Evaluation of Workability/Compactability of Warm Mix Asphalt

Transcription

1 Evaluation of Workability/Compactability of Warm Mix Asphalt Thomas Bennert Rutgers University WMA Technical Working Group December 15 th to 16 th, 2009 Seattle, Washington

2 Acknowledgements Contributors Karissa Mooney, NuStar Gerry Reinke, MTE Walaa Mogawer, UMass Dartmouth Rutgers Asphalt Pavement Laboratory staff

3 Main Objective Purpose of study was to evaluate current/practical methods for evaluating workability/compactability of WMA New additives/technologies coming on market every other week Proper dosage rate and/or applicability to different mixtures (i.e. asphalt rubber, high RAP, etc.)

4 Preliminary Findings in NCHRP 9-43

5 Materials Asphalt Binder: PG76-22 preblended with different WMA additives at different dosage rates No Additive Sasobit: 0.5, 1.0, and 1.5% Rediset: 1.0 and 2.0% 0.6% Evotherm 3G Asphalt Mixture: 12.5mm Superpave mixture, 4.9% AC, Trap Rock aggregate

6 Compactibility/Workability Binder Tests Tests Rotational Viscosity (current Mixing and Compaction Temperatures) Casola Method (NCHRP 9-39) for Mixing and Compaction Temperatures Lubricity Test (Thin-Film Rheology) Mixture Tests University of Massachusetts Workability Device Marshall Compaction Gyratory Compaction

7 Workability/Compactibility Binder Tests

8 Viscosity, Pa s 10 5 Superpave Mixing and Compaction Temperatures Compaction Range Mixing Range Temperature, C

9 Rotational Viscosity Results Binder Type Mixing Temps (F) Compaction Temps (F) High Low High Low % 3G % Sasobit % Sasobit % Sasobit % Rediset % Rediset Does not represent typical field compaction temperatures observed

10 Casola Method Test Procedure Casola Method Typical DSR sample preparation Frequency sweep at 3 to 5 temperatures Construct Phase Angle Master Curve Determine frequency where δ = 86º Calculate mixing and compaction temperatures using simple relationships established from regression models

11 Example of Casola Method Freq = Phase = Temp = 80C

12 Casola Method Calculation Read frequency, ω, at which Phase Angle hits 86 degrees Mixing Temperature ( o F) Tm = 310ω Compaction Temperature ( o F) Tc = 287ω

13 Casola Method Test Results Recommended Mixing and C ompaction Temps E valuation of Warm Asphalt Technology using the C asola Method Temperature ( o F) mix compaction W MA S ample D S R D ata C ollected proces s wam-0?-08 temp ( o C) phase ( o ) freq (ra d/s ec ) % 3G % S aso % S aso % S aso % R ediset % R ediset Does not represent typical field compaction temperatures observed

14 Rotational Viscosity and Casola Method Binder Type Mixing Temps ( o F) Compaction Temps ( o F) Casola Method Temperatures High Low High Low Mixing ( o F) Compaction ( o F) % 3G % Sasobit % Sasobit % Sasobit % Rediset % Rediset Recommended mixing and compaction temperatures are unrealistically high when compared to observations of warm mix projects

15 Thin-Film Rheology Rheology of materials in thin films are different than bulk rheology Typical DSR uses a 1000 μ film Mineral fines are smaller than 50 μ MTE began testing at 100 μ and are now working at 25μ MTE s investigations began by looking at tribology testing conducted by the lubricating and medical prosthetics industries and investigations performed by people studying rheology of platetectonics

16 Lubricity Test

17 Lubricity Test

18 NuStar WMA-02-08, 25x0 500, 0 100, 0 050, mm, cup, 125 C, Stdy NuStar WMA-02-08, 125 C, Stdy Shr, AR3-0001f-2, Steady state flow s NuStar WMA-02-08, 125 C, Stdy Shr, AR3-0001f-3, Steady state flow st NuStar WMA-03-08, 125 C, Stdy Shr, AR3-0001f-2, Steady state flow st NuStar WMA-03-08, 125 C, Stdy Shr, AR3-0001f-3, Steady state flow st NuStar WMA-05-08, 125 C, Stdy Shr, AR3-0001f-2, Steady state flow st NuStar WMA-05-08, 125 C, Stdy Shr, AR3-0001f-3, Steady state flow st NuStar WMA-07-08, 125 C, Stdy Shr, AR3-0001f-2, Steady state flow st NuStar WMA-07-08, 125 C, Stdy Shr, AR3-0001f-3, Steady state flow st viscosity (Pa.s) velocity (rad/s) CODE FORMULATION CODE FORMULATION WMA % EVOTHERM 3G WMA % SASOBIT WMA % SASOBIT WMA % REDISET WMA % SASOBIT WMA % REDISET The point to be made is that as the gap gets smaller the apparent viscosity decreases for the same rotational velocity

