Highway Materials, Soils, and Concrete
Aggregates
• Soil Definition (Engineering)
– “refers to all unconsolidated material in the
earth’s crust, all material above the
bedrock”
• mineral particles (gravel, sand, silt, clay)
• organic material (top soil, marshes)
• Aggregates
– mineral particles of a soil
– specifically, granular soil group
• gravel, sand, silt
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1
Highway Materials, Soils, and Concrete
Aggregates
• Granular Soil Group (Aggregates)
– Physical weathering
•
•
•
•
action of frost, water, wind, glaciers, plant/animals
particles transported by wind, water, ice
soils formed are called granular soil type
“grains are similar to the original bedrock”
– Larger grain sizes than clays
– Particles tend to be more or less spheres/cubes
– Bound water is small compared to overall mass
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3
Highway Materials, Soils, and Concrete
Aggregates
• Granular Soil Group (Aggregates)
– ability to achieve greater densities
• well graded granular material
– increased soil strength
– lower permeability
– reduced future settlement
• These improvements dictate the use of
aggregates in pavement layers where wheel
loads are greater
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4
Highway Materials, Soils, and Concrete
Aggregates
• In combination with asphalt cement or
portland cement to form asphalt concrete or
cement concrete respectively
• In subbases and bases of a roadway
structure
• drainage structures
• concrete blocks
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5
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
• Basic properties of these aggregates
• Tests used to evaluate these properties
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6
Highway Materials, Soils, and Concrete
Aggregates
• Aggregate Sources
–
–
–
–
–
–
–
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natural sand or gravel deposits *
crushed rock *
slag and mine refuse
rubble and refuse
artificial and processed materials
pulverized concrete and asphalt pavements
other recycled and waste materials
7
Highway Materials, Soils, and Concrete
Aggregates
• Natural sand and gravel deposits
– sand and gravel pits
– sand and gravel soils that have been
naturally sorted to eliminate most of the silt
or clay sizes then deposited in:
• glacier formations (eskers, outwash plains)
• river deposits
• beaches of current and previous lakes and seas
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8
Highway Materials, Soils, and Concrete
Aggregates
• Sand / Gravel Pit Development
– Stripping of topsoil, vegetation… from surface
– Excavation of material
• material is loose - front end loaders
– Crushing of the material
• larger size aggregate is broke down to desired size
• crushed gravel is considered high quality aggregate
• washing of aggregate cleans dust removes silt/clay
– Type of material depends on bedrock source
ENCI 579 4
• Limestone, sandstone,granite,etc.
9
Highway Materials, Soils, and Concrete
Aggregates
• Crushed Rock
– “Type of aggregates produced from
quarries depends on the type of bedrock”
– Classes of Rocks
• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks
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10
Highway Materials, Soils, and Concrete
Aggregates
• Crushed Rock
– Igneous Rocks
• Original bedrock formed from the cooling of molten
material
• Coarse grained igneous rock (granite) cooled slowly
• Fine grained igneous rocks (basalt) cooled rapidly
– Sedimentary Rocks
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• Solidification of chemical or mineral sediments
deposited under ancient seas
• Layered since original material was deposited in this
11
manner
Highway Materials, Soils, and Concrete
Aggregates
• Crushed Rock
– Sedimentary Rocks
•
•
•
•
•
•
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Limestone
Dolomite
Shale
Sandstone
Chert
Conglomerate
Calcium Carbonate
Calcium/Magnesium Carbonate
Clay
Quartz
Fine sand
Gravel
12
Highway Materials, Soils, and Concrete
Aggregates
• Crushed Rock
– Metamorphic Rocks
– Igneous or Sedimentary rocks that have been
metamorphosed due to intense heat and
pressure
•
•
•
•
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Slate
Marble
Quartzite
Gneiss
shale
limestone
sandstone
granite
13
Highway Materials, Soils, and Concrete
Aggregates
• Crushed Rock
– Igneous and Metamorphic rocks are very hard and
make an excellent source for aggregates
– Limestone and Dolomite are common sedimentary
rocks, are softer than igneous rocks but are
acceptable for aggregates
– Shale primarily composed of clay grains is weak
and disintegrates easily
– Chert also disintegrates easily
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14
Highway Materials, Soils, and Concrete
Aggregates
• Quarry Pit Development
– Opening and Stripping of the face of the quarry
– Blasting of rock with dynamite into sizes that
can be transported
– Crushing of rock into the required aggregate
sizes
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15
Highway Materials, Soils, and Concrete
Aggregates
• Slag and Mine Refuse
– Slag is a waste material resulting from the
treatment of ore to produce iron, steel, nickel, ..
