Asphalt Cements

1. Asphalt Cements New Superpave Performance Graded Specification

2. PG Specifications • Fundamental properties related to pavement performance • Environmental factors • In-service & construction temperatures • Short and long term aging

3. PG Specifications • Based on rheological testing • Rheology: study of flow and deformation • Asphalt cement is a viscoelastic material • Behavior depends on: • Temperature • Time of loading • Aging (properties change with time)

4. High Temperature Behavior • High in-service temperature • Desert climates • Summer temperatures • Sustained loads • Slow moving trucks • Intersections Viscous Liquid

5. Pavement Behavior(Warm Temperatures) • Permanent deformation (rutting) • Mixture is plastic • Depends on asphalt source, additives, and aggregate properties

6. Permanent Deformation Courtesy of FHWA Function of warm weather and traffic

7. Low Temperature Behavior • Low Temperature • Cold climates • Winter • Rapid Loads • Fast moving trucks Elastic Solid Hooke’s Law s = t E

8. Pavement Behavior(Low Temperatures) • Thermal cracks • Stress generated by contraction due to drop in temperature • Crack forms when thermal stresses exceed ability of material to relieve stress through deformation • Material is brittle • Depends on source of asphalt and aggregate properties

9. Thermal Cracking Courtesy of FHWA

10. Aging • Asphalt reacts with oxygen • “oxidative” or “age hardening” • Short term • Volatilization of specific components • During construction process • Long term • Over life of pavement (in-service)

11. Superpave Asphalt Binder Specification The grading system is based on Climate PG 64 - 22 Min pavement temperature Performance Grade Average 7-day max pavement temperature

12. Pavement Temperatures are Calculated • Calculated by Superpave software • High temperature • 20 mm below the surface of mixture • Low temperature • at surface of mixture Pave temp = f (air temp, depth, latitude)

13. Tests Used in PG Specifications Construction BBR DSR RV

14. Mi t Rq = 2 p Ri2 L W R g = Ro - Ri Concentric Cylinder Rheometers • Concentric Cylinder

15. Rotational Viscometer (Brookfield) Torque Motor Inner Cylinder Thermosel Environmental Chamber Digital Temperature Controller

16. Original Properties, Rutting, and Fatigue DSR BBR RV

17. 2 M p R3 R Q h tR = gR = Dynamic Shear Rheometer (DSR) Shear flow varies with gap height and radius Non-homogeneous flow • Parallel Plate

18. Oscillating Plate B C A Fixed Plate B Test operates at 10 rad/sec or 1.59 Hz 360o = 2 p radiansper circle 1 rad = 57.3o Time A A C 1 cycle

19. Elastic Viscous B Strain Time A A C Strain out-of-phase d = 90o Strain in-phase d = 0o

20. Complex Modulus, G* Viscous Modulus, G” d Storage Modulus, G’ Complex Modulus is the vector sum of the storage and viscous modulus

21. DSR Equipment DSR Equipment Computer Control and Data Acquisition

22. Motor Parallel Plates with Sample Area for Liquid Bath

23. 25 mm Plate with Sample

24. Rutting BBR RV DSR

25. Permanent Deformation Addressed by: G*/sin d on unaged binder > 1.00 kPa G*/sin d on RTFO aged binder > 2.20 kPa For the early part of the service life

26. Short Term Binder Aging • Rolling Thin Film Oven • Simulates aging from hot mixing and construction

27. Inside of RTFO Fan Rotating Bottle Carriage Air Line

28. Bottles Before and After Testing Opening in Bottle

29. Original mass - Aged mass Original mass x 100 Mass loss, % = Testing • Calculate mass loss after RTFO • Determine G*/sin d for RTFO aged material at same test temp. used for original asphalt cement

30. Permanent Deformation Question: Why a minimum G*/sin d to address rutting Answer: We want a stiff, elastic binder to contribute to mix rutting resistance How: By increasing G* or decreasing d

31. Fatigue BBR RV DSR

32. Fatigue Cracking Function of repeated traffic loads over time (in wheel paths)

33. Testing • Aged binder • Since long term performance problem, include: • Short term aging • Long term aging • Determine DSR parameters using 8 mm plate and intermediate test temperature

34. Pressure Aging Vessel(Long Term Aging) • Simulates aging of an asphalt binder for 7 to 10 years • 50 gram sample is aged for 20 hours • Pressure of 2,070 kPa (300 psi) • At 90, 100 or 110 C

35. Pressure Aging Vessel Rack of individual pans (50g of asphalt / pan) Bottom of pressure aging vessel Vessel Lid Components

36. Pressure Aging Vessel Courtesy of FHWA

37. Fatigue Cracking • G* (sin d) on RTFO and PAV aged binder • The parameter addresses the later part of the fatigue life • Value must be < 5000 kPa

38. Fatigue Cracking • Question: Why a maximum G* sin d to address fatigue? Answer: We want a soft elastic binder (to sustain many loads without cracking) How: By decreasing G* or decreasing d

39. Thermal Cracking BBR RV DSR

40. Bending Beam Rheometer Computer Deflection Transducer Air Bearing Load Cell Fluid Bath

41. Bending Beam Rheometer Sample

42. Bending Beam Rheometer Equipment Fluid Bath Loading Ram Cooling System

43. Bending Beam Rheometer • S(t) = P L3 4 b h3d (t) Where: S(t) = creep stiffness (M Pa) at time, t P = applied constant load, N L = distance between beam supports (102 mm) b = beam width, 12.5 mm h = beam thickness, 6.25 mm d(t) = deflection (mm) at time, t

44. Bending Beam Rheometer • Evaluates low temperature stiffness properties • Creep stiffness • Slope of response (called m-value) Log Creep Stiffness, S(t) 8 15 30 60 120 240 Log Loading Time, t (sec)

45. Is Stiffness Enough? • No. Need to assess strain needed to break specimen. • Thermal cracking occurs when strain is too great • Direct tension test • Currently (1998) in specification • New equipment is now available

46. Direct Tension Test Load Stress = s = P / A D L sf D Le ef Strain

47. Direct Tension Test Courtesy of FHWA

48. Direct Tension Test Courtesy of FHWA

49. PAV Long Term Aging RTFO Short Term Aging No aging Summary Low Temp Cracking Fatigue Cracking Rutting Construction [DTT] [RV] [DSR] [BBR]

50. Questions - ?