Asphalt is made up of heated asphalt cement or binder, mineral filler (limestone dust, Portland cement, etc), and aggregate.  The fundamental concept of a pavement section is a suitable subgrade, a compacted aggregate base, an asphalt base course (if required), an intermediate course, and a surface course. Asphalt base, intermediate, and surface courses have reduced aggregate gradation sizes respectively driven by the need to provide a proper successive foundation for traffic loading. Base courses are rough but strong in nature, intermediate (or leveling) course provides the needed improvement in localized peaks and valleys, and surface course provides the final smooth substrate for traffic.

Asphalt mixes are commonly grouped in three traffic ‘types’, heavy, medium, and light which are driven by many factors, aggregate gradation and asphalt binder content being the more significant. “Fine” particle content (75 micrometers to 4.5 millimeters) makes up a relatively small portion of asphalt mixtures, typically 30% or less of the total aggregate content.

Asphalt binder is a viscous hydrocarbon produced by residue produced by the petroleum distillation process. Binder content commonly makes up 25-30% of asphalt mix cost, depending on the mix. The most commonly used grading system today is the ‘Superpave’ ‘performance grade’ system which utilizes a temperature range, supported by laboratory performance testing. Example: 64-22, where 64 degree fahrenheit represents the average 7-day max pavement temperature, and -22 makes up the expected minimum pavement temperature anticipated. Also, asphalt cement binder ‘polymer’ modifiers have become popular in the last 10-20 years as they can increase overall performance of the mix over time in relation to the added cost. Asphalt binder is also graded by some in viscosity, most commonly represented at AC-10, AC-20, AC-30, AR-4000.

Surface lifts of asphalt typically have aggregate particles ranging up to just under 1/2″ and +/- 3/8″ (medium and light duty). Asphalt binder content for surface lifts is commonly between 5-10% of the mix volume.’Virgin’ asphalt binder content is commonly required in asphalt surface courses (except heavy duty types) at a minimum of 5% of the total mix volume. RAP (Recycled Asphalt product) is typically permitted in new surface course asphalt mixes in the amount of 10% (heavy duty mix) or 20% (light or medium duty mix).

Intermediate lifts of asphalt typically have aggregate particles ranging up to just under 1-1/2″ and 1″ (medium and light duty) with binder content ranges of 4-9%. Virgin asphalt binder is commonly required in intermediate course asphalt mixes at a minimum of 3% of the total mix volume. RAP (Recycled Asphalt product) is typically permitted in new intermediate course asphalt mixes in the amount of 35% of the total mix volume. Most engineers will not allow intermediate lifts of asphalt to be placed in excess of 3″ at a time.

Base lifts of asphalt typically have aggregate particles ranging up to just under 2″ with binder content ranges of 2-6% of the total mix volume. Virgin asphalt binder is commonly required in base course asphalt mixes at a minimum of 1-2% of the total mix volume. RAP (Recycled Asphalt product) is typically permitted in new base course asphalt mixes in the amount of 40-50% of the total mix volume. Most engineers will not allow base lifts of asphalt to be placed in excess of 6″ at a time.

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At the asphalt plant the aggregate/mineral mixture is formulated accurately in the hopper and then the binder is added at the appropriate rate and mixed thoroughly together before being released through the bottom end of the hopper into the hauling truck. The hauling truck’s bed is commonly sprayed with release agent to prevent sticking of the mixture. A cover is required over the top of the bed to trap in heat and to keep wind and rain from entering the bed and mixture. The amount of asphalt a truck can carry is based more on truck weight ratings and local jurisdictions more than actual volumetric capacity of the truck bed. For example, a quadruple axle truck will commonly be rated to haul approximately 17-19 Tons (8.5-9.5 Cubic Yards).

