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Lesson 2: Soils and Aggregates

CEE 595 Construction MaterialsWinter Quarter 2008

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Lesson 2: Soil and Aggregate Topics

• Soils– Soil classification systems– Soil related tests

• Aggregates– Aggregate Production– Aggregate Characterization

Soils

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Laterite Soil—Brazil—Aerial View

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Laterite Soil—Costa Rica--Close-up

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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.

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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).

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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.

Sieves used in ASTM D3282 and AASHTO M145

No.10 No.40 No.200

No. 10 Sieve—Close-up View

No. 40 Sieve—Close-up View

No. 200 Sieve—Close-up View

Soil Classification—Highway Oriented SystemSoil Group Granular

MaterialsSilt-Clay Materials

A-1 Well-graded mixture of stone fragments, gravel, and/or sand.

A-2 Silty or clayey gravel and sand.

A-3 Fine sand.

A-4 Silty soils.

A-5 Silty soils. Similar to A-4. Can be highly elastic.

A-6 Clayey soils.

A-7 Clayey soils. Similar to A-6 except for high liquid limits.

Soil Classification—Highway Oriented System

Soil Group

% Passing Sieve

Granular Materials

Silt-Clay Materials

A-1 No.10No.40No.200

--50% max25% max

A-2 No.10No.40No.200

----35% max

A-3 No.10No.40No.200

--51% max10% max

A-4 No.10No.40No.200

----36% min

A-5 No.10No.40No.200

----36% min

A-6 No.10No.40No.200

----36% min

A-7 No.10No.40No.200

----36% min

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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.

Liquid Limit Device

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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.

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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.

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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.

No.4 Sieve—Close-up View

Unified Soil Classification System—Additional Terminology

Soil Group Symbol Group Name

GW Well-graded gravel

GP Poorly graded gravel

GM Silty gravel

GC Clayey gravel

SW Well-graded sand

SP Poorly graded sand

SM Silty sand

SC Clayey sand

CL Lean clay

ML Silt

OL Organic silt or clay

CH Fat clay

MH Elastic silt

OH Organic silt or clay

Pt Peat

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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).

Unified Soil Classification SystemTypical Properties (USBR)Soil Group

Maximum Dry Density (pcf)

Optimum water content (%)

Permeability (ft per year)

GW >119 <13.3 27,000

GP >110 <12.4 64,000

GM >114 <14.5 >0.3

GC >115 <14.7 >0.3

SW 119 13.3 --

SP 110 12.4 >15.0

SM 114 14.5 7.5

SM-SC 119 12.8 0.8

SC 115 14.7 0.3

Unified Soil Classification SystemTypical Properties (USBR)Soil Group

Maximum Dry Density (pcf)

Optimum water content (%)

Permeability (ft per year)

ML 103 19.2 0.59

ML-CL 109 16.8 0.13

CL 108 17.3 0.08

OL -- -- --

MH 82 36.3 0.16

CH 94 25.5 0.05

OH -- -- --

Unified Soil Classification SystemTypical Properties (FAA)Soil Group

Maximum Dry Density (pcf)

Field CBR (%) Subgrade k (psi/in)

GW 125-140 60-80 300 or more

GP 120-130 35-60 300 or more

GM 130-145 40-80 300 or more

GC 120-140 20-40 200-300

SW 110-130 20-40 200-300

SP 105-120 15-25 200-300

SM 120-135 20-40 200-300

SM-SC -- -- --

SC 105-130 10-20 200-300

Unified Soil Classification SystemTypical Properties (FAA)Soil Group

Maximum Dry Density (pcf)

Field CBR (%) Subgrade k (psi/in)

ML 100-125 5-15 100-200

ML-CL -- -- --

CL 100-125 5-15 100-200

OL 90-105 4-8 100-200

MH 80-100 4-8 100-200

CH 90-110 3-5 50-100

OH 80-105 3-5 50-100

Unified Soil Classification SystemTypical Properties (FAA)Soil Group Value as a Foundation

When Not Subject to Frost Action

Potential Frost Action

GW Excellent None to Very Slight

GP Good to Excellent None to Very Slight

GM Good to Excellent Slight to Medium

GC Good Slight to Medium

SW Good None to Very Slight

SP Fair to Good None to Very Slight

SM Good Slight to High

SM-SC -- --

SC Fair to Good Slight to High

Unified Soil Classification SystemTypical Properties (FAA)Soil Group Value as a Foundation

When Not Subject to Frost Action

Potential Frost Action

ML Fair to Poor Medium to Very High

ML-CL -- --

CL Fair to Poor Medium to High

OL Poor Medium to High

MH Poor Medium to Very High

CH Poor to Very Poor Medium

OH Poor to Very Poor Medium

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Soil Related Tests

• Soil compaction• Strength or stiffness of soils

– Laboratory– Field

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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.

