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CE  535  Bituminous  Materials  and  Mixtures  

  Behavior  Depends  on    Temperature    Time  of  Loading    Age  also  important  

60C  

25C  

1  hour  

1  hour   10  hours  

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  High  Temperature    Desert  climate    Summer    

  Sustained  Loads    Slow  moving  trucks    Intersections  

viscous  liquid  

  Permanent  deformation  is  concern      Mixture  is  plastic  

 Wheel  path  rutting    Shoving  at  intersections  

  Depends  on    Asphalt  binder  (some)   Mineral  aggregate  (much  more)  

Function  of  warm  weather  and  traffic  

Courtesy of FHWA

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  Low  temperature    Cold  climate   Winter    

  Rapid  loads    Fast  moving  trucks  

elastic  solid  

  Thermal  cracks  are  concern    Internal  stresses  induced  by  temperature  change    Stresses  exceed  strength  

  Mixture  is  brittle    Transverse  cracks  

  Depends  mostly  on  asphalt  binder    Not  affected  much  by  aggregate  

Courtesy of FHWA

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  Asphalt  reacts  with  oxygen    “Oxidative”  or  “age”  hardening  

  During  construction  –  short  term   Mixing    Placing/compaction  

  In-‐service  –  long  term    Hot  climate  worse  than  cool  climate    Summer  worse  than  winter  

  Volatilization  –  short  term    Volatile  components  evaporate  during  construction  

  Physical  hardening    Not  aging...asphalt  stiffens  at  low  temperatures    Reversible  

  Durability  cracks    Mixture  is  brittle  

  Random,  wandering  cracks    Depends  on  

  Asphalt  cement  (much)   Mineral  aggregate  (some)  

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  Fundamental  properties  related  to  pavement  performance  

  Environmental  factors    In-‐service  and  construction  temperatures    Short-‐  and  long-‐term  aging  

  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)  

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PG  Binder  Specification  

The  grading  system  is  based  on  climate  

PG  64  -‐  22  

Performance  Grade  

Average  7-‐day  maximum  pavement  temperature  

Minimum  pavement  

temperature  

Calculated  Temperatures  

• Calculated  by  LTPPBind  software  • High  temperature    

– 20  mm  below  the  surface  of  mixture  •  Low  temperature  

– At  mixture  surface  

Pavement  temperature  =  f  (air  temp,  depth,  latitude)  

  High/intermediate  temperature  properties    Dynamic  shear  rheometer  (DSR)    Rotational  viscometer  (RV)  

  Low  temperature  properties    Bending  beam  rheometer  (BBR)    Direct  tension  tester  (DTT)  

  Durability  Properties    Rolling  thin  film  oven  (RTFO)    Pressure  aging  vessel  (PAV)  

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Pavement  Temperature,  C  -‐  20    20    60    135  

Low  Temp  Fatigue      Construction  Cracking  Cracking  Rutting  Workability  

Asphalt  Binder  Tests  

  Evaluates    Elastic  and  viscous  properties    Loading  time  and  temperature  effects  

  Output    Complex  shear  modulus  (G*)    Phase  angle  (δ)  

Applied  Stress  or  Strain  

Fixed  Plate  Binder  

Oscillating  Plate  

Position  of  Oscillating  Plate  

Time  A   A  

C  

A  

1  cycle  B   C  A  

B  

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Viscous:    δ  =  90  deg  Elastic:    δ  =  0  deg  

Resulting  Shear  Strain  

time  

τmax  τmax  Applied  Shear  Stress  

γmax   time  lag  =  δ

γmax  

time

Elastic  and  Viscous  Behavior  

Viscoelastic:    0  <  δ  <  90  o  

Resulting  Shear  Strain  

τmax  Applied  Shear  Stress  

γmax   δ

τmax  

G*  =     γmax  

δ  =  time  lag  

time  

time  

Viscoelastic  Behavior  

DSR  Equipment  

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Liquid  bath  

Motor  

Parallel  plates  with  sample  

Dynamic  Shear  Rheometer  

25 mm Plate with Sample

Dynamic  Shear  Rheometer  

  For  the  early  part  of  service  life    G*/sin  δ  on  unaged  binder  >  1.00  kPa    G*/sin  δ    on  RTFO  aged  binder    >    2.20  kPa  

