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 (M) regarding the material must also be observed.

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

Incinerator bottom ash 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 2 to 3 base layers, but usually at least a frost blanket layer and a bound or unbound base course.

FGSV terminology for road construction

Example of a road pavement and definition of terms according to RStO

Assignment of construction classes based on road type

Furthermore, the FGSV regulations distinguish between so-called construction classes. Each road is assigned to one of these construction classes depending on the traffic load. Seven categories with decreasing load were distinguished according to old RStO 01, starting with SV (highest load, e.g. motorways), followed by classes I to VI, where VI has the lowest traffic load, e.g. in a residential road.

Load class technically important for secondary aggregate usage

Load classes for typical design situations

With the introduction of RStO 12, the previously valid construction classes of RStO 01 were changed to load classes. Since then, an assignment between old and new class is necessary to use the FGSV rules.

German road dimensioning with load classes

Assignment of the "new" dimensioning relevant road stresses and load class according to RStO 12

The construction class or load class affects, among other things, the type of design and the road pavement structure. Construction with concrete or asphalt pavement can be carried out in all construction classes. The use of paving is only permitted from construction class III, IV, V and VI.

In regard to the requirements for aggregates for unbound layers such as frost blanket and base courses, Technical delivery terms TL Gestein-StB 04 and TL SoB-StB 04 must be observed. In earthworks, the Technical delivery terms TL BuB E-StB 09 and the Additional technical conditions ZTV E-StB 09 are particularly relevant.

Conclusion: 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 construction classes III to VI and load classes Bk0,3 to Bk3,2 respectively
  • Base and subbase courses for roads subject to low traffic as well as cycle paths and footpaths
  • Filling excavations and pipe strands outside the pipeline zone only if frequent break-ins are not to be expected

The environmental specifications for the use of incinerator bottom ash must be additionally observed. A complete overview of the resulting fields of application after comparison of construction technology and environmental specifications can be found here

Handbook on secondary aggregates

Find out more about this topic with details on structural and ecological backgrounds as well as detailed literature information and references in our latest edition of the German Handbook on secondary aggregates. The medium, which for the first time contains all information on the Secondary Aggregates Directive, is made available to interested parties free of charge.
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Secondary aggregates: Technological and environmental background information