Enough trucks will be required to place hot asphalt mix into the paver or spreading equipment’s hopper consistently to keep the equipment in constant motion and hot. The number of trucks required is dependent on the location of the asphalt mixing plant, the size of the truck bed, local traffic conditions, the area to be covered, and the amount of asphalt mix to be placed. A small paving operation may only need 1-3 trucks while a large mainline road paving operation can require as much as 4-6 trucks or more. Haul routes will sometimes need to be planned out in advance of paving operations to assure the engineer or locality will approve of road/bridge load limit guidelines and any asphalt binder tracking that might occur due to tires. A logical and efficient location must be established for trucks to wait for their turn in hopper placement and for the actual act of placement into the hopper. This process must all be organized and planned to minimize interference and disruption to passing and local traffic.

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Prior to asphalt placement the existing surface asphalt surface will need to be clean and dry to promote adhesion of tack/prime coat and subsequent asphalt lifts being placed. The cleaning operation is commonly done with a sweeper truck or tractor. Also, liquid asphalt will typically be required by way of a separate spot nozzle typically attached to a hot kettle trailer. This liquid is applied on most all of the areas perimeter, i.e. curbs, butt joints, etc (and sometimes cold joints) to promote adhesion and seal against moisture penetration (which can lead to unwanted freeze-thaw and eventual deterioration).

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Prime coat is commonly used on stone or concrete base to promote base adhesion, limit capillary moisture action upwards into asphalt lift, and to provide a more durable base if imminent paving isn’t expected. Tack coat is used between the intermediate and surface courses and promotes adhesion and a good bond between two lifts of asphalt. Typically the asphalt truck will be connected to and towed/pushed forward by the paver at the desired speed. The asphalt is then released from the hopper into the conveyor/spreader and on to the preheated screed to be placed in the appropriate lift and cross slope. (See Asphalt Paver Operation).

Placement and compaction are the most important factors in installation of successful asphalt pavement performance. Asphalt is placed in ‘lifts’ which are typically at least 3 times the thickness of the maximum aggregate size.+/- 3-10″ is common for asphalt bases, 1-3/4″ – 3″ for intermediate courses, and 1-1/4″ – 2″ for surface course, though other thicknesses are possible for special situations or asphalt product types. The purpose of installing asphalt in lifts is to  avoid mat tearing, which typically looks like longitudinal streaks.

Compaction is considered by many, the greatest determined factor in dense-graded asphalt pavement performance.  Compaction is measured by density or ‘percent air voids’ information which is gathered by testing operations. The two common testing methods are:

-on site extraction of pavement cores which are tested in the lab (most accurate but also very resource intensive and costly)

-nuclear or electrical density gauge

A rule of thumb used by some is for every 1% increase in air content that’s above the 6-7% accepted maximum, pavement life can be reduced by up to 10%. The common air content range for dense-graded asphalt mixes is 3-8%. Poor compaction can lead to a host of problems: decreased durability, raveling, rutting, freeze/thaw moisture damage, reduced fatigue life, reduced stiffness, etc.

The largest factor affecting compaction is considered by many to be asphalt mix temperature at placement. The reason for this is because of the amount of time provided in the ‘window of compactive effort’ where the temperature is at or near peak (usually 250F for Hot Mix, 290F for many modified binders mixes). Too soon and the roller will ‘roll’ the mix. Too late and the mix will be too cold to receive compaction efforts. Many consider a conducive temperature for compaction (dense-graded mixes) to be between above 230 degrees fahrenheit. The ‘cessation’ temperature is commonly around 175 degrees Fahrenheit at which point compactive efforts become inefficient. After this point rollers can still improve smoothness and surface texture, but further compaction will commonly cease. It’s important to note that thicker lifts of asphalt stay warmer longer, however ambient temperature, wind, and and sun play a significant role in peak maintenance of mix temperature. Other factors that can affect compaction are mixture (aggregate properties, binder properties/amount) and installation (roller properties/number, haul, base).

A common rule of thumb used in the field is final compacted asphalt will lose 1/4″ per inch of design lift thickness, so the screed depth is adjusted accordingly. Example; a design 2″ lift of intermediate course, will require an approximate screed depth of 2-1/2″.

