How Compaction Affects Smoothness

How Compaction Affects Smoothness Transverse Joints Patterns Stops

Joint Compaction -- Team Effort Start with good paving and minimal hand work Mat depth must allow for rate of compaction Rule of thumb: ¼” of compaction for each 1” mat depth

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

What We’re Trying to Avoid Profile Summary -- MN Hwy 65, 9/14/06, start of paving 1.1 miles

Transverse Joint Compaction Whenever possible roll from the side in static mode Pinches joint Rolling straight --drum tends to bump over joint

Transverse Joint Compaction #1 12” Hot Cold Joint

Transverse Joint Compaction #2 #1 30” Hot Cold Joint

Transverse Joint Compaction #3 #2 #1 30” 60” Hot Cold Joint

Transverse Joint Compaction Hot Cold #1 Paver Joint

Transverse Joint Compaction #2 Hot Cold #1 Paver Joint

Transverse Joint Compaction #3 #2 Hot Cold #1 Paver Joint

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

Breakdown Roller Pattern 5-pass pattern Forward adjacent to centerline Back along unconfined edge Forward in center of mat Back adjacent to centerline Medium amplitude 250 fpm

Breakdown Pattern Marks Occasionally left narrow step in the center of the mat Crossover marks resulted from unusual rolling pattern

Intermediate & Finish Roller Operating 15-20 minutes behind breakdown roller Mat temp. + 130 o F Two vibe passes, low amplitude at 237 fpm Three passes static at 264 fpm Barely reaching 92% density spec Compaction process affecting smoothness

Mapping Options [ Optional systems aid operator consistency GPS shows operator machine position and counts passes Screen turns colors as passes are completed Removes guesswork Allows corrective action There are options available for asphalt compactors to help operators maintain uniform rolling patterns. Screens in the operator’s compartment can be programmed to show the operator where the roller is located on the mat and how much of the pattern has been completed. Global positioning systems provide very accurate maps of rolling patterns. The control can be programmed with the required number of passes. Then, the screen will display different colors as the passes are completed. The operator no longer has to guess at the end of a pass for reversing. And, there is less chance that the operator will miss any of the areas in the pattern because the screen provides immediate feedback for corrective action.

Temperature options ] Optional temperature sensors help confirm temperature uniformity Located ahead of front and rear drums Activated by direction of operation Operator checks display to see if machine is in proper zone Infrared temperature sensors are another option for some asphalt compactors. On Caterpillar models, sensors are installed on front and rear drum yokes. The front sensor is activated when the machine is going forward. The rear sensor is activated when the machine is operating in reverse. The sensors are continually cleaned by compressed air that keeps dust, fumes and moisture away from the sensor lenses. The temperature systems are accurate and provide constant, visual reference at the operator’s station display for the compactor operator. Not only does the operator know where the machine is located in relation to the defined rolling pattern, the operator knows where the machine is located relative to the desired temperature zone.

How Pattern Marks Affect Smoothness Paint stripe #01 marked location of breakdown roller crossover mark Mark resulted in higher than normal deviation score

Driveways, Turnouts Breakdown roller maintains straight path Aggressive steering will mark the fresh driving lane mat Intermediate roller – OK Finish roller -best

Bends, Tight Radius Compaction Street project paving 12- feet wide 66” drum width breakdown roller Operator followed radius in continuous pass

Bends, Tight Radius Compaction Outside edge of drum is shoving hot mix Mat distorted and cracked

Bends, Tight Radius Compaction Roller operator trained to roll straight into radius Pattern takes more passes but leaves smooth tight mat

Bends, Tight Radium Compaction Bends or Junctions

Roller Reverse Marks 84-inch drum on 12-foot mat yields small reversing angle Deep mark left by outside drum edge during turn Reversing close to paver on hot, tender mix accentuates mark left by drum edge Marks may not clean up during successive passes

Roller Reverse on Adjacent Cold Mat Paving westbound lane breakdown roller could reverse on cold eastbound mat Less marking on hot mat Profilograph showed less deviation on westbound lane due to fewer roller marks

Roller Reverse on Shoulder 12-foot driving lane and 6- foot shoulder with 18” slough All compactors stop / reverse on shoulder No stop marks in driving lanes Project earned 100% of available ride bonus

What We’re Trying to Avoid Breakdown roller pattern Stops too close together Hard to erase completely with finish rolling

Compaction Issues - Rolling off Edge Never roll off unconfined edge Collapsed edge will create a joint failure Never roll off the edge of an unconfined mat. The edge will collapse under the weight of the drum and cause a problem for the paver crew as the adjacent lane is being paved. There will be uneven compaction and joint failures at points like this. It’s very easy to see that an improper operating technique was used here.

Compactor Stopped during Paver Stop Breakdown roller caught up to paver during stop Parked on mat 100’ behind paver Drums dented mat Six minute roller stop

Thermal Effect of Roller Stop Drums act as heat sink on mat Two cold dents created P2 and P3 150o F Dents will not be removed by next roller passes

Effect of Roller Stop on Smoothness Dents left by drums are easily identified -- two sets of bumps and dips about 8 feet apart 0.18 added to score in 8 feet of paving Proves that finish roller could not clean up these marks

Stopping for Water Always try to find a place to park off the driving lane Shoulders, turn-outs, driveways

Breakdown Roller Stopped for Water Compactor stopped 10 minutes on mat for water Mat cooled to 150 o F under the drums Drums created depression and bump Sometimes this is unavoidable -- right?

Thermal Image of Roller Stop Drums act as heat sink Rapid loss of heat in mat under drums Intermediate and finish passes will not remove bumps

Intersection Tie-ins Note: small roller working on tie-in to intersection

Pick-up on Pneumatic Tires Operate roller at high speed before getting on mat Use approved release agent on tires Most critical when rolling “sticky” mixes with polymer modified oil

Pneumatic Tire Marks Finish roller must be able clean up tire marks Especially problematic in cold weather Be sure tire skirts are in place

Pneumatic Tire Marks What would do when tire pick up is this severe?

How Compaction Affects Smoothness Plan your work to match the application Ask questions if you’re not sure Stop rolling when you see a problem Consult the supervisor or QC person

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[ INCONSISTENT DENSITY ] UNIT 7: COMPACTION ISSUES [ INCONSISTENT DENSITY ] Quality Control verifies: - density behind each phase - communicates results to operators - communicates changes to operators Quality control personnel are responsible for verifying density on the project. They check the density of the asphalt layer after every phase of compaction. Then, they communicate the results to the compactor operators and discuss any changes in the process that are required to improve quality. If density is inconsistent, quality control is responsible for finding reasons for the inconsistency.

[ INCONSISTENT DENSITY ] UNIT 7: COMPACTION ISSUES [ INCONSISTENT DENSITY ] Maintain pattern and working speed Paving crew and initial phase compactor operator communicate All paving speed changes are approved and told to compactor operator Some operators have difficulty repeating the same pattern as they follow the paver. They do not always hit each portion of the mat the same number of times. Therefore, density checks made by the quality control technician will vary. When this happens, the quality control technician or supervisor must work with the compactor operator to define the pattern and make sure that the pattern is being repeated.   Verify that the paving speed has not been changed. Very often changes in paving speed are not communicated to the compaction team and the quality control team. A rolling pattern that has been working well is suddenly causing the compactor to fall behind the paver and to be working in a lower temperature zone, for example. The compactor falls behind because the paving speed has been increased. And, the operator tries to alter his or her rolling pattern to stay close to the paver. Never change paving speed without doing two things. First, communicate the speed change to the compaction team. Second, verify that the initial phase compactor can keep up if the speed is being increased.