Agenda Best Paving Practices

Agenda Best Paving Practices
Team Work Project Planning Segregation Paving Principles Paving by the Numbers Compaction Questions The purpose of this presentation is to help you understand more about common mat defects that may occur on any asphalt paving project. In each section, a methodical approach is taken to troubleshooting mat defects. The first step is to present the symptom, in other words, what the defect looks like by using conventional and infrared images. The next step is to show the cause or causes of the symptom (defect). Finally, there are recommended steps for preventing or eliminating the defect. An experienced, well-trained paving crew knows how to recognize mat defects, knows what causes them, and knows how to prevent them. The learning process is continual because conditions change on every project. But, if the entire crew (plant, trucking, paving and compaction personnel) does the fundamental things correctly and follows the basic principles of asphalt paving, producing a smooth, uniform mat is usually the result. We’ll start by examining a factor is that often overlooked -- understanding grade conditions.

What is Paving Grade (Mills or Base) Plant Oil truck Trucks MTV Paver
Compactors The purpose of this presentation is to help you understand more about common mat defects that may occur on any asphalt paving project. In each section, a methodical approach is taken to troubleshooting mat defects. The first step is to present the symptom, in other words, what the defect looks like by using conventional and infrared images. The next step is to show the cause or causes of the symptom (defect). Finally, there are recommended steps for preventing or eliminating the defect. An experienced, well-trained paving crew knows how to recognize mat defects, knows what causes them, and knows how to prevent them. The learning process is continual because conditions change on every project. But, if the entire crew (plant, trucking, paving and compaction personnel) does the fundamental things correctly and follows the basic principles of asphalt paving, producing a smooth, uniform mat is usually the result. We’ll start by examining a factor is that often overlooked -- understanding grade conditions.

What is The Team Morning Communication Respect each other
Does Not look for the Negative but how to fix it Builds Customers impressions on our Work (taking pride) The purpose of this presentation is to help you understand more about common mat defects that may occur on any asphalt paving project. In each section, a methodical approach is taken to troubleshooting mat defects. The first step is to present the symptom, in other words, what the defect looks like by using conventional and infrared images. The next step is to show the cause or causes of the symptom (defect). Finally, there are recommended steps for preventing or eliminating the defect. An experienced, well-trained paving crew knows how to recognize mat defects, knows what causes them, and knows how to prevent them. The learning process is continual because conditions change on every project. But, if the entire crew (plant, trucking, paving and compaction personnel) does the fundamental things correctly and follows the basic principles of asphalt paving, producing a smooth, uniform mat is usually the result. We’ll start by examining a factor is that often overlooked -- understanding grade conditions.

Project Planning Asphalt tonnage Paving width Specifications
Grade Conditions

Project Planning Asphalt Tonnage Hot plant output Length of haul
Traffic conditions Number of trucks

Project Planning Paving Width Screed extensions Auger extensions
Material retaining plates

Project Planning Specifications Sensors Levelers Mounting hardware
Position of sensors

Understanding the Paver
Keep the paver in good condition Scheduled inspection & maintenance Follow maintenance guidelines

SEGREGATION Material production Segregation in aggregate stockpiles
Coarser , drier gradings Stockpile segregation more common today Segregation of mineral aggregate in stockpiles is more common in today’s operation because of the type of crushing operation used. Today’s materials are of a broader range. They have coarser, drier gradings than older dense gradings, and require careful handling because of a lack of cohesion from a slight moisture content.

SEGREGATION HMA plant Found in bins if not kept full
If not loading trucks correctly Loading cold bins requires conscientiousness Material placed in cold bins by a loader naturally forms a conical shape, and coarse aggregates can separate at this point by rolling down the conical sides. As the material feeds into the cold feed belt, reverse coning, in which coarse material falls to the middle of the bin, can take place. The best way to prevent this is to keep the bins as full and level as possible. Hot bins are prone to segregate Batch plant hot bins are prone to segregate by the screening process of the mineral aggregate. Screening action forces coarser aggregate to the far side of the bin, and creates a pronounced pattern from fine to coarse at the inlet screen. This pattern results from two possible factors — the screen system override, and the material’s taking the side-cone shape from the screening action. Coarser particles migrate to the far side of the bin. Clam type bin gates prevent problems Several gate models are in use on surge and silo bins. They vary from rectangular to round, and can include plates and baffles. Gates are a common spot at which segregation occurs. Most agency specs require clam or other type of gate openings that will not cause segregation. They open both transversely or longitudinally to the truckbed. Type of gate opening may be secondary to segregation in the configuration of the silo.

