1. Lesson 2: Soils and Aggregates
CEE 595 Construction Materials
Winter Quarter 2008

2. Lesson 2: Soil and Aggregate Topics
Soils
Soil classification systems
Soil related tests
Aggregates
Aggregate Production
Aggregate Characterization

3. Soils

4. Laterite Soil—Brazil—Aerial View
Aerial view of laterite soils in the vicinity of Brasilia, Brazil. Although uncommon in the US, lateritic soils are common in Africa, Australia, Brazil, China, and India—to name a few. They also exist in Hawaii. This type of soil is formed in humid, tropical conditions. High rainfall causes a leaching of silicates from the clay resulting in high oxide contents for iron and aluminum minerals. A true lateritic soil is only “one step” removed from Bauxite. The engineering properties of these soils can be quite good. However, “handling” of laterite soils can cause a breakdown of particles. Thus, laboratory tests and field compaction must be done with much care. Characterization of a lateritic soil can be a bit of a “moving target.”

5. Laterite Soil—Costa Rica--Close-up
Close-up view of laterite soils in the vicinity of Brasilito, Costa Rica.

6. 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.
Source: US Department of Interior, Bureau of Reclamation (1973)

7. 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).

8. 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.
Refer to next three images for views of sieves used to perform gradation analysis.

9. Sieves used in ASTM D3282 and AASHTO M145
No.10
No.40
No.200

10. No. 10 Sieve—Close-up View

11. No. 40 Sieve—Close-up View

12. No. 200 Sieve—Close-up View

13. Soil Classification—Highway Oriented System
Soil Group
Granular Materials
Silt-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.

14. Soil Classification—Highway Oriented System
Soil Group
% Passing Sieve
Granular Materials
Silt-Clay Materials
A-1
No.10
No.40
No.200 --
50% max
25% max
A-2
35% max
A-3
51% max
10% max
A-4
36% min
A-5
A-6
A-7
In addition to gradation requirements, must apply criteria based on Liquid Limits and Plastic Limits.

15. 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.
Definitions from ASTM D4318.

16. Liquid Limit Device

17. 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.

18. 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.

19. 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.
Definitions after ASTM D2487.

20. No.4 Sieve—Close-up View

21. 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 Pt
Peat
After ASTM D2487.

22. 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).

23. Unified Soil Classification System Typical 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 SW
119
13.3 -- SP
110
12.4
>15.0 SM
114
14.5
7.5
SM-SC
12.8
0.8 SC
115
14.7
0.3
Source data from the USBR (1973). Based on 1,500 soil tests performed by the USBR. All values are average values (in general).
Maximum density and optimum water contents based on standard compaction method (ASTM D698).

24. Unified Soil Classification System Typical 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
Source data from the USBR (1973). Based on 1,500 soil tests performed by the USBR. All values are average values (in general).
Maximum density and optimum water contents based on standard compaction method (ASTM D698).

25. Unified Soil Classification System Typical Properties (FAA)
Soil Group
Maximum Dry Density (pcf)
Field CBR (%)
Subgrade k (psi/in) GW
60-80
300 or more GP
35-60 GM
40-80 GC
20-40 SW SP
15-25 SM
SM-SC -- SC
10-20
Source: Federal Aviation Administration (1996). Information summarized from FAA table entitled “Characteristics Pertinent to Pavement Foundations.” URL:
The CBR and k values can be reviewed in the WSDOT Pavement Guide, Module 4 (Design Parameters), Section 2 (Subgrade)--
The CBR test is a relative measure of shear strength for unstabilized materials and the results are 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 subgrade k value is only used for pavement structural design. A description of this test value can also be found in the WSDOT Pavement Guide.

26. Unified Soil Classification System Typical Properties (FAA)
Soil Group
Maximum Dry Density (pcf)
Field CBR (%)
Subgrade k (psi/in) ML
5-15
ML-CL -- CL OL
90-105
4-8 MH
80-100 CH
90-110
3-5
50-100 OH
80-105
Source: FAA (1996). Information summarized from FAA table entitled “Characteristics Pertinent to Pavement Foundations.”

27. Unified Soil Classification System Typical 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 GM
Slight to Medium GC
Good SW SP
Fair to Good SM
Slight to High
SM-SC -- SC
Source: Federal Aviation Administration (1996). Information summarized from FAA table entitled “Characteristics Pertinent to Pavement Foundations.”

28. Unified Soil Classification System Typical 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
Medium to High OL
Poor MH CH
Poor to Very Poor
Medium OH
Source: Federal Aviation Administration (1996). Information summarized from FAA table entitled “Characteristics Pertinent to Pavement Foundations.”

29. Soil Related Tests Soil compaction Strength or stiffness of soils
Laboratory
Field

30. 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.
Background source: PCA (1992).

