Influence of severe climatic variability on the structural, mechanical and chemical stability of cement kiln dust-slag-nanosilica composite used for radwaste solidification Hosam M. Saleh a,⇑ , Fathy A. El-Saied b , Taher A. Salaheldin c , Aya A. Hezo b a Radioisotope Department, Nuclear Research Center, Egyptian Atomic Energy Authority, Dokki, 12311 Giza, Egypt b Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt c Nanotechnology Research Center- British University in Egypt (BUE), Nanotechnology & Advanced Materials Central Lab, Agriculture Research Center, Egypt highlights  Improvement of cement kiln dust by iron slag and nanosilica.  Flooding of the cement kiln dust modified by slag and nanosilica.  Freeze-thaw durability of the cement kiln dust modified by slag and nanosilica.  Chemical stability of the cement kiln dust-slag-nanosilica composite immobilized radioactive waste. graphical abstract article info Article history: Received 23 March 2019 Received in revised form 21 May 2019 Accepted 23 May 2019 Keywords: Cement kiln dust Nanosilica Iron slag Waste solidification Freezing/thawing cycles Water flooding Leachability abstract Cement production and its wide applications in construction and stabilization are among the oldest tech- nologies. 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 con- struction 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 137 Cs 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 con- dition. 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. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction An increasing number of studies have revealed both the advan- tages and disadvantages of ordinary Portland cement as stabilizing https://doi.org/10.1016/j.conbuildmat.2019.05.145 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: hosam.saleh@eaea.org.eg, hosamsaleh70@yahoo.com (H.M. Saleh). Construction and Building Materials 218 (2019) 556–567 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat