The Superpave (SUperior PERforming Asphalt PAVEments) system

- Pravin Mali  Limitations of Traditional Binder Specifications  SuperPave  SuperPave Asphalt Specifications  Superpave Asphalt Binder Tests 2 Limitations of Traditional Binder Specifications 3  Results used to determine if the material meets specification criteria  Results are related to pavement performance through experience  Penetration & ductility tests are purely empirical  Tests are conducted at one standard temp (i.e.. Pen @ 25°C ,Vis @ 60°C), despite different climatic conditions  Asphalt cements can have different temperature and performance characteristics within same grade (Pen or Vis)  Current empirical tests and specifications do not give information for the entire range of typical pavement temperatures 4 Empirical Asphalt Specifications  can classify different asphalts with the same grading, in fact these asphalts may have different temperature and performance characteristics  because these asphalts are graded the same one might erroneously expect the same characteristics during construction and the same performance during hot and cold weather conditions 5 6 New Superpave Performance Graded Specification 7 WHAT IS SUPERPAVE • • • • Final product of the 1987-1993 FHWA (Federal Highway Administration) strategic highway research program (SHRP) to investigate better pavement materials & design methods. Superior Performing Asphalt Pavements = SUPERPAVE Produced new standards for aggregates and bituminous binders used in paving as well as mix design changes. Asphalt cement specifications are referred to as binder specifications, intended for both modified and unmodified asphalt cements 8 Benefit of the PG Gradation (AASHTO M332)  Fundamental properties related to pavement performance  Environmental factors  In-service & construction temperatures  Short and long term aging  New test procedures and new equipment  Specified criteria remains constant but the temperature at which the criteria must be achieved changes for various grades  Tests measure physical properties that can be related directly to field performance by engineering principles  Tests are conducted at temperatures that are encountered by in-service pavements 9  High in-service temperature Viscous Liquid  Desert climates  Summer temperatures  Sustained loads  Slow moving trucks  Intersections 10  Permanent deformation (rutting)  Mixture is plastic  Depends on asphalt source, additives, and aggregate properties 11 Courtesy of FHWA Function of warm weather and traffic 12 Elastic Solid  Low Temperature  Cold climates  Winter  Rapid Loads  Fast moving trucks 13  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 14 Courtesy of FHWA 15 SUPERPAVEThe ASPHALT BINDER SPECIFICATION grading system is based on Climate PG 64 - 22 Performance Grade Min pavement temperature Average 7-day max pavement temperature 16 This is the binder specification - it is defined by AASHTO MP -1. CEC Avg 7-day Max, oC 1-day Min, oC PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 -34 -40 -46 -10 -16 -22 -28 -34 -40 -46 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -10 -16 -22 -28 -34 ORIGINAL > 230 oC (Flash Point) < 3 Pa.s @ 135 oC (Rotational Viscosity) (Dynamic Shear Rheometer) > 1.00 kPa 46 52 58 52 90 90 58 10 7 4 25 22 19 16 13 10 7 m > 0.300 100 76 82 PAV 100 (110) 110 (110) DSR G* sin  0 (Bending Beam Rheometer) (Direct Tension) -24 -30 -36 0 -18 -24 82 28 31 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 -24 -30 -36 0 -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 18 -24 > 1.00 % 70 100 (110) ( Bending Beam Rheometer) Report Value 76 Mass Loss < 1.00 % 64 (Dynamic Shear Rheometer) < 5000 kPa S < 300 MPa 100 70 DSR G*/sin  (PRESSURE AGING VESSEL) 20 Hours, 2.07 MPa DSR G*/sin  RTFO (Dynamic Shear Rheometer) 46 RV 64 (ROLLING THIN FILM OVEN) > 2.20 kPa FP -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 BBR “S” Stiffness -6 -12 -18 -24 -30 0 BBR -6 & “m”- value -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 - 0 -6 -12 -18 -24 0 -6 -12 Physical Hardening DT -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 CEC PG 46 PG 52 Spec Requirement 1-day Min, C Remains Constant Avg 7-day Max, oC o PG 58 PG 64 PG 70 PG 76 PG 82 -34 -40 -46 -10 -16 -22 -28 -34 -40 -46 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -10 -16 -22 -28 -34 ORIGINAL > 230 oC (Flash Point) < 3 Pa.s @ 135 oC (Rotational Viscosity) (Dynamic Shear Rheometer) > 1.00 kPa 46 5858 52 52 RTFO 90 90 58 100 S < 300 MPa 4 25 22 19 16 13 10 7 m > 0.300 100 76 82 PAV 100 (110) 110 (110) DSR G* sin  0 (Bending Beam Rheometer) (Direct Tension) -24 -30 -36 0 -18 -24 82 28 31 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 -24 -30 -36 0 -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 18 -24 > 1.00 % 70 100 (110) ( Bending Beam Rheometer) Report Value 76 Mass Loss < 1.00 % 64 Test Temperature (Dynamic Shear Rheometer) < 5000 kPa Changes 10 7 70 DSR G*/sin  (PRESSURE AGING VESSEL) 20 Hours, 2.07 MPa DSR G*/sin  64 (Dynamic Shear Rheometer) 46 RV 64 (ROLLING THIN FILM OVEN) > 2.20 kPa FP -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 BBR “S” Stiffness -6 -12 -18 -24 -30 0 BBR -6 & “m”- value -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 - 0 -6 -12 -18 -24 0 -6 -12 Physical Hardening DT -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30  The central theme of the Superpave Binder Specification is its reliance on testing asphalt binders in conditions that simulate the three critical stages during the binder’s life  Tests performed on the original asphalt represent the first stage of transport, storage and handling  The second stage represents the asphalt during mix production and construction and is simulated by aging the binder in a rolling thin film oven, The thin film oven test exposes thin binder films to heat and air and approximates the aging of asphalt during mixing and construction  The third stage occurs as the binder ages over a long period of time as part