Viewing Cracking Through

Transcription

1 Viewing Cracking Through a Black Space Telescope WRI Pavement Performance Symposium July 2011 Presentation by: Gayle King

2 Acknowledgements FAA/AAPTP Project 6-1 A Laboratory and Field Investigation to Develop Test Procedures for Predicting Non- load Associated Cracking of Airfield HMA Pavements Project Manager: Monte Symons PI: Doug Hanson Mike Anderson, Phil Blankenship, Gayle King BBR Mixture Testing: Mihai Marasteanuastean Rheological Consultant: Geoff Rowe

3 Are Some SuperPave Pavements Cracking Prematurely? Hesp/Queens: YES! WRI Field Aging Study: YES! John Epps: TRB Research Needs Discussion at AFK10: YES! Problem at least partially due to pavement aging.

4 To prevent age-induced cracking, first understand: Asphalt Durability Claine Petersen: A durable asphalt: 1. has physical properties necessary for desired initial product performance & 2. is resistant to change in physical properties during long-term, in-use environmental aging Petersen, J.C., Chemical Composition of Asphalt as Related to Asphalt Durability-State of-the-art, TRR. 999, 1984

5 Asphalt Oxidation Vallerga: Age-Embrittlement t Raveling Block Cracking

6 Asphalt Oxidation Predicting Pavement Failures MEDG Global l Aging Effects Model Models high temp η or G* with aging No measure of low-temperature rheology No phase angle or m-value Does not appropriately consider initial asphalt quality Mirza, M.W. and Witczak, M.W., Development of a Global Aging System for Short- and Long-Term Aging of Asphalt Cements, AAPT, 1995

7 Asphalt Durability Predicting Block Cracking Challenge question: Asphalt oxidation accelerates at high pavement temperatures, but does block cracking occur at lower temperatures? If yes, why not use low temperature physical properties to predict block cracking? Critique of Global Aging System: Christensen, D.W. and Bonaquist, R.F., Volumetric Requirements for SuperPave Mix Design, NCHRP Report #567, TRB, 2006

8 WRI Aging Study - Arizona Field Aging Harnsberger Hypothesis: Asphalts from different crude oil sources will exhibit different field performance

9 Arizona Validation Site Constructed Nov mm lifts, 19-mm NMS dense Shoulder cored Nov graded aggregate, 4.7% AC)

10 1E+09 1E+08 Effect of Pavement Depth on Aged Asphalt Properties AZ1-1, 4th Year, Shoulder Comple ex Modulus (P Pa) 1E+07 1E+06 1E+05 1E+04 1E+03 1E+02 Top Slice 2nd Slice 3rd Slice Bottom Slice 1E+01 1E+00 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04 1E+06 1E+08 1E+10 Reduced Angular Frequency (rad/s) After Oxidation: Top slice > 2 nd slice > 3 rd slice > Bottom slice

11 Effect of Pavement Depth on Aged Asphalt Properties AZ1-1, 4th Year, Shoulder Phase Angle (deg) Top Slice 2nd Slice 3rd Slice Bottom Slice E-06 1E-04 1E-02 1E+00 1E+02 1E+04 1E+06 1E+08 1E+10 After Oxidation: i Reduced Angular Frequency (rad/s) Top slice > 2 nd slice > 3 rd slice > Bottom slice

12 Comparison of m-value & S Grades AAS-1 & Exxon AC-20 at Various Aging Times Poor man s Black Space Glover, et.al. FHWA/TX-05/1872-2

13 Asphalt Oxidation Physical Changes - Ductility Conventional Wisdom: Kandhal tied block cracking severity to ductility at 60ºF (15ºC) Loss of surface fines as ductility 10cm Surface cracking evident when ductility falls to 5 cm Serious surface cracking at ductility falls below 3 cm Low-Temperature Ductility in Relation to Pavement Performance, ASTM STP 628, 1977

14 Glover s Cracking parameter Proposed cracking function based on analysis of Maxwell model G Questions: Relationship to ductility Relationship to fatigue Assumption of time-temperature superposition Relationship in Black Space (G* vs. Phase Angle) G

15 Ductility vs. G /(η /G ) (Glover et.al. 2005)

16 Rowe: AAPT Prepared Discussion G G p Simplification of Cracking Parameter tan G G and G tan 1 ' G G G hence G G G G G tan tan G G or G G therefore G