31. Soil Compaction: Moisture-Density Tests
Moisture-density testing as practiced today was started by R.R. Proctor in 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.
Background source: PCA (1992).

32. 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.
Background source: PCA (1992).

33. Typical Compaction Curves
Typical for Modified Compaction
Typical for Standard Compaction
Dry Density (lb/ft3)
Water Content (%)

34. Soil Compaction—Typical Compaction Specification
Section (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 (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 (14)D.”….
Go to next image.
Source: Washington State DOT Standard Specifications. Available online at

35. Soil Compaction—Typical Compaction Specification
Section (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.
Source: Washington State DOT Standard Specifications for Road, Bridge, and Municipal Construction, Available online at

36. 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.

37. 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 The widespread use of the CBR test was created by the US Corps of Engineers during WW 2.

38. California Bearing Ratio
The CBR test can be reviewed in the WSDOT Pavement Guide, Module 4 (Design Parameters), Section 2 (Subgrade)--
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.

39. California Bearing Ratio
Test apparatus and specimen. Photo by ELE International
Standard methods:
ASTM D1883, AASHTO T193.
Source URL:

40. Correlations between CBR, AASHTO and Unified classification systems, the DCP, and k.
Source: USACE (2001), “Unified Facilities Criteria—Pavement Design for Airfields, UFC , US Army Corps of Engineers, US Army, Washington, DC, June 30, 2001.
URL:
Original source was the Portland Cement Association (R. G. Packard).

41. 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”
For additional detail about the R-value test, refer to the WSDOT Pavement Guide Interactive, Module 4 (Design Parameters), Section 2 (Subgrade). URL:

42. Stabilometer Device (R-value)
Source: California Department of Transportation (2000), “Method for Determining the Resistance “R” Value of Treated and Untreated Bases, Subbases, and Basement Soils by the Stabilometer,” California Test Method 301, March 2000.

43. 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.
This test (DCP) is probably underused in the US. It is quick to perform and its results are correlated to various other kinds of tests—such as CBR. As such, your instructors added a bit of extra content in this Lesson on this test method.

44. 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).

45. Dynamic Cone Penetrometer
Positioning System
Engine
Mass
Data Recorder
Rod
Reference

46. DCP As Developed in the RSA

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

48. 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.

49. 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

50. DCP (if CBR > 10) Correlation
Correlation developed by the US Army Corps of Engineers (USACE)
Thus, if the DPI = 10 mm/blow, then the CBR  22.
Reference: Webster, S., Grau, R., and Williams, T. (1992), “Description and Application of Dual Mass Dynamic Cone Penetrometer,” Report GL-92-3, Waterways Experiment Station, US Department of the Army, May 1992.
Where
CBR = California Bearing Ratio (if CBR > 10)
DPI = Penetration Index (mm/blow)

51. DCP (if CBR < 10) Correlation
Correlation developed by the US Army Corps of Engineers (USACE)
Thus, if the DPI = 25 mm/blow, then the CBR  6.
Reference: Webster, S., Grau, R., and Williams, T. (1992), “Description and Application of Dual Mass Dynamic Cone Penetrometer,” Report GL-92-3, Waterways Experiment Station, US Department of the Army, May 1992.
Where
CBR = California Bearing Ratio (if CBR < 10)
DPI = Penetration Index (mm/blow)

52. CBR Examples (based on USACE Correlation)
DPI
(mm/blow)
CBR
(%) 5 48 10 22 20

53. DCP Values and Subgrade Improvement (Illinois DOT)
This work done in Illinois suggests that based on either CBR or DCP values, subgrades with CBR values of 8 or higher or DCP values of 25 mm/blow or higher do not require lime stabilization.

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

55. CBR Examples (based on RSA Correlation)DN
(mm/blow)
CBR
(%) 5 53 10 22 20 9 40 4
Note that the CBR correlations done by the US Army (Slide 52)and in South Africa are quite similar. That tends to build confidence that the correlations should be broadly applicable.

56. DCP Correlation Modulus Correlation developed in South Africa 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.

57. 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)

58. Typical DCP Plot (from RSA)

59. RSA Design Curves
Note: MISA is the same as ESALs.

60. 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.

61. DCP—Supplemental Information
Reference: MnDOT (1996), “User Guide to the Dynamic Cone Penetrometer,” Office of Pavement Research, Minnesota Department of Transportation. URL:

62. Modulus Background What is it? Nomenclature? What affects values?
Typical values?

63. Elastic Modulus
Elastic or Young’s modulus (Thomas Young 1807) can be determined for any solid material. It is the slope of the straight line portion of the stress/strain curve above, and E= stress/strain, i.e., stress required to induce unit strain (response) Remember:
stress = force/area
strain = deformation/unit length
Elastic implies recoverable i.e. deformation occurs due to applied load while load is in effect. Removal of load results in a return to original shape and size.
Elastic modulus is not a measure of strength in the classical definition. It is a measure of stiffness or response to load.

