Definition and subtypes of SDA
SDA surfaces are divided into several subtypes based on their void content and maximum grain size. 1
| Type | Maximum grain size in mm | Application area |
| SDA 4 | 4 | urban areas |
| SDA 8 | 8 | urban areas with high mechanical stress, rural areas, national roads |
| Subtypes | Target void content in % | Property / Remark |
| -12 | approx. 12% | Standard type, good combination of noise impact and mechanical strength |
| -16 | approx. 16% | Higher porosity, better noise reduction, lower mechanical strength |
1 Swiss Association of Road and Traffic Professionals VSS (2022d) ‘VSS 40 436, Semi-dense mixture; Specifications and requirements’.