SEGREGATION As the truck is picked up by the paver the tail gate is released and bed raised. Raise the bed high enough while emptying the truck to prevent material being dribbled into the hopper Maintaining a consistent paver speed is important in the operation of the paver, as the material feed system is set and affected by paver speed.

Segregation MTV or Single drops
Material dropped from a height forms conical pile Large aggregates separate and roll to sides of pile Segregation Single drop in the truck Hopper inserts When asphalt is discharged continuously from a considerable height into any container (like a truck bed), it forms a conical pile. The larger aggregates in the mix tend to roll faster and farther down the sides of the pile than the smaller aggregates and fines. The large aggregates will accumulate in pockets at the sides, the front and the back of the container. When the container is dumped, these pockets of large aggregate will show up as segregation patches.

SEGREGATION Trouble-shooting Begin/end of load segregation
Tends to have a spaced out pattern

SEGREGATION Cause: Material segregated in truck
Running conveyor deck dry. Cycling hopper wings too soon .

Dumping Load in front of 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 If the haul unit cannot maintain contact with the paver’s push rollers, the load may be dumped on the grade in front of the paver. In this situation, the only solution is use a loader or skid steer to clean up all the mix. Don’t just clear a path for the paver tires or tracks. If a big pile is left, the screed will react by rising in response to the excessive head of material in front of it. The truck driver must apply light brake pressure in some situations to prevent rolling away and dumping the load on the grade. Or, for some applications, use a paver with a truck hitch to maintain a positive connection between the truck and paver.

New MTV for Asphalt Paving

Material Dumped on Grade
Large volume dump in front of Paver Compacted pile thicker than mat Screed rides up on compacted pile Sometimes the amount of material dumped or spilled out of a hauling unit in front of the paver can be quite large and the compacted piles are definitely thicker than the mat being laid by the paver. When this happens, the screed will ride up over the compacted pile.

What happens ? Rising screed creates a bump Aggregates dragged Open texture Cold Compacted Material Screed Will Rise As the screed passes over these areas, it hits the compacted material and will rise to create a bump. Also, aggregates will be dragged by the screed because the mat is so thin. The mat in this area will show extremely open texture and pulling of materials.

Mat Defects Oversized material causes bumps Will screed be effected ?

Mat Defects Know grade conditions
High points can cause screed to break aggregates Look at Crown in road

Mat shows open texture Thermal image shows cold spot Uneven compaction and poor ride Trucks never clean out in front of paver The area of the mat inside the circle shows that aggregates have been dragged by screed as it passed over the large volume of compacted material. The cold spot in the thermal image mirrors the open textured area of the mat. During the compaction process, the large cold spot will not compact at the same rate as the adjacent hotter area. A portion of the mat will have high air voids and low density. This type defect is preventable. Trucks should never be allowed to clean out in front of the paver. They should be directed to some area off the grade to be paved.

Understanding the Paver
Factors Affecting the Screed Paving speed Head of material Screed adjustments Mix design Mix temperature Air temperature Grade temperature

Factors Affecting Screed
Constant Speed Shear factor is constant Depth remains constant

Paver Stopped Mix cools during stops Mix cools at varying rates
Leads to variations in density and smoothness 4 different temperatures Cooling Material Cooler Material Hotter Material Rolled Material When the paver is stopped for long periods, the mat begins to cool and mix in the paver begins to lose heat, also. Mix in the hopper and mix in front of the screed is cooling off. The mat under the screed is covered so it doesn’t lose much heat. The mat directly behind the screed starts to cool immediately and this area can’t be reached by the compactor. Depending on how long the paver is stopped, distinct temperature zones are created in mat. These variations in temperature can lead to variations in compaction and loss of smoothness.

