Effect of Matric Suction on Resilient Modulus of Compacted Recycled Pavement Material

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)

Mid-Continent Transportation Research Symposium 2013 Slide No. 2University of Wisconsin-Madison

Premature failure due to moisture in base layer

Base course: Moisture increases, modulus decreases Few studies on modulus-moisture for RPM



Unsaturated Zone

Saturated ZoneGround water table

“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”


Soil-Water Characteristic Curves (SWCC)

Soil Suction in log scale

Volu

met

ric W

ater

Con

tent

(q)

ya

A relationship between soil suction and volumetric moisture content/degree of saturation

Matric Suction = negative pore water pressure (Ua – Uw)

𝜃𝑟

𝜃𝑠

Air entry pressure

Residual volumetric water content

Soil Particle

Menisci water


Impact of moisture on Mr in the Mechanistic-Empirical Design Guide (M-EPDG)

Adjusting factor determined from degree at optimum degree of saturation


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

r

drM

Where, d : deviatoric stress r : recoverable strain

Resilient modulus (Mr) Primary input for Mechanistic-Empirical Pavement Design Guide (M-EPDG) Impact to all quality and performance of pavement


Background

Summary resilient modulus (SRM)

Mr representing stress state in the filed

SWCC fitting equation used in M-EPDG


Θ=𝑆−𝑆𝑟

1−𝑆𝑟=[1− 𝑙𝑛(1+ 𝜓

𝜓 𝑟 )𝑙𝑛(1+ 106

𝜓 𝑟 ) ][ 1

{𝑙𝑛 [𝑒+ (ψ /a )𝑛] }𝑚 ]

where = effective degree of saturation = degree of saturation;

= residual degree of saturation; is soil suction; , , , and are

fitting parameters; and is the base of the natural logarithm


SWCC parameters estimated by the M-EPDG equation

𝛼=0.8627 𝑑60

− 0.751

6.895n=7.5

𝑚=0.1772 𝑙𝑛𝑑60+0.7734 𝜓𝑟

𝛼 = 1𝑑60+9.7𝑒− 4

SWCC parameter estimated based on d60

Parameter n: fixed at 7.5

where d60 is particle size in mm at percent finer 60%

Materials

0

20

40

60

80

100

0.010.1110100

RPM-MILimestone-WI

Per

cent

Fin

er (%

)

Particle Size (mm)

Properties RPM-MI Limestone-WI

USCS designation GW GP-GMAASHTO designation A-1-b A-1-a

Unit weight (kN/m3) 20.3 20.2

Water content (opt) (%) 6.4 8.1Percent absorption 1.7 2.5

Basic properties and soil Classification

Grain size distributions


Limestone-WIRPM-MI


MethodsHanging column test

Large-scale testing cell (305 mm x 76 mm)

Hanging column(y, 0.05 - 25 kPa)

Vacuum aspirator(y, 25 - 80 kPa)

Large-scale testing cell Matric suction:

Hanging column (y, 0.05 to 25 kPa) Air aspirator (y, 25 to 80 kPa)


Outflow Reading

Air Aspirator1 kPa to 75 kPa

Bottom Platenwith Ceramic Plate

Water Pressure Transducer

Air Pressure Transducer

Latex membrane

Internal LVDT

External LVDT

Permeable Geotextile

Plunger

Mr test with suction control

Specimen

Modified Bottom Platen-with ceramic plate

Test performed according to NCHRP 1-37A Procedure Ia


Mr test with suction control (Cont.’)

Outflow Column

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)

Suction conditioningy supplied by vacuum aspirator y verification by checking the equilibrium outflow water

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)


𝑀 𝑟=𝑘1𝑃𝑎( 𝜃+𝜒𝜓𝑃𝑎 )𝑘2(𝜏𝑜𝑐𝑡

𝑝𝑎+1)

𝑘3

Proposed resilient modulus model

Mr prediction for unsaturated base course (Liang et al. 2008)

where , , = fitting parameters; = matric suction;

= atmospheric pressure (101 kPa); = bulk stress;

and = octahedral shear stress; is Bishop’s effective stress

parameter

𝜒=( 𝜓𝑎

𝑢𝑎−𝑢𝑤)

0.55

(Khalili and Khabbaz 1998)

Log y

S

Proposed resilient modulus model (Cont.’)

