Best Practices for Smoothness & Density

Best Practices for Smoothness & Density 55 th Annual Paving Conference Presented by Todd Mansell, CAT Paving

Outline 1. Paver Setup Smoothness 2. Balanced Paving Paver & Roller Speed Paver operation 3. Density

Lines of Communication Foreman Superintendent Truck Boss Project Manager

Understanding the Paver Tractor tows screed Accepts mix from trucks, MTV, etc. Feeds mix to screed Screed Floats on the mix Free to rise and fall according to many factors

Paver: 15 Steps to Setup &Take Off Ensures consistent takeoff every time Goal: To have a smooth transverse joint & no mat defects from the start

Step 1: Heat the Screed Prevents sticking

Step 2: Position Tow Point Cylinders Straight line-of-pull

Steps 3 through 6 3. Set paving width 4. Set crown 5. Set extender height 6. Set extender slope

Angle of Attack Angle of attack is the relationship between the nose of the screed & the trailing edge of the screed Nose up attitude Screed reaches equilibrium

Screed Adjustments Tow point fixed Screed pivots around fixed tow point

Angle of Attack Normally 1/8 to 1/4 Angle too high, screed compacting with trailing edge Erratic screed behavior Angle too low increases shear factor and wear

Increase Angle of Attack More material passes under screed Screed rises to new level As screed climbs, angle of attack decreases Re-establish same angle, but at increased depth

Changing Thickness Achieves equilibrium Resumes original angle of attack

Change Over 5 Tow Arm Lengths 65% of change occurs in the first tow arm length 35% of change occurs over 4 tow arm lengths Factor improves smoothness

Step 7: Lower Screed Place starter boards = to desired mat thickness Lower screed onto starting boards in float position Take out the slack

Step 8: Null the Screed Nulling the screed removes all the tension in the screed Use depth screws on each side until no resistance is felt The screed must be free-floating on the mix

Steps 9 through 12 9. Position end gates 10. Set auger height 11. Position feed sensors 12. Set feeder controls (conveyor ratio dial and mix height dial)

Step 13: Fill the Auger Chamber Fill auger chamber with asphalt mix to ½ auger height Use conveyors and augers Do not overfill

Feed Sensors Mechanical or sonic Control level of material Position Sensor 18" from end of augers

Sonic Feed Sensors Sonic Sensor Mounting Distance Mounting position at 18 Working range of sonic sensor 12 32

Step 14: Set Automatic Grade Control Joint Match

Step 14: Set Automatic Grade Control Smooth

Step 14: Averaging Ski for Smoothness Beam Mounted To Paver Averages Surface Variation Over Large Distance Several Types Configuration Varies Depending On Conditions

Contact (drag) Averaging Ski 30 or 40 feet long Outside of paving width For highway projects Used with a contact or sonic sensor Reduces deviations by factor of 8

Steps 15 Pull off starting boards and quickly get to paving speed Check mix feed Check auger speed Check for lines in mat

Controlling Head of Material @ ½ auger Adjust gates/ratio Adjust auger speed Adjust auger height Position of sensors

Review: Paver Setup & Operation Screed is free-floating Proper head of material is ½ auger height Depth cranks are used to change mat thickness and slope 5 tow arm lengths for full change in thickness to take place Changes in paving speed usually requires a change to mix feed settings (conveyors, mix height dial) Increased head of material causes screed to rise up Decreased head of material results in screed dropping Continuous mix feed and paver speed = smoothness!!

Smooth Transverse Joint Straight edge tells the story Too high more rolling may help Too low hand work needed to fill in

Poor Starting Point Rounded face at the joint Plunge cut too deep

Good Starting Point Cut straight starting joint Butt joint flat Tack butt joint Clean area where screed will rest

Measure Height of Starting Joint Calculate thickness of starter boards General rule vibratory screed: ¼ compaction per 1 loose depth Example: Place 2-½ loose to end up with 2 after rolling In this picture, need ½ boards

Transverse Joint Rolling Patterns Breakdown roller starts normal pattern Paver should not have to stop and wait

Transverse Joint Rolling Pattern One Lane Pinches joint at angle rather than pushing hot mix away All stop marks can be cleaned up during first normal rolling pattern

Transverse Joint Rolling Pattern Space Allows Pinch joint from the side Utility size compactor makes job easier Leaves drum edge cut mark perpendicular to direction of rolling pattern

Transverse Joint Rolling Pattern 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

