2/4/2019 W 26 A Practical Approach to Managing Density Todd Mansell, - - PDF document

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W‐26 A Practical Approach to Managing Density Todd Mansell, CAT Paving

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What is Compaction?

• Mechanical Process
• Removes specified amount
• f air voids
• Develops stone on stone

contact

• Builds strength

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What is Compaction?

• Screed develops initial density
• Vibratory screed produces

compaction energy

• Tamping and vibratory screed

produces high compaction energy

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What is Compaction?

• Compaction starts

immediately behind paver

• Asphalt layer at highest

temperature

• Limited time to develop

density

• Planning, preparation and
• perator training required

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Best Practices for Compaction

• Type of rollers
• Number of rollers
• Roller settings
• Number of passes (coverage)
• Mix temperature
• Rolling mainline
• Rolling transverse & longitudinal joints
• Pre‐compaction w/ screed
• Stopping‐Starting the roller
• Smoothness – where do we stop to get water, change direction, supported‐unsupported

edges, tie‐ins

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Lines of Communication

Foreman Superintendent Truck Boss Project Manager

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How do we achieve density?

• 1. Understand the factors affecting compaction

 Mix temperature & time available for compaction  Four forces of compaction

• 2. Understand different types of rollers and how they work

 Steel drum, pneumatic, combination, oscillation, offset drums

• 3. How to establish a rolling pattern that achieves density & smoothness

 How to determine roller settings  Determining the number of passes  Dealing with harsh & tender mixes  Good communication!! 8

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What does it take to get density?

Temperature

Temperature

Temperature

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Time Available for Compaction

Density must be achieved while the mix is still HOT

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Asphalt Binder

• Visco‐elastic material
• Hot asphalt binder acts as a lubricant

for aggregate to aid in compaction

• Cold asphalt binder becomes the glue

that bonds the aggregate together

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Temperature is Critical

300 ‐ 260 Breakdown rolling 260 ‐ 220 Intermediate rolling 220 ‐ 160 Finish rolling 160 – Stop rolling

240 ‐ 190 possible tender zone

Keep steel drums off the mix!!!

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MultiCool Website and Android App

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• Google Play App store
• http://www.eng.auburn.edu/users/timmdav/MultiCool/FinalRelease/Main.html

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PaveCool website and App

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• Creating density easiest at high

temperature

• Upper limit about 160o C (320o F)
• Watch for layer movement in fine

mixes

• Stay back if layer is tender due to

high temperature

Mix Temperature

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• Reach target density before

mat cools

• Lower limit about 90o C

(190o F)

• Work close to paver
• Increase compaction energy
• Add breakdown rollers

Mix Temperature

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Tender Zone

• Some mixes get tender

between upper and lower limits

• Surface moves under

drums or tires and cracks appear

• Work ahead of tender

zone and after

Mix Temperature

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• High ambient temperature

– asphalt retains heat – longer compaction time

• Low base temperature

– heat transfers quickly to base – shorter compaction time

• Low ambient temperature

– asphalt cools faster – shorter compaction time

• Adjust rolling pattern as

ambient conditions change

Climate Conditions

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Four Forces of Compaction

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Types of rollers

• Static steel drum
• Vibratory steel drum
• Oscillation
• Pneumatic
• Vibratory pneumatic
• Combination

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• Static pressure exerted by steel

drum roller non‐vibratory

• Weight at the drum divided by

width of the drum

Static Steel Drum Pressure

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• Heaviest model not always

highest static force

• Narrower drum increases

static force

CB64 CB54

Weight @ drum 6490 kg 14,300 lb 5402 kg 11,900 lb Drum width 213 cm 84 in 170 cm 67 in Static linear load 31 kg/cm 170 lb/in 32 kg/cm 178 lb/in

Static Force Comparison

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Vibratory Steel Drum

• Breakdown, intermediate

and finish rolling

• Settings for amplitude and

frequency

• Static mode for finish rolling

Build density from the top down

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• Impact is a dynamic force
• Drum moves into the asphalt layer

to produce high energy

• Increased production benefit
• Over‐compaction, broken

aggregate risk

Impact Force

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• Spinning eccentric weight

causes drum vibration

• Vibratory force sets

aggregates in motion

• Aggregates orient better

for stone on stone contact

Vibration

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• Impact equals

amplitude

• Defined as distance

drum moves into the asphalt layer

• Rollers have various

amplitude settings

• Operator must know

which amplitude to choose

Amplitude

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High Amplitude Low Amplitude

