1. 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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2. 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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4. 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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5. 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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6. Highway Materials, Soils, and Concrete Aggregates
Types of Aggregates
Basic properties of these aggregates
Tests used to evaluate these properties
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7. Highway Materials, Soils, and Concrete Aggregates
Aggregate Sources
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
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8. 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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9. 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
Limestone, sandstone,granite,etc.
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10. 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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11. 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
Solidification of chemical or mineral sediments deposited under ancient seas
Layered since original material was deposited in this manner
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12. Highway Materials, Soils, and Concrete Aggregates
Crushed Rock
Sedimentary Rocks
Limestone Calcium Carbonate
Dolomite Calcium/Magnesium Carbonate
Shale Clay
Sandstone Quartz
Chert Fine sand
Conglomerate Gravel
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13. Highway Materials, Soils, and Concrete Aggregates
Crushed Rock
Metamorphic Rocks
Igneous or Sedimentary rocks that have been metamorphosed due to intense heat and pressure
Slate shale
Marble limestone
Quartzite sandstone
Gneiss granite
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14. 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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15. 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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16. 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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17. 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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18. 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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19. 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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20. 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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21. Highway Materials, Soils, and Concrete Aggregates
Types of Aggregates
Nominal Size
Coarse aggregates 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 one-half of the maximum
19 mm clear aggregate
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22. 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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23. 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
plotted on semi-log paper where sieve sizes are raised to power 0.45
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24. Highway Materials, Soils, and Concrete Aggregates
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25. 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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26. 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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27. Highway Materials, Soils, and Concrete Aggregate Gradations
b) Must limit the amount of fines
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 managing % of fines is important.
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28. 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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29. Highway Materials, Soils, and Concrete Aggregates
Example 4-1
Mass of sample g
Mass after washing g
Results of dry sieving:
Retained in mm g
1.18 mm 205.3g
300 mm g
75 mm g
Pan g
Find the grain-size distribution:
Lost in washing over 75 mm= g g= 32.6 g
Passing 75 mm in sieving g
Total finer than 75 mm g
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30. Highway Materials, Soils, and Concrete Aggregates
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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31. 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
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32. 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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33. 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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34. 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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35. Highway Materials, Soils, and Concrete Aggregates
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36. Highway Materials, Soils, and Concrete Aggregates
Saturated Surface Dry
all permeable pores filled with water
Bulk Volume = VNET + VABSORBED WATER
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37. Highway Materials, Soils, and Concrete Aggregates
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38. Highway Materials, Soils, and Concrete Aggregates
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39. Highway Materials, Soils, and Concrete Aggregate Properties
Aggregate Hardness (resistant to wear)
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
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40. 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
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41. 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
Soundness Test Field Performance / Absorption Value
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42. 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
Specifications restrict the percentage of long thin particles and require aggregates particles having at least one fractured face
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43. 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
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44. 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
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46. 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
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48. Highway Materials, Soils, and Concrete Aggregate Properties
Abrasion test:
Original mass 5009g = 34.8%
Final mass 3267 g
Soundness test:
Original mass 2649g = 20.2%
Final mass 2115 g
-lower strength fines content
-drainage and frost heave potential
-durability question freeze/thaw resistance
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49. 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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50. 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 should be used, five tube samples combined
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51. 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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52. 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
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53. Highway Materials, Soils, and Concrete Aggregate Sampling and Testing
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55. Highway Materials, Soils, and Concrete Aggregate Sampling and Testing
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56. Highway Materials, Soils, and Concrete Aggregate Sampling and Testing
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57. Highway Materials, Soils, and Concrete Aggregate Sampling and Testing
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