Report

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) 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 − Θ= = 1− 106 1 − 1 + 1 + 1 + ψ/a where Θ = effective degree of saturation; = degree of saturation; = residual degree of saturation; is soil suction; , a, , and are fitting parameters; and 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 0.862760 = 6.895 = 0.177260 + 0.7734 n = 7.5 1 = 60 + 9.7 −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 University of Wisconsin-Madison Mid-Continent Transportation 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) = − where 2 +1 3 S = 1 + Log y 0.55 (Khalili and Khabbaz 1998) 1 , 2 , 3 = fitting parameters; = matric suction; = atmospheric pressure (101 kPa); = bulk stress; and = octahedral shear stress; 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 − = Θ = 1 − (Vanapalli and Fredlund 2000) where Θ = effective degree of saturation; = fitting parameter; = degree of saturation; = residual degree of saturation = 1 + Θ 2 +1 3 For summary resilient modulus ( = 208 kPa and = 48.6 kPa). = University of Wisconsin-Madison 208 + 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 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 ?