Amplitude = compactive effort

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Factor Lower Force 0.25 ‐ 0.6 mm Higher Force >0.6 mm Layer Thickness <50 mm (2.0in) >50 mm (2.0in) Base Support Rigid Flexible Binder Viscosity Low (unmodified) High (modified) Aggregate Shape Rounded Angular Ambient Temperature High Low

Amplitude Checklist

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• Frequency affects working speed
• Working speed set to generate 32‐46 impacts per meter

(10‐14 impacts/foot)

• Higher frequency allows for higher working speed

Frequency

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Impacts per foot, Frequency & Roller Speed

10 to 14

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Verify Roller Settings

• Is the equipment in good

working condition?

• Settings per test strip?

 Amplitude  Frequency  Speed (10‐12 ipf)

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Higher Amplitudes associated with Lower Frequencies

High Amplitude (<0.80 mm) = Low Frequency (>2800 vpm) Medium Amplitude (0.5 mm – 0.8 mm) = Medium Frequency (2800‐3400 vpm) Low Amplitude (0.2 mm – 0.5 mm) = High Frequency (3400 vpm)

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Calculate roller ground speed

Frequency (vpm) Impacts per foot Roller speed (fpm) = Speed = 3,000 vpm 10 ipf = 300 feet per minute

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Balanced Roller Vibration

• Optimum compaction occurs

when all forces are accepted by the asphalt layer

• Balance between forces of

compaction and the asphalt layer

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Balanced Roller Vibration

• Forces out of balance create drum bounce
• Inefficient operation
• Solve bouncing:

‐ change speed ‐ lower amplitude ‐ higher frequency ‐ one drum static ‐ both drums static

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Oscillation

• Back and forth drum movement
• Maintains contact with surface
• Less aggressive compaction

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Offset drums

Advantages

• Offset drums cover width of

layer in fewer passes

• May be a good option on thin

mats that cool quickly

• Following curbs, radius

Disadvantages

• Effectively a single drum roller

More passes may be required

• Less uniform compaction (PWL)

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Pneumatic Rollers

• Most commonly used for

intermediate rolling

• Knead the mix
• Close up surface voids and

tension cracks

• Efficient building density

Build density from the bottom up

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Manipulation or kneading action

• Manipulation occurs

due to overlapping tires

• Some forces move

sideways

• Tightens surface

texture

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Pneumatic tire rollers

• Adjust tire pressures based
• n mat thickness
• Ballast weight is usually

sand, water or steel plates

Higher Pressure Lower Pressure

Tire Pressures

• Change static force by changing ballast
• Change static force by changing tire pressure
• Increase inflation pressure to increase force
• Decrease inflation pressure to decrease force

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Keep Tire Pressures Equal

• Keep tires hot
• Within 30°‐ 40°F of pavement
• Tire pressures equal
• Warm up before paving

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Vibratory pneumatic tire roller

Adjustable amplitude settings instead of ballast

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Combination

Vibratory steel drum & pneumatic tires

Establish an effective rolling pattern

• 1. Based production and density
• 2. Equipment Selection
• 3. Balance paver & roller speed
• 4. Test Strip
• 5. Verify during production

Decision Point Decision Point

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Intermediate 90-92% 92-94% 94+ % Temp 300-260˚F 260-200˚F 200-160˚F 126 feet 200 feet 200 feet %TMD Coverage Settings Low A, static 90 psi High A, Low F 3 2 2 (1 vibe, 1 static) Breakdown Finish

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Screed compaction

Sometimes referred to as “pre‐compaction”

1. Vibratory screeds

• On/off
• Adjust frequency of vibration

2. Tamper bar screeds

• Single tamper
• Double tamper

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Vibratory screeds

• With vibration on, typically

80 to 84% density

• No vibration 78 – 82%
• Key is setting vibratory

frequency correctly

• Surface texture improved

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Tamper bar screeds

Tamper Bars Tamper Motors Eccentric Bearings

• 88% to 92% density
• Slow paving speed 6 – 15

feet per minute

• Key is setting tamper

frequency correctly

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• Develops the majority of the density in the asphalt layer
• Works immediately behind the paver where asphalt is the hottest
• Must match the production / speed of the paver

Breakdown Compaction

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What is a good target density for breakdown?

