THE GERMAN EMPIRICAL MECHANISTIC DESIGN SYSTEM PART II - DESIGN APPROACH FOR THIN SURFACED PAVEMENTS

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1 THE GERMAN EMPIRICAL MECHANISTIC DESIGN SYSTEM PART II - DESIGN APPROACH FOR THIN SURFACED PAVEMENTS NADim Seminar - Oslo Prof. Dr.-Ing. habil. Frohmut Wellner Dr.-Ing. habil. Sabine Leischner TU Dresden

2 Two design processes for flexible pavements Empirical design chart RStO M-E design procedure - RDO Asphalt Oslo, Folie 2

3 German Design Charts RStO 12 Bk 0.3 < 300, t-ESALs Minimum thickness of the asphalt layers 10 cm also for LVR in Germany Oslo, Folie 3

4 Introduction Thin asphalt surface up to 4 cm Base course (High quality UGM) Sub-base layer (Frost protection) Subgrade LVR < t-standard axles Oslo, Folie 4

5 Pavement structure with thick asphalt layer (220mm) Pavement structure with thin asphalt layer (10mm) Vertical Stresses Oslo, Folie 5

6 Introduction Vertical stresses within granular layer Pavement structure with thick asphalt layer (220mm) Pavement structure with thin asphalt layer (10mm) UGM LAYER UGM LAYER Oslo, Folie 6

7 M-E design Traffic volume Climate Material properties Modelling Layer thickness Calculation process Asphalt CTB UGL Subgrade Modify materials and/or layer thickness Proof rutting Proof fatigue Proof Plastic deformation fulfilled? no yes Sufficient designed pavement structure RDO Asphalt 09 Oslo, Folie 7

8 M-E Design Traffic volume Climate Material properties Model Layer thickness Calculation process UGL Subgrade Modify materials and/or layer thickness Accumulated damage basecourse Accumulated damage subgrade fulfilled? no yes Sufficient designed pavement structure Modified procedure für LVR Oslo, Folie 8

9 The deformation performance of UGL is highly important for TSAP. The current aggregate mix/layer characteristics (DoC/grading lines, particle strenghts) are insufficient for the evaluation of the deformation performance of UGM. Results of lab tests showed that UGM have different performance under cyclic loading even if they the have similar DoC, MC and grading lines. Oslo, Folie 9

10 Input Parameter Layer thickness: Frost protection The minimum thickness for frost protection must be determined accorditng to RStO Min: 250mm Max: 900mm Oslo, Folie 10

11 Input Parameter Traffic load LVR < 100, t-standard axles In future: Consideration of the actual axle load distribution Häufigkeit [%] BAB Stadtnaher Verkehr BAB Mischverkehr BAB Fernverkehr >20 Achslastklasse [t] [Data from UHLIG] Oslo, Folie 11

12 Material characterization Test package Conditioning test Resilient test Plastic test Sample preparation Test set-up Test package Approx 22h Oslo, Folie 12

13 RL CBR Test Oslo, Folie 13

14 Material characterization Property Mixture A Mixture B Mixture C Mixture D Mixture E Type Natural sandy-gravel Crushed rock Granodiorite Crushed rock Andesite Crushed rock FPM Crushed rock Granite with quartz Grain size 0/32 0/32 0/32 0/16 0/32 Maximum dry density [gr/cm3] 2,200 2,170 2,010 2,198 2,000 OMC [m - %] 6,0 5,8 12,1 6,7 5,0 Fine Content 2,5 2,5 2,5 3,3 - Oslo, Folie 14

15 Material characterization Ranking procedure for UGM Conditioning Test: Cell pressure of 150kPa Deviatoric stress of 300kPa Tests at 70, 80 and 90% of OMC Characteristic stiffness Characteristic plastic strain rate Oslo, Folie 15

16 Material characterization Ranking procedure for UGM Conditioning Test: Cell pressure of 150kPa Deviatoric stress of 300kPa Q 1 Material excellent material Q 2 Material - good material Q 3 Material - bad material Q 2 Material Granit (FP Material) Q 3 Material Andesit Charakteristischer Elastizitätsmodul [MPa] Charakteristischer Elastizitätsmodul [MPa] Charakteristische plastische Dehnungsrate [ /10 6 LW] Q1 Q2 Q3 80% 70% 90% GRA-0/16 Charakteristische plastische Dehnungsrate [ /10 6 LW] Q1 Q2 Q3 70% AND-0/32 80% Oslo, Folie 16

17 Material characterization Characterization of elastic deformation behavior Multistage repeated load triaxial test at CCP Oslo, Folie 17

18 Material characterization Results of the RLT tests Elastic deformation performance Plastic deformation performance Elastizitätsmodul [MPa] Zelldruck σ 3 [kpa] Deviatorspannung [kpa] Vertikale deviatorische plastische Dehnung [ ] 24,00 22,00 20,00 18,00 16,00 14,00 12,00 10,00 8,00 6,00 4,00 2,00 0,00 GRA-0/ GRA-0/ GRA-0/ Lastwechsel [-] Tausende -> Determination of the model parameters Oslo, Folie 18

19 Modeling of permanent deformation response ( ε ) ( ε ) + ( N N ) λ p,1 lab = p,1 N 0 0 Oslo, Folie 19

20 Climate Stiffness changes of the BC/subgrade due to changing moisture content during the year [ERLINSON 09] Oslo, Folie 20

21 Climatic condition Germany Sweden ZONE 1 Thaw period 45,1% ZONE 2 Thaw period 44,0% Oslo, Folie 21

22 M-E Design Traffic volume Climate Material properties Model Layer thickness Calculation process UGL Subgrade Modify materials and/or layer thickness Accumulated damage basecourse Accumulated damage subgrade fulfilled? no yes End Oslo, Folie 22

23 M-E Design Design process Asphalt UGL Subbase Subgrade 100mm 100mm 100mm 1. Calculation of plastic deformation of the UGL Representative elastic strains in the UGM at three sublayers of a thickness of 100mm 2. Vertical compressive strain/stress at top subbase 3. Vertical compressive strain/stress at top subgrade Oslo, Folie 23

24 M-E Design Plastic deformation UGL Elastic strains Basecourse Material 2 p τ Mr = k1 P a P + 1 Target W.C. k 1 k 2 k 3 [% of OWC] [MPa] [-] [-] GRA Elastic strain distribution k oct a k 3 Plastic strains λ = ( ) 4, ,57 ε r,1 lab Oslo, Folie 24

25 M-E design Performance Criteria Subgrade/FPL: plastic deformation Austroads (Australia) Based on Strain Sweden design code Based on Stress German ME design code Oslo, Folie 25

26 M-E design Material parameter: Asphalt no structural layer Layer Layer modulus (E- Modulus) Poisson s ratio Material behavior Asphalt t<20mm Asphalt t>20mm E=(5.000 MPa) (Membrane behaviour) E=5.000 MPa Standard condition E= MPa Thaw period µ = 0,35 Linear elastic µ = 0,35 Linear elastic Thaw period Oslo, Folie 26

27 Conclusiones Using the results of RLTT on UGM the basis for the ME design of TSAP was established It is possible to have pavement structures with asphalt layers of less than 40mm thickness for low trafficked pavements in Germany Only high quality UGMs that have high stiffness and low susceptibility to plastic deformation even at high moisture contents should be used in TSAP. Oslo, Folie 27

28 Acknowledgement This presentation is based on parts of the research project carried out at the request of the Federal Ministry of Transport, Building and Urban Development, represented by the Federal Highway Research Institute under research project No /2011/ERB. Oslo, Folie 28