Materials & Composition (851.02 & 851.03)
Spreading and Compacting (851.08)
Quality Control and Acceptance (851.11)
Protection of the ATFDB (851.13)
Exposure to the Elements (851.14)
Method of Measurement and Basis of Payment (851.15 & 851.16)
Documentation Requirements – 851 Asphalt Treated Free Draining Base
This work consists of constructing asphalt treated free draining base (ATFDB) course, mixed in a central plant and spread and compacted on a prepared surface. The (ATFDB) drainage layer is immediately beneath the pavement and is made of graded aggregate, asphalt-treated permeable material. Construction of this drainage layers will serve satisfactorily as drains and as structural support for the surfacing materials.
The requirements of Item 401 apply, except as modified by Supplemental Specification 851.
The aggregate gradation should conform to Table 703.01-1 and 703.04 with the exceptions detailed in 851.02 and the binder should be PG 64-22 conforming to the requirements of 702.01. The contractor is not allowed to use reclaimed asphalt concrete pavement in the mix.
The binder amount should be 1.5 to 3.5 percent by weight of the mix with the aggregate. Ensure that the aggregate does not show excess drainage at 250 °F (120 °C) and is coated with shiny black coating of asphalt binder.
Brown or dull mix appearance is not acceptable and is a sign of excess aggregate absorption of the asphalt binder or low asphalt binder content. Minor bare aggregate exposure is acceptable.
A minimum of 3 weeks before the production of the ATFDB, the contractor should submit a computed blend of aggregate and asphalt binder, using standard JMF submittal forms, and production temperature range to the Laboratory for initial design verification. The contractor should notify the Laboratory before the delivery of any material.
Final design verification is subject to field verification and actual performance. Field verification may include additional testing by the Laboratory.
The contractor should use only tandem steel wheel rollers weighing 6 to 10 tons (5.5 to 9 metric tons) for compaction.
The contractor should spread the ATFDB mix only when the atmospheric temperature is above 45 °F (7 °C).
Cease all operations if rain occurs during placement of the ATFDB, or when rain is imminent. Do not spread on frozen material.
The contractor should spread the ATFDB material in a method that produces a smooth, uniform layer before compacting. Cease all operations when signs of degradation, segregation, or contamination are evident. Communicate with the contractor and the material monitor to resolve the problem before resuming placement.
The contractor should compact the ATFDB sufficiently, by compacting the layer at least two roller passes over any given point, unless otherwise directed by the engineer for more passes. Do not over compact the ATFDB to the extent where the aggregate particles are crushed or broken. Complete rolling before the mix temperature has dropped to less than 100 °F (38 °C).
Do not cool ATFDB with water.
Form transverse construction joints by cutting back into the completed work to form a vertical face.
If significant breakup of the ATFDB occurs at or near the outer portion of a lift during the compaction operation, provide lateral support using forms or other methods approved by the Engineer at no additional cost to the Department. Do not contaminate the ATFDB with this lateral support.
When the ATFDB is placed in areas inaccessible to rollers, compact it using a method approved by the Engineer.
After compaction has been completed, do not place the next layer of pavement on the ATFDB until the next day.
The compacted thickness of the ATFDB layer should be 4 inches (100 mm). Ensure the placed ATFDB conforms to the specified thickness by randomly checking the thickness during construction. The district could run a dry-rodded unit weight to establish a conversion factor that could be used to establish the required placement rate as per 401. Also, since the loose layer does not compact much a check using a prod should be used frequently to check the layer thickness. Remove all sections found to be ±½ inch (±13 mm) from the specified thickness and replace them with ATFDB at no additional expense to the Department.
Ensure that the finished surface is uniform and varies no more than ½ inch (13 mm) from a 10-foot (3 m) straightedge applied to the surface parallel to the centerline of the pavement. Remove any section found to be out of tolerance and replace it with ATFDB within the specified tolerance at no additional expense to the Department.
The quality control and acceptance requirements of Item 403 apply, except as detailed in 851.11. Project administrators should check with the district lab to ensure material conformance to the specifications.
The ATFDB should be coated with shiny black coating of asphalt binder and not be brown or dull in appearance. Minor inconsistent bare aggregate exposure is acceptable. If the delivered mix is brown or dull in appearance, immediately inform the district lab and the contractor to adjust the asphalt binder content.
Ensure that the underdrain system is functional before placing the ATFDB. Do not allow construction equipment to crush the underdrain pipe or system as a result of the placement or compaction of the ATFDB. Ensure a positive connection between the underdrain system and the ATFDB regardless of the sequence of operations in the Contract Documents.
The ATFDB is not designed to carry construction traffic. The Engineer will allow hauling units and other construction vehicles to operate on the ATFDB provided no significant displacement, breakup, or contamination occurs. If the Engineer determines significant displacement, breakup, or contamination of the ATFDB is occurring, the Contractor shall stop operating hauling units and construction vehicles on the ATFDB. The contractor should repair or replace all damage to the ATFDB, subbase, subgrade, or underdrains caused by the hauling units or construction vehicles at no additional expense to the Department.
The ATFDB layer should be protected from fine material contamination. Adequate surface and subsurface drainage for the ATFDB, subbase, and subgrade should be provided at all times.
The Contractor may use a rubber tire paver if it does not damage the ATFDB, subbase, subgrade, or underdrains. If damage occurs, cease paving and switch the rubber tire paver with a track mounted paver before restarting the paving.
When constructing asphalt concrete pavement on the ATFDB, allow the first course to cure overnight before placing the succeeding pavement courses.
The ATFDB layer should be covered by constructing the pavement within 40 days, and before the atmospheric temperature falls below 35 °F (2 °C) for any period of time
The contractor should remove and replace all damage caused to the ATFDB, subbase, subgrade, or underdrains by the exposure to temperatures below 35 °F (2 °C) at no additional expense to the Department.
The Department will measure the accepted quantities of Asphalt Treated Free Draining Base by the number of square yards (square meters). The Department will measure the width as the width of the asphalt treated free draining base shown on the typical sections of the plans and additional widening where called for, or otherwise directed in writing by the Engineer. The Department will measure the length horizontally along the centerline of each roadway or ramp. Payment will be made at the contract bid price for work that is accepted in place.
1. State condition of base (example: primed 304, clean and dry concrete, etc.)
2. Write location on tickets where material is placed
3. Mark on ticket the time unloaded
4. Obtain temperature of the mix at project site and place this information on ticket of load checked. This should be done a minimum of four times daily or any time temperature is in question.
5. State kind of rolling equipment.
6. Calculate and document the required placement rate (Tons/Station)
7. Document on form CA-FP-4 Project documents compliance with Item 851 on Form CA-D-3A and measurements on CA-D-1 and 2
8. Document lift thickness
9. Tickets should be totaled with initialed and dated tape attached