64. Pavement Modulus Abbreviations
EAC = Asphalt Concrete
EPCC = Portland Cement Concrete
EBS = Base course
ESB = Subbase course
ESG or MR = Subgrade
These are for pavements—from AASHTO guide (1993) and are fairly commonly used.
Another common convention uses E1,....En, with layer numbering beginning at surface.

65. Stress Stiffening
Many pavement materials exhibit stress-sensitive behavior, i.e. modulus varies with stress level. This image shows stress-stiffening - next image shows stress softening.
Typical relationship is MR = K1 q K2
or MR = K1 s3K2
Stress stiffening typical of coarse grained materials such as aggregate base etc.
Log - log plot.

66. Stress Softening
Many pavement materials exhibit stress-sensitive behavior, i.e. modulus varies with stress level. This slide shows stress-stiffening - next slide shows stress softening.
Typical relationship is MR = K1 q K2
or MR = K1 s3K2
Stress stiffening typical of coarse grained materials such as aggregate base etc.
Log - log plot.
Q: Is this likely to affect deflection analysis (question applies to next slide as well)?
A: Yes, since stress level will vary with applied load and measuring equipment. Also, test load and design load may be different. Non-linearity is discussed under section 5.

67. Comparison of Moduli for Various Materials
E, psi (MPa)
Rubber
1,000
(7)
Wood
million
(7,000-14,000)
Aluminum
10,000,000
(70,000)
Steel
29,000,000
(200,000)
Diamond
170,000,000
(1,200,000)

68. Moduli for Various Materials Pavement Materials
E, psi (MPa)
HMA (0C)
3,000,000
(21,000)
HMA (20C)
500,000
(3,500)
HMA (50C)
50,000
(350)
Portland Cement Concrete
3-6 million (20-40,000)
Crushed Stone Base
20-100,000 ( )
Subgrade Soils
5-30,000 (35-210)

69. Summary of National Pavement Practices
State DOT Flexible Pavement Design Subgrade Inputs

70. Summary of National Pavement Practices
State DOT Rigid Pavement Design Subgrade Inputs

71. 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

72. 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

73. Modulus—CBR Correlation
Modulus Correlation developed by TRRL
Where
E = Elastic modulus (MPa)
CBR = California Bearing Ratio
Source: Powell, W., Potter, J., Mayhew, H., and Nunn, M. (1984), “Structural Design of Bituminous Roads,” Report LR 1132, Transportation Road and Research Laboratory.

74. Aggregates

75. 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).
Sources: USGS (2004) and USGS (1999).

76. 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
Source: USGS (2004).

77. 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.
Source: USGS (2004).

78. 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%
Source: USGS (2004).

79. View “Lesson 2a Aggregate Production at Glacier NW”

80. 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.

81. 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.
Source: USGS (1999).

82. 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
Source: USGS (1999).

83. 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.
Source: USGS (1999).

84. 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

85. 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. 

86. Aggregate Gradation

87. 0.45 Power Curves
This illustration shows linear lines for six different maximum aggregate sizes. Aggregate gradations that conform to one of these lines has the maximum packing of particle sizes. On the next image, the equation for calculating these lines is shown.

88. 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

89. Gradations and Permeability

90. Types of Gradations Uniformly graded - Few points of contact
- Poor interlock (shape dependent)
- High permeability
Well graded
- Good interlock
- Low permeability
There are several general types of aggregate gradations. Uniform gradations have large percentages of one size. Well graded aggregates have approximately equal amounts on each sieve in the stack. Gap graded aggregates have large and small but few intermediate sizes.
The properties of the aggregate gradation depends strongly on the distribution of aggregates sizes.
Gap graded
- Only limited sizes
- Good interlock
- Low permeability

91. Other Aggregate Properties
Los Angeles Abrasion
Soundness
Sand Equivalent

92. Los Angeles Abrasion Test
Start with fraction retained on No. 12 sieve

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

94. Sand Equivalent SE = (Height of Sand/Height of Clay)100
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.
Source: AASHTO T176 “Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test”
SE = (Height of Sand/Height of Clay)100
Photo Courtesy of Caltrans

95. 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
and look under “Aggregate Tests.” Access to the VSL will require your UW NetID and password.

96. 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.

97. 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 , Reprinted February 1999.
WSDOT (2003),“WSDOT Pavement Guide Interactive,” Washington State Department of Transportation, URL:
USBR (1973), “Design of Small Dams,” Second Edition, US Department of the Interior, Bureau of Reclamation.

98. Lesson 2: References
FAA (1996), “Airport Pavement Design and Evaluation,” Advisory Circular 150/5320-6D, Federal Aviation Administration, January 30,
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.