Tagungsband - BFT International

PANEL 8 // PROCEEDINGS
� Most manufacturers of concrete products
and precast elements order mineral aggregates
in accordance with DIN 12620 (or DIN 4226 on
the basis of some old supply agreements)
without thinking of what this actually means.
DIN 12620 specifies several classes of aggre-
gates but not all of them are suitable for pro-
ducing concrete in accordance with DIN EN
206-1 or DIN 1045-2. The reference to DIN
12620 does not suffice for defining the required
classes of properties.
AGREED STANDARD REQUIREMENTS Yet the
procurement of mineral aggregates in ac-
cordance with DIN 12610, in conjunction with
standard requirements specified in DIN 1045-2,
Annex U, only means that the concrete produ-
ced will safely meet its load-bearing parame-
ters and the usual durability specifications. No
requirements as to its appearance and visual
appeal are considered.
AUTHOR //
AUTOR
DAMAGE CASE: COAL IN CONCRETE PAVERS AND PRECAST ELEMENTS
– A DEFECT DESPITECOMPLIANCE WITH THE STANDARD?
SCHADENSFALL: KOHLE IN PFLASTERSTEINEN UND FERTIGTEILEN –
MANGEL TROTZ EINHALTUNG DER NORM?
� FIG. 1 Accumulation
of coal particles. //
ABB. 1 Ansammlung von
Kohlepartikeln.
Dr.-Ing: Jürgen Krell,
krell-consult, Hilden
info@krell-consult.de
Nach jeweils elf Jahren in der Zementindustrie (VDZ)
und der Betonindustrie (Readymix, heute CEMEX)
seit mehr als acht Jahren eigenes Ingenieurbüro,
gleichzeitig weiterhin in nationalen und internatio-
nalen Gremien tätig; ö. b. u. v. Sachverständiger
140 BFT 02/2011 www.bft-online.info
� Die meisten Betonhersteller bestellen Gesteins-
körnung nach DIN 12620 (zum Teil in Altverträgen
nach DIN 4226), ohne sich Gedanken darüber zu
machen, was das bedeutet. In der DIN 12620 wer-
den verschiedene Gesteinskörnungsklassen auf-
geführt, die nicht alle für die Herstellung von
Beton nach DIN EN 206-1 bzw. DIN 1045-2 geeig-
net sind. Der Verweis auf die DIN 12620 ist nicht
hinreichend, um die erforderlichen Eigenschafts-
klassen zu definieren.
REGELANFORDERUNGEN VEREINBART Aber auch
die Bestellung von Gestein nach DIN 12610 mit
Regelanforderungen nach DIN 1045-2 Anhang U
bedeutet nur, dass der damit hergestellte Beton
seine Tragwirkung sowie die übliche Dauerhaftig-
keit sicher erfüllt, es sind keinerlei Anforderungen
optischer Art berücksichtigt.
Die Einhaltung der Regelanforderungen bedeutet,
dass z. B. im Sand bis 4 mm 0,5 M-% leichtgewich-
tige organische Verunreinigungen zulässig sind.
Für einen Vorsatzbeton mit 1400 kg/m³ Sand dür-
fen das im Beton bis z. B. 7 kg/m³ Holzkohle sein.
Diese können bereits eine deutlich sichtbare Be-
einträchtigung der Pflastersteinoberfläche darstellen.
ABB. 1 deutet auf ca. 2-3 kg Kohle je Kubikmeter
Beton hin, also weit unter Regelanforderungen.
Compliance with the standard requirements
means that, for instance, sand in sizes of up
to 4 mm may contain 0.5 wt.-% of lightweight
organic contaminations. In a face mix with
1,400 kg/m³ of sand, the concrete may conta-
in up to 7 kg/m³ of charcoal. Even these con-
taminations may have a clearly visible delete-
rious effect on the paver surface. FIG. 1
suggests approx. 2 to 3 kg of coal per cubic
meter of concrete, i.e. significantly below the
standard requirements.
Disputes often go both ways, i.e. the customer
is reproached because it considers the coal
accumulation a defect, but also the aggregates
supplier, which usually refers to the contrac-
tually agreed delivery (i.e. free from defects).
At the same time, discussions arise for pre-
fabricated architectural concrete components
where some concrete constituents cause dis-
colorations, such as pyrite (FIG. 2). The standard
requirements specified in DIN 12620 permit a
certain portion of these constituents.
SPECIFIC SURFACE QUALITY OF THE CONCRETE
The DIN EN 12620 standard pertaining to mi-
neral aggregates also contains Annex G that
was added for information purposes and re-
commends additional specifications to be
agreed upon with respect to the surface qua-
lity of the concrete. These include reductions
in the ratio of “lightweight organic contamina-
tions”, which include coal-like constituents,
and agreements on the maximum ratio of co-
loring constituents.
If there is no evidence of such additional ag-
reements, the discussion with the aggregates
supplier, which makes reference to the con-
tractually agreed delivery of mineral aggre-
gates in accordance with standard require-
ments, will be unsuccessful.
GUIDANCE FOR END CLIENTS For this reason,
many concrete product and precast element
manufacturers include a provision in their Ge-
neral Terms and Conditions indicating that
stains may occur that do not constitute a de-
fect in accordance with the GT&C statement.