Once the asphalt is placed into the desired lift thickness and while the asphalt is still hot, steel wheel and pneumatic type rollers will make several (often as much as 5-10 times or more depending many factors) passes across the asphalt surface to achieve maximum final material placement density. Vibratory rollers have become rather popular as they often provide a better compaction result than static rolling. However they also require a higher degree of operator control, and must be used with caution in residential areas, areas with fragile utilities, etc. Amplitude and frequency can be adjusted for on vibratory rollers, which maximize compactive effort. In general when using vibratory rollers, higher frequencies and lower roller speeds are ideal because they increase compactive effort and provide a smoother mat. 2.5″ and greater lifts will commonly use high frequency high amplitude more (along with stiff mixes). Lifts between 1.5 and 2.5″ will typically use high frequency low amplitude mode. And thin lifts less than 1.25″ typically operated in static mode only (to reduce shoving or aggregate crushing). For most standard mix types and lift thicknesses, low-amplitude/several pass approach is common.

A ‘breakdown’ roller (vibratory smooth or pneumatic roller) is utilized first and commonly travels 2-3 mph and operates as close to the paver as possible. An ‘intermediate’ roller (typically smooth drum but sometimes pneumatic) is used second and typically travels 2.5-4 mph. A ‘finish’ roller (typically smooth drum static roller) is used at the end and usually runs from 3-7 mph. Thin lifts (1.25″ and smaller) should not receive vibratory compaction as shoving, displacement, and aggregate fracturing can occur. Also a small or ‘peanut’ roller may be used to trim out edges, corners, or hard to reach areas. Most rollers range in width between 3-7′. Many modern steel wheel rollers can be ballasted with sand or water. Rollers should never be stopped on a fresh mat as they can cause humps that are near impossible to fix.

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For pneumatic tired rollers, it’s important for the tire pressure to be correct for proper minimum contact area and contact pressure requirements. Pneumatic rollers provide a ‘kneading’ type action which improves compaction, applies more horizontal forces to the compaction effort, and rearranges the aggregate to increase the possibility of better compaction. The tires and wheels on the rollers are consistently moistened to prevent adhesion of the mixture.

It is common for asphalt base mixtures to be compacted with pneumatic and steel wheel rollers. It is common for intermediate and surface courses to utilize a steel wheel roller. Variable depth courses are commonly compacted with pneumatic and steel wheel rollers. For polymer asphalt mix, only steel wheel rollers should be used.  Any surface deviations caused by the use of pneumatic rollers must be corrected with the steel wheel rollers.

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Rollers typically start on the outside of the lane and make one complete pass. They will then move inward towards the crown of the road and overlap the previous pass by approximately 6″. Compaction is done until displacement of the asphalt occurs no more. For cold joints, it is a good idea to keep the rollers at least 12″ from the unsupported edge, until the adjacent lift is placed. It is common for longitudinal cold joints in successive lifts be staggered reducing the chance of significant joint separation, a key location for deterioration to occur. Any road ‘crowns’ should never be rolled over as they will become flattened. Along curbs, around castings, and in other hard to reach areas, mix is placed then tamped with a hand or mechanical tamp. Handwork with an asphalt rake and/or shovel is almost always required. 1-3 laborer often follow along with the paver, fixing any minor inconsistencies in placement and placing asphalt in areas where the paver can’t reach (around castings, curb bumpouts, intersections, unusual radii, etc). handwork should be minimized as it’s subject to aggregate segregation and a rougher surface texture.

Asphalt can be placed in colder temperatures, but this is highly dependent on the thickness of the lift being placed. 3″ and thicker lifts may often be placed down to 36 degrees ambient and paving surface temperatures. 1.5 – 2.9″ thick lifts typically require 40 degrees or higher, and 1-1.4″ lifts typically require 50 degree fahrenheit minimum.

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After surface course is placed, hot asphalt cement joint sealant is often placed by way of a ‘Tar Kettle’ at specific locations; often along curb joint and around concrete structure collars.

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FAQS – FREQUENTLY ASKED QUESTIONS

 

Where is hot and warm mix asphalt made?
 

Hot mix asphalt is made at a batch or drum plant.

 

In what order is the material mixed at the plant?

