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Lesson 2: Soils and Aggregates. CEE 595 Construction Materials Winter Quarter 2008. Lesson 2: Soil and Aggregate Topics. Soils Soil classification systems Soil related tests Aggregates Aggregate Production Aggregate Characterization. Soils. Laterite Soil—Brazil—Aerial View.

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lesson 2 soils and aggregates

Lesson 2: Soils and Aggregates

CEE 595 Construction Materials

Winter Quarter 2008

lesson 2 soil and aggregate topics
Lesson 2: Soil and Aggregate Topics
  • Soils
    • Soil classification systems
    • Soil related tests
  • Aggregates
    • Aggregate Production
    • Aggregate Characterization
soil classification
Soil Classification
  • Two major soil classification systems used in the US
    • “AASHTO” Classification (ASTM D3282, AASHTO M145)
    • Unified Soil Classification (USBR, 1973 and ASTM D2487)
  • Why classify a soil? (USBR)
    • Identifies and groups soils of similar engineering characteristics.
    • Provides a “common language” to describe soils.
    • In a limited manner, soil classifications can provide approximate values of engineering characteristics.
soil classification7
Soil Classification
  • How do classification systems work?
    • Determine gradation
      • Is the dominant percentage of particles larger or “granular”
      • Is the dominant percentage of particles “fine graded” (or silt-clay sizes).
    • Perform Atterberg Limit tests (more on these tests shortly).
soil classification highway oriented system
Soil Classification—Highway Oriented System
  • ASTM D3282 and AASHTO M145: Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes.
  • Classification Groups split into
    • Granular Materials: Contains 35% or less passing the No.200 sieve. These groups generally make good to excellent subgrades.
    • Silt-Clay Materials: Contains more than 35% passing a No.200 sieve. These groups generally are fair to poor as subgrades.
soil classification highway oriented system15
Soil Classification—Highway Oriented System
  • Additional tests required to perform classification grouping.
    • Liquid Limit (AASHTO T89, ASTM D4318): “The water content, in percent, of a soil at the arbitrarily defined boundary between the liquid and plastic states.” See next image to view the device used to determine LL. The higher the LL, the poorer the soil.
    • Plastic Limit (PL) and Plasticity Index (AASHTO T90, ASTM D4318): “The water content, in percent, of a soil at the boundary between the plastic and brittle states.” Plasticity Index (PI) is the “range of water content over which a soil behaves plastically.” PI = LL – PL. The higher the PI, the poorer the soil.
soil classification unified soil classification system
Soil Classification—Unified Soil Classification System
  • ASTM D2487: Classification of Soils for Engineering Purposes (Unified Soil Classification System)
  • Classification Groups split into
    • Coarse-grained soils: More than 50% retained on a No.200 sieve.
    • Fine-grained soils: 50% or more passes the No.200 sieve.
soil classification unified soil classification system18
Soil Classification—Unified Soil Classification System
  • Coarse-grained soils: More than 50% retained on a No.200 sieve.
    • Gravels: More than 50% of coarse fraction retained on No.4 sieve.
    • Sands: 50% or more of coarse fraction passes No.4 sieve.
  • Fine-grained soils: 50% or more passes the No.200 sieve.
    • Silts and Clays: LL less than 50%.
    • Silts and Clays: LL 50% or more.
unified soil classification system additional terminology
Unified Soil Classification System—Additional Terminology
  • Gravel: Particles of rock passing a 3 in. sieve but retained on a No.4 sieve.
  • Sand: Particles of rock passing a No.4 but retained on a No.200.
  • Clay: Soil passing a No.200 that exhibits plasticity (putty-like properties) within a range of water contents. Exhibits considerable strength when air dry.
  • Silt: Soil passing a No.200 that is nonplastic or very slightly plastic and that exhibits little or no strength when air dry.
unified soil classification system
Unified Soil Classification System
  • As shown in the prior image, the primary goal of this classification system is to determine the group for a specific soil (such as CL, etc.). To fully describe how this is done is too detailed for this lesson—but the process is fully described in ASTM D2487. Basically, it is a combination of sieve analyses and Atterberg Limits (LL, PL, PI).
  • The following table shows typical engineering characteristics associated with the Unified Soil Classification System (from USBR, 1973).
soil related tests
Soil Related Tests
  • Soil compaction
  • Strength or stiffness of soils
    • Laboratory
    • Field
soil compaction
Soil compaction
  • Soil compaction is the process of “artificially” increasing the density (unit weight) of a soil by compaction (by application of rolling, tamping, or vibration).
  • Standards are needed so that the amount of increased density needed and achieved can be measured.
  • Two compaction tests are commonly performed to achieve this information.
soil compaction moisture density tests
Soil Compaction: Moisture-Density Tests
  • Moisture-density testing as practiced today was started by R.R. Proctor in 1933. His method became known as the “standard Proctor” test.
  • This test (today described by ASTM D698 and AASHTO T99) applied a fixed amount of compaction energy to a soil at various water contents. Specifically, this involves dropping a 5.5 lb weight 12 inches and applying 25 “blows” per layer in 3 layers in a standard sized mold. Thus, 12,375 ft-lb per ft3 of compaction effort is applied.
soil compaction moisture density tests32
Soil Compaction: Moisture-Density Tests
  • US Army Corps of Engineers developed “Modified Proctor” or “Modified AASHTO” to accommodate compaction needs associated with heavier aircraft used in WW 2.
  • ASTM D1557 and AASHTO T180: “Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lb/ft3)”
  • Refer to relative location of compaction curves on the next image. The higher the compaction energy, the lower the optimum water content and the higher the dry density.

