Normal aggregates

For manufacturing concrete in accordance with DIN EN 206-1, normal aggregates in accordance with DIN EN 12620 shall be used with a particle density > 2000 kg/m³ and

< 3000 kg/m³. Natural, manufactured (artificial) or recycled aggregates are suitable [22].

Recycled aggregates shall be dealt with in Section 5.5.4.

5.5.1.1 Natural aggregates for normal concrete

Natural aggregates are aggregates formed from mineral deposits that have only been mechanically processed [59]. Natural stone is mainly used such as quartzitic stone, limestone, granite, gabbro, basalt and greywacke [26]. In the European Union, around 50 % of the aggregate produced is natural aggregate [62].

Content/Release of heavy metals from natural aggregates

Natural stone can contain small amounts of heavy metals such as cobalt, barium, lead or vanadium. Annex A9 provides an overview of the average heavy metal content in natural aggregates.

The Technical Rules of the Working Group of the German Länder on Waste Issues (LAGA) lay down requirements for recycling mineral wastes and residues, including for soil. For natural soil, guideline values (Z0 values) are specified that cover the predominant part of the natural range of variations for heavy metals. If these Z0 values for soil (solid materials) are not exceeded, it is presumed that soil and groundwater are not affected as legally protected resources [27]. Comparing the heavy metal content of natural stone with the Z0 values for soil shows that almost all natural stone exceeds these values. Other sources, however, state that the heavy metal content in natural aggregates does not exceed the content in soil and in the lithosphere [24].

Recommendations for the content/release of heavy metals from natural aggregates

Because of the different assessments for the heavy metal content in natural stone, it should be discussed in general whether requirements for the possible leaching of heavy metals should be made of natural stone.

5.5.1.2 Manufactured (artificial) aggregates

DIN EN 12620 describes manufactured aggregates as aggregates of mineral origin resulting from an industrial process involving thermal or other modification [59].

In particular, slags are used for manufactured aggregates to be used in normal concrete.

These can be divided into ferrous slag, melting chamber granulate, non-ferrous slag and waste incineration slag.

Ferrous slag is generated when manufacturing pig iron (blast furnace slag) and steel (steel slag). Blast furnace slag is generated when pig iron is produced from iron ore as a result of limestone reacting with gangue at high temperatures. Depending on the cooling conditions and cooling time, blast furnace slag hardens to form:

• crystalline blast furnace lump slag that can be used as concrete aggregate or

• vitreous, fine-particle, granulated slag, which is used in the manufacture of cement [23].

Steel slag is generated when producing crude steel and, depending on the respective steel production process, is described as:

• LD slag (Linz-Donawitz process)

• EF slag (electric furnace process)

In 2000, around 25 million tons of blast furnace slag and around 16.8 million tons of steel slag were produced in Europe. The recycling rate for blast furnace slag is almost 100 % in most countries [63]. In Germany, the slag is also almost completely recycled. For instance, in the year 2000 approximately 70 % of the blast furnace slag produced in Germany was used in manufacturing cement. The blast furnace lump slag is used in road construction and as concrete aggregate. Approximately 60 % of the steel slag is recycled as building material, and is particularly used in constructing highways, forest and rural roads and hydraulic structures [64].

Melting chamber granulate is generated when burning coal in melting chamber furnaces. The mineral stone accompanying the coal is rapidly cooled down and solidified by water quenching to form vitreous granulates. Slag from brown coal furnaces is not used as aggregate in Germany [26].

Non-ferrous slag is produced by melting lead, ferrochrome, copper, nickel or zinc ores or when extracting zinc oxide. Depending on the cooling time, this produces either crystalline lump slag or a vitreous, fine granulate [65].

Domestic waste incineration slag is generated from burning municipal waste. According to the definition of LAGA-Mitteilung 20, raw domestic waste incineration slag consists of a mixture of sintered combustion products, ferrous scrap, glass and ceramic shards, other mineral components and unburnt residue. The processed and stored raw slag is described in Germany as HMV slag (Hausmüllverbrennungsschlacke) [27]. Waste incineration slag is mainly used in Germany in civil engineering works (unbound base material).

In addition to the use of slags as manufactured aggregates, it is also possible to use other aggregates such as filtration and canal sand or foundry sand residue [66]. There is no information on the use of these or other materials as aggregates in the Member States.

The European Waste Catalogue lists some manufactured aggregates as waste and some as hazardous waste [67].¹² Whether and which manufactured aggregates will be classified as waste is still currently under discussion. The table below provides an overview of the manufactured aggregates listed in the European Waste Catalogue with their respective EWC codes.

