DIVISION E4.00 - Bituminous Materials
E4.01 - Bituminous Concrete Pavement
Bituminous Concrete Pavement, often referred to as Hot-Mix (HMA), Warm Mix (WMA), or simply asphalt pavement, is the most common pavement material in the state, used on approximately 82% of our roads. Inspection Staff can refer to Division 400, Section 1010, Section 1011, and Section 1014 of the Standard Specifications for Contract Requirements.
- Training videos which reference older specifications are available below, but inspectors should be mindful that the requirements noted in the video may no longer be accurate. They are provided for information only.:
E4.01.01 - Materials
]- Bituminous Concrete is made at an asphalt plant, as pictured in the example above, which combines the materials in a rotating, heated drum, ensuring a consistent coating of asphalt cement on the aggregate, and also prevents segregation of the material. Once made, the material may then be stored or immediately loaded into dump trucks from heated silos to be hauled to the project. Depending upon the amount of material that is expected to be made on a given day, a plant inspector from DelDOT's Materials & Research Section may be at the plant for Quality Control purposes.
- Temperatures - Other than ambient air, DelDOT does not specify placement temperatures. Instead, it utilizes a performance based specification with testing to ensure it obtains the desired end product. However, the temperature of the material can provide the inspector insight into how likely it is for the final product to be compliant. Any issues identified should be brought to the attention of both the Contractor and the Project Resident as soon as possible.
| Material | Upper Compaction Threshold | Lower Compaction Temperature |
|---|---|---|
| PG 64-22 | 320° | 240° |
| PG 76-22 | 330° | 250° |
- Inspectors should be alert for signs of overheated material. Blue smoke rising from the mix typically indicates the material has been overheated. While DelDOT does not specify a maximum placement temperature, excessively hot material can damage the asphalt binder and result in a pavement that does not meet performance expectations. Conversely, material that appears stiff, has poor aggregate coating, or is difficult for the crew to work may be too cold for adequate compaction.
- Mix Designs and Job Mix Formulas (JMF) - All bituminous concrete mixtures used on a project must have an approved mix design. The Contractor develops the JMF in accordance with Section 1014 of the Standard Specifications and must submit test results for review a minimum of 30 calendar days before application. The JMF defines the aggregate type, gradation, asphalt binder content, and other mixture properties. Once production begins, the Contractor may request JMF adjustments, but these must remain within the limits established in the Standard Specifications and be approved prior to implementation.
Tack
- An Emulsified Asphalt which is heated before placement and is used between layers of pavement to ensure the top layer of bituminous concrete bonds to the subsurface layers to prevent shoving and tearing, pictured below.
- Inspector Tip: All contact surfaces of curbing, gutters, manholes, and other facilities must also be coated with a uniform application of tack. A properly applied tack coat should appear as a thin, uniform, dark coating. It must be cured (changed from brown to black) before paving begins. If your shoes stick to the surface without picking up material when you walk on it, the tack is generally considered cured.
Release Agents
- Release agents are applied to the equipment which will come into direct contact with the bituminous concrete to prevent the material from adhering. As part of the Source of Supply, the Contractor should have submitted a Release Agent from the Approved Product List. Diesel Fuel should not be used as a release agent. Diesel fuel dissolves asphalt binder and can damage the pavement surface by breaking down the mix at contact points.
E4.01.02 - Equipment
Dump Trucks
- Must have clean, smooth, tightly sealed beds which are free of debris and coated only with approved release agents. Each truck should have a securely fastened cover of canvas or other suitable waterproof material that covers the bed from front to back and over the sides, to protect the mixture from the weather, and to prevent heat loss. In addition, in cool weather, the truck bed should be insulated on the front, sides, and back with plywood or other suitable material. Trucks with heated bodies may also be used, but the heat is uniformly distributed along the entire area of both side walls. Their maximum legal Gross Vehicle Weight is 73,280 lbs.
Broom Tractor/Vacuum Truck
- Used to clean the existing surface prior to tack application and paving. All surfaces that will receive tack coat and new pavement must be thoroughly cleaned of dirt, dust, vegetation, loose debris, and any other foreign material. On milled surfaces, multiple passes may be necessary to remove residual grit.
