Using the Bitumen Bond Strength Test & Sessile Drop Method

Transcription

1 2011 PAVEMENT PERFORMANCE PREDICTION SYMPOSIUM Selection of Materials for Moisture Resistance HMA Using the Bitumen Bond Strength Test & Sessile Drop Method Hussain Bahia, Raquel Moraes, Raul Velasquez University of Wisconsin-Madison July 14 th 2011 Laramie, Wyoming

2 Outline Background Development stages of the Bitumen Bond Strength Test (BBS)- Example Results Surface Energy and Contact Angle BBS vs. Contact Angle Measurements Conclusions

3 Background Three mechanisms by which moisture degrades mixture performance LossL of cohesion within binder Adhesive failure aggregate-asphalt Degradation of aggregate

4 Consequences of Moisture Damage (Hicks 91) Raveling Flushing Fatigue Cracking Pot Holes Rutting Reflection Cracking Se everity - 9 Max Likelin ness Wisconsin Minnesota Illinois Nebraska Kansas Missouri

5 WisDOT Survey (99) Types of Distresses mostly Observed Type of Distresses Number of States (Total 10) Raveling 6 Rutting 4 Fatigue Cracking 3 Shoveling 1 Bleeding 1 Potholes 1 Disintegration (bottom up) 1 Stripping 2

6 How to Estimate Potential for Mositure Damage? Go back to fundamentals Separate asphalt effects from aggregates effects Focus on asphalt We know how to characterize mineral surface We do not know what is in the asphalts Asphalt is glue=> treated as an adhesive

7 Sample Failure after Moisture Exposure Both Adhesive and Cohesive Failures Adhesive Cohesive Cohesive failure >>> Adhesive failure!

8 The Development of the BBS test Asphalt composition and aggregate g mineralogy affect cohesion and adhesion. Traffic stress ( build up of pressure in voids) is important. Test Development 3 stages: DSR : Tackiness test Cohesion DSR: Stress sweep test Interface under stress Pull-off tensile test Bitumen Bond Strength (BBS)

9 Thin Film Tackiness Using Normal Force in DSR PG (original) test at 25 C Force (N) mm/s Tack-factor 1 = [s.n] Tack-factor 2 = [s.n] -30 Tack-factor 3 = [s.n] Tack-factor 4 = [s.n] Time (s) 20

10 Comparison of Tack-Factor Binder composition is very important - Materials at Equal G*= 1.2x10 6 Pa Force (N) Binder C T [s*n] PG58-28(original): 56 PG64-28(SB)-30.95C PG64-28(SBS)-28.2C PG64-28(Elvaloy)-29.28C PG58-28(original)-31.95C PG58-28(0.5%Morlife)-29.2C PG58-28(0.5%Morlife): 48 PG64-28(SB): 110 PG64-28(SBS): 126 PG64-28(Elvaloy): Time (s) 20

11 DSR Stress Effects Test : Aggregate, Asphalt, Water Control Temperature, loading rate and stress.

12 Testing Protocol Pour water 6-7hrs at 40 C Stress Sweep Test Wet Condition Failed Sample

13 Example of Stress Effects Stress Sweep, 10Hz, 40C Sand Stone Stress Sweep, 1mm thickness, 40 C Comple ex Modulus (kpa) SBS Modified PG64-28, Wet Dry- EVA Modified Wet, EVA Modified SBS Modified PG64-28, Dry Moisture damage is much more pronounced at higher stresses Shear Stress (Pa)

14 Lessons learned from DSR led to Development of of of the Bitumen Bond Strength (BBS) DSR test is costly and time consuming Need a more practical method to measure cohesion of binders and adhesion between aggregate g and asphalt binder PATTI is an ASTM standard for paints; has been used for asphalt; modify and adapt for asphalt + aggregates. BBS test to quantify effects of components conditioning BBS test to quantify effects of components, conditioning time, conditioning solution and stress rates

15 Schematic of BBS Main components of BBS equipment are: Air Pressure Aggregate

16 BBS Apparatus and Metal Stub Rough Surface to prevent interface failure Developed in collaboration with University of Ancona-Italy Machined edge to control film thickness

17 Preparation of Substrates Solid Aggregate Substrates Saw aggregate plates of uniform surface Lap surface to insure uniform Surface Roughness Heat to application temperature Glass Plates can also be used for cohesion (full bond)