 

At a batch plant, aggregate is typically stored in piles which ultimately end of in cold feed bins which meter the aggregates and pass them onto conveyors into the drying drum. The dryer drum tumbles and heats the aggregates. For a drum plant, the heated liquid asphalt is pumped into the drum and mixed with the aggregates. For a batch plant the dried aggregate are sent to a batch tower and a mixing chamber where they are ultimately dropped through a chute directly into trucks. For a drum plant, the mixed asphalt is sent to drums or silos to be stored for short or longer periods of time.

 

How is the material loaded onto the trucks?

 

Hot mix asphalt is loaded onto trucks by way of a loading area which exists underneath the batch tower or silos.

 

How is the material weighed before it leaves the plant?

 

Trucks typically are tared on their way in for their empty weight, then weighed on a scale on their way out to find the amount of material loaded.

 

What temperature is hot and warm mix asphalt when it leaves the hopper at the plant?

 

Hot mix asphalt is typically manufactured between 265 and 330 degrees fahrenheit. For longer delivery distances asphalt can lose up to 30 degrees or more in temperature. Warm mix asphalts are manufactured and placed at temperatures ranging around 135 to 210 degrees fahrenheit

 

How much asphalt can a dump truck legally carry?

 

Legal dump truck weights can vary by state, city, county, village, and township. Gross vehicle Weight Rating can vary by make, model, year, and axle rating. It’s always good to check your local guidelines. Allowable weights are typically sorted by type of truck and how many axles are carrying the weight, since the weight would be distributed thus.. As a general guide for state and city guidelines on dump trucks: -Single Axle: 29,000 pounds – Short tandem: 36,000 pounds – Long Tandem: 50,000 – Short Tri-Axle: 47,000 pounds – Long Tri Axle: 60,000 pounds – Short Quad Axle: 60,000 pounds – Long Quad Axle: 80,000 pounds.

 

What are standard tared weights of different dump truck sizes?

 

Every truck is different so always check the make and model, but a rule of thumb for tared weights on dump trucks are: single axle: 8,000 pounds, tandem short: 12,000 pounds, tandem long: 22,000 pounds, Tri axle short: 22,000 pounds, Tri axle long: 28,000 pounds, Quad axle short: 28,000 pound, Quad axle long: 38,000 pounds

 

Can asphalt be placed in the rain?

 

Generally light sprinkles will not cause any major issues down the road (no pun intended) when placing asphalt, but moderate or heavy rain should be enough to rightfully pull the plug on the daily operation.

 

What is a situation where a heavy asphalt mix type would be ideal?

 

A heavy duty asphalt mix might be used in parking lots, drives, or roadways where heavy traffic will be expected frequently during the lifespan, for example semi trucks or dump trucks.

 

What is a situation where a medium asphalt mix type be suitable?

 

A medium duty asphalt mix might be used in parking lots, drives, or roadways where heavy traffic will be expected moderately during the lifespan, for example semi trucks or dump trucks.

 

What is a situation where a light asphalt mix type be suitable?

 

A light duty asphalt mix might be used in parking lots or driveways expected to receive light traffic and typical vehicle sizes, i.e. compact cars and trucks. Light duty mix is very commonly used in residential driveways.

 

What asphalt binder grade or ‘viscosity’ is most commonly used in asphalt mixes?

 

Asphalt cement binder used to be referred to as ‘AC-20’ etc but has recently begun to be classified and discussed by it’s Performance Grade (PG). PG 64-22 is one of the more common asphalt binder types in the midwest region for example. For areas to receive lots of slow moving traffic and lots of starting and stopping might be more conducive to a PG 70-22 or PG 76-22 asphalt cement binder. Also, region has an impact on the asphalt binder type chosen. A region with high yearly temperature fluctuation, for example -20 degrees to 95 degrees, PG 70-22 and PG 76-22 might be chosen

 

How long does it take to unload 19 tons from a truck full of asphalt, into the paver’s hopper?

 

Asphalt paver production is highly influenced by the type of paving being done (driveways, parking lots, mainline roads, etc) and the thickness of the lift. An aggressive peak production for mainline asphalt paving at a 2″ thickness might be four 18 ton quad axle trucks an hour, or 15 minutes per truck. But parking lot or driveway production would be less than this example.

