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Week 3: Soils and Aggregates
CEE 363 Construction Materials
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Week 3: Soil and Aggregate Topics
SoilsSoil classification systemsSoil related tests
AggregatesAggregate ProductionAggregate Characterization
Soils
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Laterite Soil--Brazil
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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, AASHTO M145
Actual title for 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 System—ASTM D3282, AASHTO M145
Clayey soils.A-6Clayey soils. Similar to A-6 except for high liquid limits. A-7
Silty soils. Similar to A-4. Can be highly elastic.A-5
Silty soils.A-4
Fine sand.A-3
Silty or clayey gravel and sand.A-2
Well-graded mixture of stone fragments, gravel, and/or sand.
A-1
Silt-Clay Materials
Granular Materials
Soil Group
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Soil Classification—Highway Oriented System—ASTM D3282, AASHTO M145
No.10No.40No.200
No.10No.40No.200
No.10No.40No.200
No.10No.40No.200
No.10No.40No.200
No.10No.40No.200
No.10No.40No.200
% Passing Sieve
A-7
A-6
A-5
A-4
A-3
A-2
A-1
Soil Group
----36% min
----36% min
----36% min
----36% min
--51% max10% max
----35% max
--50% max25% max
Silt-Clay Materials
Granular Materials
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Soil Classification—Highway Oriented System—ASTM D3282, AASHTO M145
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
Actual title for 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—ASTM D2487
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—ASTM D2487—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.
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No.4 Sieve—Close-up View
Unified Soil Classification System—ASTM D2487—Additional Terminology
Lean clayCL
Clayey sandSC
Silty sandSM
Poorly graded sandSP
Well-graded sandSW
Clayey gravelGC
PeatPt
Organic silt or clayOH
Elastic siltMH
Fat clayCH
Organic silt or clayOL
SiltML
Silty gravelGM
Poorly graded gravelGP
Well-graded gravelGW
Group NameSoil Group Symbol
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Unified Soil Classification System—ASTM D2487
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 (Source: USBR)
0.314.7115SC
0.812.8119SM-SC
7.514.5114SM
>15.012.4110SP
--13.3119SW
>0.3<14.7>115GC
>0.3<14.5>114GM
64,000<12.4>110GP
27,000<13.3>119GW
Permeability (ft per year)
Optimum water content (%)
Maximum Dry Density (pcf)
Soil Group
Unified Soil Classification SystemTypical Properties (Source: USBR)
------OH
0.0525.594CH
0.1636.382MH
------OL
0.0817.3108CL
0.1316.8109ML-CL
0.5919.2103ML
Permeability (ft per year)
Optimum water content (%)
Maximum Dry Density (pcf)
Soil Group
Unified Soil Classification SystemTypical Properties (Source: FAA)
200-30010-20105-130SC
------SM-SC
200-30020-40120-135SM
200-30015-25105-120SP
200-30020-40110-130SW
200-30020-40120-140GC
300 or more40-80130-145GM
300 or more35-60120-130GP
300 or more60-80125-140GW
Subgrade k (psi/in)
Field CBR (%)Maximum Dry Density (pcf)
Soil Group
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Unified Soil Classification SystemTypical Properties (Source: FAA)
50-1003-580-105OH
50-1003-590-110CH
100-2004-880-100MH
100-2004-890-105OL
100-2005-15100-125CL
------ML-CL
100-2005-15100-125ML
Subgrade k (psi/in)
Field CBR (%)Maximum Dry Density (pcf)
Soil Group
Unified Soil Classification SystemTypical Properties (Source: FAA)
Slight to HighFair to GoodSC
----SM-SC
Slight to HighGoodSM
None to Very SlightFair to GoodSP
None to Very SlightGoodSW
Slight to MediumGoodGC
Slight to MediumGood to ExcellentGM
None to Very SlightGood to ExcellentGP
None to Very SlightExcellentGW
Potential Frost ActionValue as a Foundation When Not Subject to Frost Action
Soil Group
Unified Soil Classification SystemTypical Properties (Source: FAA)
MediumPoor to Very PoorOH
MediumPoor to Very PoorCH
Medium to Very HighPoorMH
Medium to HighPoorOL
Medium to HighFair to PoorCL
----ML-CL
Medium to Very HighFair to PoorML
Potential Frost ActionValue as a Foundation When Not Subject to Frost Action
Soil Group
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Soil Related Tests
Soil compactionStrength or stiffness of soils
LaboratoryField
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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 densityas 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 testsIndex types of tests
California Bearing Ratio (CBR)Modulus of subgrade reaction (k)Stabilometer Test (Hveem method)Cone penetrometers
Resilient modulus testCBR, 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.htmThe 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”
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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/blowMaximum depth for the DCP ≈ 800 mmCorrelations 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)
1020
2210
485
CBR(%)
DPI(mm/blow)
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)
440
920
2210
535
CBR(%)
DN(mm/blow)
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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.
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E-value Examples (based on RSA Correlation)
22 (3,000 psi)40
46 (7,000 psi)20
97 (14,000 psi)10
202 (29,000 psi)5
Eeff
MPa (psi)DN
(mm/blow)
Typical DCP Plot (from RSA)
RSA Design Curves
Note: MISA is the same as ESALs. 58
DCP Testing Frequency (based on RSA recommendations)
Existing paved road8 DCP tests randomly spaced over the length of the project in both the outer wheelpath and between the wheelpaths.
Gravel road5 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?
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Elastic Modulus
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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 StiffeningStress Softening
Comparison of Moduli for Various Materials
1,200,000Diamond
200,000Steel
70,000Aluminum
7,000-14,000Wood
7Rubber
E (MPa)Material
Moduli for Various Materials Pavement Materials
20-40,000
Portland Cement Concrete
35-210Subgrade Soils
150-750Crushed Stone Base
350HMA (50°C)
3,500HMA (20°C)
21,000HMA (0°C)
E (MPa)Material
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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-strainUnits: psi, MPaTypical Values
Subgrade: 3,000 to 40,000 psiCrushed rock: 20,000 to 50,000 psiHMA: 200,000 to 500,000 psi at 70°F
Picture from University of Tokyo Geotechnical Engineering Lab
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Modulus CorrelationsUse 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 aggregatesSand and gravel: 1.13 billion metric tonsCrushed 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% unspecified20% concrete aggregates11% road bases and road stabilization7% construction fill6% HMA and other bituminous mixtures3% 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 “Aggregate Production at Glacier NW”
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Aggregate Production
PerspectiveThe 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 mixes6% aggregate for new PCC mixes3% riprap7% general fill7% 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 PropertiesMaximum Aggregate SizeGradationOther Aggregate Properties
Toughness and Abrasion ResistanceSpecific GravityParticle Shape and Surface TextureDurability and SoundnessCleanliness and Deleterious Materials
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Aggregate Characterization
Maximum Aggregate SizeMaximum sizeThe smallest sieve through which 100 percent
of the aggregate particles pass.
Nominal maximum sizeThe 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
DdP ⎟⎠⎞
⎜⎝⎛=
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 AbrasionSoundnessSand Equivalent
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Los Angeles Abrasion TestStart 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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Week 3: 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://hotmix.ce.washington.edu/wsdot_web/index.htm
USBR (1973), “Design of Small Dams,” Second Edition, US Department of the Interior, Bureau of Reclamation.
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Week 3: 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