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Titel:
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Long term leaching behaviour of cement mortars
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Auteur(s):
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Gepubliceerd door:
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Publicatie datum:
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ECN
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1-7-1997
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ECN publicatienummer:
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Publicatie type:
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ECN-C--97-042
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ECN rapport
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Aantal pagina's:
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Volledige tekst:
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102
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Niet beschikbaar.
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Samenvatting:
Within the framework of a study for Ciments 'd Obourg, a wide range ofcements from different origin has been studied. These cements cover cements
produced from natural materials and special cements derived from alternative
fuels and raw materials. In this work, different leaching tests have been
applied to be able to address the question, how limits for using alternative
fuels and raw materials can be determined and when such criteria have been
established how to come to quality control procedures for alternative fuels
and raw materials. The total composition proves to be a poor parameter to
control environmental properties of cement-products. Leachability as a
function of pH has revealed differences in cement mortar leaching not
identified before. Geochemical modelling has allowed identification of
potential solubility controlling phases over the pH range from 4 to 13. The
pH range 8-13 is most relevant for 'second life' of mortars. This provides
options for quality control. Proper parameters to model incorporation of
metals and oxyanions in ettringite phases are still not available. Stability
constants of ettringite phases for oxyanions are still too scarce. Oxyanions,
such as Mo, Cr, V, are more crucial for an environmental evaluation of long
term behaviour of cement products than metals such as Pb, Zn and Cd. From a
measurement point of view the ATA method is a poor test. A more meaningful
alternative may be a tank leach test with externally controlled pH at neutral
conditions (pH - 8) by air flushing. Similar to the situation on other
fields, the pH static leach test forms a solid basis for mutual comparison of
cement mortars as it has the possibility to make distinction between cements
based on chemical aspects. In the comparison with regulatory limits (Dutch
Building Materials Decree), the service life of concrete generally does not
pose a problem. All elements specified in the regulation are well below the
threshold for category I applications for the cement mortars tested in this
study. In evaluating of concrete construction debris some elements - As, Cr,
Cu, Mo, Ni, Sb, Sn, V and sulphate - can become critical, when a worst case
approach is used for evaluation of compliance. The metals, which are mostly
focused on, are not a real environmental problem. A further evaluation is
needed to verify this 'end of life status'. As criteria for control of cement
mortar quality the leaching as function of pH in the pH range 8-13 and the
availability are better parameters than the total composition. 21 refs.
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