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Construc)on  of  Quality  Hot  Mix  Asphalt  Pavements    -­‐  1  Day  Course  

Asphalt Materials

Greg Harder, P.E. Asphalt Institute Regional Engineer

Tully, NY

Classifica)ons  of  Asphalt  

•  Cutbacks •  Emulsions •  Asphalt Cement (Binder)

MS-22 2-­‐6  

Cutback  Asphalt  

•  Paving  asphalt  liquefied  by  blending  with  petroleum  solvents  

•  Resul?ng  material  can  be  sprayed/mixed  at  lower  temperatures  

•  Primary  uses:  –  penetra?ng  prime  coat  –  binders  for  storable  cold  mix  asphalt  

Types  of  Cutback  Asphalt  

Slow Curing (SC)

ASTM D 2026

Medium Curing (MC)

ASTM D 2027

Rapid Curing (RC)

ASTM D 2028

Gasoline or

Naphtha

Asphalt

Kerosene

Asphalt

Diesel

Asphalt

Cutbacks  are  further  divided  by  viscosity.      For  example:  

MC-30: Kinematic Viscosity Min. 30 mm2/sec @ 140°F

MC-70: Kinematic Viscosity Min. 70 mm2/sec @ 140°F

Grades  of  Cutback  Asphalt  

Solvent

Asphalt Cement

MC-30 MC-70 MC-250 MC-800 MC-3000

Kinematic Viscosity mm2/s

30 - 60 70 - 140

250 - 500 800 - 1600

3000 - 6000

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Asphalt  Emulsions  

• Microscopic  asphalt  droplets  suspended  in  water.  

• Mostly  1-­‐5  µm  diameter  

•  Emulsifiers  or  surfactants  hold  these  droplets  in  suspension.  

100 micron/0.1mm

The purpose of diluting the binder with water is to lower the viscosity.

If the emulsifying agent causes the particles to bear a negative charge, the emulsion is said to be anionic.

This allows the emulsion to be shot onto the roadway surface at much lower temperatures than straight binder.

If the emulsifying agent causes the particles to bear a positive charge, the emulsion is said to be cationic.

Asphalt  Emulsions  

Anionic emulsions (negatively charged) typically bond best with positively charged aggregates (limestones, dolomites).

Cationic emulsions (positively charged) typically bond best with negatively charged aggregates (granites, sandstones).

Asphalt  Emulsions  

The amount of binder left after the water evaporates is called the residual asphalt.

Both the amount and type of water and emulsifying agent mixed with the binder affect the evaporation rate.

The residual asphalt is expressed as a percentage of the emulsion.

The process in which the binder globules begin to coalesce and the water evaporates is called breaking.

Asphalt  Emulsions  

Emulsion  

“Un-broken” emulsion is brown

“Broken” emulsion is black

Nega)vely-­‐  Charged  Emulsions  are  classified    into  3  types  

RS (Rapid Setting)

MS (Medium Setting)

SS (Slow Setting)

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3  

CRS (Rapid Setting)

CMS (Medium Setting)

CSS (Slow Setting)

Posi)vely-­‐  Charged  Emulsions  are  also  classified  into  3  types   Addi)onal  Nomenclature  

QS  =  Quick  Set  HF  =  High  Float  1  =  Binder  residue  =  60%  Minimum  2  =  Binder  Residue  =  65%  Minimum  h  =  Hard  Pen  Asphalt  Base  s  =  SoS  Pen  Asphalt  Base  or  some)mes  

Solvent  l  and/or  p  =  Latex  and/or  Polymer  

Asphalt  Emulsions  

The most common uses of emulsions are for chip seals, tack coats, and fog seals.

The term “binder” covers both neat (unmodified) and modified asphalt cements, but doesn’t include emulsions and cutbacks.

Binders are the “glue” that holds the aggregate together in HMA.

Unlike emulsions and cutbacks, binders are typically required to be heated to over 300°F for use, unless modified for use as Warm Mix Asphalt (WMA).

Polymers can be added to the binder to enhance their high temperature performance.

