The principle of fixing frequencies of control testing depends on the number of deviations found and has been adopted in the standard EN 13108-21. With an established level of requirements (X, Y, or Z), the frequency of sampling is variable, depending on the production accuracy of the asphalt plant (i. e., the number of deviations from a recipe).
The initial frequency of sampling depends on an established category of conformity (X, Y, or Z), so at first the frequency of sampling is as follows:
• Every 150 tons of a manufactured mixture (for level X)
• Every 250 tons of a manufactured mixture (for level Y)
• Every 500 tons of a manufactured mixture (for level Z)
Samples should be representative of the entire production; the relevant clauses of EN 12697-27 and EN 12697-28 should be taken into account.