Tack Truck
- A tack truck must (pressurized distributer) be able to heat and evenly distribute the emulsion and should have an automated ground speed control device interconnected with the emulsion pump to maintain the specified application rate at varying speeds. The spray bar nozzles must produce a uniform fan spray, and the shutoff must be instantaneous with no dripping. Nozzles should all be turned at the same angle to the spray bar (approximately 30 degrees) and the spray bar should be set at the proper height above the pavement surface to provide for a double or triple lap of the emulsion.
- Inspector Tip: Before tack operations begin, verify that all nozzles are open, clean, and set at the same angle. A streaked or non-uniform appearance on the surface indicates a problem — inspect for clogged nozzles, improper pump speed, or incorrect spray bar height. Stop the operation until the issue is corrected.
Material Transfer Vehicle
- Material Transfer Vehicles (MTVs) receive the bituminous concrete from the haul trucks and remix the material before feeding it to the paver. This process minimizes aggregate segregation and temperature differentials by re-blending the cooler outer edges of the truck's load with the hotter material from the center. MTVs also provide additional surge volume, which allows the paver to operate continuously without stopping or bumping for truck exchanges. On high-profile or arterial roadways, the use of an MTV can significantly improve ride quality and mat uniformity.
Paver
- A self-propelled unit with a screed or strike-off assembly that automatically controls grade leveling and slope, is heated, and is capable of spreading and finishing bituminous pavement materials to the specified lane widths and thicknesses. There are three different types of pavers for an inspector to be aware of:
- Track Paver - Provides better traction and stability on soft or uneven surfaces, and is commonly used on larger paving projects.
- Rubber Tire Paver - More maneuverable and travels faster between paving locations, but may be more susceptible to steering deviations.
- Spray Bar Paver - Equipped with an integrated tack spray application system for thin-lift paving operations, as referenced in Section 401 of the Standard Specifications.
Regardless of type, pavers have several common components the inspector take note of prior to and during the completion of the work:
- Push Rollers - Should freely rotate when against a truck tire and should be cleaned periodically. Poorly maintained push rollers could cause the speed or direction of the paver to change.
- Hopper - Should be clean at the start of every shift.
- Apron - Prevents material from falling out of the hopper.
- Wings - Can be folded in. If a Contractor folds these wings, the inspector should take care to ensure no cold mix is incorporated into the pavement. The hopper should be at least half full before the wings are dumped, and the slat conveyors should not be visible when the wings are emptied.
- Slat Conveyors - Feed material to the screed. Each side operates independently, allowing the operator to vary the amount of material fed to either side.
- Flow Gates - Control the flow of material on the conveyors. These should be adjusted to provide a uniform head of material in front of the screed.
- Screed - Is a free-floating leveling device used to strike off the pavement, providing the pavement shape and its initial compaction. Damage to the screed will be reflected in the mat and should be repaired. The screed has several components:
- Augers - Located immediately in front of the screed, used to spread material deposited from the conveyors across the screed. The augers should maintain a consistent volume of material in front of the screed to avoid changes in thickness. At the center of the paver, adjacent to the auger gear box, there should be a reversed pitch auger or paddle to push material under the gear box and avoid a segregation streak down the center of the mat.
- Extensions - Portions of the screed that can be adjusted in or out depending upon the required mat width. When rigid extensions are used, auger extensions should also be added so that material is distributed to within approximately 12 inches of the end gate.
- Shoe - Located on the screed extension, can be adjusted up or down to contain material.
- Safety Edge Shoe - An attachment on the screed extension to provide a safety edge on the finished pavement, as required by Section 401 of the Standard Specifications.
- Sensors - Used to maintain a consistent amount of material in advance of the screed (automatic feed control sensors). Additional sensors may be used to set the pavement height via grade reference controls such as a floating ski, string line, joint matching shoe, or mobile mat reference system.
- Cranks -
- Used to adjust the angle of attack of the screed. This will change the thickness of the pavement. Once established, it should be adjusted rarely.
- Cranks are also used to "break" the screed for paving a crown, though this is typically avoided.
