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Highway Materials, Soils, and Concrete Aggregates

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Highway Materials, Soils, and Concrete Aggregates Soil Definition (Engineering) refers to all unconsolidated material in the earth s crust, all material above ... – PowerPoint PPT presentation

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Title: Highway Materials, Soils, and Concrete Aggregates


1
Highway Materials, Soils, and Concrete Aggregates
  • Soil Definition (Engineering)
  • refers to all unconsolidated material in the
    earths 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

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

3
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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

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

6
Highway Materials, Soils, and Concrete Aggregates
  • Types of Aggregates
  • Basic properties of these aggregates
  • Tests used to evaluate these properties

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

21
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 one-half of the maximum
  • 19 mm clear aggregate

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

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

24
Highway Materials, Soils, and Concrete Aggregates
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

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)

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.

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

29
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
  • Total finer than 75 mm 36.4 g

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

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

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.

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

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

35
Highway Materials, Soils, and Concrete Aggregates
36
Highway Materials, Soils, and Concrete Aggregates
  • Saturated Surface Dry
  • all permeable pores filled with water
  • Bulk Volume VNET VABSORBED WATER

37
Highway Materials, Soils, and Concrete Aggregates
38
Highway Materials, Soils, and Concrete Aggregates
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

40
Highway Materials, Soils, and Concrete Aggregate
Properties
  • Aggregate Hardness (contd)
  • 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

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

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

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

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 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
  • -durability question freeze/thaw resistance

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

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

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

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

53
Highway Materials, Soils, and Concrete Aggregate
Sampling and Testing
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Highway Materials, Soils, and Concrete Aggregate
Sampling and Testing
56
Highway Materials, Soils, and Concrete Aggregate
Sampling and Testing

57
Highway Materials, Soils, and Concrete Aggregate
Sampling and Testing
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