ECV 3603 Highway Engineering II
Lecture 2 - Aggregates
Aggregates
1) Igneous
– Basalt, granite, ect.
2) Sedimentary Rocks
– Sand stones, chert
3) Metamorphic
– Both Igneous & Sedimentary
– Under heat pressure transformed to crystal type
– Ex. Marble
4) Gravel
5) Sand – Most resistant final residue of deter
Sizes range from no. 8 – no. 20
6) Slag – A bi-product of metallurgical process like processing of
steel, tin, copper
In general physical properties are required for highway work. Chemical
properties may be required for bonding effects
Aggregate
Igneous: Crystal line in nature
If grains are > 2mm – Coarse
If grains are < 0.2mm – fine
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Classification of Igneous Rocks.
Based on Composition:
Acidic
Silica, %
> 66
S.G.
< 2.75
Color
Light
Presence of free Quartz Yes
Intermediate
55 – 66
Basic
< 55
>2.75
Dark
No
Chemical Properties/Physiochemical Prop.
Example
wetting, adhesion, Stripping. The above are important in understanding
bonding:
Physical Properties
Photostate: Pg. 95, 96, 97, 98, 100, 104 (Supplimentary).
Effect of Mineralogy
– Aggregate should not have clay – more than 6 %.
Bonding
AC + Limestone – Good
AC + Silceous – Average
2
Petrographic Examination (ASTM C295)
1. Measure amount of mineral type
2. Check physycal and chemical properties.
a) Particle shape
b) Surface texture
c) Hardness
d) Pore Characteristics
e) Chemical activities
f) Mineral Composition
Mineralogy – ASTM C294
Minerals found in aggregates:
1) Silica (Quartz)
2) Feldpar (Plagioclaze)
3) Ferromagnesium (Muscovite)
4) Carbonate Minerals (Calcite, dolomite)
5) Clay Mineral (Illites, Kaolinites)
Mineralogy can be used to predict the behavior of aggregate materials
but process like
1) Oxidation
2) Hydration
3) Leaching
4) Weathering
Can affect the aggregate performance.
Impurites that can affect aggregate performance in HMA such as:
–
–
–
–
Clay
Shale
Silt
Iron oxide
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– Gypsum
– Water Soluble Salts
Hydrophillic ( water loving) – Acidic in nature.
Hydrophobic (Water hating) – Basic in nature
– Siliceous Agg. (eg. Quartz) become (–) charge when in the presence
of water.
– Dolomite
– Positive.
Surface Texture
A rough, sand – paper like surface is good. But loss of workability
and need more A.C.
Particle (Shape) Index Test (ASTM D3398).
Apparatus:
1. Cylindrical steel mold 150 mm (6inch Ø) by 175 mm (7 inch)
high.
2. Steel Rod 15.8 mm (5/8) Ø 600 mm (24inch) long. (tamping
end is round)
Ia = 1.25 V10 – 0.25 V50 – 32.0
Ia = Particle Index Value
V10 = % Voids in agg., compacted with 10 blows/layer.
4
Quarry operations – skip.
Primary Crushing
– Jaw
Secondary Crushing – Jaw/ sand cone
Tertiary Crushing
– sand Cone
Suitability of Agg. is determined by:
1) Size and gradation
2) Cleanliness/deleterious materials
3) Toughness/hardness
4) Durability/soundness
5) Surface Texture
6) Particle Shape
7) Absorption
8) Affinity for A.C.
Aggregate Testing
1) Agg. Impact Value (AIV)
2) Agg. Crushing Value (ACV)
3) 10 % fines
4) Soundness
5) Specific gravity & Absorption
6) Flakiness & Elongation
7) Angularity Test
8) Particle shape index
9) Polished stone value
10) Gradation Analysis
11) L.A. Abrasion
Note: You are responsible to determine the testing standards for the
above tests.
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1) Aggregate Impact Value
– Passing 12.5mm retained on 10mm
– Wash & dry @ 1000C – 1100C
– Fill mould in 3 layers tamping each layer 25 times – level the
surface.
– Weigh sample.
– Drop weight – 15 blows
– Sieve sample through 2.36mm sieves.
Wt. of sample passing 2.36
Original Wt.
x
100 %
2) Aggregate Crushing Value
–
–
–
–
–
–
150mm Ø mould, 16mm Ø tamping rod 600mm long.
14.0mm sieve size, 10mm, 2.36.
Comp. test machine – at least 400KN.
Testing time 10 minutes.
% wearing for ACV
10 % fines.
3) Specific Gravity
– Includes overall vol. aggregate plus all
pore vol.
b) Effective specific gravity – Includes overall vol. aggregate minus
vol. of larger pores that absorb A.C.
c) Apparent specific gravity – Only the aggregate vol.
a) Bulk specific gravity
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Volumetric Measurement
Very important ones.
App. S.G. =
A
A–C
Bulk S.G. =
A
B–C
Absorption % =
(B–A)
A
100
A = Wt. oven dried.
B = S.S.D.
C =Wt. in water
e-*
x
App.S.G.
= 2.750
Absorption
= 2%
Wt. of dry aggregate = 100 g.
Determine the Bulk S.G.
Vol. of aggregate = Dry wt. aggregate
App.S.G.
Bulk S.G. =
100
36.364 + 2.0
= 2.607
7
= 100 g =
2.75
= 100
38.364
36.364 ml
Average Specific Gravity:
G = P1 + P2 + ------- + Pn
P1 P2
Pn
G1 G2
Gn
P = Wt. Percentage.
e
x
S.G. of blended aggregate
Bulk S.G. of aggregate 1 = 2.500 (1/3)
Bulk S.G. of aggregate 2 = 3.000 (1/3)
Bulk S.G. filler
3 = 2.850 (1/3)
Note: You are responsible for Example 5.1 in the book
Gradation
Affect
1) Stiffness
2) Stability
3) Durability
4) Permeability
5) Workability
6) Fatigue resistance
7) Skid resistance
8) Resistance to moisture damage.
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Aggregate Packing Analysis
 Max Agg. Density will be good
 But VMA must be controlled. Allowing room for asphalt content
 Use CAMA for thorough analysis
Fuller-Thomson Equation:
P = 100 (d / D)n
d = Ø of sieve in question
P = Total % passing
D = Max size of the aggregate
n = 0.5 for max density
Should select gradation that will allow enough asphalt film thickness, for
maximum durability. So minimum VMA is required.
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