Roller
- Rollers are used to compact the bituminous concrete to the required density. Per Section 401 of the Standard Specifications, the Contractor must provide self-propelled static or vibratory steel wheel type rollers equipped with scrapers, or pneumatic-tire oscillating type rollers equipped with smooth tires of equal size and diameter. All rollers must be equipped with a system for moistening each wheel or roller while in use. The Contractor must use a number and weight of rollers sufficient to compact the mixture to the required density without crushing aggregate or displacing the mixture. Rollers must not mar the surface.
- Steel Drum Roller - Used as both a breakdown (initial) and finish roller. Steel drum rollers may be operated in static mode or vibratory mode. For relatively thin lifts (less than 1-1/2 inches), the roller should typically be operated in static mode. For lifts of 1-1/2 inches and greater, a low amplitude vibratory setting is generally appropriate, with amplitude increasing as lift thickness increases. The roller drums must be kept moist to prevent pickup of mix on the drum surface. Rollers should be free of flat spots, dents, or buildup of material on the drums.
- Rubber Tire (Pneumatic) Roller - Uses a kneading action to compact the material. Pneumatic rollers seal the surface and are particularly effective at compacting the material into cracks and depressions on leveling courses. All tires must be the same size, ply, and pressure. Tire pressure affects the compactive effort; lower pressure may be needed for tender mixes, while stiffer mixes benefit from higher pressure. The tires must be kept hot to prevent pickup of fines — some pneumatic rollers are equipped with skirts around the bottom to retain heat from the mat.
Inspector Tip: Watch for rollers that are not operating correctly — flat spots or buildup on steel drums will create marks in the finished surface. Rollers should operate at a consistent speed (typically 3 to 5 mph for steel drum rollers) and should not stop on the hot mat, as this can create depressions. The roller should be moving at all times when on uncompacted material. When steel drum rollers are changing direction, they should not be in a vibratory mode.
E4.01.03 - Operations
Pre-Pave Meeting
Before paving operations begin, a pre-pave meeting must be held in accordance with Section 401 of the Standard Specifications. The meeting should include the Engineer, the Contractor's paving superintendent, the Department's Materials & Research Section representative, and other appropriate parties. The purpose of this meeting is to establish expectations and discuss the specifics of the paving operation.
Topics to be discussed at the pre-pave meeting should include:
| 1 | Joint layout and longitudinal joint placement |
| 2 | Material delivery rates and haul times |
| 3 | Paving widths and lift thicknesses (application rates) |
| 4 | Equipment to be used (paver, rollers, MTV, tack truck) |
| 5 | Roller patterns and compaction plan |
| 6 | Striping layout and temporary pavement markings |
| 7 | Maintenance of traffic during paving operations |
| 8 | Mix design and JMF — any special provisions |
| 9 | Quality control/quality assurance sampling and testing procedures |
| 10 | Weather and temperature limitations |
| 11 | Paving schedule and sequencing |
| 12 | Safety — responsibilities and emergency contacts |
| 13 | Communication between the plant and the paving site |
Minutes of the pre-pave meeting should be documented and maintained in the project file. Clear lines of communication between the plant and the paving crew should be established at this meeting — a fast means of communication is essential so that any changes to the mixture or operational issues can be promptly addressed.
Inspector Tip: Use the pre-pave meeting to clarify your role and expectations. Discuss where you will be positioned during paving, how you will communicate concerns, and what immediate actions will be taken if deficiencies are observed. Ensure the Contractor understands that paving may be stopped if specification requirements are not being met.
Inspection of Subgrade
Before any paving begins, the surface to be paved must be inspected and accepted. The condition of the underlying surface directly affects the quality and ride of the finished pavement. The inspector should verify the following:
- The surface is clean, dry, and free of loose material, dirt, vegetation, and debris. If the surface has been milled, multiple broom passes may be necessary to remove residual grit and dust.
- The subgrade or base course meets the required density, grade, and cross-slope as specified in the contract plans. Any soft spots, rutting, or areas of distress must be corrected before paving proceeds.
- Drainage structures (manholes, inlets, valve boxes) have been adjusted to the correct elevation, or a plan is in place to adjust them during the paving operation.
- All existing pavement deficiencies identified for repair (such as full-depth patching or crack repair) have been completed.