• Job spec is 92‐97%
• Our job target for final density is 94%
• A good goal for breakdown compaction is

95% of our overall target density 0.95 x 94% ≈ 90%

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• Normally immediately after breakdown compaction
• Goal is to develop final target density

Intermediate Compaction

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What is a good target density for intermediate?

• Job spec is 92‐97%
• Our job target for final density is 94%
• A good goal for intermediate compaction is

100% of our overall target density 1.0 x 94% = 94%

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• Goal is to clean up marks left by previous rollers
• Mat just warm enough to allow clean up at the surface
• May get some density gain

Finish Compaction

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• Verify equipment and patterns

develop required density

• Plan each phase of compaction
• Can be done first day of job

– Sometimes required in advance – Don’t fake it

• Communicate plan to all crew

members

Test Strips

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• Check screed laid density
• Monitor temperature of the

asphalt layer

• Document start and stop of

tender zone, if any

Test Strips

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• Check density across width of

the asphalt layer

• Check density after each

breakdown pass

• Outline the gauge placement
• Write numbers that operator

can see

Test Strips

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• Pull core as soon as possible
• Verify accuracy of on‐site testing

gauge

Test Strips

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Determine the number of roller passes

• Set target density values for each roller

 95% of target for breakdown roller  100% of target for intermediate roller  Remove marks with finish roller – sometimes more density

• Determine number of passes with QC team

 Start behind screed  Breakdown roller, intermediate, finish  Take density & temp readings after each roller pass

• Trial and error to ‘fine tune’ roller pattern

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Number of roller passes

Breakdown Intermediate Finish 12-ton DDV 14-ton tire 8-ton DDV Settings High A, Low F 1 vibe, low A, high F, 1 static 1st Pass Temp 275 250 200 Density 88% 92% 94% (vibe) 2nd Pass Temp 260 245 193 Density 90% 93% 94% (static) 3rd Pass Temp 252 230 Density 91% 93.5% 4th Pass Temp Density

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• Add passes
• Increase amplitude
• Increase tire pressure or

ballast

• Change rollers
• Work closer to the paver
• Lower working speed

Getting More Density on the Test Strip

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• Each project is different
• Each project requires analysis
• Meeting end result

specifications requires planning and communication

Summary

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Foreman Superintendent Truck Boss Project Manager

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Establish an effective rolling pattern

• 1. Based production and density
• 2. Equipment Selection
• 3. Balance paver & roller speed
• 4. Test Strip
• 5. Verify during production

Decision Point Decision Point

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What are the job specs?

• What is the minimum density requirement for mainline? 92‐97%
• Joint density? 90% Shoulders? n/a
• Smoothness? IRI improvement? 60% ‐ one lift
• How will density be measured and accepted? Cores?

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Planning ≈ 20 minutes

Pre‐ paving planning

 Tons per day  Number of trucks needed  Paver speed  Roller speed  Rolling Pattern

• Density
• Smoothness

Tools available

 NAPA IS‐120  Paving Production Calculator

App

 Amplitude Selection App  PaveCool or MultiCool Apps

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Balancing Plant, Trucking, Paver, Roller

• Expected 2,500 tons/day
• 8‐hr paving window
• End dumping (18‐ton)
• 12‐ft wide, unconfined edge
• 2‐inch overlay
• 12.5mm polymer‐modified mix
• Autumn < 70°F
• Given 3 rollers
• 84” steel vibratory (Cat CB64)
• 79” steel vibratory (Cat CB54XW)
• 82” pneumatic (Cat CW34)

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Need 7 pieces of information

Use Paving Production Calculator

• r use NAPA IS‐120 Worksheets
• 1. Plant tph & silo capacity
• 2. Paving window
• 3. Average truck capacity

4. Truck cycle time 5. Mat thickness (loose) 6. Mat width 7. Loose mix density

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Input 7 pieces of information…

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Number of Trucks = 20

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Paver speed using end dumps

• Use 75% efficiency for end‐

dumping

• Use 100% for MTV

36 fpm

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Paver Speed, trucking & plant is balanced

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What is a good target density for breakdown?