Asphalt  Binders  

Superpave  Asphalt  Binder  Specifica)ons  

The grading system is based on Climate

PG 64 - 22

Performance Grade

Meets all requirements up to this temperature (°C) Note: These grades are

specified in 6° increments

Meets all requirements down to this temperature (°C)

High  Temperature  @  98%  Reliability        

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Low  Temperature  @  98%  Reliability   PG  Binder  Grades  

0 10 20 30 40 50 60 -10 -20 -30 -40 70 80

PG 64-22

PG 70-28

The Rule of 92

PG 64-22 Probably Unmodified PG 70-28 Probably Modified

This is the

benefit of the

modifier

TEMPERATURE ºC

Asphalt  Descrip)on  and  Sources    

Asphalt  Cement  or  Asphalt  Binder  –  Black,  cemen??ous,  waterproof  material    –  Originally  mined  from  a  natural  lake  (s?ll  opera?ng  today:  Lake  Asphalt  of  Trinidad  and  Tobago)  

–  Most  asphalt  today  comes  from  the  refining  process  

   

MS-22 2-­‐2  thru  2-­‐4  

Typical  Crude  Make-­‐Ups  

Venezuelan Arabian-Heavy Nigerian-Light

58 27

20

14 26

28

30

21 33

16

3 6

7 10

1 Asphalt Residue

Hv. Gas Oil

Lt. Gas Oil

Gasoline

Kerosene

Not All Crudes Are The Same

Basic Refining Concepts MS-22 2-­‐2  thru  2-­‐4  

Asphalt Behavior Depends On:

•  Temperature •  Time of Loading •  Aging (properties change

with time)

MS-22 2-­‐4  thru  2-­‐6  

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Asphalt Behavior at Varying Temperatures

Viscous

Elastic

Temperature

Asphalt is a viscoelastic material that has both the properties of an elastic solid and a viscous liquid, depending on the temperature

Elastic Solid

Viscous Liquid

MS-22 Figure  2.04  

Asphalt Flow Behavior

140 F 1 hour

10 hours 77 F

1 hour

MS-22 Figure  2.03  

Effect of Loading Rate on Binder Selection

Example  • Toll  road      PG  64-­‐22  

• Toll  booth                  PG  70-­‐22  

• Weigh  sta?ons    PG  76-­‐22  

90  kph  (55  MPH)  

Slow  

Stopping  

Effect of Traffic on Binder Selection

•  10  to  30  million  ESALs  •  Consider  increasing  one  high  temperature  grade  

•  >    30  million  ESALs  •  Increase  one  high  temperature  grade  

• Newer  recommenda?ons  are  based  on  more  gradual  bumping  in  LTPPBind  version  3.0+  

80  kN  ESALs  

NOTE:    Mul?ple  Stress  Creep  Recovery  (MSCR)  test  specifica?on  will  replace  traffic  grade  bumping.  

Asphalt aging over the pavement life

Visc

osity

Time

A B

C

D1 D2 D3

Bulk Storage and Handling

Mixing, Placing, and Compaction

Long-term, In-place Aging

High Temperature Behavior

•  High  in-­‐service  temperature  – Desert  climates  –  Summer  temperatures  

•  Sustained  loads  –  Slow  moving  trucks  –  Intersec?ons  

Viscous Liquid

MS-22 2-­‐4  

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Low Temperature Behavior

Elastic Solid

•  Low  Temperature  –  Cold  climates  – Winter  

•  Rapid  Loads  –  Fast  moving  trucks  

MS-22 2-­‐5  

“Ideal” Asphalt Binder

•  Low stiffness at construction temperature

•  High stiffness at high in-service temperature

•  Low stiffness at low in-service temperature

•  Excellent long-term durability

Polymer-modified Asphalt Binder

Visc

osity

Temperature

General Performance

Polymer-modified

Unmodified

Polymers

•  Elastomers  • Plastomers  • Combina?ons   poly  �  mer  

 “many  parts”  

Imag

e co

urte

sy In

frapa

ve

Elastomers

• Natural  Latex  Rubber  •  Synthe?c  Latex  

•  Styrene-­‐butadiene  (SB)  • Block  Copolymer  

•  Styrene-­‐butadiene-­‐styrene  (SBS)  

• Reclaimed  Rubber  

Imag

e co

urte

sy In

ject

ec.c

om

Plastomers

• Polyethylene  • Polypropylene  •  Ethyl-­‐vinyl-­‐acetate  (EVA)  • Polyvinyl-­‐chloride  (PVC)  

EVA is a plastic that is used to create stiffer

insoles for your shoes

PVC Pipe

Imag

e co

urte

sy s

lpip

e.co

m

Image courtesy cyclingfitness.com

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Quantifying the Effects of PMA for Reducing Pavement Distress

This  study  (published  in  Feb  2005)  used  na?onal  field  data  to  determine  enhanced  service  life  of  pavements  containing  polymer  modified  binders  versus  conven?onal  binders.    The  data  is  from  a  variety  of  climates  and  traffic  volumes  within  North  America.  

