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22 CHAPTER 7 Construction 7.1 Equipment Calibrations as possible while an observer watches where the emulsion hits the pavement from each nozzle left open. Emulsion overlaps 7.1.1 Distributor indicate that the bar is too high, and a gap indicates that the Because a uniform application of material laterally and lon- bar is too low. Note that the bar will rise as the distributor gitudinally on the pavement is required, the machines used for empties during spraying, but this rise does not usually cause this purpose, whether controlled by computer or not, must significant streaking that requires spray bar adjustment. be calibrated prior to arrival on the project. First, the nozzles Uniformity of lateral flow from the spray bar should be installed in the spray bar should be the appropriate size for determined by collecting a measured volume of emulsion the planned transverse application rate. Nozzles of equal size in containers placed under each nozzle. This process can be are required for a uniform transverse application rate. When done using standard 6-in. by 12-in. concrete cylinder molds the transverse rate is lower in the wheel paths, the nozzles lined with one-gallon freezer bags (Shuler 1991). One bag is should be sized accordingly. However, the number designa- positioned under each nozzle and emulsion is sprayed into the lined cans until approximately 75% full. Flow is then stopped tion of the nozzle should be checked for flow rate against the and each lined can is weighed. The weight of each lined can published flow rate of the manufacturer using a laboratory should be within 10% of the average for all of the nozzles. Any flow bench. Nozzles used in the spray bar should be checked nozzles that deviate from this should be replaced and the test as a group. Nozzles deviating by more than 10% of the aver- rerun. The cylinder molds can be re-used and the bags with age flow rate of the group should be discarded, replaced, or the contents discarded appropriately. corrected to allow flow that conforms to the average flow rate. Longitudinal calibration of the distributors is done by Nozzles that are calibrated to provide uniform lateral flow measuring the volume of the distributor before spraying must be re-installed in the spray bar following manufacturer's and after spraying 70% to 90% of the distributor volume. recommendations and ensuring that each nozzle is aligned The volume sprayed can be determined using the dipstick at the correct angle to provide desired spray overlap. Noz- supplied with the distributor. The longitudinal spray rate zle angle can usually be adjusted using the wrench provided can then be calculated by determining the area sprayed. This by the distributor manufacturer, an adjustable wrench, or value should then be compared to that displayed by the dis- appropriate-sized open-end wrench. Nozzle angle usually tributor computer, if equipped, to evaluate computer accu- ranges between 15 and 30 degrees. racy; if the rate applied differs from design by more than 5%, After the nozzle angle is set properly, the height of the spray corrective action should be taken and the calibration rerun. bar must be adjusted. If the bar is not set to the proper height, This calibration should be made each day. The following is an excess or lack of emulsion will form ridges or streaks on an example of such a calibration: the pavement, as depicted in Figure 5. This adjustment process is accomplished by shutting off Assuming: the appropriate nozzles to determine where the spray pattern 1,800-gal capacity asphalt distributor, 12-ft-wide spray contacts the pavement, as shown in Figure 6. Every other noz- width, trial spray distance = 4,630 fe, 0.32 gal/yd2 design zle should be turned off for a double-lap application, and two spray rate, dipstick reading beginning of shot = 1,765 gal, nozzles should be turned off for every one that is left on for a dipstick reading end of shot = 185 gal triple-lap application. The distributor operator should spray 1. Check volume shot. 1,765 - 185 = 1,580 gal emulsion onto the pavement surface for as short an interval a. 1,580/1,765 = 89.5% > 70% and < 90%. OK.