Application of Mechanistic Tests for Performance of HMA Mixtures

Transcription

1 Application of Mechanistic Tests for Performance of HMA Mixtures Louay Mohammad, Ph.D. Louisiana Transportation Research Center Louisiana State University 2009 Louisiana Transportation Conference February 8-11, 2009 Baton Rouge, Louisiana

2 Outline HMA Design Review performance Tests Results Summary Recommendation

3 Aggregates Composition of Compacted HMA Mixture Provide a strong stone skeleton to resist repeated load applications Asphalt cement Glue aggregate particles into a cohesive mass Additives Air Enhance performance Total Volume VOLUME air asphalt aggregate aggregate MASS Total Mass

4 How Does One Determine the Proportions of Asphalt Cement Aggregate Others

5 Perform Mixture Design

6 Perform Mixture Design Select an optimum amount of asphalt cement content to satisfy a prescribed Criteria Combined + = = Opt. AC Content

7 What Are the Criteria? Volumetrics Voids in the Total Mix, VTM Voids in the Mineral Aggregate, VMA Voids Filled with Asphalt, VFA Densification Stages during lab compaction process Total Volume VOLUME air asphal t aggregat e aggregate MASS Total Mass

8 Background Superpave volumetric mix design No mechanical proof test» Marshall mix design Ensure satisfactory performance: did use strict requirement» material specifications» volumetric mix criteria. Mechanical tests mix verification for intermediate and high volume traffic» advanced materials characterizations tests :» Superpave Shear Tester Not widely used

9 Background Material Characterization Torture Stiffness» Stress/Strain Strength» Failure» ITS Dynamic Modulus Stiffness vs Strength Modulus Strength Stiffness

10 Resulting Mixture is Expected to Perform! Courtesy: L. Cambas

11 L III Implementation of Superpave -- Phase I L I Nine Overlay Projects throughout the State Three Different Traffic Levels» Level I -- 4 L I» Level II -- 3 L II» Level III -- 2 Thirteen Mixtures Two Mix Types L I L I L II» 25 mm (5)» 19mm (8) L III

12 All Mixtures Met Superpave Volumetric Specifications Do these mixes have similar performance?

13 Overall Relative Rut Susceptibility Ranking Level I 3 Fair Relative Rut Susceptibility 2 1 Good Excellent 25 mm 19 mm 0 LA 4 BC LA 22 BC LA 22 WC LA 121 BC LA 121 WC LA 353 BC/WC

14 Overall Relative Rut Susceptibility Ranking -- Level II 3 Fair Relative Rut Susceptibility 2 1 Good Excellent 25 mm 19 mm 0 US 90 BC Us 61 (2) BC LA 22 BC US 61 (1) WC

15 The Search Mechanistic Tests Pavement Performance Intermediate Temperature Fatigue endurance High Temperature Permanent deformation Features Fundamental Easy to Use Reliable Cost

16 Performance Tests

17 Performance Tests Mixture Rutting Performance of Mixtures Loaded Wheel Tracking Test Flow Number Fatigue Performance Semi Circular Bend Test Indirect Tensile Strength Test Loaded Wheel Tracking Test

18 Rutting Performance of Mixtures original profile original profile Asphalt Mixture weak asphalt layer shear plane

19 Loaded Wheel Tracking Test AASHTO T Damage by rolling a steel wheel across the surface of a sample Cylindrical Core or SGC Slab 320 mm long, 260 mm wide, and 80 mm thick 50 o C, Wet or dry Deformation at 20,000 passes is recorded Wheel Diameter: mm (8 inch) Wheel Width: 47mm (1.85 inch) Fixed Load: 703 N (158 lbs) Rolling Speed: 1.1 km/hr Passing Rate: 56 passes/min

20 Sample Preparation, LWT Kneading Compactor

21 LWT Test Results 6 Rut Depth, mm GRF GRM GRC LSF LSM LSC SSF SSM SSC

22 Rut Depth, mm LWT Test Results I-10 Vinton SMA 12.5 mm WC (Vinton WC) I-10 Egan Superpave 12.5 mm WC (Egan WC) 25.0 mm BC (Egan BC) US 190 Port Allen Superpave 25.0 mm BC (190BC) LA 964 Marshall 19.0 mm WC (964WC) 25.0 mm BC (964BC) 0 VintonWC EganWC EganBC 964WC 964BC 190BC Mixtures