18 Failure Types in BBS Cohesive Failure Adhesive Failure

19 BBS Test Data Analysis Pressure at failure is recorded and pull-off tensile strength (POTS) is calculated by : where: ee POTS BP Ag A ps C A g = contact area of gasket with reaction plate (mm 2 ) BP = burst pressure (kpa) A ps = area of pull stub (mm 2 ) 600 C = piston constant 500 Pullou ut Tension [psi] FH 64-22,neat,24h,40C, granite,new patti,rate 5,dry Time [s] run 1 run 2 run 3

20 Important Aspects of BBS Aggregate plate preparation: smooth surface Binder application and curing under controlled conditions prior to testing Film thickness: controlled with legs in stub Consistent loading rate is critical Examine or image failure surface Adhesive failure Cohesive failure Pullou ut Tension [psi] FH 64-22,neat,24h,40C, granite,new patti,rate 5,dry Time [s] run 1 run 2 run 3

21 Examples of Results Effects of Moisture and Binder Modification hours 96 hours ull off Strength (MPa) P GRANITE 3.5 LIMESTONE 3.0 Pull of ff Strength (MPa) GRANITE LIMESTONE 0.0

22 Effect of Aggregate Type Significant Asphalt Binder CRM neat CRM %Elastomer 1 CRM %Acid *CT (hr) Failure Type Granite Limestone Dry Cohesion Cohesion 6 Cohesion Cohesion 24 Cohesion Cohesion 48 Adhesion Cohesion 96 Adhesion Adhesion Dry Cohesion Cohesion 6 Adhesion Cohesion 24 Adhesion Cohesion 48 50%A -50%C Adhesion 96 Adhesion Adhesion Dry Cohesion Cohesion 6 Cohesion Cohesion 24 Cohesion Cohesion 48 Cohesion Cohesion 96 Cohesion Cohesion *Conditioning Time (CT)

23 Effect of Loading Rate- Not Significant Pull-off Tensile Strength (kpa), FH neat, Granite 70 psi/s 240 psi/s Dry Wet - 24h Loss of strength (%) 29.3% 29.9% CRM %LSBS, Granite 70 psi/s 120 psi/s 180 psi/s Dry Wet - 24h Loss of strength (%) 26.4% 21.9% 20.9% FH %PPA, Limestone 100 psi/s 200 psi/s Dry Wet - 24h Loss of strength (%) 33.9% 32.8% January 05,

24 Effect of Conditioning Media De-icing Chemicals Significant

25 Effect of Temperature- Significant Asphalt Binder Type CT (hr) Sol Granite Pull-off Tensile Pull-off Tensile Strength (kpa) Strength (kpa) 25 ºC 20 ºC FH64-22+PPA Dry Tap CRM58-28+PPA Dry Tap Asphalt Binder Type CT (hr) Sol Limestone Pull-off Tensile Pull-off Tensile Strength (kpa) Strength (kpa) 25 ºC 20 ºC FH64-22 neat Dry Tap January 05,

26 BBS Reproducibility Very Good gth (MPa) Pull-off Stren hours Operator 1 Operator 2 Pull-off Stren ngth (MPa) hours Operator 1 Operator hours

27 Verification of BBS Results Using Surface Energy / Contact Angle Fundamentals of Bonding: Thermodynamic Parameters

28 Sessile Drop Method Surface Energy of Binders FH Neat FH % Acid FH % elast_ % Acid CRM Neat CRM % Acid Contact Angle ( ) CRM % elast_ %Acid CRM % elast_2

29 Good-van Oss-Chaudhury (GVOC) Theory GVOC theory : a practical methodology to estimate interfacial energy of apolar and electron acceptor/electron donor molecule Basic concept: Surface and interfacial energy consist of two components: where: γ surface energy γ LW apolar or Lifshitz-van der Waals component of electrodynamic origin γ AB polar component caused by Lewis acid-base interactions where

30 Contact Angle and Surface Energy Relation between surface tensions of solid, liquid, solid-liquid interface, and contact angle was expressed by Young (1804) : where γ S is solid surface free energy, γ SL is solid-liquid interfacial free energy, γ L is liquid surface tension, and θ is contact angle.

