Stiffness Comparisons of Mastics Asphalt in Different Test Modes

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1 Stiffness Comparisons of Mastics Asphalt in Different Test Modes Hyunwook Kim, Scientist, Ph.D., Kiril Sokolov, Research Engineer, M.S., Manfred N. Partl, Head of Laboratory, Dr.Sc. Empa, Swiss Federal Laboratories for Materials Testing and Research 2 nd Workshop on 4PB at Guimarães, Portugal, September 2009

2 Outline 1. Introduction 2. Materials 3. Experimental program 4. Testing results 5. Summary and Conclusion 6. Ongoing Research on 4PB

3 Introduction Four-point bending beam (4PB) tests have been widely used in many countries to obtain complex modulus and to predict fatigue behavior of bituminous materials. In Switzerland, two-point bending beam (2PB) tests and co-axial shear tests (CAST) have been practically used for predicting the stiffness and fatigue behavior of bituminous materials. Recently, a Swiss research project, Performance Orientated Specification for Bituminous Mixtures VSS 2006/503, was initiated to compare two different test methods (2PB and 4PB) and to standardize 4PB tests in Switzerland. Before initiating the research project, some initiative verification tests were conducted with mastics asphalt in 4 different test methods and a 4PB aluminum bar.

4 Materials SN a (EN : 2006)

Experimental Program Test Methods and Specimen Geometries (EN 12697-26, 2004) Test method Geometry (mm) UCT D=50, H=100 IDT D=100, H=40 CAST D outer =150, D inner =56, H=40 4PB L=500, W=H=50 where, D

5 Experimental Program Test Methods and Specimen Geometries (EN , 2004) Test method Geometry (mm) UCT D=50, H=100 IDT D=100, H=40 CAST D outer =150, D inner =56, H=40 4PB L=500, W=H=50 where, D is a diameter, H is a height or a thickness, L is a length, W is a width, D outer is a outer diameter, and D inner is a inner diameter. Test Conditions IDT CAST Temperature, C -20, -10, 0, 10, 20 Frequency, Hz 0.01, 0.1, 1, 5, 10 Sinusoidal strain amplitude: 50μm 4PB UCT

Co-Axial Shear Tests (CAST) The CAST was designed at Empa in the 1980s and

2005, Sokolov et al. 2005, and Kim et al. 2009).

amplitude along the steel core, δ a = Displacement amplitude along the

6 Co-Axial Shear Tests (CAST) The CAST was designed at Empa in the 1980s and has been continuously developed further and improved (Gubler et al. 2005, Sokolov et al. 2005, and Kim et al. 2009). Fa G* = A( G*) δ a where, G* = Complex modulus in shear, F a = Force amplitude along the steel core, δ a = Displacement amplitude along the steel core, A(G*) = Coefficient function derived from FEA by recursive iteration, Poisson s ratio of 0.38 was assumed. 6

L=400 Test Set-up 0 40 190 290 440 7 500 50 50 Specimen Dimension: 50 x 50 x 500 (B x H x L) Extended Size (B, H): 30mm 67mm Verification with

7 Four-Points Bending Beam (4PB) Tests The test set-up was made by Junker in 1987 and has been modified until now. Recently, we completed the operating program by LABVIEW for 4PB tests and made additional holding clamps to cover a wide range of specimen size. L=400 Test Set-up Specimen Dimension: 50 x 50 x 500 (B x H x L) Extended Size (B, H): 30mm 67mm Verification with a EMPA aluminum bar Strain amplitude ( m) Predicted Complex modulus (GPa) Error (%) Targeting Complex modulus (GPa) * Frequency range (Hz): 1, 5, 10, 20, 30

8 Fitted Mastercurves of 4 Different Tests 1.E+04 1.E+04 UCT IDT Complex modulus (Mpa) 1.E C -10 C 1.E+02 0 C 10 C R temp = 0 C 20 C Sigmoidal 1.E+01 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 1.E+09 Frequency (Hz) Complex modulus (Mpa) 1.E C -10 C 1.E+02 0 C 10 C 20 C R temp = 0 C Sigmoidal 1.E+01 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 1.E+09 Frequency (Hz) 1.E+04 CAST 1.E+04 4PB Complex modulus (Mpa) 1.E+03 1.E+02 1.E+01 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 1.E+09 R temp = 0 C Frequency (Hz) -20 C -10 C 0 C 10 C 20 C Sigmoidal Complex modulus (Mpa) 1.E+03 1.E C R temp = 0 C -10 C 0 C Unexpected results at 10 C & 20 C Sigmoidal 1.E+01 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 1.E+09 Frequency (Hz)