ER 215

IS 215

Direct Comparisons – Rutting

0 0.2 0.4 0.6 0.8

1 1.2 1.4 1.6 1.8

2

0 0.2 0.4 0.6 0.8 1 1.2

Rut Depths on PMA Sections, inches

Rut

Dep

ths

on C

ompa

nion

Se

ctio

ns, i

nche

s

Distress Comparisons – Transverse Cracking

0.0 50.0

100.0 150.0 200.0 250.0 300.0 350.0 400.0 450.0 500.0

0.0 100.0 200.0 300.0 400.0 500.0 Transverse Cracking - PMA Sections, ft.

Tran

sver

se C

rack

ing

- Com

pani

on

Sect

ions

, ft.

Distress Comparisons – Fatigue Cracking

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

0.00 20.00 40.00 60.00 80.00 Fatigue Cracking - PMA Sections, %

Fatig

ue C

rack

ing

- Com

pani

on

Sect

ions

, %

The  use  of  polymer  modified  binders  has  grown  tremendously  over  the  past  several  years  

However,  the  most  widely  used  binder  specifica?on  in  the  U.S.,  AASHTO  M  320,  was  based  on  a  study  of  neat  (unmodified)  binders,  and  may  not  properly  characterize  polymer  modified  binders  

MSCR  Implementa?on   PG  Grading  Alone  Does  Not  Always  Predict  Performance  

•  Study  of  the  two  mixes  with  the  same  aggregate  structure,  but  different  binders.  

 PG 63-22 modified, no rutting PG 67-22 unmodified, 15mm rut

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• Current  spec,  G*  and  δ  are  measured  in  the  linear  visco-­‐elas?c  range.  

•  For  neat  binders,  flow  is  linear(strain  increases  in  a  constant  propor-on  to  stress)  and  therefore  not  sensi?ve  to  the  stress  level  of  the  test.  

•  For  polymer-­‐modified  binders,  the  response  is  not  linear  and  very  sensi?ve  to  the  stress  level  of  the  test.    The  polymer  chains  can  be  rearranged  substan?ally  as  the  stress  increases.  

Why  doesn’t  M  320  properly  characterize  polymer-­‐modified  binders?   Why  Do  We  Need  New  Binder  Test?  

• PG  Binders  • Most  Common  “Neat”  Binder  Grades  

• PG  64-­‐22  • PG  67-­‐22  

• Most  Common  “Modified”  Binder  Grade  • PG  76-­‐22    

Works  OK  for  neat  binders  

Doesn’t  work  as  well  for  modified  binders  

What  happened  as  a  result  of  M  320’s  inability  to  fully  characterize  polymer-­‐modified  binders?  

• Most  states  began  requiring  addi)onal  tests  to  the  ones  required  in  AASHTO  M  320  

• These  mostly  empirical  tests  are  commonly  referred  to  as  “PG  Plus”  tests  

• These  tests  are  not  standard  across  the  states  –  difficult  for  suppliers  

• Even  some  of  the  tests  that  are  the  most  common,  e.g.  Elas)c  Recovery,  are  not  run  the  same  way  from  state  to  state  

PG  Plus  Spec  

No  PG  Plus  Spec  

States  with  a  “PG  Plus”  Specifica)on  

ER  Informa)on  and  Test  Time  

•  The Elastic Recovery Test is an excellent tool to establish the presence of polymer modification. –  It takes about 4 hours to prepare and test

samples for this information.

•  However, it is a poor tool to evaluate the rutting performance of polymer-modified binders. –  The MSCR test can use the same sample

already being run in the DSR to give more information in a few extra minutes.