31 Work of Cohesion Surface energy is defined as amount of work required to create a unit area of new surface of specific material Work of cohesion can be defined as: where: γ surface energy

32 BBS vs. Work of Cohesion Higher Work of Cohesion Higher Pull-off Strength Pull-off Str rength - Wet 24 4h (MPa) R² = Work of Cohesion (mj/m 2 ) Asphalt binders that showed cohesive failure with limestone aggregate after wet conditioning (96h)

33 Work of Adhesion Dry State Follows directly from definition of interfacial free energy and is expressed by Dupré ( 1869): where W a is work of adhesion, or work required to separate solid from liquid surface, γ S is solid surface free energy, and γ L is liquid surface tension. γ SL is the solid-liquid interfacial free energy

34 Work of Adhesion Dry State Relation between contact angle and surface free energies can be written as Young-Dupré equation: known unknown Measured If GvOC parameters are known for at least three liquids Contact angles of these liquids on a solid are measured, Results can be used to determine surface energy of solid:

35 Contact Angle Method After determined three surface energy components of asphalt binder and three surface energy components of aggregate: It is possible to calculate work of adhesion between asphalt binder and aggregate g in presence of water (i.e., work of debonding) Water CRM Limestone

36 Work of Debonding Dupré s equation can be used to calculate work of adhesion between asphalt binders and aggregates g in presence of water (i.e., work of debonding): in which subscripts B, W and A represent asphalt binder, water, and aggregate respectively, = work of debonding when water displaces asphalt binder from aggregate surface γ BW = work done for formation of new binder-water interface γ AW = work done for formation of new aggregate-water g interface = external work necessary to destroy of binder-aggregate interface γ BA

37 Work of Debonding Work of debonding can be translated in terms of Good-van Oss- Chaudhury surface energy parameters: where γ LW is apolar or Lifshitz-van der Waals component, γ + is Lewis acid parameter, and γ - is Lewis base parameter of surface energy. Subscripts B, W and A refer to asphalt binder, water, and aggregate, respectively

38 BBS vs. Work of Debonding Higher magnitude of Work of Debonding, greater is thermodynamic potential for water to cause debonding Higher Loss of Strength of asphalt binders Strength (%) Loss of R² = Work of Debonding (mj/m 2 ) Asphalt binders that showed adhesive failure with granite aggregate after wet conditioning g( (96h)

39 BBS -AASHTO Standard d Procedure e

40 Concluding Remarks Bitumen Bond Strength (BBS) test can effectively measure effects of conditioning time and modification on bond strength of asphalt-aggregate. Conditioning of specimens in water causes a change infailure mechanism from cohesive in dry condition to adhesive after water conditioning. Polymers and Polyphosphoric Acid (PPA) are found to improve adhesion between asphalt and aggregate as well as cohesion within binder. Statistical analysis indicates that BBS test is repeatable and reproducible

41 Concluding Remarks BBS results compared reasonable well with wettability results from contact angle measurements: Addition of certain chemicals could increase potential for wettability of binders which translates in higher dry bond strength. Effect of anti-stripping measured in mixture testing (TSR) can also be observed in BBS results. Weak correlations between TSR and BBS results indicate importance of aggregate surface characteristics (roughness, porosity) for moisture damage.

42 Acknowledgements Asphalt Research Consortium (ARC) is funded by FHWA this Asphalt Research Consortium (ARC) is funded by FHWA, this support is greatly appreciated

43 Thank You! Questions?

44 BBS vs. TSR Mixture Testing Dry Conditioning Wet Conditioning Loss of Pull-off Pull-off TSR Pull-off Asphalt Binder ITS ITS Strength Strength (% of loss) Strength (psi) (psi) (MPa) (MPa) (%) Elastomer Elastomer3+AS Plastomer Plastomer1+AS Plastomer Plastomer2+AS Plastomer Plastomer1+AS Plastomer Plastomer2+AS Effect of AS can be measured in both TSR and BBS.

45 BBS vs. TSR Mixture Testing Very low indirect tensile strength measured compared to other mixes

46 BBS and TSR Ranking 1 is best BBS Wet TSR Wet Asphalt Binder Rank Rank Elastomer Elastomer3+AS Plastomer Plastomer1+AS Plastomer Plastomer2+AS Plastomer Plastomer1+AS Plastomer Plastomer2+AS 5 3