Materials, Highway 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
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gravel, sand, silt
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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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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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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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Highway Materials, Soils, and Concrete Aggregates Types of Aggregates Basic properties of these aggregates Tests used to evaluate these properties
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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
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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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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
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Limestone, sandstone,granite,etc.
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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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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 11 manner
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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
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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
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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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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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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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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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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
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chips, dust, powder that are produced from crushing
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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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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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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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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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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
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plotted on semi-log paper where sieve sizes are raised to power 0.45
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Highway Materials, Soils, and Concrete Aggregates
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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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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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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 27 managing % of fines is important.
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Highway Materials, Soils, and Concrete Aggregates
Washed Sieve Analysis
as a result it is important in determining the amount the passing 75m 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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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 m 75 m 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 ENCI 579 4 used 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
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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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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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Highway Materials, Soils, and Concrete Aggregates Relative density calculations are made as follows: Apparent RDA = MD/ (VN x W) Bulk W)
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RDB = MD/(VB x
Saturated, surface-dry RDSSD = MSSD/ (VB x W) 34
Highway Materials, Soils, and Concrete Aggregates
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Highway Materials, Soils, and Concrete Aggregates
Saturated Surface Dry
all permeable pores filled with water
Bulk Volume = VNET + VABSORBED WATER
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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 Volume of absorbed water 2268.4 - 2239.1 = 29.3 g 29.3 g 1 g/cm3 = 29.3 cm3
Bulk Volume Therefore
835.4 cm3 + 29.3 cm3 = 864.7 cm3 RDA = RDB = RDSSD = % Abs = 2239.1 g 835.4 cm3 x 1 g/cm3 2239.1 g 864.7 cm3 x 1 g/cm3 2268.4 g 864.7 cm3 x 1 g/cm3 29.3 g 2239.1 g = 2.68 = 2.59 = 2.62 = 1.31% 37
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Highway Materials, Soils, and Concrete Aggregates
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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 39
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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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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
Specifications restrict the percentage of long thin particles and require aggregates particles having at least one fractured face 42
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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 (...