Fundamentals of Paving Smoothness

Transcription

1 Paving Smoothness Overview Fundamentals of Paving Smoothness Ty Huls Smoothness Measurements Smoothness on the Job Site Smoothness at the Paver Smoothness at the Rollers Continuous Paving Job Site Example California Profilograph Smoothness Measurements No claim is made that the roughness or riding quality of a pavement is directly or completely reflected by the profile index. It should again be emphasized that strictly speaking, the devices reported herein do not furnish a direct index to riding qualities. Francis N. Hveem, 1960 (designer of the California Profilograph) 40 years later... Why doesn t the Profilograph reflect the Riding Comfort of a roadway? 1

2 Measuring Bumps & Dips Bump Bump Dip International Roughness Index (IRI) Network Level Testing The IRI was proposed by The World Bank as a standard roughness statistic. The IRI is reproducible, portable, and stable with time. The IRI simulates a standard vehicle with a perfect road meter. The IRI describes profile roughness that causes vehicle vibrations. New Pathway Services Digital Inspection Vehicle How Much Can We Improve? Overview of Improvement Direction Eastbound Westbound 1 st Lift Avg inches 56.1 inches 2 nd Lift Avg inches 35.6 inches Improvement 42% 37% Smoothness On The Job Site 2

3 Material Dumped on Grade Material Dumped on Grade High spots caused by mix dumped on grade Trucks clean out pulling away from paver Direct trucks away from paver to clean out Mat may not show any visual defect from small pile of mix Thermal image shows cold pile spread by screed Uneven compaction results Maybe a bump High Spot in Grade Smoothness High points cause thin mats High Point Material Thickness Less Than 1 1/2 Times Aggregate Size Ratio of mat thickness/aggregate size too low Open texture Non-uniform density Bumps High point in grade material too thin Low Spot in Grade Trucking Material thickness too great Compacts as a dip Compacts as a low density area May not show up visually Thermal image shows hot spot Low Point Material Thickness Greater Than Surrounding Areas Mat defects can be caused by paver and truck interface Training is key to preventing mat defects related to trucking 3

4 Dumping Load in Front of Paver Truck Alignment with Paver Truck rolls away from paver -- dumps load Clean up the entire pile Leaving big pile causes screed to rise Truck must apply light brake pressure Use truck hitch Misaligned truck causes steering problems Affects paver operation and smoothness Have ground man help trucks line up with paver Truck Bumping the Paver Preventing Defects - Trucking Common problem -- truck backs into paver Screed marks mat severely Often can t be cleaned up -- bump Truck always stops short of paver - never back into paver Use truck hitch to maintain paver/truck contact Driver applies light brake pressure to maintain paver contact Align trucks in center of hopper Keep bed raised when dumping -- never dribble mix into hopper Fill Auger Chamber Smoothness at the Paver Manually auger material across screed face Alternately use conveyor then auger to establish 1/2 level Do not overfill 4

5 Head of Material Correct head of material is 1/2 auger Head of Material - Too Low Proper head of material covers one half the auger shaft Low level causes screed to drop Often happens during truck exchanges Head of Material - Too High Forces acting on screed increase Screed rises Often results from use of feeder system manual overrides Consistent Paving Speed Fundamental aspect of smooth paving Keep paving speed constant Speed changes cause bumps or dips Adjust feeder system if speed must be changed. Constant Paving Speed Paving Speed Too Fast FPM Minutes Time Spent at Same Speed Time Stopped Time Accelerating & Decelerating Take each truck at same speed Use mix production in orderly fashion Target 75% paver efficiency FPM Minutes Time Spent Accelerating & Time Spent at Same Decelerating Increased Speed Decreased Time Spent Stopped Increased Speed surpasses plant / trucking capabilities Prolonged stops Inefficient paving Accelerating and decelerating too long 5