• Blast furnace slag from iron mills is a common
aggregate
– Mine tailings can also be used for aggregates
• Rubble and Refuse
– recycling of pulverized concrete from structures
– recycled asphalt pavements in base courses
– recycled rubber, crushed glass in base courses
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16
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
– Fine Aggregate
• aggregate particles mainly between the 4.75 mm
size and the 75um sieve.
– Coarse Aggregate
• aggregate particles mainly larger than 4.75 mm
– Pit Run
• aggregate from a sand or gravel pit with no
processing
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17
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
– Crushed Gravel
• pit gravel (or sand) that has been put through a
crusher either to break the rounded gravel particles
into smaller sizes or to produce rougher surfaces
– Crushed Rock
• aggregate from the crushing of bedrock. All particles
are angular and not rounded as in gravel
– Screenings
• chips, dust, powder that are produced from crushing
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18
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
– Concrete Sand
• sand that has been washed to remove dust and fines
– Fines
• silt, clay, or dust particles smaller than 75um usually
the undesirable impurities in aggregates
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19
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
– Nominal Size
• Not economical to have 100% of the particles of an
aggregate be within a specified size range.
• Reduce as much reject as possible from a pit in
order to efficiently use the material resources of a pit
• Usually 5% - 10% of the aggregate particles can be
allowed to be larger or smaller than specs
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20
Highway Materials, Soils, and Concrete
Aggregates
• Types of Aggregates
– Nominal Size
• Coarse aggregates 19-4.75 mm nominal aggregate
• Fine aggregate
4.75 mm nominal aggregate
– Clear
• a single size coarse aggregate is called clear. Most of
the particles are between the specified maximum
size and a minimum size which is defined as onehalf of the maximum
• 19 mm clear aggregate
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21
Highway Materials, Soils, and Concrete
Aggregates
• Aggregate Properties
– Gradation (grain size analysis)
• grain size distribution for highway bases and asphalt
mixes that will provide a dense strong mixture
• ensure that the voids between the larger particles are
filled with medium particles. The remaining voids
are filled with still smaller particles until the smallest
voids are filled with a small amount of fines.
• Ensure maximum density and strength using a
maximum density curve
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22
Highway Materials, Soils, and Concrete
Aggregates
Theoretical Maximum Density Curves
• Fuller Maximum Density Curve
P = (d/D)0.5
P = % passing sieve size ‘d’ and ‘D’ represents
the maximum sieve size (100% passing)
• Federal Highway Administration
P = (d/D)0.45
–
ENCI 579 4
plotted on semi-log paper where sieve sizes are
raised to power 0.45
23
Highway Materials, Soils, and Concrete
Aggregates
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24
Highway Materials, Soils, and Concrete
Aggregate Gradations
• Strength or resistance to shear failure in road
bases and pavements is increased greatly if
the mixture is dense graded
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25
Highway Materials, Soils, and Concrete
Aggregate Gradations
a) larger particles are in contact with each other
developing frictional resistances to shearing
failure. Particles are tightly bond together due to
the inter-locking effect of smaller particles. This
effect is higher in (a) than (b)
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26
Highway Materials, Soils, and Concrete
Aggregate Gradations
b) Must limit the amount of fines
ENCI 579 4
– silt and clay particles are relatively weak
– dust on larger aggregates will interface with
the aggregate/asphalt bond
– Excessive fines in a base or subbase may lead
to drainage on frost leaving problems
– Excessive fines (smaller aggregates) results
in weak structures because larger particles are
not in contact with each other strength
– Sn (smaller particles) are weaker. Therefore
27
managing % of fines is important.
