Chip seal consists of the application of polymer modified asphalt emulsion covered by an aggregate course. It is applied as a single or double chip seal for use as a surface course on all types of pavements and on paved berms. Chip seal can also be used as an intermediate course for a hot mix asphalt surface course.
The purpose of a chip seal is to seal and protect the underlying course from weathering and from wear by traffic. A coating of asphalt material helps seal existing pavement cracks and joints and the cover aggregate provides a skid-resistant surface.
When applied on berms, the cover aggregate provides delineation of the traffic lanes from the berms by a change in surface color and texture.
A Chip Seal Operation
The Inspector must make a general examination of the distributor to ensure compliance with the requirements of this specification and 407.03. The equipment used for the application of a tack coat is the same as used for the application of the polymer binder for chip seal but must include a computerized rate control that automatically adjusts the binder pump to the unit ground speed. This control must have a gauge or meter (in gallons) that is easily read. The spray nozzles must be appropriate for the material and rate specified. In addition, the approval of the distributor is based on observation of the operation and check measurements of the actual application rate, performed as described in the following paragraphs. The Inspector should have the Contractor demonstrate the use of the required volume measuring device, thermometer, and application controls. Work should not be permitted to start if this equipment is unsatisfactory.
The operation of the distributor is judged by visual observation. The quantity of material flowing from each nozzle should appear uniform. The angle of each "fan" of material with the spray bar should appear to be the same; the angle is specified by the manufacturer. The material should be applied uniformly across the width of the pavement with no visible streaks and with no apparent variations in thickness from the beginning to the end of the run.
Distributor with Improperly Aligned Nozzles (at Different Angles)
Streaking or ridging will not be tolerated when applying polymer binder for chip seal work. This type of defect is generally caused by nozzles that are not all at the same angle in respect to the spray bar. The Inspector must approve or prohibit use of a particular distributor accordingly.
The results of the foregoing observations and the results of the test section are recorded for each distributor proposed for use, together with a means of identification (license plate or equipment number) and indication of approval or non-approval. This information is entered in the project record as a supplement to the Inspector's Daily Report.
After the initial inspection, continued approved status of a given distributor depends on continued satisfactory results determined visually or by additional checks when deemed advisable.
Asphalt Distributor Applies the Polymer Binder
Only Type II pneumatic rollers conforming to 401.13 are permitted for embedding the cover aggregate, however the maximum capacity shall not apply.
Type II Pneumatic Tire Rollers
The aggregate spreader must be self propelled with a variable width aggregate hopper (8 to 16 feet) and shall conform to specification 422.03. The spreader must produce a uniform application of aggregate without gaps or ridges at the rate specified. Spreaders must have pneumatic tires, a screen to prevent oversized material from passing through to the roadway, revolving cylinders, and adjustments.
Aggregate Spreader Spreads the Aggregate on top of the Polymer Asphalt Binder
Rotary brooms are used for the initial surface preparation to sweep the roadway prior to the application of the polymer binder. After the cover aggregate application a rotary broom or sweeper is required to sweep excess aggregate from the completed surface without dislodging the embedded aggregate. Be sure that aggregate is not being swept onto adjacent lawns.
For chip seals, the weather limitations are specified in 422.04. This section requires a minimum pavement and air temperature of 60 °F (16 ºC). Work should not begin if temperatures are forecast to be below 50 °F (10 ºC) within 24 hours from the start of work. Do not place the chip seal if the existing pavement temperature is 140 °F (60 ºC) or above. This work is not to be done before May 1 or after September 1.
The Contractor is required to provide a test strip to demonstrate that the equipment and operations can meet the requirements of the specifications. Do not waive the test strip.
The test strip must be 1000 feet long by one lane width wide. The test strip must be continuous. The test strip is used to determine the binder application rate, the aggregate application rate, and the aggregate gradation.
During the test strip the aggregate spreader will calibrated by applying aggregate to a piece of cardboard of a known size (generally 1 square yard). The material is collected from the cardboard and weighed to determine the application rate (pounds/square yard). Based on acceptance of the test strip this will be the rate of cover aggregate application.
The proper binder application rate will be determined. Initially the binder should be applied at the target rate specified. The depth of embedment of the aggregate will be checked visually. A good rate of application will provide an average of 2/3 embedment of the chip in the binder after rolling. The Engineer will make adjustments to the rate as needed to obtain the proper embedment. The rate will be calculated using the test strip dimensions and the number of gallons used as measured by the distributor gauge or meter (gallons/square yard).
The Engineer will review the test strip the following day. The acceptance criteria of 422.11 will be used to determine acceptance of the test strip. These criteria include proper chip embedment; binder streaking, ridging, and flushing; loss of cover aggregate; and joint construction. The Engineer may require another test strip if there are problems with the application.