6 Erratic Paving Speeds Acceleration to High Paving Speed FPM Minutes Time Spent Accelerating & Decelerating Varying Time Spent at Same Speed Varying Time Spent Stopped Increased Operator varies speed to match availability of trucks Variable mat temperature Variable mat texture Feeder System Changing Decrease in Depth Long acceleration time starves auger chamber Screed drops Loss of smoothness Deceleration from High Paving Speed Paver Stopped Feeder System Changing Increase in Depth Long deceleration time overloads auger chamber Screed climbs Loss of smoothness Cooling Material Hotter Material Cooler Material Rolled Material Mix cools during stops Mix cools at varying rates Leads to variations in density and smoothness Paver Stopped Improving Smoothness - Feeder System Screed may dent mat during prolonged stops Mat covered by screed stays hot Mat behind screed cools faster Compaction rate affected by variation in temperature Feeder system has major impact on mat quality Deliver material in a uniform manner Consistency and fundamentals are the keys 6

7 Auger Height - Starting Adjustment Auger Height - Too Low 51 mm (2") Auger height affects head of material and mat texture 51 mm (2 ) above mat is normal position Check auger height at the start of each shift Texture stripes appear directly behind the augers Especially common when mix has large aggregates Raise augers until mat is tight and uniform Auger Height - Too High Check Auger Speed Head of material too high -- screed rises Angle of attack decreased so screed runs flat Open texture across entire mat Lower augers and correct angle of attack Check auger speed Keep auger speed in 20 to 40 RPM range Avoid ON / OFF operation Auger Speed Correct Auger Speed Low - Stripes Point Temp Point Temp P1 313 F P6 312 F P2 319 F P3 313 F P4 315 F P5 312 F Auger speed affects mat texture, segregation and temperature Target rpm Conveyor flow, sensor position and sensitivity affect auger speed Make adjustments when paving speed changes Mix moves in non-uniform manner Mix rolls under chain case and bearing supports May see segregation stripes or temperature stripes Increase auger speed by reducing conveyor flow 7

8 Auger Speed High - Stripes Smoothness at the Rollers Causes segregation stripes at outer edges May see centerline stripe Open texture loses heat faster Reduce auger speed by increasing flow off conveyors Roller Stop / Reverse on Shoulder 3 x 84 steel drum compactors 72 shoulder plus 21 slough All stop / reverse marks on the shoulder All roller marks on driving lane parallel to line of paving No dents to clean up Pattern used when centerline had unconfined edge Roller Stop / Reverse on Cold Side Conventional pattern used when paving match lift All roller stops / reverses on cold side Can be done when cold side does not have heavy traffic What We re Trying to Avoid Breakdown roller pattern on base lift Stops too close together Hard to erase completely with finish rolling Water Stops Always off Driving Lane Stop on the shoulder Stop on turnouts Anywhere but on the diving lane Make sure truck has long hose 8

9 Continuous Paving Continuous Paving Use of loading or transfer machine goals: To stabilize a paving operation so the paver can maintain a constant unchanging paving speed, eliminating the stops and starts traditionally associated with trucks dumping directly into the paver. Continuous Paving - Trucking Continuous Paving 3 Batch Method to load truck 1.Drop first batch in front of truck bed. 2.Drop second batch in tail of truck bed. 3.Drop third batch in center of bed. Trucking: Number of trucks Truck beds Tarps Haul route Release agent Truck height Communication Hitches Trucker experience Segregation Uniform, uninterrupted flow of material through the paver Constant head of material Consistent paving speed Allows operator to set feeder system to flow at a constant rate Keep Insert Full Continuous Paving Empty Insert Keep hopper or insert at least 2/3 full Less drop height minimizes segregation Emptying insert may create random segregation Match paver speed to mix delivery Don t pave out mix in insert Tendency to empty insert at end of pass or at bridge approach Expect segregation / smoothness patches if insert or MTV is emptied 9