Balancing Paver & Roller Speed = Profile & Density Based on hot plant output and rate of mix delivery to job site Goal = continuous paving

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)

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

Need 7 pieces of information Use Paving Production Calculator or 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

Input 7 pieces of information

Number of Trucks = 20

Paver speed using end dumps Use 75% efficiency for end-dumping Use 100% for MTV 36 fpm

Paver Speed, trucking & plant is balanced

Now, let s look at the rolling pattern 1 x Cat CB64 (84 wide drum) 1 x Cat CB54-XW (79 wide drum) 1 x Cat CW34 (82 compaction width)

Breakdown Intermediate Finish %TMD 90-92% 92-94% 94+ % Temp Coverage 300-260 F 260-200 F 200-160 F 2 2 2 (1 vibe, 1 static) Settings High A, Low F 90 psi Low A, static 120 feet 200 feet 200 feet

Vibratory Steel Drum Breakdown, intermediate and finish rolling Settings for amplitude and frequency Static mode for finish rolling

Amplitude = compactive effort High Amplitude Low Amplitude

Frequency = speed x impacts per foot Low Frequency High Frequency Roller speed is constant

Impacts per foot, Frequency & Roller Speed 10 to 14 Impacts per foot

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%

Amplitude App 0.020 0.029

Test Strips 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

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 1 st Pass Temp 275 250 200 Density 88% 92% 94% (vibe) 2 nd Pass Temp 260 245 193 Density 90% 93% 94% (static) 3 rd Pass Temp 252 230 Density 91% 93.5% 4 th Pass Temp Density

12-Foot Wide Lane: 84 x 2 passes 84 84 Roller A Roller B 6 Overhang 12 Overlap 6 Overhang 12 Wide Mat

Amplitude 0.020-0.029 for CB64

Roller speed using 84 drum Wider drum Lower frequency Higher amplitude 5-Pass pattern 40 fpm 40 fpm > 36 fpm

Establish an effective rolling pattern 1. Based production and density 2. Equipment Selection 3. Balance paver & roller speed 4. Test Strip Decision Point Decision Point 5. Verify during production

How far back?? Breakdown

Length of the Roller Pass Speed = Distance Time Roller speed based on frequency (ipf) Time available for compaction (MultiCool) Solve the equation for distance

Length of the Roller Pass Distance = Speed x Time

Roller Ground Speed Distance = Speed x Time Speed Calculation Frequency = 2,520 vpm We want 10 impacts per foot 2,520 10 = 252 fpm

Time Depends on Temperature 300 260 Breakdown rolling 260 220 Intermediate rolling 240 190 possible tender zone 220 160 Finish rolling 160 Stop rolling Keep steel drums off the mix!!!

MultiCool Website and Android App Google Play App store http://www.eng.auburn.edu/users/timmdav/multicool/finalrelease/main.html

MultiCool from 275 F to 252 F (breakdown roller only) Time 3 minutes

Length of the Roller Pass Roller speed = 252 fpm Time = 3 minutes Distance = Speed x Time = 252 x 3 = 756 ft (in 3 minutes)

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 Pass 1 Pass 2 **If conditions change re-calculate the length of roller pass

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

Top 5: Checklist for Smoothness 1. Set a target paving speed for continuous paving. 2. Make quick stops & starts with paver when end dumping. 3. Consider an MTV for non-stop paving. 4. Maintain constant head of material @ ½ auger height. 5. Position feed sensors for continuous auger movement.

Top 5: Checklist for Density 1. Breakdown roller should cover mat in 3 drum widths or less. 2. Balance breakdown roller speed with paver speed @ 10 ipf. 3. Goal: Breakdown roller achieves 95% of target density. e.g. 0.95 x 94 90% 4. Determine the maximum roller distance behind the paver. Based on cooling rate of the mat from MultiCool or PaveCool 5. Stop the roller at an angle to the mat.

Locking in the joint

Paving Multiple Lifts for Density t:nmas NCAT Report 9-27 (2004) Fine mixes (12.5mm) 3:1 or greater Coarse mixes (19mm) SMA 4:1 or greater 4:1 or greater

Paving Multiple Lifts for Smoothness Generally best results with maximum 2 3 lifts Do NOT use automatic slope control if it can be avoided DO use automatic grade control Joint-match using averaging ski Pave mainline first, then tie-ins (driveways, shoulders, ramps, etc.) Wait until bottom layers have cooled sufficiently @ mid-depth

Joint matching with ski for smoothness

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

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