FUNDAMENTAL-ASPECTS OF CEMENT SOLIDIFICATION AND STABILIZATION

Cement matrix materials intended for immobilisation vary considerably in their formulation. It is often economically and technically advanta geous 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 physi cochemical properties of the matrix are lime dependent. This affects e specially conclusions which might be reached from accelerated short-te rm leach tests: the intrinsic performance of blended cement matrices i mproves with maturation. The matrix interactions with waste species ar e characterised using chromium, molybdenum, uranium and arsenic as exa mples. Formation of relatively insoluble precipitates, by reaction of waste species with cement components, provides chemical control over l each rates and accounts for many of the observed retentive properties. It is concluded that further focused research is needed to characteri se the future performance of cement matrices in open system environmen ts, where chemical exchanges occur between cements and the disposal en vironment. (C) 1997 Elsevier Science B.V.