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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.

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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.

Water Content (%)

Dry Density (lb/ft3)

Typical Compaction Curves

Typical for Modified

Compaction

Typical for Standard

Compaction

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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.

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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.

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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.

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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.

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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.

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California Bearing Ratio

Test apparatus and specimen. Photo by ELE International

Standard methods: ASTM D1883, AASHTO T193.

Correlations between CBR, AASHTO and Unified classification systems, the DCP, and k.

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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”

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Stabilometer Device (R-value)

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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.

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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

Rod

Reference

Mass

Engine

Data Recorder

Positioning System

DCP As Developed in the RSA

Semi-Automatic DCP

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

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DCP

• 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.

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DCP

• 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

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DCP (if CBR > 10) Correlation

• Correlation developed by the US Army Corps of Engineers (USACE)

1.12DPI

292CBR

Where

CBR = California Bearing Ratio (if CBR > 10)

DPI = Penetration Index (mm/blow)

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DCP (if CBR < 10) Correlation

• Correlation developed by the US Army Corps of Engineers (USACE)

Where

CBR = California Bearing Ratio (if CBR < 10)

DPI = Penetration Index (mm/blow)

2)(DPI)][(0.017019

1CBR

CBR Examples (based on USACE Correlation)

DPI(mm/blow)

CBR(%)

5 48

10 22

20 10

DCP Values and Subgrade Improvement (Illinois DOT)

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DCP Correlation

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

1.27410(DN)CBR Where

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

CBR Examples (based on RSA Correlation)

DN(mm/blow)

CBR(%)

5 53

10 22

20 9

40 4

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DCP Correlation

• Modulus Correlation developed in South Africa

(DN)1.06166log3.04758logEeff

Where

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.

E-value Examples (based on RSA Correlation)

DN(mm/blow)

Eeff

MPa (psi)5 202 (29,000 psi)

10 97 (14,000 psi)

20 46 (7,000 psi)

40 22 (3,000 psi)

Typical DCP Plot (from RSA)

RSA Design Curves

Note: MISA is the same as ESALs.

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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.

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DCP—Supplemental Information

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Modulus Background

• What is it?• Nomenclature?• What affects values?• Typical values?

Elastic Modulus

S

tres

s

Strain

Figure 1.2 Illustration of a Stress-Strain Plot and the Difference in the Elastic Range of a Material and

Strength

Strength is generally a measure associated with the failure of a material

Elastic Range of a

Material

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Pavement Modulus Abbreviations

• EAC = Asphalt Concrete

• EPCC = Portland Cement Concrete

• EBS = Base course

• ESB = Subbase course

• ESG or MR = Subgrade

Stress Stiffening

Stress Softening

Comparison of Moduli for Various Materials

Material E, psi (MPa)

Rubber 1,000(7)

Wood 1.0-2.0 million(7,000-14,000)

Aluminum 10,000,000(70,000)

Steel 29,000,000(200,000)

Diamond 170,000,000(1,200,000)

Moduli for Various Materials Pavement Materials

Material E, psi (MPa)

HMA (0C) 3,000,000(21,000)

HMA (20C) 500,000(3,500)

HMA (50C) 50,000(350)

Portland Cement Concrete

3-6 million (20-40,000)

Crushed Stone Base 20-100,000 (150-750)

Subgrade Soils 5-30,000 (35-210)

Summary of National Pavement Practices

State DOT Flexible Pavement Design Subgrade Inputs

Summary of National Pavement Practices

State DOT Rigid Pavement Design Subgrade Inputs

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

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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

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Modulus—CBR Correlation

• Modulus Correlation developed by TRRL

Where

E = Elastic modulus (MPa)

CBR = California Bearing Ratio

0.64(17.6)CBR E

Aggregates

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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).

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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

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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.

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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%

View “Lesson 2a Aggregate Production at Glacier NW”

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Aggregate Production

• Perspective– The eruption of Mt. St. Helens in 1980

was estimated to produce 3.7 billion yd3 of debris. 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.

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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.

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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

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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.

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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

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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. 

Aggregate Gradation

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0.45 Power Curves

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Calculation of the Max Density Curve

n

D

dP

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

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Gradations and Permeability

• 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

Types of Gradations

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Other Aggregate Properties

• Los Angeles Abrasion• Soundness• Sand Equivalent

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Los Angeles Abrasion Test

Start with fraction retained on No. 12 sieve

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Sample submerged in magnesium or sodium sulfate—causes salt

crystals to form in the aggregate pores

Soundness Test

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Sand Equivalent

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

Photo Courtesy of Caltrans

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.

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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.

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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.

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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.

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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