Fundamental aspects of cement solidification and stabilisation

Cement matrix materials intended for immobilisation vary considerably in their formulation. It is often economically and technically advantageous to add blending agents: e.g. slag and fly ash. These affect the chemical, mineralogical and microstructural constitution of the system. However, blending agents react slowly with the result that the physicochemical properties of the matrix are lime dependent. This affects especially conclusions which might be reached from accelerated short-term leach tests: the intrinsic performance of blended cement matrices improves with maturation. The matrix interactions with waste species are characterised using chromium, molybdenum, uranium and arsenic as examples. Formation of relatively insoluble precipitates, by reaction of waste species with cement components, provides chemical control over leach rates and accounts for many of the observed retentive properties. It is concluded that further focused research is needed to characterise the future performance of cement matrices in open system environments, where chemical exchanges occur between cements and the disposal environment. (C) 1997 Elsevier Science B.V.