Typical Compaction Curves

Typical for Modified Compaction

Typical for Standard Compaction

Dry Density (lb/ft3)

Water Content (%)

soil compaction typical compaction specification
Soil Compaction—Typical Compaction Specification
  • Section 2-03.3(14)C, Method C: “Compacting Earth Embankments”
    • “Each layer of the entire embankment shall be compacted to 95 percent of the maximum density as determined by the compaction control tests described in Section 2-03.3(14)D. In the top 2 feet, horizontal layers shall not exceed 4 inches in depth before compaction. No layer below the top 2 feet shall exceed 8 inches in depth before compaction.”….
    • “Under Method C, the moisture content shall not vary more than 3 percent above or below optimum determined by the tests in described in Section 2-03.3(14)D.”….
    • Go to next image.
soil compaction typical compaction specification35
Soil Compaction—Typical Compaction Specification
  • Section 2-03.3(14)D: “Compaction and Moisture Control Tests”
    • “The maximum density and optimum moisture for materials with less than 30 percent, by mass, retained on the US No.4 sieve shall be determined …[by]… AASHTO T99.”
    • The are many more requirements that relate to specifying soil compaction but these two images provide a quick but focused example.
strength or stiffness of soils
Strength or Stiffness of Soils
  • Typical tests of soil strength are:
    • Shear strength tests
    • Index types of tests
      • California Bearing Ratio (CBR)
      • Modulus of subgrade reaction (k)
      • Stabilometer Test (Hveem method)
      • Cone penetrometers
    • Resilient modulus test
    • CBR, R-value, cone penetrometers, and resilient modulus tests will be briefly covered.
california bearing ratio
California Bearing Ratio
  • The CBR test is a relative measure of shear strength for unstabilized materials and the results are stated as a percentage of a high quality crushed limestone—thus all results are shown as percentages. A CBR = 100% is near the maximum possible. CBRs of less than 10% are generally weak soils.
  • The test was originally developed by O. J. Porter of the California Division of Highways in 1928. The widespread use of the CBR test was created by the US Corps of Engineers during WW 2.
california bearing ratio38
California Bearing Ratio
  • The CBR test can be reviewed in the WSDOT Pavement Guide, Module 4 (Design Parameters), Section 2 (Subgrade)--http://hotmix.ce.washington.edu/wsdot_web/index.htm
  • The CBR test is only conducted on unstabilized materials (soils or aggregates).
  • The test is most always done in the laboratory; however, a field test is available but rarely conducted.
california bearing ratio39
California Bearing Ratio

Test apparatus and specimen. Photo by ELE International

Standard methods:

ASTM D1883, AASHTO T193.

r value
  • This test was developed in California by Hveem and Carmany in the late 1940’s.
  • In effect, it is a relative measure of stiffness since the test apparatus operates somewhat like a triaxial test.
  • The test is mostly used by western states for highway base and subgrade characterization.
  • Use of this test is likely declining a bit.
  • ASTM D2844 and AASHTO T190: “Resistance R-Value and Expansion Pressure of Compacted Soils”
dynamic cone penetrometer dcp
Dynamic Cone Penetrometer (DCP)
  • Originally developed in the Republic of South Africa (RSA). South Africans have used and developed related tools and analyses for over 25 years.
  • Standard test method
    • ASTM D6951: “Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications”
    • Equipment can come with different hammer weights—which can effect correlations.
  • Equipment can be purchased from companies such as Salem Tool Co., Salem, MI; Kessler Soils Engineering Products, Inc; or Dynatest Inc for about $1000--$2000.
dynamic cone penetrometer dcp44
Dynamic Cone Penetrometer (DCP)
  • Standard test method
    • ASTM D6951: “Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications”
    • Equipment can come with different hammer weights:
      • 8 kg (17.6 lb.)
      • 4.6 kg (10.1 lb.)
    • USACE CBR—DCP correlations are contained in the ASTM standard test method (see correlations in subsequent images).

Dynamic Cone Penetrometer

Positioning System



Data Recorder



semi automatic dcp
Semi-Automatic DCP

Photos of Florida DOT equipment (June 2004). This type of DCP saves time and labor.

  • Examples of DCP use by the Minnesota DOT
    • Pavement rehabilitation strategy determination.
    • Locate layers in pavement structures.
    • Supplement foundation testing for design.
    • Identify weak spots in constructed embankments.
    • Use as an acceptance testing tool.
    • Location of boundaries of required subcuts.
  • Assumption: A correlation exists between the strength of a material and its resistance to penetration.
  • Typical measure is DCP Penetration Index (DPI)
  • Measured in mm/blow or inches/blow
  • Maximum depth for the DCP  800 mm
  • Correlations follow
dcp if cbr 10 correlation
DCP (if CBR > 10) Correlation
  • Correlation developed by the US Army Corps of Engineers (USACE)


CBR = California Bearing Ratio (if CBR > 10)

DPI = Penetration Index (mm/blow)

dcp if cbr 10 correlation51
DCP (if CBR < 10) Correlation
  • Correlation developed by the US Army Corps of Engineers (USACE)


CBR = California Bearing Ratio (if CBR < 10)

DPI = Penetration Index (mm/blow)

dcp correlation
DCP Correlation
  • CBR Correlation developed in South Africa (for values of DN>2 mm/blow)


DN = Penetration of the DCP through a specific pavement layer in mm/blow. The DN is a weighted average. DN is similar to DPI.

dcp correlation56
DCP Correlation
  • Modulus Correlation developed in South Africa


R2 = 76% and n = 86 data points

Eeff = Effective elastic modulus for a 40 kN load.

DN = Weighted average DCP penetration rate in mm/blow.

rsa design curves
RSA Design Curves

Note: MISA is the same as ESALs.

dcp testing frequency based on rsa recommendations
DCP Testing Frequency (based on RSA recommendations)
  • Existing paved road
    • 8 DCP tests randomly spaced over the length of the project in both the outer wheelpath and between the wheelpaths.
  • Gravel road
    • 5 DCP tests per kilometer with the tests staggered between the outer and between wheelpaths.
    • Perform additional test at significant locations identified via visual distress survey.
modulus background
Modulus Background
  • What is it?
  • Nomenclature?
  • What affects values?
  • Typical values?
pavement modulus abbreviations
Pavement Modulus Abbreviations
  • EAC =Asphalt Concrete
  • EPCC =Portland Cement Concrete
  • EBS =Base course
  • ESB = Subbase course
  • ESG or MR = Subgrade
summary of national pavement practices
Summary of National Pavement Practices