Paver Stopped -- Variable Temperature
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 When the paver resumes paving after a prolonged stop, the place where the paver stopped may not be visible. The mat shown on the right has a lot of large aggregates so it supported the weight of the screed without leaving dents in the mat surface. (The paint stripe indicates where the screed was when the paver stopped.) A fine mix may show the screed imprint. The image produced by an infrared camera does show exactly where the paver stopped. In this example, the paver was stopped six minutes. The outline of the screed is clear -- that’s hotter mix that was shielded by the screed plate. Cooler mix behind the screed was exposed to the air and began to lose heat. The compaction rate will be different in the different temperature zones.

Screed Adjustments Screed counterbalance set correctly when settlement mark is eliminated in one roller pass Mark Is Gone Normal Settling Marks

Screed Adjustments After Rolling Before Rolling Settling is excessive when mark remains after roller pass Adjust counterbalance pressure by 25 psi

High Speed -- Segregation Stripes
Speed increased 50% because trucks stacked up Auger speed at rpm because of increased demand Large aggregates segregated - visible stripes No temperature variation In this example, the paving speed was increased by 50% -- from 40 fpm to 60 fpm. The operator increased the speed because there were a number of haul units in front of the paver. The paving width was 15’ and the paving depth was 3”. As the paving speed increased, the feeder system also began to run faster. With the augers turning rpm, the large aggregate in the mix began to segregate and stripes were visible behind the chain case box and the auger support bearings. Mat quality was adversely affected by varying the paving speed. The segregation stripes did not cause significant temperature variation in this example, but that may occur, too.

Low Speed -- Patch Segregation
Reducing speed makes feeder system run on/off Mix does not move in a uniform manner Patch segregation where augers stop Also cool spot in mat When the paving speed is reduced, the feeder system will be affected in the opposite manner. At low paving speed, the feeder system tends to run on/off, unless it is adjusted immediately. The head of material in front of the screed is not moving in a uniform manner and patch segregation can occur. In this example, the left auger is running erratically and patch segregation is evident in the left side of the mat. The thermal image does reveal a cool spot where the patch segregation shows in the mat.

Controlling head of material Paving speed Flow gate/feeder ratio setting Feed sensor

Paving Speed Paving speed constant Feeder system set to match paving speed Changes in paving speed may require feeder system adjustments

Flow Gates Set Properly Material level at center of auger chamber at half level Material level in center area controls auger speed

Feeder Ratio Set Properly Same principle as flow gates Adjust material level in center to half auger

Material Height Dial Controls feed sensor on/off Maintain material level at ends of augers

Sonic Sensor Alignment The sensor should be targeted perpendicular to the material face

Auger Speed Auger speed uniform 20-40 rpm Auger speed too high or too low can cause stripes in the mat

Auger Speed Low -- Stripes
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 If the augers are running ON/OFF or are running at very low speeds, mix will not move across the face of the screed in a uniform manner. Larger aggregates in the mix will tend to segregate in the “dead” areas under the chain case and outer bearing supports. The head of material in front of the extensions is another area where segregation stripes can occur when the auger speed is too low. Some mixes may not show visible striping when the auger speed is low. But, a thermal image can reveal low temperature areas that indicate mix moving in a non-uniform manner. To increase auger speed, decrease the amount of mix coming off the conveyors. Adjust flow gates or ratio control dials depending on the type of paver being used.

Auger Speed High -- Stripes
Causes segregation stripes at outer edges May see centerline stripe Open texture loses heat faster Reduce auger speed by increasing flow off conveyors When the auger speed is too high, you may stripes in several places especially if the mix has large aggregates. It is common to see segregation stripes at the outer edges of the mat as the high speed augers tend to cast the large stones to the area in front of the extensions. You may also see a centerline stripe. The thermal image confirms the open texture that loses heat faster. To reduce auger speed, increase the flow of material coming off the conveyor.