Highway Materials, Soils, and Concrete
Aggregates
Washed Sieve Analysis
• as a result it is important in determining the
amount passing the 75mm sieve
• sample is dried and washed, wash water poured
out over the 75 um sieve
• material retained is returned to the sample for
sieve analysis
• total amount passing 75 um is equal to the
amount lost in washing and % passing 75 um
sieve
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28
Highway Materials, Soils, and Concrete
Aggregates
Example 4-1
Mass of sample 446.7 g
Mass after washing 414.1 g
Results of dry sieving:
Retained in 4.75 mm
0.0g
1.18 mm
205.3g
300 mm
127.9g
75 mm
76.4g
Pan
3.8g
Find the grain-size distribution:
Lost in washing over 75 mm= 446.7 g - 414.1 g= 32.6 g
Passing 75 mm in sieving
3.8 g
ENCI 579 4
29
Total finer than 75 mm
36.4 g
Highway Materials, Soils, and Concrete
Aggregates
Calculations:
Sieve
4.75 mm
1.18 mm
300 mm
75 mm
Pan
Retained
(g)
0
205.3
127.9
76.4
36.4
446.0
Percentage Cumulative
Retained
Passing
0
100%
46.0
54
28.7
25.3
17.1
8.2
8.2
100%
Note: Only 0.7 g was lost during sieving, which is an
acceptable loss.) If a washed sieve analysis is not
required, usually for coarse aggregates the procedure
for grain-size analysis of soils (see Section 1-3.3) is
used
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30
Highway Materials, Soils, and Concrete
Aggregates
• Aggregate Properties
– Gradation (grain size analysis)
• High density mixtures are important in terms of
density and asphalt cement required. Asphalt must
coat each particle and fill in most of the void space.
If you fill in void space with cheaper material such
as aggregates you save asphalt
ENCI 579 4
31
Highway Materials, Soils, and Concrete
Aggregates
• The relative density (specific gravity) and
absorption of aggregates are important
properties especially in asphalt cement
mixtures
– In the mix designs, it is important to measure
accurately the volumes occupied by the
aggregate and any water that may have
seeped into the pores in the particles.
Therefore voids must be considered in the
aggregate.
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32
Highway Materials, Soils, and Concrete
Aggregates
• For aggregates
– Dry Mass = MD
– Total Mass = MSSD
• (dry mass MD + absorbed water MWA)
– Bulk Volume = VB
• (includes volume of absorbed water)
– Net Volume = VN
• VN = VB - volume of absorbed water
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33
Highway Materials, Soils, and Concrete
Aggregates
• Relative density calculations are made
as follows:
Apparent
RDA = MD/(VN x rW)
Bulk
RDB = MD/(VB x rW)
Saturated, surface-dry RDSSD = MSSD/(VB x
rW )
Percentage absorption % Abs = MWA/MD
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34
Highway Materials, Soils, and Concrete
Aggregates
ENCI 579 4
35
Highway Materials, Soils, and Concrete
Aggregates
• Saturated Surface Dry
– all permeable pores filled with water
Bulk Volume = VNET + VABSORBED WATER
ENCI 579 4
36
Highway Materials, Soils, and Concrete
Aggregates
Example 4-2 The dry mass of a sample is 2239.1 g. The mass in saturated surfaceis 2268.4 g. The net volume is 835.4 cm3. Find the relative density values.
