Influence of severe climatic variability on the structural, mechanical and chemical stability of cement kiln dust-slag-nanosilica composite used for radwaste solidification

Abstract

Cement production and its wide applications in construction and stabilization are among the oldest technologies. Cement kiln dust is a by-product generated by cement industry with unpleasant features. Its weak integrity can be improved by mixing it with 20% of iron slag, another industrial waste generated during steel production, and a small amount of nano-additive, namely 0.1% nanosilica. This way, modified cementitious composites of improved characteristic were developed, which performed suitable for construction and waste stabilization applications.In the present study, the novel composite material has been thoroughly examined to critically assess its performance and resistance under drastic environmental conditions that are likely to occur especially in areas exposed to severe climatic variability. The impact of flooding in water of various compositions and in strongly acidic and alkaline media was investigated. Leachability of the new composite specimens in these aqueous media and when subjected towards freezing/thawing cycles was evaluated during 90 days; especially the mechanical and chemical stability of the new composite as safe containment for radioactive 137Cs waste was studied. Compressive strength, porosity, mass change and spectroscopic investigations are the tools used in this study to check the performance of the modified cementitious composite at each condition. Although prone to deterioration after drastic freezing-thawing cycles, the new composite material displayed excellent stability under excessive flooding, and holds promise as future material of choice to immobilize and finally dispose radioactive waste in a safe and sustainable fashion.