 

How are the paver and trucks positioned on a job site to pave?

 

Most tracked or tired asphalt pavers push the truck forward as the truck bed slowly raises to release the materials into the hopper. If several dump trucks are required to pave, they will most commonly line up in front of the paver in the order in which they arrived from the asphalt plant. If room ahead of the paver becomes restricted they may have to wait in another location.

 

How do the trucks and pavers move in unison?

 

The dump truck will commonly back up to a few feet away from the pavers hopper and push bar. The paver will then slowly move forward and gently tap and then begin pushing the truck forward to resume paving. Some pavers might also have arms that reach around into the wheels rims to assure a good hold and guide.

 

How much asphalt can be hauled on a single, double, triple, quadruple, and quint truck?

 

Legal dump truck weights can vary by state, city, county, village, and township. Gross vehicle Weight Rating can vary by make, model, year, and axle rating. It’s always good to check your local guidelines. Allowable weights are typically sorted by type of truck and how many axles are carrying the weight, since the weight would be distributed thus. As a general guide for max allowable asphalt weights on trucks based on typical GVWR and weight ratings: -Single Axle: 7 tons – Short tandem:  9 tons – Long Tandem: 13 tons – Short Tri-Axle: 13 tons – Long Tri Axle: 16 tons – Short Quad Axle: 16 tons – Long Quad Axle: 18 tons.

 

How much does asphalt weigh by the cubic yard?

 

Each mix design can be different so always check the mix design for the yield and conversion rate. A general guideline for typical mixes are: Asphalt Base Material: 1 cubic yard = +/- 2 ton, Intermediate Course: 1 cubic yard = +/- 2.03 Ton, Surface Course: 1 cubic yard = +/- 2.03 Ton

How long does it take for prime coat to set before paving can be started?
 

The heavier the application rate the longer it will take prime coat to cure. Some engineers will allow paving after the material has ‘broken’, others will require the prime coat to set completely. There are many different types of prime coats, slow-set; medium set; quick-set, each with different specifications and setting times. For a slow set prime coat, 24 hours is typically required for proper setting though some engineers will require up to 48 hours or more.

 

How long does it take for tack coat to set before paving can be started?

 

The heavier the application rate the longer it will take tack coat to ‘break’ and set up. Some engineers will allow paving after the material has ‘broken’, others will require the tack coat to set completely. There are many different types of tack coats, slow-set; medium set; quick-set, each with different specifications and setting times. A ‘Trackless Tack’ product should ‘break’ in +/- 15 minutes. A standard rapid setting tack coat product can take 30-45 minutes to ‘break’

 

Can road cleaning prior to paving be done with a standard broom tractor with a water tank?

 

If the surface to be paved only requires light cleaning, and it’s a warm sunny day, a standard broom tractor may be sufficient. For a dirty, dusty, pavement or milled surface, a ‘pickup’ or vacuum style brooming truck may be required to properly clean the surface.

 

Where is asphalt liquid applied prior to paving?

 

Typically the requirement is that all vertical faces that will come in contact with as asphalt course should be coated with liquid. This will commonly include gutters, curbs, castings, and the vertical face of an existing cold joint pavement.

 

At what temperature range should hot mix asphalt be placed?

 

Typically hot mix asphalt should be compacted when it is within the range of 175 – 225 degrees fahrenheit.

 

At what temperature should warm mix asphalt be placed?

 

Warm mix asphalt is commonly placed at temperatures 30 to 120 degrees below that of hot mix asphalt.

 

At what temperature should polymer-modified asphalt mix be placed?

 

This depends on the mix design and the liquid used, but generally speaking most polymer modified asphalt is produced at temperatures between 300 and 350 degrees fahrenheit and should be installed at similar temperatures.

 

What happens if a roller begins asphalt compaction when the mix is too hot?

 

Generally higher temperatures are better when it comes to asphalt compaction. One scenario when overcompaction might cause problems is if a vibratory roller makes too many passes on a light duty mix which can cause material displacement, structural instability, and ‘bow weaves’. The mix may bulge in front of the drums and the mix will move but not compact.

