Investigation of lime stabilised contaminated material

Stabilisation of contaminated materials using inorganic cementitious agents is becoming more widely used in the UK. The method has particular advantages for bulk fill operations such as highway earthworks. Research has been carried out at the Transport Research Laboratory into the long-term durability of lime stabilised material. The trial material was a soft organic silty clay with metal contamination. Testing in a combined permeability and leaching apparatus with distilled water and dilute sulphuric acid as leachants is described and the results compared with those obtained using the National Rivers Authority (NRA) interim leaching test. mples had retained their high shear strength by the end of the leaching tests. Permeabilities were consistently very low, in the range 1×10−9 to 6×10−9 m s−1, and the pH of the eluate remained stable at >12. The chemistry of the eluate showed an initial peak in concentration of mobile ions such as sodium and chloride, whereas the calcium concentration remained steady throughout. Concentrations of most of the metals in the eluate were below detection limits, but concentrations of copper, nickel and phenols showed a similar pattern to sodium and chloride, with high initial concentrations decreasing as the test progressed. The results suggest that the stabilised material retains its integrity in the long-term. However, the mobility of individual contaminants appears to depend on their speciation, and further work is required to evaluate this. Tests are also being carried out to assess the behaviour of stabilised materials in the field, to compare with the results of the laboratory tests described in this paper.