• Job spec is 92‐97%
• Our job target for final density is 94%
• A good goal for breakdown compaction is 95% of our overall target density

0.95 x 94% ≈ 90%

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Amplitude App ≈ 0.020” – 0.029”

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Test Strip to Determine # Passes Required

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Number of roller passes

Breakdown Intermediate Finish 12-ton DDV 14-ton tire 8-ton DDV Settings High A, Low F 1 vibe, low A, high F, 1 static 1st Pass Temp 275 250 200 Density 88% 92% 94% (vibe) 2nd Pass Temp 260 245 193 Density 90% 93% 94% (static) 3rd Pass Temp 252 230 Density 91% 93.5% 4th Pass Temp Density

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84” 84” 12’ Wide Mat 6” Overhang 12” Overlap 6” Overhang Roller B Roller A

12-Foot Wide Lane: 84” x 2 passes

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Amplitude 0.020”- 0.029” for 84” drum machine

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Roller speed using 84” drum 40 fpm > 36 fpm

• Wider drum
• Lower frequency
• Higher amplitude
• 5-Pass pattern

40 fpm

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Establish an effective rolling pattern

• 1. Based production and density
• 2. Equipment Selection
• 3. Balance paver & roller speed
• 4. Test Strip
• 5. Verify during production

Decision Point Decision Point

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How far back ?? Breakdown

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Length of the Roller Pass

Speed = Distance Time

Time available for compaction (MultiCool) Roller speed based on frequency (ipf)

Solve the equation for distance

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Length of the Roller Pass

Distance = Speed x Time

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2,520 10

Roller Ground Speed

Distance

Speed Calculation Frequency = 2,520 vpm We want 10 impacts per foot

= Speed x Time

= 252 fpm

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300 ‐ 260 Breakdown rolling 260 ‐ 220 Intermediate rolling 220 ‐ 160 Finish rolling 160 – Stop rolling

240 ‐ 190 possible tender zone

Keep steel drums off the mix!!!

Time Depends on Temperature

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MultiCool Website and Android App

• Google Play App store
• http://www.eng.auburn.edu/users/timmdav/MultiCool/FinalRelease/Main.html

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MultiCool from 275°F to 252°F (breakdown roller only)

Time ≈ 3 minutes

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Length of the Roller Pass

= Speed x Time = 252 x 3 = 756 ft (in 3 minutes)

Roller speed = 252 fpm Time = 3 minutes

Distance

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Length of the Roller Pass

756 feet traveled in 3 minutes We have a 5-pass pattern (from test strip) to cover the mat twice 756 ÷ 5 = 151 feet Assume 80% roller efficiency 151 x 0.80 = 120 Length of roller pass = 120 feet * * If conditions change – re-calculate the length of roller pass

Pass 2 Pass 1

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Sequence & Timing

Intermediate 90-92% 92-94% 94+ % Temp 300-260˚F 260-200˚F 200-160˚F 120 feet 200 feet 200 feet %TMD Coverage Settings Low A, static 90 psi High A, Low F 2 2 2 (static) Breakdown Finish

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Rolling patterns based on the situation

• Tender mixes

 Steel stay off!

• Stiff or harsh mixes

 Pneumatic breakdown  Echelon rolling

• Longitudinal joint

 Confined vs. unconfined edge 92

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Efficient Compaction of Stiff & Tender mixes

• Stiff mixes
• generally very stable and can take high compactive forces
• compact easier at higher temperatures
• use higher amplitudes
• Tender mixes
• temperature sensitive through a specific temperature range
• achieve density before tender zone – rolling in echelon OR
• wait until mix cools below tender zone and resume rolling

Pneumatic breakdown on a stiff mix

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• Deep marks left in thick, hot

layers

• Deep marks left during

breakdown phase

• Difficult to clean up
• Stay back or decrease tire

pressure

Deep Pneumatic Tire Marks in Breakdown Tender Mix

Checking Cutting

Rolling tender mixes

• Does not compact in specific

temperature range or zone

• Roll in echelon
• Resume compaction below

tender zone temp

• Do NOT run a steel drum in the

tender zone

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Rolling in Echelon (side-by-side)

• Take advantage of

TEMPERATURE

• Make more passes before

the mix cools

• Can be done without a finish

roller

• Ideal to use same size rollers

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Echelon with same & different rollers