 

What happens if a roller begins asphalt compaction when the mix is too cold?

If an asphalt mix is not up to temperature for proper compaction, excessive air voids will exist in the asphalt which increases permeability of the pavement and can cause premature deterioration of the pavement. Also, If hot mix asphalt temperatures dip below 170 or 180 degrees, the liquid becomes hard enough that the rollers can begin to break aggregates and may even cause or start premature craking in the asphalt lift.
At which temperature does asphalt hot mix no longer become compactable?
 

Hot mix asphalt compaction efforts starts to diminish in productivity around 175 degrees and below.

 

How much thickness will a lift of asphalt lose after it has been fully compacted?

 

Different mix designs may yield different densities and void percentages, but a general rule of thumb for many hot mix asphalts is a loss of 1/4″ after the paver for every inch of asphalt in a lift.

 

In which situation is a pneumatic roller suitable?

 

Pneumatic rubber tire roller are most suitable for base pavements or variable depth intermediate courses. Pneumatic rollers should never be used on lifts of

 

In which asphalt paving situation is a vibratory roller suitable?

 

Vibratory rollers are commonly used on 1.5″ and thicker lifts of asphalt, which are primarily base and intermediate lifts. For lifts thinner than 2″, the first breakdown pass is often vibratory, with remaining passes in static mode. For lifts thicker than 2″, static mode is often only used to smooth out objectionable roller marks

 

In which asphalt paving situation is a static roller suitable?

 

Static roller mode is most commonly used when less structural thin lifts, typically less than 1.5″, are placed. A vibratory roller on thinner lifts can cause structural failure, surface defects, or premature deterioration.

 

In which asphalt paving situation is a high frequency high amplitude setting on the roller most suitable?

 

Thicker lifts (2″ and larger), higher asphalt liquid viscosity, Angular aggregates, flexible base support.

 

In which asphalt paving situation is a high frequency low amplitude setting on the roller most suitable?

 

Thinner lifts (1.25-1.75″), lower asphalt liquid viscosity, rounded aggregates, rigid base support

 

What is a breakdown roller and it’s task?

 

A breakdown roller is the first compaction done on the asphalt lift being placed directly behind the paver, where the temperature is high enough to keep the liquid viscosity low so the particles can arrange in the closest orientation possible. The greatest increase in density per roller pass occurs with breakdown rolling and is most often done with a vibratory roller. It can be done with a pneumatic roller as well.

 

How many passes should a breakdown roller make?

 

This often depends on the mix type and depth, but 2-3 passes overlapping slightly on each prior, is typically sufficient for the breakdown roller before the intermediate or finish roller comes in.

 

What size and type of roller is suitable as a breakdown roller?

 

This is dependent on the mix type and lift thickness, but vibratory steel wheel and pneumatic are the most common rollers used for breakdown compaction.

 

What is the intermediate roller?

 

An intermediate roller is used after the breakdown roller and can be any roller type, but pneumatic rollers are sometimes used as they provide a kneading action vs a vibratory steel wheel roller. It is common for contractor to use a smooth drum roller for both intermediate and finish rolling purposes.

 

What is the finish roller and it’s task?

 

A finish roler is used after the breakdown or intermediate roller and it’s puprose is primarily to remove objectionable roller marks, very little structural compaction is achieved by the finish roller passes.

 

What size and type of roller is suitable as the finish roller?

 

Static steel wheel rollers are most commonly used as a finish roller.

 

What is used to wet the rollers drum during asphalt compaction?

 

Water is commonly used to keep the rollers wet and from pulling up asphalt, though water and other based release agents are available as well.

 

When and where in the paving operation is a hand rake and laborer required?

 

A laborer with hand tools will be required for hand raking and placement anywhere the paver cannot reach. This is commonly a small starting area before the paver, intersections, driveways, around catch basins or manholes, small patches, and anywhere else the paver cannot access or be productive with. Also hand raking laborers will follow behind the paver and spread or ‘marble’ the material at the longitudinal joint to assure a smooth clean roller pass at the joint.

 

Where is hot asphalt liquid required after the final asphalt surface course?

