Got Density?

Asphalt Pavement Assn. of IndianaWinter Conference

December 2010

Why measure density?

• Surrogate for other properties– Strength– Durability– Permeability

• Easy and fast

Rutting vs. Air Voids

0

5

10

15

20

25

30

35

40

Rutting, mm

Low Medium High

Relative Air VoidsRef: WesTrack

Rutting vs. Air Voids

-200

-150

-100

-50

0

0 2 4 6 8 10 12

Air Voids, %

Dep

th,

mm

Within Wheelpath Between Wheelpath Original

Ref: Mn/ROAD

1/2” Rutting in One Year

Fatigue vs. Air Voids

0

0.5

1

1.5

2

2.5

3

4 5 6 7 8

Avg. Air Voids, %

Est

imat

ed F

atig

ue L

ife

0.60%

1.20%

1.80%

Ref: WesTrack

Permeability

Permeability

Retained Penetration vs Air Voids

10

100

4 6 8 10 12 14 16

Air Voids

Ret

ain

ed P

enet

rati

on

, %

Ref: NCAT Text Book

0

10

20

30

40

50

60

7 8 9 10 11 12

Air Voids

Pavem

en

t L

ife

Red

ucti

on

, %

SHA Survey Literature WSPMS

Pavement Life vs. Air Voids

Getting Density

• Lift Thickness

• Temperature

• Compaction Support

• Equipment

NCHRP Report 531

• Relationships of HMA In-Place Air Voids, Lift Thickness, and Permeability (NCHRP 9- 27)

• Recommended minimum lift thicknesses:– 3 X NMAS for fine-graded mixes– 4 X NMAS for coarse-graded mixes

• Thin lifts cool faster– less time available for compaction

MultiCool

• FREE Software for Computing Compaction Window– Base Temp– Weather Conditions– Lift Thickness– Mix Temp– Latitude

• Available at www.hotmix.org

MultiCool

Temperature

150

175

200

225

250

275

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Time, minutes

Tem

per

atu

re,

F

1.5" 2" 3"

80OF Surface & Air Temperature, 5 mph wind

150

175

200

225

250

275

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Time, minutes

Tem

per

atu

re,

F

1.5" 2" 3"

50OF Surface & Air Temperature, 5 mph wind

Temperature

150

175

200

225

250

275

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Time, minutes

Tem

per

atu

re,

F

1.5" 2" 3"

30OF Surface, 40OF Air Temperature, 15 mph wind

Temperature

Compaction Support

Weak!!!

Weak SupportLeads to Poor Compaction!

Compaction Support

Strong!!!

Strong SupportHelps Compaction!

Balancing Production

• Balance of plant production, trucking, paver speed and rollers

• Slow and steady wins the race– Speeding up to get rid of trucks not

recommended.• Hurts ride• Non-uniform compaction

Joint Density

• Controlling segregation important

• Proper joint construction important

• Sealers

• Echelon paving

• Joint density specification

Longitudinal Butt Joint

Notched Wedge Joint

12”

1” minimum

Max Agg. Size

Notched Wedge Joint Attachment

Joint Rolling - Unconfined Edge

First Pass - Steel Wheel Rollers Inside of edge ~ 6”

Second Pass - Steel Wheel Rollers Overhang edge 3-6”

3” - 6” off joint3” - 6” on joint

Longitudinal Joint

Hot M

at

Cold

Mat

Longitudinal Joint

1/2 - 3/4 “ overlap

Longitudinal Joint

Unrolled

Rolled

Minimizing Joint Problems

• Minimize Joints

• Pave in Tandem!

• May Require More Lane Closures

• But, It Minimizes Return Trips!

Final Quiz

Q - What is the maximum number of rollers needed on a paving project?

A - Whatever it takes to get density.

2

3 41

5

6

The Future is Bright!

• Better Tools to Help Us!

• Oscillatory Compaction

• Intelligent Compaction– GPS Location– Mat Stiffness

Don’t Forget Quality

• Diamond Achievement Commendation

• Diamond Quality Commendation

• Diamond Paving Commendation