State DOT Flexible Pavement Design Subgrade Inputs

summary of national pavement practices70
Summary of National Pavement Practices

State DOT Rigid Pavement Design Subgrade Inputs

resilient modulus m r
Resilient Modulus (MR)
  • Measure: stress-strain
  • Units: psi, MPa
  • Typical Values
    • Subgrade: 3,000 to 40,000 psi
    • Crushed rock: 20,000 to 50,000 psi
    • HMA: 200,000 to 500,000 psi at 70°F

Picture from University of Tokyo Geotechnical Engineering Lab

modulus correlations
Modulus Correlations
  • Use with caution

MR = (1500) (CBR)

Fine-grained materials with soaked CBR ≤ 10

MR = 1,000 + (555)(R-value)

Fine-grained soils with R-Value ≤ 20

MR = (2555)CBR0.64

New AASHTO Design Guide

modulus cbr correlation
Modulus—CBR Correlation
  • Modulus Correlation developed by TRRL


E = Elastic modulus (MPa)

CBR = California Bearing Ratio

aggregate production
Aggregate Production
  • Aggregate production in the US is large—some annual production figures include:
    • Natural aggregates
      • Sand and gravel: 1.13 billion metric tons
      • Crushed stone: 1.49 billion metric tons
    • Recycled aggregates: 200 million metric tons produced from demolition wastes (includes roads and buildings).
aggregate production76
Aggregate Production
  • Sand and gravel (estimated for 2003)
    • 1.13 billion metric tons of sand and gravel produced in the US in 2003.
    • Value $5.8 billion
    • Produced by 4,000 companies from 6,400 operations in all 50 states. Leading production states are: California, Texas, Michigan, Arizona, Ohio, Minnesota, Washington, Wisconsin, Nevada, and Colorado.
    • How were these aggregates used?
      • 53% unspecified
      • 20% concrete aggregates
      • 11% road bases and road stabilization
      • 7% construction fill
      • 6% HMA and other bituminous mixtures
      • 3% other applications
aggregate production77
Aggregate Production
  • Crushed stone (estimated for 2003)
    • 1.49 billion metric tons of crushed stone produced in the US in 2003.
    • Value $8.6 billion
    • Produced by 1,260 companies from 3,300 operations in 49 states. Leading production states are: Texas, Florida, Pennsylvania, Missouri, Illinois, Georgia, Ohio, North Carolina, Virginia, and California.
    • How were these aggregates used? 35% was for unspecified uses followed by construction aggregates mostly for highway and road construction and maintenance, chemical and metallurgical uses (including cement and lime production), agricultural uses, etc.
aggregate production78
Aggregate Production
  • Crushed stone—cont.
    • Of the crushed stone produced it was composed of these source rock types:
      • Limestone and dolomite: 71%
      • Granite: 15%
      • Traprock: 7%
      • Sandstone, quartzite, marble, etc: 7%
aggregate production80
Aggregate Production
  • Perspective
    • The eruption of Mt. St. Helens in 1980 was estimated to produce 3.7 billion yd3 ofdebris. This amounts to about 5.6 billion metric tons of material (assuming a unit weight of 125 lb/ft3). The total annual production of sand and gravel, crushed stone, and recycled aggregates amounts to about 50% of the St. Helens debris.
aggregate production81
Aggregate Production
  • Recycled aggregates (1999)
    • 200 million metric tons of recycled aggregates produced (or generated) in the US in 2000.
    • 100 million metric tons of recycled asphalt paving materials recovered annually. 80% of this material is recycled with the other 20% going to landfills. Of the 80% that is recycled—2/3 used as aggregates for road base and 1/3 reused as aggregate for new HMA.
aggregate production82
Aggregate Production
  • Recycled aggregates (1999)—cont.
    • 100 million metric tons of recycled concrete is recovered annually.
      • 68% of recycled concrete reused as road base.
      • 9% aggregate for HMA mixes
      • 6% aggregate for new PCC mixes
      • 3% riprap
      • 7% general fill
      • 7% other applications
aggregate production83
Aggregate Production
  • Recycled aggregates (1999)—cont.
    • Only 15% of recycled aggregates reused in HMA or PCC mixes—why?—Due to quality issues (the lack thereof).
    • Economics of recycling according to USGS (1999 data)
      • Capital investment for an aggregate recycling facility about $4.40 to $8.80 per metric ton of annual capacity.
      • Processing costs: Range from $2.76 to $6.61 per metric ton. Average production of fixed site processing facilities is 150,000 ton/year.
      • Prices best for aggregate-poor southern states.
aggregate characterization
Aggregate Characterization
  • Aggregate Physical Properties
    • Maximum Aggregate Size
    • Gradation
    • Other Aggregate Properties
      • Toughness and Abrasion Resistance
      • Specific Gravity
      • Particle Shape and Surface Texture
      • Durability and Soundness
      • Cleanliness and Deleterious Materials
aggregate characterization85
Aggregate Characterization
  • Maximum Aggregate Size
    • Maximum size