- On existing HMA or PCC surfaces being overlaid, the surface should be inspected for areas that may require wedging to correct elevation differences, superelevation corrections, or rut filling prior to placement of the leveling or surface course.
Inspector Tip: Walk the project before paving starts. Look for areas of standing water, soft subgrade, improperly adjusted structures, or debris that may have accumulated since the surface was prepared. Document any concerns and bring them to the attention of the Contractor and the Project Resident before the paver arrives. It is far easier and less costly to address issues before paving than after.
Release of Material
Per Section 104.6 of the Standard Specifications, no bituminous concrete materials shall be shipped to the project without first being released by the DelDOT Inspector. The Contractor must notify the Materials & Research Section of the quantity and time of the scheduled release by 3:00 P.M on the previous business day. When DelDOT releases materials for shipment, this does not guarantee that the materials meet specifications or are suitable for use — the Contractor remains solely responsible for the suitability of the materials shipped.
Depending upon the scale of the day's production, a plant inspector from DelDOT's Materials & Research Section may be stationed at the plant for quality control and quality assurance purposes. The plant inspector monitors mix production, verifies temperatures, observes loading operations, and takes samples for testing. The field inspector should maintain communication with the plant inspector to stay informed of any production issues that may affect the material arriving on site.
Inspector Tip: Be aware of the testing and acceptance process established in the contract, including any Special Provisions related to Quality Control/Quality Assurance (QC/QA) of Bituminous Concrete (Special Provision 401699). Understand the lot and sublot structure, random sampling locations, and the consequences of failing test results. If you are unsure of the testing protocol for your project, consult with the Project Resident or the Materials & Research Section before paving begins.
Application of Tack
A tack coat must be applied on all dry and broom-cleaned surfaces that will receive new bituminous concrete. This includes all PCC and bituminous pavement surfaces, newly constructed HMA widening, and all contact surfaces of curbing, gutters, manholes, and other facilities.
The three essential requirements of a properly applied tack coat are:
- It must be thin — excess tack can create a slip plane and cause flushing.
- It must be uniform — streaked or spotty applications indicate equipment problems.
- It must be cured before paving — the emulsion must break (change from brown to black) before the paver passes over it. If trucks backing into the paver pick up emulsion on their tires, the tack is not cured.
Tack should be applied in advance of the paving operation, but not so far ahead that it is exposed to traffic, contaminated with dust, or left unsurfaced overnight. Only enough tack should be applied that can be covered the same day. Plan the width of application to ensure tack is present under the matching longitudinal joint. Avoid spraying adjacent completed surfaces that will remain exposed. Bridge railings, piers, curb and gutter pans, and guardrails must be protected from overspray by the use of shields.
At locations where the hot-mix is tapered to meet an existing roadway, a tack coat of bituminous material must be uniformly applied on the tapered area.
Whenever the temperature of a previously placed mat falls below a workable temperature prior to placement of the adjacent mat, the vertical edges of the initial mat should be coated with tack before the new mixture is placed against the surface.
The inspector is required to obtain a sample of tack for testing by Materials and Research. Please see Tack Coat Emulsion Sampling Procedure for detail.
Inspector Tip: Before the tack truck begins, verify the nozzles, spray bar height, and application rate. Walk the tacked surface after application — it should appear as a thin, uniform, dark brown coating. Watch for bare spots (especially at the far edges of the spray pattern), pooling, and streaking. If the application is non-uniform, stop the operation until the Contractor corrects the problem and demonstrates that a uniform application can be made.
Receiving Materials and Ticket Control
Every load of bituminous concrete delivered to the project must be accompanied by a material ticket from the plant. This ticket should be in electronic format. The inspector should verify the information on the ticket is correct before marking it delivered. When marking the ticket delivered, the inspector is able to assign an item number, station, and notes to the ticket within EDOT. To aid in completing digital as-builts of the pavement, the inspector should be at or near the paver, and mark the tickets delivered when the material begins dumping into the hopper. The inspector should also verify key information before allow material to enter the paver, such as:
- Truck number
- Time of departure from the plant
- Tonnage
- Mix type / JMF identification
- Temperature at the plant (if recorded)
The inspector should also check the temperature of the material upon arrival at the project using a calibrated thermometer. Temperature readings should be taken by inserting the thermometer probe into the center of the load in the truck bed. Record the temperature on the load ticket or in the daily inspector's diary. Compare the arrival temperature against the plant temperature to assess heat loss during transport.