𝑀 𝑟=𝑘1𝑃𝑎( 𝜃+Θ𝜅𝜓𝑚

𝑃𝑎)𝑘2

(𝜏𝑜𝑐𝑡

𝑝𝑎+1)

𝑘3

assumed that

where = effective degree of saturation = fitting parameter;

= degree of saturation; = residual degree of saturation

𝜒=Θ𝜅=(𝑆−𝑆𝑟

1−𝑆𝑟)𝜅

For summary resilient modulus ( = 208 kPa and = 48.6 kPa).

𝑆𝑅𝑀=𝑘𝐴( 208+𝛩𝜅𝜓𝑃𝑎

)𝑘𝐵


(Vanapalli and Fredlund 2000)


SWCC of studied material fitted with Fredlund andXing (1994) Model

Results

0

0.2

0.4

0.6

0.8

1

0.01 0.1 1 10 100 1000

Deg

ree

of S

atur

atio

n (S

)

Matric Suction (kPa)

M-EPDG Prediction

RPM-MI

Limestone-WI

RPM-MI (R2 = 0.96)

Limestone-WI (R2 = 0.98) Unimodal SWCC for RPM-MI, bimodal

SWCC for Limestone-WI

ya < 1kPa

SWCC predicted from M-EPDG:

Low ya (< 0.6 kPa)

Rapidly drop of slope when y > ya

Low yr (> 10 kPa)


0

100

200

300

400

500

0 0.2 0.4 0.6 0.8 1

RPM-MI

Limestone-WIS

RM

(MPa

)

Degree of Saturation

Relationship between degree of saturation and Mr

SRM decrease as degree of saturation increase


R2 = 0.90RPM-MI

SRM versus matric suction

0

100

200

300

400

500

600

1 10 100

RPM_MIProposed ModelLiang et al. (2008)

SR

M (M

Pa)


kA

= 3.44, kB =15.35, = 1.92

Proposed model: R2 = 0.90

Liang et al. (20): R2 = 0.88

0

100

200

300

400

500

600

1 10 100

Limestone-WIProposed ModelLiang et al. (2008)

SR

M (M

Pa)


kA

= 0.1, kB =19.28, = 0.49

Proposed model: R2 = 0.65

Liang et al. (20): R2 = 0.63

Tested at y = 1.5 kPa, 10 kPa, 20 kPa, 40 kPa, and 65 kPa

RPM-MI: SRM 216 – 290 MPa

Limestone-WI:SRM 75 – 191 MPa


0

200

400

600

800

0.1 1 10 100

RPM-MILimestone-WI

SR

M (M

Pa)


ya

yr

a = -0.31; = 0.30, ks = 6.81

SRMopt

of RPM-MI = 358.3 MPa

SRMopt

of Limestone-WI = 173.7 MPa91 MPa (Saturated)

333 MPa (Residual Wn)

185 MPa

688 MPa

SRM versus matric suction fitted to the M-EPDG prediction

Change as y corresponding to SWCC Start to increase rapidly

when y > ya

Tend to constant when y > ya

SRMres/`SRMsat = 3.7 (both materials)

SRMM-EPDG/`SRMmeasured:

1.9 – 2.9 for RPM-MI 1.7 – 4.2 for DGA-WI

SRM predicted from the M-EPDG Equation:


0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800

Proposed ModelLiang 2008MEPDG

Pro

pred

icte

d S

RM

(MP

a)

Measured SRM (MPa)

Proposed Model: R2 = 0.93

Liang et al. (2008): R2 = 0.93

1:1 Line

Comparison between predicted versus measured SRM using proposed model in comparison to Liang et al. (2008) and M-EPDG Equation

Variation of measured and predicted SRM


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)

Liang, R.Y., Rabab’ah, H., and Khasawneh, M. Predicting Moisture-Dependent 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 for the Determination of the Shear Strength of Unsaturated Soils. Geotechnique, Vol. 48. No. 5, 1998, pp. 681-687.


References


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

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Effect of Matric Suction on Resilient Modulus of Compacted Recycled Pavement Material