17 Rowe: AAPT Prepared Discussion Simplification of Cracking Parameter Putting the equation in simple format: G G *cos or or tan tan Note frequency is constant G*(Cosδ) 2 /sinδ x ω G * cos sin Only real variables are G* and fn( fn((cos ) 2 /sin Limiting value of 9E-04 MPa/sec at rad/sec becomes 2 G* cos2/sin 180kPa

18 Laboratory Binder Testing Experimental Matrix Asphalt Binders West Texas Sour (PG 64-16) Gulf-Southeast (PG 64-22) Western Canadian (PG 64-28) Table 1: Asphalt Binder Testing Matrix Unaged PAV20 PAV40 PAV80 DSR Mastercurve DSR Function (Texas A&M) DSR Monotonic (Wisconsin) Ductility, 15 C Force Ductility BBR DTT

19 BBR: Gulf-Southeast (GSE) Temper rature, C Tc,S(60) Tc,m(60) PAV Aging Time, Hrs

20 BBR Cracking Parameter - ΔTc ΔTc = T c ( ) ( ) (m-value = 0.30) - T c (S = 300 MPa) Relationship to ductility Relationship to G /(η /G ) /G Relationship to R-value (CA model)

21 Effect of PAV Aging Time on T c 12.0 Difference Between Tc,m and Tc,S ( C) WTX GSE WC PAV Aging Time, Hrs

22 Ductili ity, cm Pre edicted Relationship between G /(η /G ) vs Ductility 14 y = 0.79x R² = y = 0.82x R² = Single Point 2 Mastercurve Measured Ductility, cm

23 Relationship between G /(η /G ) and ΔTc 1E-01 G /( (η /G ), MPa/s 1E-02 1E-03 1E-04 1E-05 1E-06 West Texas Sour Gulf Southeast Western Canadian 1E Difference Between Tc,m(60) and Tc,S(60), C

24 Black Space Diagram: Western Canadian Asphalt Binder 1.00E E+08 G* *, Pa 1.00E E E+05 Original PAV-20 PAV-40 PAV E E Phase Angle, degrees

25 Western Canadian PG Plot of R-values in Black Space 1.00E+09 WC PG E E+07 G*, Pa 1.00E E E E+03 Rowe AAPT Aging R-value shown gives shape of master curve Phase Angle, degrees PAV0 PAV20 PAV40 PAV kpa

26 Binder Aging Study G* (15 C and rad/s) Original 20 hr PAV 40 hr PAV 80 hr PAV WTX 98,900 1,329,000, 1,495,000, 5,226,000, GSE 58, , ,800 2,079,000 WC 5, , ,900 1,615,000 δ (15 C and rad/s) Original 20 hr PAV 40 hr PAV 80 hr PAV WTX GSE WC

27 PAV Aging in Black Space Ui Using R Values Vl G* & δ at 15 C, rad/s log G* (Pa) Block Cracking 80 hr PAV 40 hr PAV20 hr PAV FAIL 0 hr PAV PASS Phase Angle WTX GSE WC R value = 1 R value = 2 R value = 3

28 PAV Aging in Black Space Ui Using G'/(η'/G') '/G') 8 G* & δ at 15 C, rad/s 7 log G* (Pa) 6 5 Block Cracking 80 hr PAV No Block Cracking 40 hr PAV 20 hr PAV 4 WC 3 0 hr PAV Phase Angle G'(n'/G') = 180 kpa G'/(n'/G') =450 kpa WTX GSE

29 PAV Aging in Black Space Ui Using G* x sin δ G* & δ at 15 C, rad/s FAIL log G* (Pa) WTX PASS 80 hr GSE PAV 40 hr WC PAV 20 hr G*x sind = 5000 kpa PAV G*x sind = 1000 kpa hr PAV Phase Angle

30 Low Temperature Mixture Rheology BBR Stiffness & m-value Bending Beam Rheometer (BBR) Rectangular beams - standard BBR geometry (Marasteanu) $200 tile saw cuts surface mix specimens Condition & test in BBR at -18 to -6ºC

31 BBR Mixture Testing West Texas Sour Evolution of Stiffness with Aging West Texas Sour Mix Evolution of m value with aging West Texas Sour Mix Stiffne ess (Mpa a) C 12C m value C C Mixture Aging C, hours Mixture Aging C, hours