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  Why  a  minimum  G*/sin  δ  to  address  rutting    A  stiff,  elastic  binder    contributes  to  mixture  rutting  resistance  

  Increase  G*  or  decrease  δ  

  G*(sinδ)  on  RTFO  and  PAV  conditioned  residue    The  parameter  addresses  the  latter  part  of  fatigue  life  

  Value  must  be  <  5,000  kPa  

  Why  a  minimum  G*(sinδ)  for  fatigue  cracking    A  softer,  more  elastic  binder  is  less  prone  to  fatigue  cracking  

  Decrease  G*  or  δ  

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  Evaluates    Consistency  during  handling,  pumping  

  ASTM  D  4402    Other  Names  

  Brookfield  viscometer    Output  

  Viscosity  at  135C    Viscosity  temperature  chart  for  mixture  design  

Sample  chamber  

Spindle  

Asphalt  sample  

Applied  torque  

Rotational  Viscosity  

Motor  and  controller  

Temperature  controller  

Thermo  -‐  container  

Spindle  extension  

Rotational  Viscosity  

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Rotational  Viscometer    

Inner  Cylinder  

Torque  motor  

Thermosel  Environmental  

Chamber  Digital  Temperature  

Controller  

.1

.2

.3

.5

1

10 5

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Viscosity, Pa s

Compaction Range

Mixing Range

Mixing  and  Compaction  Chart    

  Evaluates    Low  temperature  stiffness  properties    

  Output    Creep  stiffness  (S)    Logarithmic  creep  rate  (m)  

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Air  Bearing  

Load  Cell  

Deflection  Transducer  

Fluid  Bath  

Computer  

Constant  (creep)  load  

Deflection  

Time  

Deflection  

Time  

Load  

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Cooling System

Fluid Bath Loading Ram

Log  creep  stiffness  

Log  loading  time  (s)  

slope  =  m-‐value  

60  8  15  30          120              240    

  Determined  for  RTFO  and  PAV  conditioned  residue    Creep  stiffness  (S)  <  300  Mpa   m-‐value  >  0.300  

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  Why  a  maximum  S  to  address  thermal  cracking    A  softer,  more  elastic  binder  better  resists  cracking  at  low  temperatures  

  Decrease  S  at  low  temperatures    Why  a  minimum  m-‐value  to  address  thermal  cracking    A  softer,  more  elastic  binder  better  resists  cracking  at  low  temperatures  

  Increase  m-‐value  at  low  temperatures,  binder  stiffness  changes  more  rapidly  

  Is  stiffness  enough    Not  necessarily,  assess  strain  needed  to  break  specimen  

  Thermal  cracking  occurs  when  strain  is  too  great  

  Direct  tension  test    Currently  in  specification      New  equipment  

Stress  

Strain  

Brittle  

Brittle-‐ductile  

Ductile  

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  Evaluates    Low  temperature  ability  to  stretch  

  Output    Tensile  strain  at  failure  

elongation Original length

Original length

Load

Load

Length at failure

Elongation at failure

failure strain =

Courtesy of FHWA

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  Test  RTFO  and  PAV  conditioned  binder    Failure  strain  >  1  percent  

  Rolling  Thin  Film  Oven    Simulates  construction  aging    Determines  mass  loss  

  Pressure  Aging  Vessel    Simulates  long  term  aging  

  Output    Conditioned  residue  for  testing  with  DSR,  BBR,  and  DTT  

163 C empty  bottle  before  

coated  bottle  after  

controls   fan  

bottle  carriage  air  jet  

Rolling  Thin  Film  Oven  

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Opening  in  Bottle  

  Simulates  approximately  5  years  of  in-‐service  binder  aging  

  50  gram  sample  conditioned  for  20  hours    Pressure  at  2,070  kPa  (300  psi)    Temperature  of  90  (194),  100  (212),  or  110C  (230F)  

  Depends  on  expected  in-‐service  climate  

Pressure  Aging  Vessel  

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Fatigue  Cracking  Rutting  

RTFO  Short  Term  Aging  No  aging    

Construction  

[RV]   [DSR]  

Low  Temp  Cracking  

[BBR]  

[DTT]

PAV  Long  Term  Aging