19 NuStar 1 1 NuStar WMA-04-08, WMA-04-08, 25x0 500, 0 100, 125 C, 0 050, Stdy Shr, Steady mm, state cup, flow 125 C, step Stdy NuStar WMA-02-08, 125 C, Stdy Shr, Steady state flow step NuStar WMA-03-08, 125 C, Stdy Shr, Steady state flow step NuStar WMA-07-08, 125 C, Stdy Shr, Steady state flow step NuStar WMA-05-08, 125 C, Stdy Shr, Steady state flow step NuStar WMA-06-08, 125 C, Stdy Shr, Steady state flow step viscosity (Pa.s) normal force (N) E5 shear rate (1/s) CODE WMA FORMULATION 1.0% SASOBIT CODE FORMULATION CODE FORMULATION WMA % EVOTHERM 3G WMA % SASOBIT WMA % SASOBIT WMA % REDISET WMA % SASOBIT WMA % REDISET WMA WMA WMA WMA WMA % REDISET 0.6% EVOTHERM 3G 1.0% REDISET 0.5% SASOBIT 1.5% SASOBIT

20 Shear Rate vs Applied Torque Greater the shear rate that can be sustained before peak is achieved the more workable the mixture should be.

21 Final Thin-Film Rheology Rankings SHEAR RATE FROMNORMAL FORCE TEST AT WHICH PEAK TORQUE OCCURS AT 105 C AND 50µ GAP SHEAR RATE, SEC NEAT 0.5% SASOBIT 0.6% EVOTHERM 3G 2% REDISET 1% REDISET 1% SASOBIT 1.5% SASOBIT f f

22 Asphalt Binder Test Workability Rankings Best Worst Rotational Vis 2% Rediset 1% Sasobit 1% Rediset 0.5% Sasobit PG % Sasobit 0.6% 3G Casola PG % 3G 2% Rediset 1% Rediset 1% Sasobit 0.5% Sasobit 1.5% Sasobit Lubricity 0.6% 3G 2% Rediset 1% Rediset 1.5% Sasobit 1% Sasobit PG % Sasobit

23 Workability/Compactibility Mixture Tests

24 UMass Workability Mixer Continually measures temperature and torque on mixing blade Torque is the unit representing workability (i.e. higher torque values, poorer workability) Device essentially measures resistance of loose mix to move/flow Method generally assumed to be baseline for comparisons

25 Workability Starting at 320 o F Torque (in-lb) Control 0.5% Sasobit 1.0% Sasobit 1.5% Sasobit 1.0% Rediset 2.0% Rediset 0.6% Evotherm 3G Temperature (F)

26 Workability Starting at 270 o F Torque (in-lb) Control 0.5% Sasobit 1.0% Sasobit 1.5% Sasobit 1.0% Rediset 2.0% Rediset 0.6% Evotherm 3G Temperature (F)

27 Marshall Compactor Historically, the Marshall Compactor has been known to be sensitive to mixture temperature Therefore, if HMA becomes less workability due to cooling (or temperature changes) perhaps it can be used to assess general workability/compactibility of WMA

28 Marshall Compaction Procedure Mix HMA samples at 315F, 270F, and 230F Cure for 2 hours and compact loose mix at 15F lower than mixing temperature 300F, 255F, and 215F Measure air voids of compacted samples Construct trendline (exponential fit) of compacted air voids vs compaction temperature

29 Marshall Compacted Air Voids Compacted Air Voids at 75 Blows (%) % Sasobit 1% Sasobit 1.5% Sasobit 1% Rediset 2% Rediset 0.6% 3G

30 Marshall Compactibility Trends Compacted Air Voids (%) % Sasobit 1.0% Sasobit 1.5% Sasobit 1.0% Rediset 2.0% Rediset 0.6% 3G Compaction Temperature (F)

31 Gyratory Compactor Known to be generally insensitive to compaction temperatures (at least in typical range) Looked at: NCHRP 9-43: Gyrations to 92% of G mm Compacted density at 100 gyrations Compaction rate (mm/gyration) to achieve predetermined density (7% air voids) Same sample prep/conditions used as in Marshall compaction