9 Comparison Results Complex Modulus (MPa) 1.E+04 1.E+03 1.E+02 UCT IDT CAST 4PB 1.E+01 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 Reduced Frequency (Hz) 1.E+04 Fitted by a Sigmoidal Function (Fonseca and Witzack, 1996) log E * = δ + β γ (log f + r loga T ) 1+ e α where, E* = Complex modulus, δ = Parameter describing the minimum value of G*, f r = Frequency of loading at the reference temperature, α = Parameter describing the span between max and min value of G*, β, γ = Parameter describing the shape of the sigmoidal function, a T = Shift factor, determined with Williams-Landel-Ferry (WLF) relationship. Unstable mastics asphalt at high temperature? (from Solid to Fluid) Different testing mode or boundary conditions? (Comp. Vs. Shear / Bending) Different specimen geometry? (Force movement, Volume of strain zone, Size-effect) Complex Modulus (MPa) 1.E+03 1.E+02 1.E+01 UCT IDT CAST 4PB Phase Angle ( )

10 Summary and Conclusions Testing program and test set-ups for 4PB was successfully implemented and verified with an aluminum bar in Switzerland. Four different test methods for determining the complex modulus were compared with sigmoidal fitted mastercurves and black diagrams. Reasonably, complex modulus tests were comparable but there were increased discrepancies at high temperatures, above 10 C. However, all results were limited to mastics asphalt, MA8. It must be checked out for different mixture types to make some conclusions. Also, it might be interesting to investigate the fatigue behavior of bituminous materials with different fatigue tests. (Related references: Beneditto et al (Stiffness), 2004 (Fatigue) from RILEM studies)

11 Ongoing Research on 4PB: Program VSS 2006/503, Performance Orientated Specification for Bituminous Mixtures EMPA LAVOC Notes Number of Mixture WC + 4 BC + 4 Base C + 2 LAB (EME C1 and EME C2) Number of Samples (18 required in EN) Total: 18 per each mixture, 4 Modulus + 14(4) Fatigue Experimental Test 4PBB 2PBB European Standard Tests (Specimen Dimension) Test Conditions (Stiffness) 10, 15, 20 C 3, 10, 25 Hz 10, 15, 20 C 3, 10, 25 Hz 4 replicates Test Conditions (Fatigue) 20 C 30 Hz 10 C 25 Hz Where, 4PBB: 4 point bending beam, 2PBB; 2 point bending beam Where, WC: wearing coarse, BC: binder coarse 6 replicates with 3 strain levels 18 specimens *12 mixtures = 216 specimens

12 Ongoing Research on 4PB: Field Samples Materials Field Cores Layer Denomination Depth [mm] Laying year Section Layer AC B Binder-1 A9 Conthey-Sion AC T Base-1 PA A2 Bellinzone Sud- Wearing-1 AC B 22H Bellinzone Nord Binder-2 AC T 22H Base-2 SMA A3 Aargau Wearing-2 AC Binder-3 AC MR Bern Wearing-3 AC 22 S Binder-4 AC 22 S Aargau: Binder (AC B 22 H) N1/05 Limmattal AC MR Wearing-4 AC A1 Yverdon-Berne: Binder-6 AC EME 22 Tronçon Yverdon Base-3 Arrissoules AC F Subbase-1 PA Wearing-5 AC 16S A1 Yverdon-Berne: Binder-7 AC B Tronçon Payerne-Avenches: Base Subbase-2 Laboratory Mix EME C LAB-1 EME C LAB-2

Microstructure and Crack Propagation Kim et al., Materials and Structures, Vol.

13 Example: Micromechanical Fracture Model External Total: 149,922 particles, 298,855 contacts Fracture Frictional Strain Fracturing in aggregates (a) Microstructure and Crack Propagation Kim et al., Materials and Structures, Vol.42, pp , Kim and Buttlar, Int. J. Solids and Structures, Vol.46, ,

14 Thank You!!! Nano -Micro -Meso 2D Thank You!!! Modulus Test Full-Scale 3D Laboratory Tests Reinforcement FEM Fatigue Test DEM Fracture Test Visualization DEM FEM X-ray CT Small-Scale APT Full-Scale APT Leys

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