Effect of Matric Suction on Resilient Modulus
of Compacted Recycled Pavement Material
Kongrat Nokkaew (Presenter)
James M. Tinjum, Tuncer B. Edil
Mid-Continent Transportation
Research Symposium 2013
Research Motivations
Recycled pavement material (RPM)
crushed asphalt surface mixed with underlying base course
(i.e. subgrade and subbase)
Advantages
 Excellent mechanical properties
(e.g. high modulus, low moisture susceptibility)
 Life-cycle benefit
(e.g. low transportation needs, no landfill cost)
 Environment-friendly
(reducing green house gas emissions, energy
and natural aggregate consumption)
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 2
Premature failure due to moisture in base layer
Base course:
 Moisture increases, modulus decreases
 Few studies on modulus-moisture for RPM
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 3
Unsaturated Zone
Ground water table
Saturated Zone
“Pavements are compacted near optimum
water content unsaturated, and place above
the ground water table. As a result, Pavement
are unsaturated most of service life”
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 4
Soil-Water Characteristic Curves (SWCC)
Soil Particle
Volumetric Water
Content (q)
𝜃𝑠
𝜃𝑟
Air entry pressure ya
Menisci water
Residual volumetric
water content
Soil Suction in log scale
 A relationship between soil suction and volumetric moisture
content/degree of saturation
 Matric Suction = negative pore water pressure (Ua – Uw)
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 5
Impact of moisture on Mr in the MechanisticEmpirical Design Guide (M-EPDG)
 Adjusting factor determined from degree at optimum degree
of saturation
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 6
Objectives
 To evaluate the influence of matric suction on Mr for
compacted RPM in comparison to conventional crushed
limestone
 To established a model for predicting Mr from matric suction
and the soil-water characteristic curve (SWCC)
 To compare Mr from proposed model to those from M-EPDG
equation
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 7
Background
Resilient modulus (Mr)
 Primary input for Mechanistic-Empirical Pavement Design
Guide (M-EPDG)
 Impact to all quality and performance of pavement
d
Mr 
r
Where, d : deviatoric stress
r : recoverable strain
Summary resilient modulus (SRM)
 Mr representing stress state in the filed
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 8
SWCC fitting equation used in M-EPDG
𝜓
𝑆 − 𝑆𝑟
𝜓𝑟
Θ=
= 1−
106
1 − 𝑆𝑟
𝑙𝑛 1 +
𝜓𝑟
𝑙𝑛 1 +
1
𝑙𝑛 𝑒 + ψ/a
𝑛
𝑚
where Θ = effective degree of saturation; 𝑆 = degree of
saturation; 𝑆𝑟 = residual degree of saturation; 𝜓 is soil suction;
𝜓𝑟 , a, 𝑛, and 𝑚 are fitting parameters; and 𝑒 is the base of the
natural logarithm
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 9
SWCC parameters estimated by the M-EPDG
equation
−0.751
0.8627𝑑60
𝛼=
6.895
𝑚 = 0.1772𝑙𝑛𝑑60 + 0.7734
n = 7.5
𝜓𝑟
1
=
𝛼
𝑑60 + 9.7𝑒 −4
where d60 is particle size in mm at percent finer 60%
 SWCC parameter estimated based on d60
 Parameter n: fixed at 7.5
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 10
Materials
100
RPM-MI
Limestone-WI
Percent Finer (%)
80
60
RPM-MI
40
Basic properties and soil Classification
20
USCS designation
AASHTO designation
GW
A-1-b