32 Gyrations to 92% of G mm Number of Gyrations to Achieve 92% of Gmm % Sasobit % Sasobit % Sasobit % Rediset 46 2% Rediset % Evotherm 3G

33 Gyrations to 92% of G mm Proposed Compaction Temperature, 149C ( 300F) 0.5% 1.0% 1.5% 0.6% % Rediset 2% Rediset Sasobit Sasobit Sasobit Evotherm Compaction Temperature - 26C ( 260F) Compaction Temperature - 48C ( 215F) 0.5% 1.0% 1.5% 0.6% % Rediset 2% Rediset Sasobit Sasobit Sasobit Evotherm % 1.0% 1.5% 0.6% % Rediset 2% Rediset Sasobit Sasobit Sasobit Evotherm Based on Compaction Results of PG76-22

34 Gyrations to 92% of G mm Compaction Temperature - 26C ( 260F) Compaction Temperature - 48C ( 215F) 0.5% 1.0% 1.5% 0.6% % Rediset 2% Rediset Sasobit Sasobit Sasobit Evotherm % 1.0% 1.5% 0.6% % Rediset 2% Rediset Sasobit Sasobit Sasobit Evotherm Based on the respective asphalt binder

35 Gyrations to 92% of G mm Best Worst Best Worst Preliminary NCHRP 9-43 (Based on PG76-22) < 0.35 N design <125% (-26C) <125% (-48C) 0.6% Evotherm 3G 0.6% Evotherm 3G 0.5% Sasobit 1% Rediset 1.0% Sasobit 0.6% Evotherm 3G 2% Rediset 0.5% Sasobit 1.0% Sasobit 1.5% Sasobit 2% Rediset 1% Rediset % Sasobit 2% Rediset 1.0% Sasobit % Sasobit 0.5% Sasobit 1% Rediset Preliminary NCHRP 9-43 (Based on Respective Binder) < 0.35 N design <125% (-26C) <125% (-48C) 0.6% Evotherm 3G 1.0% Sasobit 0.5% Sasobit 1% Rediset 0.5% Sasobit 1.0% Sasobit 2% Rediset 1.5% Sasobit 1.5% Sasobit 1.5% Sasobit 2% Rediset 1% Rediset % Evotherm 3G 2% Rediset 1.0% Sasobit % Evotherm 3G 0.5% Sasobit 1% Rediset 76-22

36 Compacted Density at 100 Gyrations Compacted Air 100 Gyrations (%) % Sasobit 1.0% Sasobit 1.5% Sasobit 1% Rediset 2% Rediset 0.6% 3G

37 Gyratory Compactability Trends Compacted Air Voids (%) PG % Sasobit 1.0% Sasobit 1.5% Sasobit 1.0% Rediset 2.0% Rediset 0.6% 3G Compaction Temperature (F)

38 Gyratory Compaction Rate Gyratory Compaction Rate (mm/gyration) Compacted to predetermined density of 7% air voids (+/- 0.2%) % Sasobit 1.0% Sasobit 1.5% Sasobit 1% Rediset 2% Rediset 0.6% 3G

39 Final Rankings Binder Type Rotational Viscosity Casola Method Lubricity 221 o F PG % Evotherm 3G % Sasobit % Sasobit % Sasobit % Rediset % Rediset Binder Type Asphalt Workability Marshall NCHRP 9-43 <125% (Compact NCHRP 9-43 <125% (Compact NCHRP 9-43 <125% (Compact NCHRP 9-43 <125% (Compact Temp -48C) 215 o F 215 o F Temp -26C) Temp -48C) Temp -26C) PG % Evotherm 3G % Sasobit % Sasobit % Sasobit % Rediset % Rediset Based on PG76-22 Based on Respective Binder

40 Conclusions Conventional mixing and compaction temperature assessment does not seem to correspond to field observations Gyratory compactor was generally insensitive to compaction temperature when compared to Marshall Lubricity Test (binders), UMass Workability and Marshall Compaction showed comparable ranking NCHRP 9-43 close, but some discrepancies

41 Conclusions (continued) Testing indicated that additives preblended in asphalt binder could be screened using Lubricity test Future work required on criteria Can be used to currently compare additives and/or dosage rate Field assessment (plant or laboratory mixture production) could be evaluated using the Marshall compactor, Bucketmixer type device, and NCHRP 215 o F

42 Thank you for your time! Thomas Bennert Rutgers University