7.2.2 Spraying of Binder
Bitumen sprayers are designed to provide a constant rate of binder output across the width of the spray bar. The desired application rate is thus obtained by varying the forward speed of the sprayer and the bitumen pump speed. Accurate spraying to design rates of application requires precise control of both these functions, by means of routine calibration.
Binder application rates are usually checked at the end of each sprayer run against the design so that any adjustments to the sprayer can be made to maintain rates within a reasonable tolerance.
With the adaptation of microprocessor controls, bitumen sprayers are now being developed that can alter the width while spraying and, in some instances, provide for variable transverse rates such as different rates of application in wheelpath areas and outside wheelpaths.