23 LWT Test Results PG PG 70-22M PG 76-22M Mixture Type

24 Repeated Load Permanent Deformation Test F N IPC UTM-25 Specimen dimension 100mm X 150mm A haversine axial compressive stress is applied Loading: 0.1 Second Rest Period: 0.9 Second 30 psi 54.4 C F N : Number of cycles Tertiary Failure 10,000 cycles Time Cycles F N

25 Sample Preparation -- F N 150mmX170mm 100mmX150mm

26 Repeated Load Permanent Deformation Test -- F N F N CYCLES PG PG 70-22M PG 76-22M Mixture Type

27 Repeated Load Permanent Deformation Test -- F N F N CYCLES Flow Number, Cycles VintonWC EganWC EganBC 964WC 964BC 190BC Mixtures

28 Relationship B/W LWT Rut Depth & F N Average Rut Depth (mm) y = 10909x R 2 = Average Flow Number

29 Relationship B/W LWT Rut Depth & F N Rut Depth (mm) R 2 = Flow Number

30 Indirect Tensile Strength Test Test Protocol Cylindrical Specimen: 100mm x 63.5mm 50.8 mm/min vertical deformation rate Temperature: 25C Indirect Tensile Strength Indirect Tensile Strength Toughness Index

31 2P ITS = πdt = 0.52 ε p H t Toughness Index TI = ( A ε ( ε ε A p p Indirect Tensile Strength Test ) )

32 Indirect Tensile Strength, psi 25C 250 PG PG 70-22M PG 76-22M Aged

33 ITS Strain, % -- 25C PG PG 70-22M PG 76-22M Aged

34 Toughness Index 1 PG PG 70-22M PG 76-22M Aged

35 Indirect Tensile Strength Test Result ITS, psi Fine Granite Fine Limestone Coarse Limestone Medium Sandstone

36 Indirect Tensile Strength Test Result 1 Toughness Index Fine Granite Fine Limestone Coarse Limestone Medium Sandstone

37 Comparison to Field Performance IT Strength, psi Field Mixtures Superpave/PG This Study

38 Comparison to Field Performance IT Strength, psi Strain, % Field Mixtures Superpave/PG This Study

39 Semi Circular Bend (SCB) Test Test Temperature: 25 C Unaged and Aged Mixtures Three Notch Depths J , 31.8-, and 38.0-mm Load: 0.5 mm/min vertical deformation rate Load & Ver Def recorded The critical value of fracture resistance c = U b 1 1 U 2 1 b a a Load (kn) U 2 U 1 notch a1 notch a Deflection (mm) U is the total strain energy to failure Jc: the critical strain energy release rate

40 Determination of J c Load (lb) Deformation (in.) 25.4 mm notch 31.8 mm notch 38 mm notch 1 J c = ( ) b du da Total Area (Fracture Energy),kNmm Notch (mm)

41 Sample Preparation SCB 150mm x 57mm 38mm 31.8mm 25.4mm

42 Advantages of SCB Test Utilize gyratory compacted cylindrical specimens or cores obtained from the field multiple specimens can be obtained from one core reducing the error caused by heterogeneities among samples

43 SCB Test Results PG PG 70-22M PG 76-22M Jc, Kj/m Aged

44 SCB Test Results Jc, kj/m Fine Granite Fine Limestone Coarse Limestone Medium Sandstone

45 Comparison to Field Performance Jc, kj/m 2 Field Mixtures Superpave/PG This Study

46 Comparison B/W Jc & TI 1.2 Jc (Kj/m2) Aged mixtures y = 1.54x R 2 = 0.75 Unaged Mixtures y = 1.26x R 2 = TI Unaged Mixtures Aged Mixtures

47 Summary Mixes that meet Superpave volumetric specifications does not indicate similar performances Performance tests are necessary to identify mixture characteristics FN values have a fairly good relationship with the LWT rut depths Mixture ranking order obtained from the FN and LWT test results was quite consistent with the field use of those mixtures Results form SCB test exhibited good correlation with the TI

48 Recommendation Rut Performance test LWT Rut depth of 6 mm 50C, Wet Fatigue Endurance Indirect Tensile strength test» ITS > 150 psi» IT Strain > 0.55» TI > 0.55 Semi Circular Bend Test» JC > 0.60 Kj/m 2

49 T H A N K Y O U