Mass of absorbed water
2268.4 - 2239.1 = 29.3 g
Volume of absorbed water
29.3 g
1 g/cm3
Bulk Volume
835.4 cm3 + 29.3 cm3 = 864.7 cm3
Therefore
RDA =
2239.1 g
835.4 cm3 x 1 g/cm3
= 2.68
RDB =
2239.1 g
864.7 cm3 x 1 g/cm3
= 2.59
RDSSD =
2268.4 g
864.7 cm3 x 1 g/cm3
= 2.62
% Abs =
ENCI 579 4
= 29.3 cm3
29.3 g
2239.1 g
= 1.31%
37
Highway Materials, Soils, and Concrete
Aggregates
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38
Highway Materials, Soils, and Concrete
Aggregate Properties
• Aggregate Hardness (resistant to wear)
ENCI 579 4
– It is important that aggregates for pavement
surfaces not become rounded or polished
thereby reducing skid resistance
– Load cycles in the pavement structure tend to
break aggregates or fines will result changing
the gradation (finer) resulting in reduced
strength of the pavement structure
– Broken aggregates are not cemented into the
structure, again reducing strength
39
Highway Materials, Soils, and Concrete
Aggregate Properties
• Aggregate Hardness (cont’d)
– Resistance to degradation during mixing,
transportation, placing and compacting is important
as soft particles may break changing the gradation
– Los Angeles Abrasion Test measures the hardness
of aggregates
– Deval Apparatus
– Aggregate Impact Value Test
– Polished Stone Value Test
ENCI 579 4
40
Highway Materials, Soils, and Concrete
Aggregate Properties
• Aggregate Durability
– resistance to degradation due to cycles of wetting
and drying, heating and cooling, and freezing and
thawing
– freezing and thawing
• pore spaces in the aggregate are often saturated and
on freezing expands
• repeated cycles can cause the aggregate to break
• sedimentary rocks are vulnerable because of planes
of weakness between layers
ENCI 579 4 – Soundness Test Field Performance / Absorption Value
41
Highway Materials, Soils, and Concrete
Aggregate Properties
• Aggregate Particle Shape/Surface Texture
– bonding capability with asphalt cement
• particles with rough fractured faces allow a better
bond with asphalt cements than rounded smooth
particles
– resistance to one particle sliding over another
– flat, thin, long aggregate particles break easier
than cubical particles
ENCI 579 4
• Specifications restrict the percentage of long thin
particles and require aggregates particles having at
least one fractured face
42
Highway Materials, Soils, and Concrete
Aggregate Properties
• Deleterious Substances
– harmful or injurious materials including various
types of weak or low quality particles or
coatings found on the surface of aggregates
• dust (material passing the 75 um sieve)
• clay lumps, shale, coal particles, friable particles,
chert (weak in terms of freezing and thawing)
– These substances effect the bond between
cements and aggregates and break easily
– Petrographic analysis Sand Equivalency Test
ENCI 579 4
43
Highway Materials, Soils, and Concrete
Aggregate Properties
• Aggregate Crushing Strength
– crushing strength is the compressive load that
aggregate particles can carry before breaking
– relatively unimportant for most aggregates
strength is higher than the strength of an asphalt
mix
• Chemical Stability
– refers to specific problems due to chemical
composition
ENCI 579 4
44
ENCI 579 4
45
Highway Materials, Soils, and
Concrete Aggregate Specifications
– Specifications by highway departments takes
into account the aggregate properties we just
discussed
– Requirements for aggregates to be used in bases
and subbases differ from aggregates to be used
in asphalt mixes
– specifications include local experience,
availability of materials and type of project
ENCI 579 4
46
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47
Highway Materials, Soils, and Concrete
Aggregate Properties
Abrasion test:
Original mass 5009g 5009-3267 = 34.8%
Final mass 3267 g
5009
Soundness test:
Original mass 2649g 2649-2115 = 20.2%
Final mass 2115 g
2649
-lower strength fines content
-drainage and frost heave potential
ENCI 579 4
48
-durability question freeze/thaw resistance
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
• The characterization of an aggregate source
depends on how representative the samples are
taken from the aggregates
– size of samples are specified
– samples should be obtained from the final product
if possible, after all the steps in processing and
transportation have been completed
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49
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
– Samples taken from a production or discharge
should be taken at various times and across the
entire cross section of discharge and combined
to form one sample
– Sampling from stockpiles requires care due to
possible segregation of material. Three samples
should be taken, one from the top third, middle
third, bottom third and combined
– Sample tubes for fine aggregate stockpiles
ENCI 579 4 should be used, five tube samples combined 50
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
– Samples taken from a truck or railway car should
be done from a cross sectional trench, three
combined to form one sample
– Combined samples should be done with equal size
component samples
– Randomness should be used to determine location
or time to eliminate personal bias
– Ensure proper identification of the sample
– Samples should be properly secured
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51
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
– Samples tested in the lab must be representative of
the samples delivered to the lab
• Sample Splitting
– testing aggregates composed of significant amounts
of both coarse and fine aggregates the sample must
be split on the 4.75 mm sieve and the two fractions
sieved separately
– If not, the amount of sample on the fine sieves may
be too great for effective sieving
ENCI 579 4
52
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
ENCI 579 4
53
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54
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
ENCI 579 4
55
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
ENCI 579 4
56
Highway Materials, Soils, and Concrete
Aggregate Sampling and Testing
ENCI 579 4
57