Pavement Preservation Checklist Series
03- Thin Hot-Mix Asphalt Overlay Checklist
PDF file (0.2 mb)
This checklist is one of a series created to guide State and local highway maintenance and inspection staff in the use of innovative pavement preventive maintenance processes. The series is provided through the joint efforts of the Pavement Preservation Program of the Federal Highway Administration (FHWA) and the Foundation for Pavement Preservation (FP2).
FHWA uses its partnerships with FP2, the American Association of State Highway and Transportation Officials, and State and local transportation agencies to promote pavement preservation.
To obtain other checklists or to find out more about pavement preservation, contact your local FHWA division office or FP2 (at http://www.fp2.org/), and check into these Web pages:
- Is this project a good candidate for a thin hot-mix overlay?
- What is the existing pavement section?
- What is the average daily traffic and the percentage trucks and busses?
- Is rutting present? If so, is the rutting due to mix instability?
- Is cracking present? If so, to what extent?
- Is the pavement structurally sound (no alligator cracking or potholes)?
- Do other pavement distresses exist? If so, to what extent?
- Polished aggregate
- Have drainage deficiencies been corrected?
- Review project for bid/plan quantities.
- Is this treatment cost-effective?
- Bid specifications and special provisions
- Construction sequence
- Mix design(s)
- Traffic control plan
- Construction manual
- Material safety data sheets
- Are materials from an approved source?
- Asphalt cement
- Tack coat
- Asphalt grade is based on environmental and traffic factors.
- Aggregate(s) meet consensus and source properties.
- Aggregate(s) meet required polish (skid) value.
- Mix(es) are from an approved hot-mix plant.
- Mix(es) design, asphalt content, target gradation, and air voids meet specifications.
- Asphalt/aggregate mix has been checked for moisture susceptibility.
- Nominal maximum aggregated size is less than one-third the overlay thickness for dense graded mixes.
Preoverlay Inspection Responsibilities
- Aggregate stockpiles are clearly marked, separated, and free of contamination.
- Aggregate cold feeds have been calibrated.
- All cold feed gates and belts are in working order.
Asphalt Storage Tank
- The asphalt storage tank is capable of keeping the asphalt temperature within the required specification range.
- The plant is properly calibrated and the scales have been checked.
- Production rates have been determined versus various aggregate moistures to provide a mix free of moisture.
- Temperature gauges and asphalt flow meter have been checked for accuracy.
- Mixing times have been established to assure the aggregate will be thoroughly coated with the asphalt cement.
- The plant is capable of providing the completed mix at the proper temperature and within the required timeframe.
Surge/Storage Silo (if applicable)
- The maximum mix storage time has been established.
Lime and Filler Silo (if applicable)
- The feeder system has been calibrated.
- Trucks are equipped (if required) with tarpaulins that meet State or local regulations.
Tack Coat Distributor
- The distributor is properly calibrated.
- The nozzles are unplugged and are able to apply a uniform tack coat at the specified rate.
- Is a pick-up machine being used?
- Is a material transfer vehicle being used?
- Is the paving machine well maintained and in good working order?
- Tires are properly inflated or tracks properly adjusted.
- Flow gates
- Slat conveyor
- Hopper wings
- What type(s) of rollers will be used for breakdown, intermediate, and finish rolling?
- A sufficient number of rollers of adequate size are available to achieve the desired compaction.
- Water spray bars, wetting pads, and scraping bars are working on all rollers to avoid material buildup.
- Steel drums are free of grooves and dents and not warped.
- Rubber tires (if applicable) are inflated to within +/-34.5 kPa (+/- 5 psi).
- Vibratory plates or hand tampers are available for areas inaccessible to rollers.
- Pavement distress and drainage deficiencies have been corrected.
- Cracks greater than 7.9 mm (5/16 in) have been sealed within 3.2 mm (1/8 in) or flush with existing surface.
- Alligator cracks and potholes have been removed and patched.
- Rutting has been milled where it is the result of mix deficiencies and milled or leveled where it is due to wear or postconstruction consolidation.
- Grade and cross-slope have been established.
- Manholes, catch basins, and utility appurtenances have been raised to the level of the new overlay.
- A scratch or leveling course, if required, is applied prior to the overlay.
Project Operational Considerations
- Air and surface temperature meet agency requirements.
- Paving does not begin if rain is imminent.
- Check temperature, wind, humidity, sun/clouds (and lift thickness). All will affect how quickly a mix cools and the time available for compaction.
- Signs and devices match the traffic control plan.
- The set-up complies with local agency requirements or the Federal Manual on Uniform Traffic Control Devices (MUTCD).
- Any unsafe conditions are reported to a supervisor.
- The pavement will not be opened to traffic until it has cooled to 60 °C (140 °F) or the agency's required temperature.
- The surface is clean and dry.
- The tack coat is being applied uniformly at proper rate.
- The tack coat is cured prior to placement of overlay.
- Sample aggregate stockpiles and compare gradation of each to design.
- Sample aggregate from cold feeds and compare combined gradation to design.
- Sample aggregate for moisture and make any necessary adjustments to the hot-mix plant.
- Take random samples of aggregate per the approved quality control plan.
- Sample hot-bin (if applicable) aggregates and run gradation, calculating percentage required from each bin to meet the design gradation.
- Check that asphalt cement is within the required specification range.
- Check plant mix for uncoated aggregate.