LimestoneWI
GP-GM
A-1-a
Unit weight (kN/m3)
20.3
20.2
Water content (opt) (%)
Percent absorption
6.4
1.7
8.1
2.5
Properties
0
100
Limestone-WI
10
1
0.1
0.01
Particle Size (mm)
Grain size distributions
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
RPM-MI
Slide No. 11
Methods
Hanging column test
Large-scale testing cell
(305 mm x 76 mm)
Vacuum aspirator
(y, 25 - 80 kPa)
 Large-scale testing cell
 Matric suction:
 Hanging column (y, 0.05 to 25 kPa)
Hanging column
(y, 0.05 - 25 kPa)
University of Wisconsin-Madison
 Air aspirator (y, 25 to 80 kPa)
Mid-Continent Transportation
Research Symposium 2013
Slide No. 12
Mr test with suction control
Air Aspirator
1 kPa to 75 kPa
Plunger
Air Pressure
Transducer
External LVDT
Latex membrane
Water Pressure
Transducer
Internal LVDT
Specimen
Permeable Geotextile
Bottom Platen
with Ceramic Plate
Outflow Reading
 Test performed according to NCHRP 137A Procedure Ia
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Research Symposium 2013
Modified Bottom Platenwith ceramic plate
Slide No. 13
Mr test with suction control (Cont.’)
Material preparation:
 Type I material (150 mm in diameters and 305 mm in height)
 Prepared at optimum wn and 95% of rd (modified Proctor effort)
Sample saturation:
 To remove residual suction from sample compaction
 Assumed to be saturated when K is constant and outflow
is more than 3 pore volume of flow (PVF)
Suction conditioning
 y supplied by vacuum aspirator
 y verification by checking the equilibrium outflow water
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 14
Proposed resilient modulus model
Mr prediction for unsaturated base course (Liang et al. 2008)
𝜓𝑎
𝜒=
𝑢𝑎 − 𝑢𝑤
where
𝑘2
𝜏𝑜𝑐𝑡
+1
𝑝𝑎
𝑘3
S
𝑀𝑟 = 𝑘1 𝑃𝑎
𝜃 + 𝜒𝜓
𝑃𝑎
Log y
0.55
(Khalili and Khabbaz 1998)
𝑘1 , 𝑘2 , 𝑘3 = fitting parameters; 𝜓 = matric suction;
𝑝𝑎 = atmospheric pressure (101 kPa); 𝜃 = bulk stress;
and 𝜏𝑜𝑐𝑡 = octahedral shear stress; 𝜒 is Bishop’s effective
stress parameter
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 15
Proposed resilient modulus model (Cont.’)
assumed that
𝑆 − 𝑆𝑟
𝜒 = Θ𝜅 =
1 − 𝑆𝑟
𝜅
(Vanapalli and Fredlund 2000)
where Θ = effective degree of saturation; 𝜅 = fitting parameter;
𝑆 = degree of saturation; 𝑆𝑟 = residual degree of saturation
𝑀𝑟 = 𝑘1 𝑃𝑎
𝜃 + Θ𝜅 𝜓𝑚
𝑃𝑎
𝑘2
𝜏𝑜𝑐𝑡
+1
𝑝𝑎
𝑘3
For summary resilient modulus (𝜃 = 208 kPa and 𝜏𝑜𝑐𝑡 = 48.6 kPa).
𝑆𝑅𝑀 = 𝑘𝐴
University of Wisconsin-Madison
208 + 𝛩𝜅 𝜓
𝑃𝑎
𝑘𝐵
Mid-Continent Transportation
Research Symposium 2013
Slide No. 16
Results
SWCC of studied material fitted with Fredlund and
Xing (1994) Model
1
RPM-MI (R2 = 0.96)
Limestone-WI (R 2 = 0.98)
Degree of Saturation (S)
0.8
 Unimodal SWCC for RPM-MI, bimodal
SWCC for Limestone-WI
 ya < 1kPa
0.6
 SWCC predicted from M-EPDG:
RPM-MI
 Low ya (< 0.6 kPa)
0.4
 Rapidly drop of slope when y > ya
Limestone-WI
0.2
 Low yr (> 10 kPa)
M-EPDG Prediction
0
0.01
0.1
1
10
100
1000
Matric Suction (kPa)
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 17
Relationship between degree of saturation and Mr
500
RPM-MI
Limestone-WI
SRM (MPa)
400
300
200
100
0
0
0.2
0.4
0.6
0.8
1
Degree of Saturation
SRM decrease as degree of saturation increase
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 18
SRM versus matric suction
600
k = 3.44, k =15.35,  = 1.92
SRM (MPa)
500
A
B
2