Variable Width Paving Requires control & judgment May require manual over-ride

Head of Material -- too low
Head of material low in front of extension Open texture due to decreased mat thickness Variations in density and smoothness Hard to match curbs and adjacent mat In this example, the head of material is too low in the area in front of the left screed extension and there is a visible texture difference in the mat. The texture is more open because the mat thickness has decreased in the affected area. The larger aggregates in the mix are close to the surface and are being pulled by the screed. When compacted, the area behind the left screed extension may show variations in density. Smoothness will be affected. And, the crew will probably have a hard time trying to match curbs or longitudinal mat joints.

Head of Material -- too high
Gross overfill causes large hump in the mat May need to shovel out Can be caused by improper sensor position or calibration When the auger chamber is grossly overfilled, a large hump will be created in the mat. It may be necessary to shovel out some of the mix to reduce the level and minimize the mat defect. This condition can also be caused by a feeder sensor being improperly positioned or improperly calibrated.

Adjustable Augers Adjustable height augers help mat texture Help prevent segregation

Auger Height -- too low Texture stripes appear directly behind the augers Especially common when mix has large aggregates Raise augers until mat is tight and uniform When the auger height is too low, it is common to see two texture stripes in the mat directly behind the right and left augers. This is particularly true when paving with a base course mix that usually has large aggregates. As the augers are turning, large aggregates may be left near the surface of the mat if the augers are too low. These texture stripes are not always seen as cold stripes in a thermal image. To tighten up the mat surface, raise the augers in small increments until the surface of the mat is tight and uniform in appearance.

Auger Height -- too high
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 When the auger height is too high, the head of material will also be too high and the screed will ride up. To counter the forces which lift the screed, the angle of attack is usually decreased so the screed runs nose down or flat. As a result, the texture of the mat will generally be open across the entire width of the mat. The screed will be harder to control in this condition and mat smoothness will suffer. You may also see large temperature differentials across the mat. Lower the augers and correct the screed angle of attack until the mat texture is tight and uniform.

Controlling Yield Do not correct based on one measurement
Make series of measurements Average measurements Correct based on average Improves ride ability & yield

Screed Adjustments Screed Reaction Time
Screed reacts to change in angle of attack over 5 tow arm lengths 65% of change occurs in the first tow arm length 35% of change occurs in the last 4 tow arm lengths Factor improves ride ability

Joint Construction Setting Up: Paving By The Numbers Heat screed
Center tow points Set paving width Adjust crown , height & slope on screed

Joint take offs . Lower screed onto starter boards Pull slack out
Null out screed Set end gates Adjust auger height Adjust feeder sensors . One of the most important fundamentals of smooth paving is maintaining a consistent paving speed. Normally, you can set up the paver to pave smoothly at any speed that matches the delivery of mix to the job site. The important thing is to keep the speed constant. If the paving speed is changed drastically, the screed will either rise or fall and mat smoothness will suffer. Also, if paving speed changes, the demands on the feeder system change. So the feeder system controls will have to be adjusted to match the new material demands. For quality paving results, always follow the basic fundamentals of paver set-up and keep the operation consistent.

Joint take offs . Feeder mix height, or gates Manual feed augers 1/2
Turn on Auto mode Set Paver speed for the day (based on tonnage delivered to job) . One of the most important fundamentals of smooth paving is maintaining a consistent paving speed. Normally, you can set up the paver to pave smoothly at any speed that matches the delivery of mix to the job site. The important thing is to keep the speed constant. If the paving speed is changed drastically, the screed will either rise or fall and mat smoothness will suffer. Also, if paving speed changes, the demands on the feeder system change. So the feeder system controls will have to be adjusted to match the new material demands. For quality paving results, always follow the basic fundamentals of paver set-up and keep the operation consistent.

Cold Screed What happens: Mix sticks to cold screed plates
Screed drops Scuffed texture Heat screed before starting to pave If paving begins before the screed or a portion of the screed has been heated to a temperature close to the temperature of the mix, mix will stick to the bottom of the screed plate. In the example shown, one screed heater is not working and a portion of the screed is cold. The cold screed will push material in front of it instead of sliding over the mat surface. The screed will drop and will produce a scuffed texture. The screed plate will warm up as it is exposed to the hot mix, but the mat will be substandard while the screed is cold. The proper procedure is to have the screed heated sufficiently before beginning to pave.

Joint Construction What Happened Here?

