Department of Civil, Construction and Environmental Engineering Performance-based design and testing methods for granular road surface materials (IHRB Project TR-685) 2017 Mid-Continent Transportation Research Symposium August 16, 2017 Cheng Li, Ph.D. Postdoctoral Research Associate [email protected]Project Principal Investigators: Drs. Jeramy Ashlock, Bora Cetin, and Charles Jahren
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Department of Civil, Construction and Environmental Engineering
Performance-based design and testing methods for granular road surface materials (IHRB Project TR-685)
2017 Mid-Continent Transportation Research SymposiumAugust 16, 2017
Department of Civil, Construction and Environmental Engineering
60% of IA road network is unpaved: 68,400 of 114,000 miles
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3
5
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$14,784 per mile for a 30ft wide road
Reference: Li, C., Ashlock, J. C., White, D. J., & Vennapusa, P. (2015). Low-Cost Rural Surface Alternatives: Demonstration Project., IHRBProject TR-664, Iowa Department of Transportation, Ames, IA, p. 242.
Department of Civil, Construction and Environmental Engineering
Performance and durability of granular road surface materials are a function of several influence factors
• Gradation (particle size distribution and top size)
• Plasticity (dust and stability)
• Aggregate Quality (degradation and abrasion)
• Aggregate morphology (shape and angularity)
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Gradation
Department of Civil, Construction and Environmental Engineering
Particle packing of aggregate materials governs its mechanical performance, especially in wet conditions
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Reference: Xiao, Y., E. Tutumluer, Y. Qian, and J. A. Siekmeier. Gradation Effects Influencing Mechanical Properties of Aggregate Base-Granular Subbase Materials in Minnesota. Transportation Research Record: Journal of the Transportation Research Board, 2267, 2012, pp. 14-26.
Department of Civil, Construction and Environmental Engineering
Hypothesis: the target is too wide and does not specify the most critical parameter: particle packing
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#10
#40
#100
#200#41/2"
5/8"
SandGravel Silt
Grain Diameter (mm)
0.0010.010.1110100
Per
cent
Pas
sing
(%)
0102030405060708090
100Iowa DOT Class A & B
Existing Aggregate (varied gradations)
Existing AggregateVirgin AggregateVirgin with Existing
1"3/
4"
1/4"
#60
#20
3/8"
Clay
1.5"
Department of Civil, Construction and Environmental Engineering
Gravel Content (%)
10 20 30 40 50 60 70 80
Soak
ed C
BR (%
)
0
10
20
30
40
50
60
70
80
ExistingExisting+Virgin
100% Existing
100% Virgin
<#40, % vs Soaked CBR, %
Sand Content (%)
10 20 30 40 50 60
Soak
ed C
BR (%
)
0
10
20
30
40
50
60
70
80
ExistingExisting+Virgin
100% Virgin
100% Existing
Fines Content (%)
0 5 10 15 20 25 30
Soak
ed C
BR (%
)
0
10
20
30
40
50
60
70
80
ExistingExisting+Virgin
100% Existing
100% Virgin
An optimum gradation in terms of shear strength exists for a given well-graded granular material
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Department of Civil, Construction and Environmental Engineering
Grain Diameter (mm)
0 5 10 15 20 25 30
Per
cent
Pas
sing
(%)
0102030405060708090
100
Gradations of well-graded granular materials can be described by two parameters using Fuller’s model
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𝑝𝑝𝑖𝑖 = 𝐷𝐷𝑖𝑖𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚
𝑛𝑛× 100
where subscript “𝑖𝑖” represents a particular sieve; 𝑝𝑝𝑖𝑖 = percentage passing the 𝑖𝑖 sieve;𝐷𝐷𝑖𝑖 = opening size of the 𝑖𝑖 sieve; 𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚 = the maximum size of aggregate; and 𝑛𝑛 = shape factor of gradation curve.
Existing AggregateFuller's Model
pi = (Di / Dmax) n
R2 = 0.9803Dmax = 23.6 mmn = 0.2794G/S = 0.67
Department of Civil, Construction and Environmental Engineering
Fuller’s model with two parameters can be used to develop performance-based specifications
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Department of Civil, Construction and Environmental Engineering
PSD curves with a wide range of shape factors can meet the current gradation specification band
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#10
#40
#100
#200#41/2"
SandGravel Fines
Particle Size (mm)
0.010.1110100
Perc
ent
Pass
ing
(%)
0102030405060708090
100
Iowa DOT Spec. Band1"
3/4"
#60
#20
3/8"
n = 0.10
n = 0.15
n = 0.70
Department of Civil, Construction and Environmental Engineering
The current gradation specifications cannot ensure performance
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Plasticity
Department of Civil, Construction and Environmental Engineering
Bentonite treatment significantly reduced dust and provided a much drier surface during thawing
#1A Dirty MacadamA-1-a (USCS: GP-GM)Percent of fines = 9.9%Percent of clay = 1.8%PI = NP
#1B Dirty Macadam+BentoniteA-2-6(0) (USCS: GC)Percent of fines = 14.3%Percent of clay = 5.0%LL=30, PL=12, and PI=18
#2 Dirty Macadam+Chloride
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March 28, 2015
Reference: Li, C., P. K. R. Vennapusa, J. Ashlock, and D. J. White. (2017) Mechanistic-Based Comparisons for Freeze-Thaw Performance of Stabilized Unpaved Roads. Cold Regions Science and Technology, Vol. 141, 2017, pp. 97-108.