Before a chip seal is applied to an existing surface, all material accumulations, debris, foreign objects, dust, leaves, soil etc. that would interfere with the adhesion of the asphalt material must be removed. Proper cleaning of the surface requires power brooming and may necessitate hand scraping and power blading of heavy accumulations. Hand brooming may be necessary. Special attention should be given to the edges of the roadway to assure proper coverage of the width intended.
Only asphalt binder materials meeting the requirements of 422.07 are permitted. Check the specifications for project conformance. Asphalt binder is shipped under ODOT’s Asphalt Materials Certification Requirements as detailed in Supplement 1032. Ensure that the material used on the project is from a certified source.
A uniform application in the transverse and in the longitudinal direction is important. Continued application should not be permitted when visible defects occur. Where it is demonstrated that distributor results are erratic, discontinue use of the equipment until the problem is corrected.
The binder must be maintained at 150 to 185 °F (65 to 85°C) during application and at the beginning of the day. Binder is not to be reheated at a rate faster than 25 °F (14°C) per hour when it has been allowed to cool to below 150 °F (65 °C).
With all other conditions being equal, the application rate of asphalt material depends on the average size of the cover aggregate particles. In a good chip seal, the average size aggregate will be embedded for approximately 2/3 of its height after thorough seating by rolling. This can be checked by pulling out chips by hand and visually inspecting how much of the chip is coated. When the binder application rate is too heavy, the particles may become totally embedded, resulting in a flushed or bleeding surface. When the application rate is too light, the particles may not be held with sufficient firmness to resist dislodging by traffic, and a loss of cover aggregate will result.
The binder application rate required to produce proper embedment for a given particle size also may depend upon the porosity, absorption, and firmness of the surface to be sealed. The rate required by the specifications may need field adjustment depending upon the actual nature of the surface. Considerable judgment is required to determine the proper application rate and to avoid undesirable effects of bleeding or raveling. If proper stone embedment is not obtained, the Engineer must be notified and the application rate adjusted and documented.
The binder application must be started and stopped on a removable protective cover of paper, cardboard, metal or other material that protects the adjacent pavement or previous chip seal from being coated. The use of the protective cover allows the binder to be applied at the full rate at each ending and beginning point but does not allow the binder to be applied to existing pavement or over applied on a previously constructed chip seal. The binder application must not be lapped, such as where one day’s production meets the next. The protective cover must be removed immediately after use.
Chip Seal Prior to Rolling
Only aggregate that has been approved is permitted for use. Collect the weight tickets when the material is received at the paving site.
The previously established spreading rate of aggregate must be verified using a 1 square yard of cardboard, weighing, and determining pounds per square yard. The Contractor must make adjustments to the spreader as necessary to meet the test section calibrated rate.
The aggregate must be sufficiently free from dust and moisture to permit immediate adhesion of the asphalt material. Material delivered to the site with water running from the bed of the truck must be rejected.
Application of cover aggregate in excess of requirements for complete coverage and that would be considered a nuisance to the public will require the work to be stopped. It is unacceptable to rely on brooming or vacuuming to remove excess aggregate. The spreading operation requires recalibration in these cases.
The Contractor must establish stations for the project at 1000 feet intervals before placing any material. The stationing must be clearly marked and be maintained throughout the project. Stationing is typically provided using wooden lath along the roadway and the markings should be easy to read.
The binder distributor, aggregate spreader, and rollers must be as close to each other as possible. The binder distributor cannot be more than 150 feet ahead of the aggregate spreader.
The longitudinal joint must be placed on a lane line or as the Engineer directs. For double chip seals, the longitudinal joint for the first course is to be placed 6 inches off the centerline and the second course is to be placed on the centerline.
Where a double chip seal is required by the plans, the first course must be cured, swept and capable of withstanding construction traffic. Any deficiencies or damage must be corrected before placing the second course of chip seal.
Rolling of the chip seal cover aggregate is required to begin immediately behind the aggregate spreader. Three rollers minimum are required. Do not allow the aggregate to go unrolled for more than 5 minutes. This is to ensure that the aggregate particles will be embedded in the asphalt binder before the binder sets up. If the binder sets up before the aggregate is rolled the result will be loose stone that must be removed. That section of roadway would be unacceptable and would require rework.
The specifications require a minimum of two complete roller passes of the cover aggregate. A single complete pass is forward and back over the same area. Each new pass must be overlapped by ½ of the roller width. While making these passes, the speed of the roller must be slow enough, not greater than 5 miles per hour (8 km/h), to avoid displacing or dislodging the aggregate particles from the asphalt. If stone is being picked up by the rollers, have the Contractor adjust the speed.
After the binder sets up for a single or double chip seal the new surface must be swept within 4 hours using a power broom or pickup sweeper to remove all loose aggregate. The Contractor cannot reuse this aggregate in the double chip seal course. There may be issues that do not allow the Contractor to sweep within the 4 hour timeframe like stone moisture, high humidity slow binder cure rate, rain, etc. In this case the Engineer may suspend the operation until the problem is resolved or more favorable conditions prevail that allow sweeping within 4 hours.