- Random sample and test plant mix, checking it against mix design:
- Percentage asphalt
- Air voids
- Other agency requirements
- Sufficient trucks are available to allow the paver to keep moving at a uniform speed.
- Trucks are clean and free of solvents before the mix is loaded.
- Trucks have tarpaulins to cover mix (when required).
- Trucks are insulated (when required).
- Trucks are loaded in a manner that avoids segregation.
- Paving screed is preheated before starting placement.
- Mix arriving at the paving site is within the specified temperature range.
- Mix is being placed at the proper grade and cross-slope and at the specified thickness.
- Surface texture is uniform, free of segregation, tearing, or scuffing.
- Placement is providing a smooth riding surface.
- Automatic screed control is used whenever possible. (If manual controls are used, avoid frequent changes.)
- Construction joints (transverse and longitudinal) are tight with a smooth transition.
- Quantity yields or thicknesses are checked throughout the placement.
- A roller pattern has been established that achieves the proper in-place air voids.
- The established rolling pattern is being followed.
- Check density of finished mat: are air voids within specifications?
- Steel-wheeled vibratory, steel-wheeled static, or rubber-tired rollers are used for breakdown and intermediate rolling.
- Steel-wheeled static rollers or vibratory rollers in the static mode are used for finish rolling.
- Vibratory rollers are operated-
- at an amplitude and frequency as selected according to mix harshness and lift thickness (for thin lifts, high frequency and low amplitude are usually used).
- at maximum frequency and at a speed that provides a minimum of 1 impact per 2.54 cm (1 in).
- in the static mode when lift thickness is 2.54 cm (1 in) or less.
- Rubber-tired rollers-
- have tires warmed up to prevent pick-up.
- are used on scratch/leveling courses.
Opening to Traffic
- The pavement can be opened to traffic after the mix has been compacted and the mat has cooled to 60 °C (140 °F) or the agency's required temperature.
Common Problems and Solutions
- Plant mix discharge temperatures too low: Moisture in the stockpile may be higher than initially planned; decrease production rate.
- Uncoated aggregate in the plant mix:
- Moisture may be in the aggregate.
- Worn or missing flights may be in the hot-plant drum dryer.
- Mixing time may be too short (check slope of drum for drum mix plants).
- Segregation in the mix:
- Use multiple drops instead of a single drop when loading the trucks from the hot-mix plant storage silo.
- The haul truck should raise the truck bed slightly to break the load before unloading into the paver hopper.
- When the paver wings are folded, do it slowly and be sure mix remains above the flow gates.
- Keep a constant head of material to the paver's auger and screed.
- Harsher or stiffer mixes will require more care when placing and compacting.
- Lack of in-place density:
- The aggregate gradation may be outside of the target gradation.
- Asphalt content may be too low.
- Roller pattern or the frequency or amplitude of the vibratory roller may need adjusting.
- Plant mix may be below optimal rolling temperatures.
- Check the density of the underlying mat, which will influence nuclear gauge readings on thin overlays. If this is the case, a control strip can determine the maximum achievable density.
- Nominal maximum aggregate size may be too large for lift thickness. Use different mix or increase thickness.
- Plant mix has a lean or dull appearance: The mix may contain too little asphalt or an excess of minus No. 200 sieve material.
- Plant mix slumped in the haul truck: Properly mixed material in a haul truck will have a dome shape. If the load of mix has a flat shape, there may be excessive asphalt or moisture.
- Tears in the plant mix after rolling: Tearing of the surface occurs if the mix is too cold, too dry, has too many fines, has excess moisture, or has been overrolled.
- Poor surface smoothness or rough ride:
- Multiple stop-starts of the paver.
- Excessive paver speed.
- Improper use of manual screed controls.
- Vibratory rollers operating at excessive speed (impacts spaced too far apart).
- Poor joint construction practices.
Information in this checklist is based on or refers to the following sources:
- Manual on Uniform Traffic Control Devices, Millennium Edition. 2000. Federal Highway Administration.
- An Overview of Surface Rehabilitation Techniques for Asphalt Pavements. Pub. No. FHWA-PD-92-008. 1992. Federal Highway Administration.
- Pavement Maintenance Effectiveness: Preventive Maintenance Treatments. Instructor's Guide, pp. 111-133. Pub. No. FHWA-SA-96-028, 1996. Federal Highway Administration.
- Pavement Maintenance Effectiveness: Preventive Maintenance Treatments. Participant's Handbook, pp. 113-132. Pub. No. FHWA-SA-96-027, 1996. Federal Highway Administration.
- Thin-Surfaced Pavements, Synthesis of User Practices. NCHRP Synthesis 260. 1998. Transportation Research Board, National Cooperative Highway Research Program.
For more information on pavement preservation, visit these Web sites:
For more information on the Pavement Preservation Checklist Series, contact:
Construction and System Preservation Team
Office of Asset Management
Federal Highway Administration, HIAM-20
U.S. Department of Transportation
1200 New Jersey Avenue SE, Room 3211
Washington, DC 20590
National Center for Pavement Preservation
Michigan State University
2857 Jolly Road
Okemos, MI 48864
Foundation for Pavement Preservation
8613 Cross Park Drive
Austin, TX 78754
Telephone: 866-862-4587 (toll free)
Publication No. FHWA-IF-02-049
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The Federal Highway Administration provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.
U.S. Department of Transportation
Federal Highway Administration