Preparation of Surface (407.05)
Application of Asphalt Material (407.06)
Application of Cover Aggregate (407.07)
Quantities for Payment (407.08)
The
tack coat is an application of liquid asphalt material on an existing pavement
surface, used as an aid in bonding a new asphalt concrete course to the
existing pavement surface. Tack coats
are specified for all resurfacing work.
Since most resurfacing work is performed with traffic maintained,
special attention must be given to traffic control requirements.
The
inspection and approval of asphalt distributors used to apply tack coat
material are governed by the ability to fulfill 407.06
and 407.03. Mechanical sweepers and other related hand
equipment may be of any type that will accomplish the required results.
The tack coat should not be applied when the surface temperature of the existing pavement is below the minimum placement temperature for the pavement course to be placed. The minimum placement temperatures for pavement courses are specified in 401.06. The surface temperature is to be recorded on the Inspector’s Daily Report.
The preparation of the existing pavement surface for the application of a tack coat is a cleaning operation. All material accumulations on the existing surface should be removed which would interfere with the adhesion of the tack coat or with the placing and performance of the asphalt course. This material includes dust, loose aggregate, soil, leaves, and pieces or lumps of other foreign material deposited on the surface. Cleaning may require brooming, handscraping, and perhaps power blading of heavy accumulations. Special attention should be given to the edges to assure proper coverage of the full width intended.
Emulsions
may be applied on damp surfaces. The
pavement should not be wet. There should
be no visible, flowing water on the surface.
A field review of the existing pavement surface should be made soon after the award of contract in order to determine tack coat requirements. Requirements should be determined and transmitted promptly to the Contractor to facilitate job planning. Guides for determining quantity of tack coat needed are given under the following types of resurfacing:
When
the contract requires traffic to be maintained, tack coat application should not
be allowed to start until the provisions of the traffic maintenance item have
been met. Alternate movement of one-way
traffic must be in place before the distributor is brought into the starting
position. Give special attention to the
Contractor’s operation relative to traffic movement. Every reasonable effort should be made to keep “pick up” of the
asphalt material, prior to paving, to a minimum. This may involve tacking in sections and allowing time for
curing.
Only asphalt material meeting the requirements of 407.02 can be used. Loads of asphalt material delivered to the project should carry evidence of approval as defined under section 106. This evidence of approval and the material weight tickets must be validated at the paving site.
The inspector should make a general inspection of the distributor to become familiar with the particular equipment and to detect any variance from the specifications that can be observed. In particular, 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. 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.
For large areas, the application rate is determined by the application of a given quantity of an asphalt material over a known area. The rate is calculated using the gallons (liters) indicated by the volume indicating device on the distributor, the known length of the distributor run, and the measured width covered. The distributor may be approved only when the measured application rate is within plus or minus 10 percent of the required rate. The application rate for small areas, where volume measurement is not practical, may be judged visually.
The operation of the distributor is judged by visual observation. The quantity of material flowing from each nozzle should appear to be uniform. The angle of each "fan" of material with the spray bar should appear to be the same; the particular angle is specified by the manufacturer. The material should be applied uniformly across the width of the spray bar with no visible streaks and with no apparent variations in thickness from the beginning to the end of the run.
The results of the foregoing observations and check tests 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.
The
asphalt material should be sprayed uniformly on the pavement surface. If streaking occurs, the Contractor must
adjust the distributor. Streaking is
caused by faulty distributor adjustment or operation, resulting in the asphalt
material being placed in ridges.
Contrary to popular belief, these ridges will not “flow” together. The result is insufficient asphalt material
between the ridges to bond the new asphalt paving course to the existing
pavement surface.
Cover aggregate shall only be used in areas where the asphalt material will be exposed to traffic.
If cover aggregate is used, approved cover aggregate is required to be sufficiently dry to permit adhesion of liquid asphalt. When the cover aggregate is placed on an asphalt emulsion tack coat, the aggregate may be moist, but not to the extent that free water drains from the truck bed.
For all types of asphalt materials, the cover aggregate should be placed as close behind the distributor as is practical.
The
Contractor is required to apply only the quantity of cover aggregate needed to
prevent “pick up” by traffic.
Determine
gallons (liters) from weigh tickets or weighed partial loads. For weights or volumes that are questionable
or unknown a volume-measuring device is required before accepting the
material. Cover aggregate is included
in the bid price for the tack coat.