The smallest sieve through which 100 percent of the aggregate particles pass.

    • Nominal maximum size

The largest sieve that retains some of the aggregate particles but generally not more than 10 percent by weight. 

calculation of the max density curve
Calculation of the Max Density Curve

where P = % finer than the sieve

d = aggregate size being considered

D = maximum aggregate size being used

n = parameter which equals 0.45—represents the

maximum particle packing


Types of Gradations

  • Uniformly graded

- Few points of contact

- Poor interlock (shape dependent)

- High permeability

  • Well graded

- Good interlock

- Low permeability

  • Gap graded

- Only limited sizes

- Good interlock

- Low permeability

other aggregate properties
Other Aggregate Properties
  • Los Angeles Abrasion
  • Soundness
  • Sand Equivalent

Los Angeles Abrasion Test

Start with fraction retained on No. 12 sieve

soundness test
Soundness Test

Sample submerged in magnesium or sodium sulfate—causes salt crystals to form in the aggregate pores

sand equivalent
Sand Equivalent

This is a test to determine the amount of clay in fine aggregate.

Aggregate passing a No. 4 sieve is agitated in a water-filled transparent cylinder. Liquid is water and flocculating agent. After settling, the sand separates from the flocculated clay. Measure each.

SE = (Height of Sand/Height of Clay)100

Photo Courtesy of Caltrans

virtual superpave laboratory
Virtual Superpave Laboratory

Aggregate tests done for HMA are featured in the Virtual Superpave Laboratory (VSL). The VSL will be used in subsequent lessons but it is appropriate to briefly examine the aggregate section now. To do this, go to http://guides.ce.washington.edu/UW/VSL

and look under “Aggregate Tests.” Access to the VSL will require your UW NetID and password.

lesson 2 discussion forum
Lesson 2: Discussion Forum
  • Assume that you are participating in a toll road design-build project and the site is new—no previous soil or aggregate source data is readily available. Please discuss the following question—What exploration, sampling, and testing would you recommend so that the soils underlying the new pavements could be reasonably characterized? It is understood that the content of this Lesson will not answer this question fully.
lesson 2 references
Lesson 2: References
  • USGS (2004), “Mineral Commodity Summaries,” US Geological Survey, January 2004.
  • USGS (1999), “Natural Aggregates—Foundation of America’s Future,” USGS Fact Sheet—FS 144-97, Reprinted February 1999.
  • WSDOT (2003),“WSDOT Pavement Guide Interactive,” Washington State Department of Transportation, URL: http://guides.ce.washington.edu/UW/WSDOT
  • USBR (1973), “Design of Small Dams,” Second Edition, US Department of the Interior, Bureau of Reclamation.
lesson 2 references98
Lesson 2: References
  • FAA (1996), “Airport Pavement Design and Evaluation,” Advisory Circular 150/5320-6D, Federal Aviation Administration, January 30, 1996. http://www.faa.gov/arp/pdf/5320-6dp1.pdf
  • PCA (1992), “PCA Soil Primer,” Publication EB007.05S, Portland Cement Association, Skokie, Illinois.
  • WSDOT (2004), “Standard Specifications for Road, Bridge, and Municipal Construction,” M41-10, Washington State Department of Transportation. http://www.wsdot.wa.gov/fasc/EngineeringPublications/Manuals/SS2004.PDF