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Echelon – steel drum

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Echelon - pneumatics

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Other Mix Types

• Warm Mix
• Similar to conventional hot mix (for WMA injection process)
• Chemical (wax) similar to conventional, but may “set” quickly at end
• SMA – high temperature, high amplitudes
• Polymer‐modified
• High temperature compaction
• SBS, anti‐strip
• Open‐graded (OGAC, PFC, etc.)
• Need to “seat” the mix. Often static roll or gently vibrate

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Rolling the longitudinal joint

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Keep end gates on the paver down

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Fluff Factor (roll down) ¼” per 1”

2” after compaction 2½ ” ½

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Unsupported edges

6” overhang

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Supported edge – roll from hot side

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Proper Amount of Horizontal Joint Overlap

½ ” to 1” overlap

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Proper Amount of Horizontal Joint Overlap

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Roll from hot side

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Locking in the joint

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Locking in the joint

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• All other phases should
• verlap the hot / cold

joint

• Pneumatic compactors

especially good at pinching joints

Use Pneumatic to Seal the Joint

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Transverse Joint Compaction

• Straight edge tells the story
• Too high – more rolling may

help

• Too low – hand work needed

to fill in

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Poor Transverse Joint Starting Point

Incorrect Starting Reference

• Rounded face at the joint
• Plunge cut too deep

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• Cut straight starting joint
• Butt joint flat
• Tack butt joint
• Clean area where screed will rest

Good Transverse Joint Starting Point

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• Measure height of starting

joint

• Calculate thickness of starter

boards

• General rule vibratory screed:

6 mm (1/4 in) compaction per 25 mm (1 in) loose depth

Good Transverse Joint Starting Point

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Correct Pre-Compaction Height

• Select starter boards of proper

thickness

• Support main screed and

extender screed

• Board length

0.9‐1.2 m (3‐4ft)

• Start with good paving and

minimal hand work

• Mat depth must allow for rate of

compaction

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• Breakdown roller starts

normal pattern

• Paver should not have

to stop and wait for joint to be prepared and compacted

Transverse Joint Rolling Patterns

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Recommended Rolling Pattern

• Approach joint at angle in static mode
• Leave stop mark at an angle to direction of compaction
• Continue to roll until joint is flat and smooth

Transverse Joint Rolling Patterns

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Transverse Joint Rolling Patterns

• Pinches joint at angle

rather than pushing mix away

• All stop marks can be

cleaned up during first normal rolling pattern

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• Can pinch joint from the side if space permits
• Utility size compactor makes job easier
• Leaves drum edge cut mark perpendicular to

direction of rolling pattern

Transverse Joint Rolling Patterns

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• First pass most of drums on cold

side

• Check flatness
• Second pass, if needed, move

farther onto hot side

• All passes static
• Should not have to vibrate to

pinch a transverse joint

Transverse Joint Rolling Patterns

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Steel Drum: Best Practices

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Stopping Near the Paver

• Worker safety is the primary

consideration

• Be aware of personnel around the

paver

• Stop at least 15 feet behind the paver
• Shut off vibratory system as roller

slows down

Turn off vibration before stopping

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• Roller stops always made at an angle
• Turn off vibration just before roller starts turning
• Next pass forward rolls through stop mark
• Stop marks are staggered as roller moves ahead to keep up with paver

Stop at an angle to the mat

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Staggered Stop Marks

• Don’t stop in same

area

• Major smoothness

issue

• Roll through stop

marks

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• Most common cause of

downtime

• Film of water must cover

steel drum

• Small amount of pick‐up

becomes big problem

Asphalt Pick-Up On Dry Drum Surfaces

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• Too much force
• Speed too slow
• Cannot use roller to

correct height mismatch

Vibratory Drum Impact Marks

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• Never park on hot asphalt
• Leaves dents that will not clean up
• Park on cold asphalt
• Park on shoulder, if available

Parking on the Mat

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• Plan water refill stops
• Stop on shoulder or

turnout or cold asphalt – never on driving lane

• Make sure water hose is

long enough for all situations

Stopping for Water Refill

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If necessary, use boards to allow roller to get off hot asphalt during water refills

Stopping for Water Refill

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• Wide, solid drum will distort hot asphalt compacting tight radius
• Outer edge of drum stretches the hot asphalt

Tight Radius Compaction

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• Split drum rollers
• Drum halves turn at different

speeds when steering around radius

• Outer edge turns faster to

avoid distortion

Tight Radius Compaction

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• Do not turn during stops
• Stop slowly
• Finish roller should be able

to clean up stops marks

• Be careful when using

modified oils – sticky asphalt

Pneumatic Roller: Best Practices

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• Use biodegradable release

agent

• Heat tires and move up to

desired temperature zone

• Keep tire surface within 25°C

(40°F) of mat temperature

Asphalt Pick-Up On Rubber Tires

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• Once tires are hot – keep them hot
• Tire skirts
• Don’t park during interruptions

Asphalt Pick-Up On Rubber Tires

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Who’s responsibility is it?

