Calibrating and Inspecting the Asphalt Distributor for TVAR�

There are several additional distributor checks which should be done by the contractor and observed by the inspector when TVAR is used.
Nozzle Selection and Position.
 The selection of nozzles to provide the desired asphalt rate variation is a contractor decision to be verified during the additional distributor calibration run or runs.�
The inspector, however, must define the desired wheel path locations to allow the contractor to position the larger nozzles appropriately. Potential nozzle configurations to establish three-foot wheel path locations for various roadway widths are shown in Table 4-8. Many factors affect where the majority of traffic will track on a given roadway. The inspector may elect to use a different nozzle configuration than that shown to better approximate average wheel path locations on given roadways.
Table 4-8. Suggested Nozzle Configurations�
Lane Width,�Feet
Center Line to�Wheel Path�Nozzles
Inside Wheel Path Nozzles
Between Wheel�Path Nozzles
Outside Wheel�Path Nozzles
Wheel Path to�Pavement Edge�Nozzles
9
1
9
6
9
2
10
2
9
6
9
4
11
4
9
6
9
4
12
5
9
8
9
5
12 (with edge line)
6
9
8
9
4
13
7
9
8
9
6
This table is based on recommendations provided by the Brownwood and Bryan Districts.�
Setting Computerized Distributor Controls.
 Modern asphalt distributors have computer controls for the asphalt rates to be applied. The contractor and inspector must understand the meaning of the asphalt rate entered into the distributor’s computerized controller(s).�
When a distributor with a single spray bar is being used, unless otherwise indicated in the distributor’s operation manual, the computer setting establishes the total amount of asphalt to be applied. Therefore, when transversely varying asphalt rate with a single spray bar, the correct asphalt rate to be set on the distributor’s computer controller is the average asphalt application rate. The average asphalt application rate is determined by the formula below.�
[(L/100) x (V/100) x R] + R = Average Rate
Where�
L = % of larger nozzles = (number of larger nozzles/total number of nozzles) x 100�
V = % increase in asphalt rate selected for outside of the wheel paths, and�
R = design rate of asphalt application for the wheel paths in gallons/SY.�
Correct determination and entry of the average asphalt rate into the distributor’s computer controller is a critical point for inspection prior to beginning TVAR seal coat operations. When a distributor with dual spray bars and having separate computer controllers is being used, the asphalt rate to be entered into each computer is the specific rate expected from the spray bar that each computer controls. Equipment operator’s manuals should be consulted to verify proper computer entries.�
Calibrating the Distributor to be Used for TVAR.
 The asphalt distributor must be calibrated as required for uniform asphalt rate applications as well as being demonstrated capable of applying asphalt at the TVAR percentage(s).�
When the distributor is capable of varying the asphalt rate incrementally and over a wide range, the inspector should request that the contractor demonstrate specified application accuracy and uniformity with no asphalt variation across the bar and also at two variation rates, 15 and 30 percent. Proving ability to apply asphalt in these three manners adequately demonstrates capability throughout the covered range provided that the same selection of nozzle sizes is being used.