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Cement binding

Concrete lobby group BCA is predicting widespread take up the technique of stabilisation and solidification of contaminated sites using cement. The method is well established in the US and is beginning to be used in the UK because it is able to treat both metal and some organic contamination (NCE Concrete Engineering November 1997).

A US example is the 90th South Battery site in West Jordan, Utah. During the widening of 90th street, heavy metal contaminated soils were discovered, which had resulted from lead and acid battery waste disposal.

The clean up involved the contractor excavating 1,900m3 of contaminated soil, which was found to contain lead, arsenic, aluminium, magnesium and iron. Pieces of plastic battery casings were also discovered and there were traces of battery acid contamination.

Prior to treatment all particles were graded to less than 32mm in size.

As the pH of the soil ranged from 5 to 7, approximately 5% of limestone fines were added to raise the pH range from 7 to 8. The pre-treated soil was then mixed with the stabilisation and solidification binding reagent. This consisted of a mixture of 75% OPC together with 25% cement kiln dust. The soil binder was mixed together by a continuous flow pugmill. Water was added to aid hydration.

The stabilisation and solidification treatment used 280t of cement and 94t of cement kiln dust.

After treatment the concentrations for lead, for example ranged from below detection to 0.72mg/kg. Before treatment they had hit the 60,000mg/kg mark.

Reader reply no 808

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