• Paver Speed?
• Paver operator?
• Roller Speed?
• Roller operator?
• Quality Control?
• Meeting Density & Smoothness targets?
• Quality Control?

Foreman Superintendent Truck Boss Project Manager Quality Control

138

Caterpillar: Confidential Green

• Paving crew provides

‐ uniform screed laid density ‐ uniform thickness ‐ uniform temperature

Inconsistent Density

2/4/2019 47

139

Caterpillar: Confidential Green

• Compaction crew

maintains ‐ uniform pattern ‐ uniform force ‐ uniform speed ‐ uniform temperature zones

Inconsistent Density

140

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• Quality Control verifies:

‐ density behind each phase ‐ communicates results to

• perators

‐ communicates changes to

• perators

Inconsistent Density

141

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• Maintain pattern and working

speed

• Paving crew and breakdown

roller operator communicate

• All paving speed changes are

approved and told to roller

• perator

Inconsistent Density

2/4/2019 48

Plan for Excellent Compaction!

• Collect information
• Set targets
• Calculate paving speed
• Calculate roller speed
• Balance tons, paver, rollers
• Confirm test strip
• Check, check, check…
• Make changes as needed

143

Caterpillar: Confidential Green

Rolling Pattern tools you have…

• 1. Finding the Time available for Compaction – MultiCool, measure
• 2. Calculating roller speed 10‐14 ipf (formula, NAPA IS‐120, Apps)
• 3. Length of roller pass (Distance = Speed x Time)
• 4. Different roller trains to consider ‐ echelon, pneumatic breakdown
• 5. Compaction Troubleshooting guide

Asphalt Compaction Troubleshooting

*Is the mix temperature behind the paver hot enough? > 280°F Record the following

• Mix temp behind paver
• Number & type of rollers
• Roller settings (freq/amplitude)
• Pattern (# coverages)
• Air temperature
• Base temperature
• Asphalt lift thickness
• Mix type
• Average percent compaction
• Roller operators’ names

No Yes

Is the mix exhibiting tender behavior under the roller(s)? Verify that the nuke gauge lift thickness setting is less than the actual lift thickness being placed. Verify that the roller settings of amplitude, frequency and speed are correct per test strip. Check with the lab or plant to see if binder content of the mix and/or gradation changes have occurred. Verify the nuke gauge calibration with the mix and lift thickness. If mix is too cool, notify the Job Supervisor immediately. Keep the steel drum rollers OFF the mix until the tender behavior stops or they will tear up the mat. You can use a rubber tire in tender zone without doing any damage. Typically lowest amplitude for lifts less than 2” thick. Higher amplitudes for lifts > 3” thick. If changes have occurred, assess the impact of these changes on compaction. Call the QC Manager if

• necessary. Got your phone list??

*K *Know the the recommende mmended compacti mpaction

• n temperat

eratur ure for for the the mi mix des design bei being us

• used. Kn

Know the the Ti Time Avai ailabl able for for Compacti mpaction.

• n.

Ar Are co comp mpaction goals goals be being ing ac achie hieved?

Are the rollers close to the paver? Yes No Move them into hot zone. No

2/4/2019 49

145

Caterpillar: Confidential Green

• Operators and quality control

personnel must understand factors that affect compaction

• Gather information
• Evaluate information
• Plan the work
• Communicate the plan

Summary

Caterpillar: Confidential Green

Thank You

Session Evaluations/PDH’s

• Complete session feedback in

mobile app, your comments appreciated.

• Professional Development

Hours logged in session feedback.

See you again at:

• CONEXPO‐CON/AGG 2020

– March 10‐14, 2020 – Las Vegas, NV – 140+ education sessions

• World of Asphalt 2021

– March 16‐18, 2021 – Atlanta, GA – 120+ education sessions

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