Joint Construction Quality joints are no accident
Proper joints takes practice Team work

Influences on Asphalt Compaction
Many factors, not controlled by operator, influence compaction Mix design Road design Mix temperature Climatic conditions Know how to respond to these factors The factors that influence asphalt compaction can be grouped into four main categories: Mix design Road design Mix temperature, and Ambient temperature, moisture and wind The compactor operator can’t control these factors. But, it’s important that the operator have information about these factors because he or she must consider them when developing the compaction techniques needed for each unique project.

Setting up the Compaction Train
Equipment and techniques vary on each project Break down Intermediate Finish (Pneumatic?) Phases of compaction are usually the same Any time we lay down hot mix asphalt, we must compact it – no matter what type of structure is being paved. The equipment and compaction techniques vary somewhat depending on the project. How we set up to compact a highway project is different from what we do on city streets or county roads or parking lots. But whether the paving and compaction occurs on an interstate or on a low volume road – whether it’s new construction or rehabilitation, the phases in the compaction process are normally the same.

Test Strip How many do this ?
Test strip sets rolling pattern Verifies that target density can be achieved Straight run part of project Nuclear density gauge checks progress while mat is still hot The test strip verifies that the equipment and rolling pattern achieves the target density set for each phase of compaction. A test strip can be a separate element or part of the paving project. Nuclear density gauges provide a quick means of checking density progress while the mat is still hot enough to make changes in the rolling pattern on the test strip. The mat surface temperature is also checked frequently on the test strip. The test strip should be a straight run and of sufficient length to permit the compactor to reach normal working speed. Always use the equipment planned for the job and the rolling pattern you plan to use.

Balanced Compactor Vibration
Forces transmitted evenly when in balance Mat accepts vibratory forces (Amplitude) Compaction maximized Smooth machine operation Let’s think of it this way. When everything is in balance – amplitude, frequency and drum weight, then impact and vibration forces are transmitted into the mat smoothly. Everything is working together close to what is called system resonance. That’s the natural frequency of the machine and the material. In this condition, most of the vibratory force is transmitted into the mat. The actual transmitted compactive force is optimized and machine operation is smooth.

Compaction Issues – Impact Marks
Amplitude too high Vibrating cool mat - roll closer to the paver Finish rolling too cool- move closer to intermediate roller Finish roller too light Impact marks are different from the appearance of fractured aggregate, but can be caused by some of the same operating techniques. Compacting with too high an amplitude can create marks that cannot be smoothed out by the finish roller. If marks do not roll out, reduce the amplitude of the breakdown roller or operate in the static mode. If impact marks occur when the mat is cooling, move the zone of finish rolling closer to the paver to take advantage of higher mat temperature. Remember, as the mat cools and the asphalt cement gets stiff, it is very hard to get any movement of cement or aggregates. Finally, if the roller is not heavy enough to remove marks left by the previous rollers, switch to a heavier finish roller.

Compaction Issues Drum straddling the joint Vibrating on cool mat
(Fractured rocks) Maybe need to consider rolling joint in “Static” mode Keeping most of drum on Hot mat Fractured rocks)Another challenge is prevention of fractured aggregates in the mat. Fractured aggregate shows up as un-coated rock surfaces in the mat. In the example seen here, there are lots of fractured aggregates along the longitudinal joint. This was caused by operating the vibratory compactor with the drums straddling the joint. Too much of the load was concentrated on a small area of the mat. The solution is to roll in the static mode with most of the drum on the hot mat and just a small overlap on the cold side. Other possible causes of fractured aggregate are: -- operating at too high an amplitude, -- using a roller that is too heavy, or -- vibrating when the mat is too cool.

Compaction Issues – Tire Marks
Pneumatic roller in breakdown position on thick, hot lift Ballast or tire pressure too high Tires too narrow Rolling too hot Finish rolling too cool Tire marks are one of the easiest mat defects to identify, but it may be difficult to pinpoint the cause of the marks. In general, the use of a pneumatic roller in the breakdown or intermediate position on a thick lift of high temperature mix will cause deep tire marks. The marking is accentuated by heavy ballast or high tire pressure and narrow tires. If finish compaction with a static steel drum compactor is completed while the mix is sufficiently hot, the tire marks will probably be smoothed out. However, if finish rolling is done when the mat has cooled significantly, the marks will not clean up. To minimize marking, make sure that pneumatic rollers are used in the correct position in the compaction train. If deep marks occur, discontinue pneumatic compaction and substitute a smooth drum roller or wait until the mat is cooler.