Proposed model: R = 0.90
400
2
RPM-MI:
Liang et al. (20): R = 0.88
300
2
RPM-MI R = 0.90
200
SRM 216 – 290 MPa
RPM_MI
Proposed Model
Liang et al. (2008)
100
0
1
10
100
Matric Suction (kPa)
600
k = 0.1, k =19.28,  = 0.49
SRM (MPa)
500
A
Limestone-WI
Proposed Model
Liang et al. (2008)
B
2
Proposed model: R = 0.65
400
2
Liang et al. (20): R = 0.63
300
Limestone-WI:
SRM 75 – 191 MPa
200
100
0
1
10
Matric Suction (kPa)
100
 Tested at y = 1.5 kPa, 10 kPa, 20 kPa, 40 kPa, and 65 kPa
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 19
SRM versus matric suction fitted to the M-EPDG
prediction
y
800
SRM predicted from the
M-EPDG Equation:
RPM-MI
Limestone-WI
r
 Change as y corresponding to SWCC
688 MPa
 Start to increase rapidly
SRM (MPa)
600
when y > ya
400
y
 Tend to constant when y > ya
333 MPa (Residual W )
n
 SRMres/`SRMsat = 3.7 (both materials)
a
 SRMM-EPDG/`SRMmeasured:
a = -0.31;  = 0.30, k = 6.81
200
s
185 MPa
SRM
opt
of RPM-MI = 358.3 MPa
SRM of Limestone-WI = 173.7 MPa
opt
91 MPa (Saturated)
0
0.1
1
10
 1.9 – 2.9 for RPM-MI
 1.7 – 4.2 for DGA-WI
100
Matric Suction (kPa)
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 20
Variation of measured and predicted SRM
800
700
Propredicted SRM (MPa)
600
1:1 Line
500
400
2
300
Proposed Model: R = 0.93
2
Liang et al. (2008): R = 0.93
200
Proposed Model
Liang 2008
MEPDG
100
0
0
100
200
300
400
500
600
700
800
Measured SRM (MPa)
Comparison between predicted versus measured SRM using proposed
model in comparison to Liang et al. (2008) and M-EPDG Equation
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 21
Conclusions
RPM-MI provides higher SRM than limestone-WI
SRM increases as matric suction increase
The proposed model fits the test results well (R2 = 0.93)
over the full range of studied suction
SRMs predicted from M-EPDG are not conservative during
measured range of y (1 – 100 kPa)
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 22
References
 Liang, R.Y., Rabab’ah, H., and Khasawneh, M. Predicting MoistureDependent Resilient Modulus of Cohesive Soils Using Soil Suction
Concept. Journal of Transportation Engineering, Vol. 134, No. 1, 2008, pp.
34-40.
 Vanapalli, S.K., and Fredlund, D.G. Comparison of Different Procedures to
Predict Unsaturated Soil Shear Strength. Proc., of Sessions of Geo-Denver
2000, Advances in Unsaturated Geotechnics, ASCE, Reston, VA, 195-209.
 Guide for Mechnistic-Empirical Design for New and Rehabilitated Pavement
Structure. Final Report, 2004, NCHRP Project 1-37-A.
www.trb.org/mepdg/guide.html. Accessed July 23, 2013.
 Khalili, N., and Khabbaz, M.H. A Unique Relationship for 𝜒 for the
Determination of the Shear Strength of Unsaturated Soils. Geotechnique,
Vol. 48. No. 5, 1998, pp. 681-687.
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 23
Acknowledgements

James Tinjum (Advisor)

Tuncer Edil (Dissertation Committee)

William Likos (Dissertation Committee)

Benjamin Tanko (Undergraduate Assistant)

The Solid Waste Research Program (UW-Madison)

Recycled Materials Resource Center-3rd Generations

The Royal Thai Government

GeoFriends

Especically Xiadong Wang, Mababa Diagne, Ryan Shedivy
and Jiannan Chen
University of Wisconsin-Madison
Mid-Continent Transportation
Research Symposium 2013
Slide No. 24
Questions ?