In the European system of standardization of asphalt mixtures according to the series of standards EN 13108, the issues of control and quality assurance have been deliberated in EN 13108-21:2006 Bituminous Mixtures—Material Specifications— Part 21: Factory Production Control (with Amendment AC/September 2008). This standard contains an outline of requirements regarding the system of quality assurance during the production process of a mix. Generally speaking, the FPC is in conformity with principles from ISO 9001, so that part of the standard will not be discussed here. Requirements for the production control can be found in the normative Annex A, entitled “Tolerances and Test Frequencies for Finished Asphalt,” which stipulates admissible deviations and frequencies of controlling manufactured and delivered mixes.
14.8.1 Levels of Requirements
EN 13108-21 provides three levels of requirements related to the expected accuracy of production—level X, level Y, and level Z.
Level Z is a basic one and its application secures the fulfillment of the requirements connected with the evaluation of conformity. Levels X and Y require assurance of a higher frequency of control testing and can be adopted when such increased control is required. The determination of different levels of requirements for various types of mixes or specified contracts is also possible (e. g., a higher level for bridge deck surfacing). In these circumstances, the selection of an appropriate level (X, Y, or Z) indicates the significance of the minimum risk of nonconformity. Consequently, the frequency of testing production samples depends on the accepted level of requirements (i. e., the desired level of conformity).