Department of Civil, Construction and Environmental Engineering
Bentonite was found to be effective to improve the stability and slaking of crushed limestone fines
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Department of Civil, Construction and Environmental Engineering
Add 4% bentonite to the surface material passing #40 sieve or control the PI between 7 and 15
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Moisture Content (%)
0 3 6 9 12 15 18
UC
S (M
Pa)
0.01
0.1
1
10
100
0% Bentonite2% Bentonite4% Bentonite6% Bentonite
Aver
age
Slak
ing
Tim
e (m
in.)
10
100
1000
OMC+2%After Drying
0% Bentonite
2% Bentonite
4% Bentonite
6% Bentonite
Department of Civil, Construction and Environmental Engineering
Different lab tests for measuring plasticity of soils were evaluated
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Conventional Atterberg Limit tests
Fall Cone Liquid and Plastic Limit Test
Bar Linear Shrinkage(BLS) Test
Cas
agra
nde
Cup
AS
TM R
olle
r
Department of Civil, Construction and Environmental Engineering
South Africa DOT’s performance-related unpaved road surface material selection chart
Shrinkage Product Bar Linear Shrinkage % passing #40 sieve= ×
Reference: Paige-Green, P. The Influence of Geotechnical Properties on the Performance of Gravel Wearing Course Materials. Ph.D. Dissertation, University of Pretoria, South Africa, 1989.
Department of Civil, Construction and Environmental Engineering
The BLS can be correlated to the PI but is not a sensitive parameter indicating plasticity of soils
where,𝜇𝜇 = an average measurement of all possible operators and all possible
parts,𝛼𝛼𝑖𝑖 = effects of different parts,𝛽𝛽𝑖𝑖 = effects of different operators,𝛼𝛼𝛽𝛽𝑖𝑖𝑖𝑖 = joint effects peculiar to particular part/operator combinations, and𝜀𝜀𝑖𝑖𝑖𝑖𝑖𝑖 = measurement error.
Reference: Vardeman, S. B., and Jobe, J. M., 1999, Statistical quality assurance methods for engineers, John Wiley, New York.
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Department of Civil, Construction and Environmental Engineering
The overall errors caused by the test method itself and operators were statistically evaluated
a An unpaved road surface material with 0%, 3%, 6%, 9%, and 12% bentoniteb The three operators were trained at the same time on all the five tests
The fall cone and ASTM roller devices yielded better repeatability and reproducibility than conventional tests
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ParametersLiquid Limit Plastic Limit
CasagrandeCup
Fall Cone Test
ASTMRoller
Fall Cone Test
Repeatability 0.6% 0.5% 0.4%
NoCorrelation
Reproducibility 1.7% 0.5% 0.6%
Overall R&R 1.8% 0.7% 0.7%
% of overall R&Rdue to reproducibility 89% 50% 73%
Department of Civil, Construction and Environmental Engineering
Recommended lab tests for determining liquid and plastic limits of soils
Liquid limit Plastic Limit
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Aggregate Quality and Morphology
Reference: Li, C., Ashlock, J., White, D., Jahren, C., and Cetin, B. (2017). "Gyratory Abrasion with 2D Image Analysis Test Method for Evaluation of Mechanical Degradation and Changes in Morphology and Shear Strength of Compacted Granular Materials." Construction and Building Materials, 152, 547—557, https://doi.org/10.1016/j.conbuildmat.2017.07.013
Department of Civil, Construction and Environmental Engineering
State DOTs and most researchers use LA abrasion tests to evaluate the quality of granular material
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From https://www.youtube.com/watch?v=FUGUk-4wEyA
(From ASTM C131)
#12 sieve is used to separate the specimen
Department of Civil, Construction and Environmental Engineering
Five different materials types from three different sources yielded similar LA abrasion test results
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Parameters Existing Surface Aggregate
Virgin Surface Aggregate
Road Rock
Class A Stone
Concrete Stone
Abbreviation ESA VSA RR CAS CSSource Granular road Quarry 1 Quarry 1 Quarry 2 Quarry 2