32 BBR Mixture Testing Gulf-Southeast Evolution of Stiffness with Aging Gulf Southeast Mix Evolution of m value with aging Gulf Southeast Mix Stif ffness (M Mpa) C 18C m value C C Mixture Aging hours Mixture Aging C, hours

33 BBR Mixture Testing Western Canadian Evolution of Stiffness with Aging Western Canadian Mix pa) S tiffness (M C 18C Mixture Aging C, hours

34 BBR Stiffness vs. Loading Time Inversion, but no loading damage!

35 BBR m-value vs. Loading Time Inversion, but no loading damage!

36 Using Hirsh Model & Shenoy Critical Cracking Theory Cooling Rate Impact on Critical Cracking Temperature Western Canadian 48 hour mix aging - 14 Cooling Rate 1 degree/hour 12 Thermal 10 degrees/hour 10 Stress TC-1 degree/hour (MPa) TC-10 degree/hour Temperature (ºC)

37 BBR Mixture Bending Test: Impact of Aging & Cooling Rate on Critical Cracking Temp Critical Cracking Temperature, -10 C WTS -1C/hr WTS -10C/hr G-S -1C/hr G-S -10C/hr WC -1C/hr WC -10C/hr Mix Aging C - hours Conclusion: Cooling rate less important as materials age

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39 Hypothesis for: Cracking at Low Temperatures Thermal Cracking Driven by Thermal Shrinkage Stresses on Cooling Primary Function: Low Temp. Binder Stiffness Block Cracking Driven by Curling Stresses from Temperature & Stiffness Gradients Primary Function: ΔTc (decreasing phase angle) Crack-Initiation Temp increases with oxidation: Decreasing BBR m-value and DSR phase angle Decreasing DTT failure strain Decreasing R-value Decreasing Fracture energy

40 Conclusions Black Space Diagrams can be used to compare cracking parameters and select preferred failure criteria. ΔTc and G*x(cosδ)2/sinδ)xω correlate closely with ductility for unmodified asphalts. Failure curves using R-value do not correlate well with ductility nor the other two parameters (ΔTc & Glover) Microcracking can occur as aged mixtures cool (m<0.12; S>20, Mpa)

41 Research Needs Environmental effects models Predict rate of oxidative aging Predict initiation i i i of block cracking Tools to optimize timing strategies for pavement preservation Performance specifications Binder purchase specifications Use of RAP and asphalt shingles

42 Asphalt Durability Don t forget the oxidation chemistry!

43 Asphalt Oxidation Chemistry The Products Petersen, Mill, Greene Oxidation Products Carbonyls form in three steps: Ketones Carboxylic Acids, Aldehydes d Acid anhydrides Sulfoxides; Disulfoxides For evolving rheology, carbonyls matter, sulfoxides don t! What about further aromatization?

44 Asphalt Oxidation Chemistry The Kinetics Petersen (WRI), Van Gooswilligen, Mill, Glover Oxidation Kinetics Temperature dependence G* & Carbonyl follow Arrhenius (exp (1/T) Evolving rheology at low temperature: S fairly stable, m- value drops rapidly Pressure dependence - exponential Defined rate determining step (Bitumen, O 2, catalyst) Classic phenols inhibitors don t work Identified reaction inhibitors (Azide, CN-) Auto-oxidation doesn t fit kinetics!

45 Asphalt Oxidation Chemistry The Mechanisms WRI/Glover Dual Carbonyl Oxidation Mechanisms 2 reaction rates both 1st order in bitumen One fast, but slows or stops with time Indole/Carbazol condensations (see fuels oxidation work by Pedley/Hiley, Mushrush, Harrison, Beaver) One slow, but continues indefinitely Non-porphoryrin organometallic catalysts Vanadyl Acetyl-Acetonate Branthaver/Tort Manganese complexes - Chemcrete

46 The Mechanisms N-ETIO Oxycyclics King/Beaver N-ETIO Electron Transfer Initiated Oxidation For indole condensations, two electron transfers occur before rate determining step (Beaver) Rate-determining step is initiated by a forbidden triplet-to-singlet electron spin flip (King) Oxycyclics explain the rate determining step, Petersen s carbonyl products (even anhydrides), and the influence of catalysts (King) Classic inhibitors (anti-oxidants) id t don t work N-ETIO Oxycyclics fit both (dual) mechanisms

47 Thank You. Questions?