 12.5
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Target Gradation
Acceptable gradation band specified
Mix design selects a job mix formula (JMF) which falls within band and meets design criteria
Superpave 5 nominal sizes (37.5, 25, 19, 12.5, and 9.5 mm)
Four sieve sizes used to set upper and lower limits
Staying out of the restricted zone in suggested to minimize problems with natural sands
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Washed sieve analysis
Part 1 - Washing
1. Dry aggregate and determine mass
2. Wash and decant water through 0.075 mm sieve until water is clear
3. Dry aggregate to a constant mass
Part 2 - Sieving
1. Place dry aggregate in standard stack of sieves
2. Place sieve stack in mechanical shaker
3. Determine mass of aggregate retained on each sieve
Part 3 - Computation
1. Add mass washed into mass passing 0.075 mm
2. Calculate percent passing as usual
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Washed Sieve
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Individual Sieve Stack of Sieves
Mechanical Sieve
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Stack in
Mechanical
Shaker
Mechanical Sieve
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Blending Stockpiles
Basic formula for combining stockpiles to achieve a target gradation is:
p = Aa + Bb + Cc + .
where:
p = percent of material passing given sieve
size for the combined agg
A, B, C, .. = percent passing given sieve for each agg.
a, b, c, = proportion (decimal fraction) of A, B, C, to be used in blend, a + b + c + = 1.00
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Blending Stockpiles
1. Plot individual gradations
2. Plot specification limits
3. Can be used for initial assessment Can blend be made from available
materials?
Identification of critical sieves
Estimate trial proportions
Possible outcome (F 3-15)
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All possible combinations fall between A and B
Gradation B
Control points for
12. 5 nominal max. size
Gradation A
0
10
20
30
40
50
60
70
80
90
100
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Percent Passing, %
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No poss. combination of A and B will meet spec.
Gradation B Gradation A
Control points for
12. 5 nominal max. size
0
10
20
30
40
50
60
70
80
90
100
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Percent Passing, %
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100
All poss. combinations pass through cross-over point
Blends containing more A than B will be closer to A
Gradation A
Gradation B
Control points for
12. 5 nominal max. size
0
10
20
30
40
50
60
70
80
90
100
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Percent Passing, %
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Trial and Error
Aided by experience and plots of indiv. gradation curves and spec limits
Calculated grading compared with spec adjust until pass
Guided by reasoning, maths, experience
Use of spreadsheet now common
Steps in trial and error:
1. Select critical sieves in blend
2. Determine initial proportions which will meet critical sieves
3. Check calc. blend against specification
4. Adjust if necessary and repeat above steps
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Blending of Aggregates
Agg. B Agg. A
Blend Target
Material
%
Passing
%
Passing
% Used
U.S. Sieve %
Batch
%
Batch
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
3/8
90
30
7
3
1
0
0
100
100
100
88
47
32
24
10
100
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Blending of Aggregates
Agg. B Agg. A
Blend Target
Material
%
Passing
%
Passing
% Used
U.S. Sieve %
Batch
%
Batch
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
3/8
45
15
3.5
1.5
0.5
0
0
100
100
100
88
47
32
24
10
100
50 % 50 %
First Try
(remember trial & error)
90
30
7
3
1
0
0
50
90 * 0.5 = 45
30 * 0.5 = 15
7 * 0.5 = 3.5
3 * 0.5 = 1.5
1 * 0.5 = 0.5
0 * 0.5 = 0
0 * 0.5 = 0
100 * 0.5 = 50
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
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Blending of Aggregates
Agg. B Agg. A
Blend Target
Material
%
Passing
%
Passing
% Used
U.S. Sieve %
Batch
%
Batch
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
3/8
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
45
15
3.5
1.5
0.5
0
0
100
50
50
44
23.5
16
12
5
50
50 % 50 %
90
30
7
3
1
0
0
50
95
65
47.5
25
16.5
12
5
100
100
100
88
47
32
24
10
100
Lets Try
and get
a little closer
to the middle of
the target values.
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Blending of Aggregates
Agg. B Agg. A
Blend Target
Material
%
Passing
%
Passing
% Used
U.S. Sieve %
Batch
%
Batch
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
3/8
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
27
9
2.1
0.9
0.3
0
0
100
70
70
61.6
32.9
22.4
16.8
7
70
70 % 30 %
90
30
7
3
1
0
0
30
97
79
63.7
33.8
22.7
16.8
7
100
100
100
88
47
32
24
10
100
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Blended Aggregate Specific
Gravities
Once the percentages of the stockpiles have been established, the combined aggregate
specific gravities can also be calculated
Combined G = 100
P1 + P2 + . Pn
G1 G2 Gn