Inspectors should routinely check the pavement yield throughout the operation. This is the simplest way to catch application rate errors early. If the total tons delivered significantly exceeds or falls short of the planned quantity for the area covered, investigate whether the lift thickness needs adjustment. Yield can be easily checked using the EDOT application and the Superpave Production charts from Materials and Research. As a general rule of thumb, 110-115 pounds per square yard equals approximately 1 inch of compacted thickness.
Placing Materials
It is the Contractor's responsibility to uniformly place the bituminous concrete to the specified grade and thickness. It is the inspector's responsibility to ensure that the Contractor is providing a specification product. If the inspector observes the Contractor not providing a specification product, the paving process should be stopped until corrections are made.
The paver should operate at a consistent speed to produce a uniform mat texture and ride quality. Stop-and-go paving operations must be avoided; every time the paver stops, the screed settles, producing a bump in the finished surface. The speed of the paver should be coordinated with the rate of material delivery from the plant and the plant's production rate to minimize interruptions. When changing trucks, the transfer should be made as smoothly as possible. If using an MTV, truck exchanges can occur without affecting paver speed.
As the first load of mixture is being spread, the inspector should check the texture of the unrolled surface for uniformity. Adjustments to the screed, vibrators, flow gates, or augers may be necessary; these should be completed within the first two loads placed. The mat behind the screed should exhibit a consistent, uniform texture — look for:
- Segregation — Areas where the coarse aggregate has separated from the fine aggregate, appearing as coarse, open-textured patches within the mat. Segregation patterns can help identify the cause (e.g., centerline segregation may indicate missing reverse-pitch auger paddles; edge segregation may indicate the auger extensions are too short for the paving width).
- Tearing — Indicates the screed is pulling the surface apart, often caused by a cold screed plate, material temperature too low, or improper screed settings.
- Screed Marks — Longitudinal marks from screed plate damage, misaligned extensions, or material buildup under the screed.
- Auger Shadows — Alternating dark and light longitudinal bands indicating inconsistent material volume in front of the screed.
The paving operation must be conducted to minimize inconvenience to traffic and to protect existing and finished surfaces. Unless otherwise permitted, no single lane of any course should be constructed to a length that cannot be completed to full width the following day. All resurfacing operations must be properly signed with "Pavement Drop-Off" or "Uneven Pavement" notices in accordance with approved traffic control plans.
Inspector Tip: Pay close attention to the area directly behind the screed. This is where most defects are first visible and where corrections can still be made. Once the rollers have compacted the material, defects become much more difficult and expensive to fix. Also watch for the Contractor folding the hopper wings into an empty hopper — this dumps cold material into the mix and can cause a defect in the mat. The hopper should be at least half full before the wings are folded.
Joints
Joints are one of the most critical aspects of HMA construction and require close attention from the inspector. Poorly constructed joints are a leading source of premature pavement deterioration. Per Section 401.3 of the Standard Specifications, joints must be constructed to meet surface and compaction requirements, and all vertical contact surfaces must be tacked before placing new mixture against them.
Longitudinal Joints: The longitudinal joint between the travel lanes and the shoulder should be placed on the shoulder side with a 6-inch offset from the lane line. Longitudinal joints between adjacent passes should be constructed while the first mat is still warm, if possible (echelon paving). When paving against a cold joint, the edge of the previously placed mat should be tacked and the new material should slightly overlap the existing mat to create a tight joint. The roller should then "pinch" the joint by first making a pass within 6 inches of the joint, ensuring material is fully pushed against it, and then by running with the drum extending approximately 6 inches over the existing lane, providing compaction.
Transverse Joints: When the paving operation is discontinued (end of day, end of a run), a transverse joint must be constructed. The length of the temporary ramp taper should be approximately 5 feet for each inch of mat thickness. Before paving resumes, the cold end of the previous mat must be cut back to a clean, vertical face, and the face must be tacked before new material is placed against it.
