how to calculate the rate of spray of prime coat in road construction.

Tray Test is used to calculate the rate of spread of prime or tack coat. The test uses a 20cm X 20 cm X 3 cm tray placed on the surface to be primed at some intervals in the path of the sprayer/emulsion distributor. They are placed between the wheel’s path/tracks.

5 samples are collected for a test and a minimum of 3 tests are conducted for a day of work.

Weight of the emulsion on the tray is calculated by finding the difference in the final and the initial weight of the tray. Weight per unit sq.m or weight per 10 sq.m is obtained and checked with specified limits mentioned in MORT&H Table 500–3 (prime coat) and 500–5 (Tack coat) or other relevant IRC specifications.

Initially before the start of the priming work, a demonstration trial is done based on the following parameters:

1. Equipment type for spraying operation
2. Size of nozzle
3. Pressure at spray bar
4. Speed of forward movement of sprayer equipment.

Above values are ascertained and calibrated for a required rate of spray as per the specification by using tray test prior to the start of actual work.