 

For final sealing purposes the surface course is typically sealed at all non-asphalt joints: around catch basins, manhole collars, concrete curb joint. Longitudinal or transverse joints are not typically sealed with asphalt cement until later on when maintenance is required to limit water intrusion into a susceptible joint.

 

How long will asphalt material stay hot in the waiting trucks?

 

In moderate to warm weather, asphalt will stay up to proper temperature for an hour or more in a covered and insulated truck.

 

What are some of the causes and risks of having a segregated area of asphalt?

 

Segregation may be caused by the asphalt plant, improper truck loading, hand placement, and paver oeration. A segregated area is often susceptible to eventual raveling or premature deterioration.

 

What temperature and how long after asphalt paving can vehicle traffic be permitted on as asphalt pavement?

 

Generally asphalt is at peak compaction as soon as the rollers are finished meaning it can be driven on right away assuming the traffic load is light and/or there is no abrubt starting or stopping or wheel turning. The pavement may still be at or well above 150 degrees fahrenheit after rolling, when the pavement cools below 150 degrees it is even more suitable to be driven on. This decision is often made by the civil engineer on the project.

 

What kind of material is used to clean out truck beds after the asphalt is dumped from the truck?

 

Water -soluble, biodegradable, non-hazardous, soy or other based liquids are most often used on public asphalt paving projects. Diesel fuel used to be used years ago but it has been found to be detrimental to the structure of the asphalt mix. Such release agents may be ood for 3-5 loads of asphalt maybe more in some cases. Powdered laundry detergent has been used as well as an asphalt truck bed release agent.

 

What kind of rollers are required for asphalt base paving?

 

Base asphalt compaction typically requires a minimum of one pneumatic tire roller and one steel wheel roller.

 

How closely should the breakdown roller follow behind the paver?

 

The breakdown roller should follow as closely behind the asphalt paver as possible as this is the highest temperature area where peak compaction can be achieved.

 

How should unconfined edges of asphalt pavement be compacted with a roller?

 

Unconfined asphalt edges should be rolled with a vibratory steel drum roller which hangs out approximately 6″ from the asphalt edge with the vibratory mode set at maximum

 

What is the common tolerance requirement for a pavement lane or road’s longitudinal profile (i.e. crown) when

being compared to planned elevations?

 

Many engineers will allow an elevation deviation of +/- 1/2″ longitudinally from plan grades.

 

What is a typical tolerance for the cross slope of an asphalt pavement lane or road?

 

Many engineers will allow a variance up to 3/8″ in 10 feet for the plan’s intended cross slope of the lane or road.

 

What is typically expected of asphalt pavement in terms of the surface smoothness tolerance?

 

Many engineers require that a pavement does not deviate any more than 1/4″ in 10 feet from what the elevation should be according to plan elevations in the subject area.

For a 7 man road or parking lot paving crew with a paver and 2 rollers, what are the classifications, tasks, and duties of each worker?
 

There are commonly 5 operators, a foreman, and 2 laborers within a 7 man paving crew (but each company is different in their crew makeup/tasks). One operator handles the primary paving operation up high on the paver; steering, controlling trucks and dump beds, and maintaining hopper capacity. Then two more operators stand down low on the paver on each side managing the screed, managing the augur and mat consistency, and moving the screed edge arms in and out to line up with curbs or layout lines. Then two more operators utilize the rollers, often interchanging between breakdown, intermediate, and finish rolling. Lastly the laborer will perform any other functions required like; rake/lute use at longitudinal joint to maintain smoothness after rolling joint, traffic control, or any other task needed. The foreman often takes on any of these tasks required while managing the overal workflow and making difficult decisions. For areas that cannot be reached by the paver, most or all of the crew workers will grab a rake or lute and hand place the material as needed.

 

What size rollers are used for road paving, parking lots, driveways, etc?

 

Each project, application, and company can be different in equipment used but for a typical road paving project, a 11-14 ton single or double drum roller is used for breakdown and a 10-12 ton double drum roller might be used for finish rolling. A larger driveway or entrance drive might be rolled with a 8-12 ton roller and a smaller 2-3 ton roller for finish rolling.

 

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