of the hot mix asphalt pavement layer. This stage is simulated for the specification by the pressure aging vessel. The procedure exposes binder samples to heat and pressure in order to simulate years of in-service aging in a pavement 19 20 21  Superpave Binder Aging Procedures  Asphalt binder ages:  volatilization of light oils present in the asphalt  oxidation by reacting with oxygen in the environment  Rolling Thin Film Oven Test (RTFOT)  simulates both types of aging in the mixing and placement of asphalt mix because of the high temperatures and air flow involved in the process  Pressure Aging Vessel (PAV)  simulates in service aging 22 1. Binder Aging 2. RTFO 3. PAV 4. DSR 5. RV 6. BBR 7. DTT Pressure Aging Vessel (PAV) Rolling Thin Film Oven Test (RTFOT) • Simulates both types of aging in the mixing and placement of asphalt mix because of the high temperatures and air flow involved in the process • Volatilization of light oils present in the asphalt • Oxidation by reacting with oxygen in the environment • Simulates in service aging • Binder samples that have been aged in the PAV have already been aged in the RTFOT • Consequently, the PAV residue represents binder that has been exposed to all of the environmental conditions to which binders are subjected to during production and service 24  Rolling Thin Film Oven Test (RTFOT) (AASHTO T240 ASTM D 2872)  provides aged asphalt binder that can be used for further testing of physical properties  determines the mass quantity of volatile lost during the process  indication of the aging that may occur in the asphalt during mixing and construction operations  specified as 1% maximum 25 26  Pressure Aging Vessel (PAV)  AASHTO PP1  simulates the effects of long term in-service aging of asphalt  Uses binder that has previously been aged in the RTFOT since asphalt that is exposed to long term aging has also been through the mixing and construction process  exposes the binder to high pressure and temperature for 20 hours 27 28 29  Dynamic Shear Rheometer (DSR) (AASHTO TP5)  Asphalt Behavior depends on both loading time and temperature and this test evaluates both effects  measures rheological properties  complex shear modulus  phase angle  intermediate to high temperatures 30  Dynamic Shear Rheometer (DSR)  used to characterize both elastic and viscous behavior  G* (G star) complex shear modulus  measures the total resistance of the asphalt to deformation  elastic component (recoverable deformation)  viscous component (non-recoverable deformation)   (delta)  indicates the relative amounts of recoverable and non-recoverable deformation 31 32  Values of G* and  for asphalts are highly dependant on temperature and frequency of loading  High temperatures  behavior is viscous with no capacity for recovering or rebounding   = 90°  Low temperatures  behavior is elastic witch rebounds from deformation   = 0° 33 34 35 36  Dynamic Shear Rheometer (DSR)  Permanent Deformation  G*/sin  at test temperature > 1.00 kPa original binder  G*/sin  at test temperature > 2.20 kPa RTFOT binder  Fatigue Cracking  G* (sin ) at test temperature < 5000 kPa PAV binder 37  Rotational Viscometer (ASTM D4402)  Used to determine the flow characteristics of the asphalt binder  Ensure that the asphalt is fluid enough to be pumped and handled at the hot mix facility  Measured on the original asphalt binder 38  Bending Beam Rheometer (BBR) (AASHTO TP1)  Measures low temperature properties of asphalt that are too stiff to be measured by the DSR  BBR (stiffness) used in conjunction with the Direct Tension Test (strength and stretching ability before breaking)  BBR measures deflection or creep under a constant load and temperature 39  Bending Beam Rheometer (BBR)  Test temperatures are related to a pavement’s lowest service temperature when the asphalt binder acts more like an elastic solid  PAV asphalt binder  Test measures the performance characteristics of binders as if they had been exposed to hot mixing and some inservice aging 40 41  Bending Beam Rheometer (BBR)  Applying a constant load (980mN) to the center of the asphalt beam and measuring the deflection during the 4 minute test creep stiffness (S) and creep rate (m) can be calculated  Creep load simulates thermal stresses that gradually build up in a pavement when temperature drops  Creep Stiffness (S) resistance of the binder to creep loading and the m-value is the change in asphalt stiffness with time during loading 42 43 44 Bending Beam Rheometer (BBR) Low temperature cracking  Creep Stiffness (S) @ 60s < = 300 Mpa  S is between 300 to 600 Mpa the Direct Tension test may be used in lieu of the creep stiffness requirement  m value (m) @ 60s > = 0.3 45  Direct Tension Tester (AASHTO TP3)  strong relationship between stiffness of asphalt binders and the amount of stretching they undergo before breaking  asphalts that undergo considerable stretching before failure are called “ductile”  those that break without much stretching are called “brittle”  it is important that asphalts be capable of a minimal amount of elongation 46  Direct Tension Tester  typically stiffer asphalts are more brittle and softer asphalts more ductile  creep stiffness as measured by the BBR is not adequate enough to completely characterize the capacity of asphalts to stretch before breaking  some asphalts exhibit high creep stiffness but can also stretch farther before breaking  therefore SHRP specifications recognize these stiff but ductile binders 47  Direct Tension Tester  these asphalts are allowed to have high creep stiffness (300 to 600 Mpa) if they can also display reasonable ductile behavior at low temperatures  if creep stiffness < 300 Mpa the direct tension test is not required  PAV asphalt binder  test measures the performance characteristics of binders as if they had been exposed to hot mixing and some in-service aging 48 49 Construction Rutting Fatigue Cracking Low Temp Cracking [DTT] [RV] No aging [DSR] [BBR] RTFO Short Term Aging PAV Long Term Aging 50