Mul$ple  Stress  Creep  Recovery  Test

• Performed on RTFO-aged Binder • Test Temperature

•  Environmental Temperature •  Not Grade-Bumped

• 10 cycles per stress level •  1-second loading at specified shear stress

•  0.1 kPa •  3.2 kPa

•  9-second rest period

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Mul$ple  Stress  Creep  Recovery  Test

• Calculate Recovery for each Cycle, Stress •  Difference between strain at end of recovery period

and peak strain after creep loading • Calculate Non-recoverable Creep Compliance

(Jnr) •  Non-recoverable shear strain divided by applied shear

stress •  “J” = “compliance” •  “nr” = “non-recoverable”

ALF  Study  -­‐  7  Asphalt  Binders  

AZ CRM ---- 70-22

1

PG 70-22 Control

2

Air Blown

3

SBS

4

TX TBCR

5

TP

6

PG 70-22 + Fibers

7

PG 70-22

8

SBS 64-40

9

Air Blown

10

SBS

11

TP

12

ALF  Loading

•  The  pavement  was  heated  to  a  constant  64ºC.  •  The  FHWA  ALF  uses  an  18,000  lbs  wheel  load  with  no  wheel  wander.  

•  The  speed  is  12  MPH.  •  This  is  a  extreme  loading  condi?on  far  more  sever  than  any  actual  highway.  

y = -7.4519x + 10.956R2 = 0.1261

0

2

4

6

8

10

12

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8rutting inches

G*/s

in d

64C

Rela$onship  between  G*/  sinδ  and  ALF  ruFng

Exis?ng  SHRP  specifica?on  has  poor  rela?onship  to  rulng  for  modified  systems.  

Rela$onship  between  Jnr  and  ALF  ruFng

y = 4.7357x - 1.1666R2 = 0.8167

0

0.5

1

1.5

2

2.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

ALF Rutting in

Jnr

MSCR  can  adjust  for  field  condi?ons  and  has  excellent  rela?ons  to  performance.  

New  PG  Grading  System  (MSCR)

Requirements  

• S  =  Standard:      Jnr    ≤    4.5  kPa-­‐1    

• H  =  Heavy:        Jnr    ≤    2.0  kPa-­‐1        

• V  =  Very  Heavy:    Jnr    ≤    1.0  kPa-­‐1    

• E  =  Extreme:        Jnr    ≤    0.5  kPa-­‐1  

 

 

12/9/14  

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y  =  29.371x-­‐0.263  

0  

10  

20  

30  

40  

50  

60  

70  

80  

90  

100  

0   0.5   1   1.5   2  

Avg.  %  Recovery  @  3.2  kPa

 

Avg.  Jnr  @  3.2  kPa  

MSCR:  Elas)c  Response  

For  Jnr3.2  values  >  0.1:  %Rec3.2    must  be  greater  than(29.371*(Jnr3.2-­‐0.263))      For  Jnr3.2  values  <  0.1:  %Rec3.2  must  be  greater  than  55%  

Data  above  the  curve  -­‐  significant  elas9c  response    

Data  below  the  curve  -­‐  low  elas9c  response  

"E"  Grade   "V"  Grade   "H"  Grade  

0  

10  

20  

30  

40  

50  

60  

70  

80  

90  

100  

0   0.5   1   1.5   2  

%Re

c  @  3.2  kPa

 tested

 at  6

4C  

Jnr  @  3.2  kPa  tested  at  64C  

MSCR  DATA  -­‐  PG  76-­‐22  

SUPPLIER  1  

SUPPLIER  2  

SUPPLIER  3  

SUPPLIER  4  

SUPPLIER  5  

GRADE 64E

GRADE 64V

GRADE 64H

WHAT  IS  CURRENTLY  BEING  SUPPLIED?  

CURRENT  GRADE  –  M320   NEW  GRADE  –  M332  

PG  76-­‐22   PG  64E-­‐22  

PG  76-­‐28   PG  64E-­‐28  

PG  70-­‐28   PG  64V-­‐28  

PG  64-­‐22P     PG  64V-­‐22  

PG  58-­‐34   PG  58H-­‐34  

MODIFIED  GRADES  IN  THE  NORTHEAST  

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Disclaimer: To ensure the most accurate and current information, the specific agency should be contacted

Page 1 of 1

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$$O$)",>43$\$314>U5$%0&>43$6243@>

When would a polymer-modified asphalt typically be used?

Adjustment  to  High-­‐Temp  Grade  

Traffic  Load  Rate  ESALs  (M)   Standing   Slow   Standard  

<  0.3   -­‐   -­‐   -­‐  0.3  -­‐  <  3   2   1   -­‐  3  -­‐  <  10   2   1   -­‐  10  -­‐  <  30   2   1   -­‐  ≥  30   2   1   1  

AASHTO M 323 - Table 1

12/9/14  

11  

MS-­‐26  

For  More  Binder  Informa$on

MS-­‐25