A calorimetric and microstructural study of solidified toxic wastes. Part 2: A model for poisoning of OPC hydration

Abstract During cement-based processing of certain hazardous wastes the hydration reactions thought to be responsible for solidification can be poisoned and appear to be retarded indefinitely. A number of wastes known to be capable of poisoning hydration were added to ordinary Portland cement (OPC) and classified on the basis of interference effects observed. This paper reports the results from a characterisation of these wastes and the subsequent addition to OPC of waste components identified as significant in single and combined additions. The effects of these additions were examined by conduction calorimetry and microstructural techniques. A comparison of results showed that it was possible to reproduce the poisoning effects observed previously with real wastes by an addition of combined metal hydroxides only. These results suggest that poisoning results from the synergistic effects of compounds contained in the waste. A model, representing the early hydration of OPC, has been modified and is presented and its application in explaining poisoning of hydration is discussed.

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