Marshal Land Super Pave Utah Asphalt 2008

Marshall and Superpave Mix Design Procedures Pedro Romero, Ph.D., P.E. The University of Utah

Why Mix Design? 

Determine a cost-effective blend and gradation of aggregates and asphalt that yields a mix having:     

Sufficient asphalt to ensure durability Sufficient stability to prevent rutting Sufficient voids to prevent flushing Maximum voids to limit permeability Sufficient workability to allow placement

History (Marshall)  

Bruce Marshall (Mississippi DOT) late 30’s WES began to study it in 1943 for WWII 



Evaluated compaction effort  No. of blows, foot design, etc.  Decided on 10 lb. Hammer, 50 blows/side  4% voids after traffic

Initial criteria were established and upgraded for increased tire pressures and loads

Marshall Mix Design  

Select and test aggregate Select and test asphalt binder 



Establish mixing and compaction temperatures

Develop trial blends 



Heat and mix asphalt binder and aggregates Compact specimen (100 mm diameter)

Mixing/Compaction Temps Viscosity, Pa s 10 5 1 .5 .3 .2 .1

Compaction Range Mixing Range 100

110

120

130

140 150 160 170 180 190 200 Temperature, C

Marshall Design Criteria Light Traffic ESAL < 104 Compaction Stability N (lb.)

Medium Traffic 10 4 < ESAL< 106

Heavy Traffic ESAL > 106

35

50

75

3336 (750)

5338 (1200)

8006 (1800)

Flow, 0.25 mm (0.1 in)

8 to 18

8 to 16

8 to 14

Air Voids, %

3 to 5

3 to 5

3 to 5

Voids in Mineral Agg. (VMA)

Varies with aggregate size

Marshall Mix Design Tests 





Bulk specific gravity of compacted sample Maximum specific gravity of loose mix Stability and flow    

60oC water bath (30 to 40 minutes) 50 mm/min loading rate Maximum load = stability Vertical deformation = flow

Marshall Stability and Flow

Marshall Design Air Voids, %

Stability

Unit Wt.

4%

Asphalt Binder Content, %

Asphalt Binder Content, %

Asphalt Binder Content, %

Target optimum asphalt binder content = average

Marshall Design (Cont’d) Flow

VMA, %

Upper limit

OK

OK Minimum

Lower Limit Asphalt Binder Content, %

Asphalt Binder Content, %

Use target optimum asphalt binder content to check if these criteria are met

Marshall Design Method 

Advantages   



Attention on voids, strength, durability Inexpensive equipment Easy to use in process control/acceptance

Disadvantages   

Impact method of compaction Does not consider shear strength Load perpendicular to compaction axis

History (Superpave) 

Resulted from Strategic Highway Research Program 





1987-1993

Combined strengths of previous methods with European concepts Based entirely on VOLUMETRICS

Old versus New?

Superpave Compactor 

Simulate field densification  







traffic climate

Accommodate large aggregates Measure compactability Conducive to QC

Superpave Gyratory Compactor 

Basis   





 

Corps of Engineers Texas Gyratory French operational characteristics

150 mm diameter mold up to 37.5 mm NMAS

Height measurement Gyrations based on traffic

?

ram pressure 600 kPa

1.25 degrees

?

30 gyrations per minute

AASHTO T 312

Gyratory Compaction

Ndesign Table Compaction Level Ninitial

Traffic Level

Ndesign

Nmaximum

Gyrations

%Gmm

< 0.3

6

< 91.5

50

75

0.3 to < 3.0

7

< 90.5

75

115

3.0 to < 30.0

8

< 89.0

100

160

> 30.0

9

< 89.0

125

205

Steps of Superpave Mix Design

1. Materials Selection 3. Design Binder Content 2. Design Aggregate Structure

Step 1: Materials Selection 



Choose correct asphalt binder Choose aggregates that meet quality requirements for the mix

Asphalt Binder Specification The grading system is based on Climate

PG 64 - 28

Performance Grade

Min pavement temperature Average 7-day max pavement temperature

Aggregate Consensus Properties Coarse Aggregate Angularity

Fine Aggregate Angularity

Traffic Level < 100 mm

> 100 mm

< 100 mm

> 100 mm

< 0.3

75 / ---

50 / ---

40

40

0.3 to < 3.0

85 / 80

60 / ---

45

40

3.0 to < 30.0

95 / 90

80 / 75

45

40

> 30.0

100 / 100

100 / 100

45

45

Step 2: Aggregate Structure  



 

Establish trial aggregate blends Estimate optimum asphalt binder content Manufacture and compact trial blends Evaluate the trial blends Select the most promising blend

Aggregate Gradation

Next steps 

Sample preparation 

  



Select mixing and compaction temperatures Preheat aggregates and asphalt Mix components Compact specimens

Extrude and determine volumetrics

Short Term Aging





Allows time for aggregate to absorb asphalt binder Helps minimize variability in volumetric calculations 

Most volumetric terms change depending on the amount (volume) of absorbed asphalt binder

Compaction

Three Points on SGC Curve % Gmm

Nmax

Ndes

Nini

10

100 Log Gyrations

1000

3.Design Binder Content % Gmm

increasing binder

96

10

100 1000 Log Gyrations

Design Asphalt Binder Content VMA

VFA %Gmm % asphalt binder at Ndes

% asphalt binder

Va

DP % asphalt binder

% asphalt binder

% asphalt binder

Superpave Mixture Requirements 

Mixture Volumetrics  Air Voids (V ) a Mixture Density Characteristics  Voids in the Mineral Aggregate (VMA)  Voids Filled with Asphalt (VFA) Dust Proportion NO STRENGHT TEST 

 

Requirements in Common 

 

Sufficient asphalt binder to ensure a durable pavement Sufficient stability under traffic loads Sufficient air voids 





Upper limit to prevent excessive environmental damage Lower limit to allow room for initial densification due to traffic

Sufficient workability

Questions? compaction Asphalt content

stability

Panel Discussion   

Darin Furnell, SLC Corporation William Larson, Utah DOT Jeff Chollar, Staker Parsons