Technologically sound: incinerator bottom ash (IBA)

Roads and earthworks are subject to clear construction specifications. The definition of national technical regulations for road and transport systems are the responsibility of the various committees of the German Road and Transportation Research Association (Forschungsgesellschaft für Straßen- und Verkehrswesen, short FGSV). The regulations cover the areas of traffic planning, traffic management, traffic engineering, road design, road construction, road operation and road maintenance. The publications of the FGSV are generally endorsed by the German federal states. However, they can make changes so that requirements in federal states can differ slightly.

IBA is part of the official technical framework

With regard to the requirements for incinerator bottom ash in road construction and earthworks, numerous publications must be observed. In addition to the R-guidelines, the Technical delivery terms (TL), Additional technical conditions (ZTV) and Technical testing regulations (TP), which apply to all aggregates, special Technical bulletins regarding the material must also be observed.

Technically relevant regulations for IBA of the German Road and Transportation Research Association

Secondary aggregates in road construction: relevant regulations of the German Road and Transportation Research Association (FGSV)

Road design principles

Regarding the road structure, the Guidelines for the standardisation of pavement structures of traffic areas (Richtlinien für die Standardisierung des Oberbaus von Verkehrsflächen, short RStO 12) must be observed. The following illustration depicts a simplified road cross section. A distinction is made between the naturally existing subsoil, the subgrade and subbase and the pavement structure. The latter consists of two to three base layers, but usually at least a frost blanket layer and a base course.

FGSV terminology for road construction

Example of a road pavement according to German RStO

Assignment of load classes based on road type

The FGSV regulations distinguish construction classes. Each road is assigned to one of these construction classes depending on the traffic load. A distinction is made between classes with decreasing traffic load, starting with Bk100 (highest load, such as motorways or rural roads), followed by classes Bk10 to Bk0.3, with Bk0.3 for the lowest traffic volume, e.g. for a residential road. The load class affects, among other things, the type of construction and the structure of the road surface. 

Load class technically important for secondary aggregate usage

Load classes for typical design situations

Structural suitability of IBA

From a structural point of view, incinerator bottom ash can be used as a substitute building material in the following road applications:

  • subgrade
  • hydraulic soil improvement, soil consolidation
  • dam, embankment, backfill
  • frost blanket course in load classes Bk0,3 to Bk3,2
  • base and subbase courses for roads subject to low traffic as well as cycle paths and footpaths

The environmental specifications for the use of incinerator bottom ash must be observed additionally. 

Handbook on secondary aggregates

Find out more about this topic with details on structural and ecological backgrounds in our latest edition of the German Handbook on secondary aggregates. The medium, which contains all relevant information of the Secondary Aggregate Directive, is made available to interested parties as printed copy and online.

Secondary aggregates: Technological and environmental background information