Make sure sweeping extends 1 foot beyond the edge of the roadway to remove any loose aggregate that could migrate back to the roadway.
Before opening the road to traffic, the contractor must place “Loose Stone” and “35 MPH” signs on the same post spaced at 0.5 mile intervals. Signs must conform to Item 614.
Where traffic is using the chip seal on two lane roads in the work area, the Contractor must provide a pilot vehicle at 25 mph to guide traffic through the work zone.
The Contractor is responsible for all damage claims that result from his operations and the chip seal surface until the application of the final pavement markings or the application of a fog seal if it is required.
The Contractor is required to provide quality control of the chip seal process and must stop placement and notify the Engineer and DET if any of the parameter tolerances are exceeded. The Contractor must identify and correct problems and receive permission from the Engineer to restart the chip seal operation. Additionally the Department can obtain samples at any time. Aggregate samples can be taken from the stockpile or from the spreader to test for conformance. If Department testing shows out of compliance material, work can be stopped.
The Contractor is to provide an asphalt binder sample on a daily basis for the Department.
The binder application rate cannot exceed ±0.02 gallons per square yard from the established application rate.
Aggregate must meet a specific moisture content and gradation as provided in 422.10. The Contractor is required to reject material that does not meet these requirements. If water is seen running from the truck bed when aggregate is brought to the job it must be rejected.
The Contractor must provide a daily quality control report to the Engineer that includes the specific information as listed in 422.10.
1. The finished surface shall have no more than four tears or untreated areas greater than 1 inch wide and 4 inches long in any 120 square yard area.
2. Joints are neat and uniform; there is no buildup, uncovered areas, or other unsightly appearance.
3. Longitudinal joints have less than a 2 inch overlap
4. Transverse joints have no more than ¼ inch difference in elevation as measured across the joint using a 6 foot straightedge.
5. The edge of the chip seal does not vary more than 2 inches in any 100 feet along a shoulder or edge.
6. Typical stone embedment is 2/3 of a typical chip
Deficiencies in chip seal construction often do not show up until the surface has been under traffic for a period of time. The Engineer and Contractor will review the completed chip seal in 25 to 35 days after placement. Surface patterns that show streaking or ridging; bleeding/flushing; and loss of cover aggregate are to be specifically evaluated. The Contractor is required to perform corrective work when any one defect exceeds 20% of any 120 square yard area. The following are descriptions of these defects and likely causes.
Streaking is caused by faulty distributor adjustment or operation, resulting in the asphalt being placed in ridges. Contrary to popular belief, these ridges will not "flow" together, particularly when the cover aggregate is applied immediately after the application of asphalt material as required by the specifications. Streaking results in insufficient asphalt material between the ridges to hold the aggregate in place. This aggregate is loose and will be “kicked up” by traffic. This leaves only the aggregate that was embedded in the ridged asphalt producing a streaked appearance.
Streaking and Ridging in Completed Chip Seal
Bleeding and flushing is defined as a migration of asphalt material to the surface, completely or almost completely submerging the cover aggregate. Continuous bleeding is likely the result of too high a rate of application. Spotty bleeding usually is the result of variations in the surface of the existing pavement. Bleeding at tie-ins between distributor loads is the result of an overlap of the previous run.
Bleeding or Flushing of a Chip Seal
Loss of cover aggregate is the detachment, loosening or stripping away of the aggregate material from the asphalt binder leaving behind a black shiny surface. This is a serious form of chip seal failure because of the traffic hazard created by the exposure to the slippery film of uncoated asphalt binder material and loose aggregate particles. It may be caused by one or more of the following:
1. Too light an application of the asphalt material
2. Penetration of the asphalt material into the underlying surface
3. Use of an improper grade of asphalt material for existing conditions
4. Delay in spreading the aggregate on the asphalt emulsion (binder has set up)
5. Excess aggregate application
6. Lack of adequate rolling
7. Use of wet or dirty aggregate
8. Opening the roadway to traffic before adequate curing has taken place
Loss of Cover Aggregate
1. Inspect and document all equipment as to its suitability based on the specification requirements (distributor, aggregate spreader, rollers).
2. The results of the test section must be documented including calibration of the aggregate spreader, adjustments to binder application rate, and the Engineer’s review comments.
3. Bills of lading for the binder and aggregate must be included in the project records.
4. During chip seal placement document air and pavement temperatures; binder and aggregate application operations; rolling procedure; brooming; traffic control procedures including all signing and use of pilot car.
5. The Contractor must provide a Quality Control report with the information listed in section 422.10 of the specifications.
6. Inspect and document the completed chip seal for initial and daily acceptance.
7. Inspect and document the completed chip seal for final acceptance within 25 to 35 days after placement.
8. Measure and calculate for payment accepted chip seal using the actual width of placement and the length along the centerline of the roadway. Payment is in square yards.