Table 15: EWC codes for manufactured aggregates according to the European Waste

Catalogue [67]

Manufactured aggregates EWC code Waste type

10 01 01 Bottom ash, slag and boiler dust from power stations and other combustion plants 10 01 14* Bottom ash, slag and boiler dust from

co-incineration containing dangerous substances (classified as hazardous waste)

Melting chamber granulate

10 01 15 Bottom ash, slag and boiler dust from

co-incineration other than those mentioned in 10 01 14

12 When classifying aggregates as waste, it needs to be ensured that the definition according to Art. 1 a) of the Waste Framework Directive 75/442/EEC is met, whereby wastes are defined as any substance or object which the holder discards or intends or is required to discard [70].

Manufactured aggregates EWC code Waste type

19 01 11* Bottom ash and slag containing dangerous substances from incineration or pyrolysis of waste (classified as hazardous waste)

Slag from waste incineration plants

19 01 12 Bottom ash and slag other than those mentioned in 19 01 11

10 04 01* Slags from primary and secondary production from lead thermal metallurgy (classified as hazardous waste)

10 05 01 Slags from primary and secondary production from zinc thermal metallurgy

10 06 01 Slags from primary and secondary production from copper thermal metallurgy

Non-ferrous slag

10 08 08 Salt slag from primary and secondary production from other non-ferrous thermal metallurgy

10 09 07* Casting cores and moulds which have undergone pouring and contain dangerous substances Foundry sand residue

10 09 08 Casting cores and moulds which have undergone pouring other than those mentioned in 10 09 07

In Germany the application standard DIN V 20000-102 (pre-standard) for the European standard DIN EN 12620 requires that only natural aggregates and the manufactured aggregates granulated blast furnace slag according to DIN 4301 [68], crystalline blast furnace slag and melting chamber granulate may be used [69]. If other aggregates are to be used in Germany, the environmental compatibility has to be proved by means of a allgemeine bauaufsichtliche Zulassung ('national technical approval') [13] in order to maintain the national level of protection.

Content/Release of heavy metals from manufactured aggregates

In some cases, steel slag and melting chamber granulate show an increased heavy metal content for chromium, cupper, mercury and vanadium relative to natural aggregates [26].

Annex A9 provides an overview of the average heavy metal content of slags.

As part of the IBAC research project, the results of batch tests for melting chamber granulates, blast furnace and steel slags were assessed. The batch test according to DIN 38414-S4 [29] was used as the leaching method. The assessment of the batch tests showed that the leachate values complied with the Z2 values of the respective waste-specific regulation of LAGA-Mitteilung 20 [27] as well as with the insignificance thresholds ("no effect levels") of the DIBt Guideline Soil/Groundwater [20]. However, the detection limits for chromate and cadmium were too high, so that it was not possible to reach any conclusions concerning these parameters.

There are no results from long-term static tests for the release of dangerous substances from concrete test specimens manufactured with the corresponding slag. For granulated blastfurnace slag and blast furnace lump slag, the IBAC study presumes that they have a positive influence on the leaching rates due to their properties [26].

The heavy metal content of melting chamber granulates depends on the fuel used. Thus the IBAC study recommends that the heavy metal content of melting chamber granulates should be tested before use. In the case of deviations from the usual heavy metal content (see Annex A9), more detailed examinations of the leaching behaviour should be conducted using

a batch test or, if necessary, a static test, and an assessment made according to the DIBt Guideline Soil/Groundwater [26].

Recommendations for the content/release of heavy metals from artificial aggregates

In Germany, there are requirements for the material recycling of mineral residues/wastes, which were elaborated by the Working Group of the German Länder on Waste Issues (LAGA) [27]. These Technical Rules have been introduced in various Länder¹³ where they are therefore legally binding. The Technical Rules include requirements for recycling slag from iron, steel and casting foundries, slag from waste incineration plants for municipal waste, and foundry sand. The DIBt Guideline Soil/Groundwater also requires concrete constituents to comply with the requirements of the LAGA. To ensure that the German level of protection is maintained when using mineral materials that are by-products of industrial processes, the leaching of heavy metals should be tested on the original material. The leachate value of the mineral material should comply with the Z2 values of the respective waste-specific Technical Rule of the LAGA. An ordinance on federal level based on LAGA-Mitteilung 20 is currently under discussion. This would lead to the specified values becoming binding in all Länder. The European standard for aggregates, DIN EN 12620, also recommends that specific manufactured aggregates should be carefully tested [59].

There is still a need to examine whether concrete produced with manufactured aggregate complies with the insignificance thresholds ("no effect levels") of the DIBt Guideline Soil/Groundwater even if the aggregate does comply with the classification values of LAGA-Mitteilung 20.

When considering the release of dangerous substances, Guidance Paper H also refers to the possibility of restricting the content when there is a clear relation between the content and the release in the installed state. When using manufactured aggregates, the correlation between the content and the release of heavy metals could be tested using long-term static tests and thus reduce the amount of leaching tests necessary.