The SMA mixture production process, like that of other asphalt mixtures, is subject to procedures to control its mixed components and other selected properties. These procedures differ among various countries, but in almost all cases, the control of gradation and binder content form their common root.
The control of the production process mostly consists of periodically checking the components of the produced mixture in relation to the approved laboratory recipe. Generally, two methods applied world wide may be distinguished as follows:
• The control of the aggregate gradation on selected sieves and the content of soluble binder within given tolerances of production accuracy
• The control of SMA volume properties (e. g., the content of voids in a mineral aggregate (VMA) and the content of voids in a compacted asphalt mixture)
It is good to emphasize the control of the volumetric properties during the production process; it is even more logical to verify the volume ratios determined at the design stage during production. Furthermore, control of the aggregate gradation alone, within allowable tolerances, does not guarantee the correct volume ratio of coarse aggregates, mastic, and air voids.
9.5.1 Control according to the German Document ZTV Asphalt-StB 07
The quality of the produced mixture may be determined by ZTV Asphalt-StB 07. The following tests are included in the scope of methodical control activities (Table 26 ZTV Asphalt-StB 07):
• Gradation on selected sieves
• Soluble binder content
• R&B softening point of the recovered binder
• Bulk density and air-void content in compacted Marshall samples
The factory production control (FPC) organization and the whole verification of a conformity system[58] 2 + is in accordance with requirements contained within the European Standard EN 13108-21.