Inspector Tip: Walk the longitudinal joints after rolling. A well-constructed joint should be tight and uniform with no visible gap or ridge. Run a straightedge across the joint — if you can feel or measure a deviation, the joint needs attention. Joint density is one of the most common areas of deficiency; ensure the Contractor's roller pattern adequately addresses joint compaction.
Safety Edge
Paving where the final edge of pavement is not confined by curb, must have a safety edge applied, as noted in the Standard Construction Details. The inspection should check that the safety edge device is installed on the screed prior to releasing pavement. Once placement begins, the inspector should review if the device is providing the required result.
Compaction
Compaction is the process of increasing the density of the placed material and is essential to the long-term performance of the pavement. Inadequate compaction leads to premature rutting, moisture infiltration, oxidation, and reduced pavement life.
The Contractor's roller pattern should be established at the pre-pave meeting and verified during the first day of paving. A typical roller pattern consists of:
- Breakdown Rolling — The first rolling pass, typically performed with a vibratory or static steel drum roller, beginning immediately behind the paver while the material is still hot enough to be compacted effectively. Breakdown rolling achieves the majority of the required density.
- Intermediate Rolling — Additional passes to achieve the target density. Pneumatic tire rollers may be used for intermediate rolling, particularly on base and leveling courses, as they knead the material into cracks and depressions.
- Finish Rolling — The final rolling pass, typically performed with a static steel drum roller, to remove roller marks and smooth the surface.
Rollers should operate at a consistent speed and should not stop or reverse direction on the hot mat, as this can displace material and create marks or depressions. The roller operator should begin at the low side of the pavement and work toward the high side, each pass overlapping the previous by approximately half a drum width. At joints, the roller drum should extend approximately 6 inches over the joint onto the previously placed lane.
Compaction Testing: The Contractor performs quality control of pavement compaction by testing in-place pavement density. The Contractor is limited to taking a single core on the first day of paving or after the change of a JMF for gauge calibration. Core holes must be repaired in accordance with the QC/QA Special Provision. The Engineer will perform quality assurance testing and evaluate compaction quality in accordance with the contract provisions.
Inspector Tip: The window for effective compaction is limited by the temperature of the material. Once the mix cools below approximately 175°F, additional rolling becomes ineffective and may actually damage the surface. In cool or windy weather, this window is shorter. Communicate with the Contractor if you observe rolling that is not keeping pace with the paver. The roller must stay close enough behind the paver to compact the material while it is still at an adequate temperature.
Cooling / Release to Traffic
After final rolling is complete, the pavement must be allowed to cool sufficiently before it is opened to traffic. Releasing traffic too early can cause rutting, shoving, and permanent deformation of the new pavement surface.
Per the Standard Specifications, all HMA lifts must be placed, compacted, and allowed to cool to at least 130°F — or cool enough to support construction equipment without visible distortion or distress — before placing any subsequent HMA layers. The same principle applies to opening the pavement to public traffic. In practice, the pavement should be cool enough that a vehicle tire does not leave a visible impression.
Wearing Surface Tolerance: DelDOT uses a rideability specification to ensure the final surface is acceptable however, DelDOT's previous specification provide good guidance on if a surface deviation may need correction. The inspector should check for deviations in the finished surface, that exceed 1/4-inch in 10 feet, at locations where defects are most likely to occur, such as transverse joints, utility structures, lane transitions, and areas where the paver stopped.
If the contractor cannot complete spreading and compacting a full truck load of mixture by sunset, the truck should not be unloaded unless the Engineer has granted approval for nighttime paving.
Before releasing the roadway to traffic, the inspector should verify that:
- All temporary pavement markings have been placed or restored.
- Pavement drop-off signs or "Uneven Pavement" signs are in place where required.
- Drainage structures are accessible and functioning.
- The pavement surface is free of loose material, debris, and equipment.
Inspector Tip: Check the pavement surface temperature with a thermometer or infrared temperature gun before releasing to traffic. In warm weather, especially in direct sunlight, the pavement may take longer to cool than expected. If the pavement is still soft under your shoe, it is not ready for traffic. Document the time the roadway is opened to traffic in your daily diary.
E4.02 - Crack Sealing
Return to Part E - Standard Construction Procedures And Equipment.