Compaction Issues - Tire Pick-up
Non-stick emulsions and soap solutions help prevent pick-up Hand-held sprayers or on-board water spray Apply to clean tires before rolling begins Discontinue after tires heat up Re-apply if tires cool There are a variety of non-stick emulsions. Some are applied to the tires’ surfaces with hand-held sprayers. Other types of non-stick agents may be mixed with water in the machine’s on-board water spray system. These emulsions coat the tires and form a barrier between the tire surface and the hot asphalt. It is important to apply any non-stick agent to the tires before moving onto the hot asphalt. The tire surfaces must be clean and completely coated or the hot mix will begin to stick to uncoated spots. Once the tires become hot from contact with the asphalt, you can stop spraying the non-stick emulsion. But, remember to keep the tires hot or you may have to re-start the spray system.

Compaction Issues - Dry Drum
Dry drums pick up hot mix Practice proper spray system maintenance --use clean water -- change filters -- check spray nozzles -- check distribution mats Hot asphalt will also stick to a steel drum if the surface of the drum is dry. All steel drum asphalt compactors have drum water spray systems that must be kept in good working condition. Here are some tips for drum spray system operation and maintenance. Fill the spray system tanks with clean water. Contaminants in the water supply can plug spray nozzles and create uneven water distribution on drums. Change spray system filters on schedule. Clogged filters restrict water flow and can cause problems, especially on hot, windy days. Make sure the filter screens in the tank fill necks are clean and in good condition. Don’t discard these filters. They help to keep large contaminants out of the tanks. Check that spray nozzles are aimed properly so there is uniform coverage across the drum surfaces. Make sure that water distribution mats are in good condition and in contact with drum surfaces. Their function is to spread the water evenly. It is certain that asphalt sticking to the drum or tires will interfere with mat smoothness. There are other smoothness issues you need to watch out for, too.

Compaction Issues - Stopped on Mat
Never park a roller on a hot mat Deep mark won’t roll out Park back on compacted mat or on shoulder if possible Never park a compactor, pneumatic or steel drum, on the hot mat directly behind the paver. If the asphalt cement in the mat is still warm enough to allow aggregate movement, the weight of a stationary compactor will dent the mat and you’ll probably have a mark that won’t roll out. And, of course, don’t stop the compactor while straddling an unconfined edge. Stop compactors far enough behind the paver on the portion of the mat that is cool and compacted sufficiently to support the compactor with deforming. You may have to roll off the mat to an adjacent lane or shoulder if you’re stopping for a long time.

Compaction Issues - Stopped Straight
Straight stop creates bulge Bulge may not roll out Will it create deficiencies ? Stop at degree angle Turn toward center of mat Stopping a compactor to reverse direction also requires care. First, don’t stop straight as you see in this view. The straight stop causes a bulge in the mat which may not roll out during subsequent passes. Come to a slow stop while turning in an arc that produces a stopping mark that is at a 30 to 45 degree angle. Stopping at an angle makes it easier to roll out the mark left by the drum on the next series of passes. It is also a good practice to develop a rolling pattern with angled stops made toward the center of the hot mat – not crossing the longitudinal joint onto an adjacent lane or shoulder. Rolling across an uneven joint, like the one shown here, can cause a bump that will show up on the profilograph.

Compacting Test strip Has Density ever been met.
Operator experience at each position. Compactor sequence is different for the wear course. It is preferable to use a double drum vibratory unit for breakdown of harsh mixes. A heavy pneumatic in the breakdown position may leave marks in the mat that cannot be removed. Use the pneumatic in the intermediate position to complete compaction with minimum risk of tire marks. Again, finish the mat with a double drum in the static mode.

Best/Worst Paving Practices
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Agenda Best Paving Practices

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