ECN publication
Long term leaching behaviour of cement mortars
Published by: Publication date:
ECN 1-7-1997
ECN report number: Document type:
ECN-C--97-042 ECN publication
Number of pages: Full text:
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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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