10 ND Hwy 12, Project NH Smoothness Job Site Example Widening to 18 Blended, stabilized sub-base 24.5 lane miles Paving completed September - October 2005 Cross Section Hwy 12 Plan Inspection Found worn Screed Plates Worn screed plates replaced Screed adjusted to assure proper float following published Caterpillar procedures All screed gauges calibrated Continuous Paving at Constant Speed Transfer device separates truck from paver Paving speed calculated based on 450 TPH from plant; 18.5-foot* paving width; 3-inch paving depth Paving speed: 30 fpm * 6 width for slough Previous Averaging - Traveling Stringline Traveling Stringline was normal reference Reduce grade deviations by a factor of two Simple to use, less maintenance Good for projects with no smoothness spec 10

11 Averaging Ski - Centerline Side 40-foot, multi-foot ski Installed new springs to improve float Reference outside paving width Center of ski in line with tow point Reduce grade deviations by a factor of eight Fore and Aft Leveler - Shoulder Side 10-foot, articulated ski in front of screed Stringline over the screed Aft beam rides on mat Reference inside the paving width Correct profile built in base lift Replaces slope control Grade Sensor at Tow Point Mounting hardware moved to tow arm Sensor positioned just behind tow point Provides slow screed reaction Corrections occur over a long distance Smoothness enhanced First Lift Paving - 18 Wide 2-foot, bolt-on screed extension on each side 4-foot auger extension on shoulder side with bearing hanger 4-foot mainframe extension Sonic feeder sensor installed on end gate First Lift Paving - Great Looking Mat Uniform screed pressure provided uniform texture Screed extremely stable Automation not reacting to unstable screed riding on trailing edge of plates Even screed plate wear at end of project Driving Lane - Checking Slope Sub-base slope was 2% Slope sensor controlled slope on right side Very few corrections needed by slope system Slope on driving lane maintained at 2% Grade sensor reading averaging ski controlled mat thickness on left side Mat thickness consistent at 2 7/8 across driving lane 11

12 Shoulder Paving - Screed Lost Float Right extension sloped to 4% on 6 shoulder Sub-base slope varied on shoulder Caused low yield on base lift Caused higher than normal IRI scores Caused feeder system issues Shoulder - Feeder System Ran Erratically Variable mat thickness over shoulder due to variable grade Very difficult to maintain head of material and auger speed Repositioned sensor to read head of material close to end of auger shaft Variations in head of material cause screed to ride up and down Shoulder - Slope Affected Windrow Management Variations in mat depth cause variations in demand for mix through the paver Stops to adjust windrow volume Stops to add mix to hopper Bad for efficiency and for smoothness Lift Paving - Slough Box Same 18-foot width setup plus 21 slough box on shoulder side Base lift provided proper profile Feeder system ran consistently Lift Paving - Great Looking Mat! Uniform texture Uniform temperature 2% slope driving lane 4% slope shoulder 3 depth to make up for low yield on base lift Constant Speed Yields Uniform Temps Mat surface temperature consistently within 15 degrees F edge to edge Core temperature between degrees F Good temperature control for breakdown compactor P1 239 o F P2 235 o F P3 239 o F P4 237 o F P5 229 o F 12

13 Other Issues - Joint Construction Cut back to a good surface -- flat with correct profile Follow Paving by the Numbers Use starter boards of correct thickness and length Other Issues - Mix Samples Pull mix samples from shoulder -- not driving lane Hand work needed to fill in holes -- always seen on IRI score All samples pulled from shoulder top lift Hwy 12 Good communication with QC personnel Other Issues - Oversize Material Occasional appearance of oversize in the mat More handwork Dust balls from the drum mixer -- asphalt plant maintenance item Other Issues - Traffic Control Some intersections and business access on Hwy 12 Mostly left unprotected Some traffic crossed mat before compaction completed Tires marks dented the mat and seen on IRI scores Need to plan for traffic control at intersections The Crew - Committed to Quality Great communication between managers, crew members and quality control Willing to try new techniques Able to adopt successful techniques into the daily routine IRI Scores East Bound Lane Lot No. Average IRI Incentive Incentive Category $42, % 13

14 IRI Scores West Bound Lane Lot No. 1 Average IRI 36.7 Incentive Incentive Category Questions? Smoothness Study $42, % Problems with Skis 14