5 th International Slag Valorisation Symposium | Leuven | 03-05/04/2017 401 THE EFFECT OF Cs AND Sr ON THE MECHANICAL PROPERTIES OF BLAST FURNACE SLAG INORGANIC POLYMER FOR RADIOACTIVE WASTE IMMOBILISATION Niels VANDEVENNE 1 , Remus Ion IACOBESCU 2 , Yiannis PONTIKES 2 , Katrijn GIJBELS 1 , Sonja SCHREURS 1 , Wouter SCHROEYERS 1 1 Hasselt University, CMK, Nuclear Technological Centre (NuTeC), Faculty of Engineering Technology, Agoralaan - Gebouw H, 3590 Diepenbeek, Belgium 2 Department of Materials Engineering, KU Leuven, 3001 Heverlee, Belgium niels.vandevenne@uhasselt.be Introduction In pursuit of a sustainable society, researchers and industries have been increasingly studying the conversion of industrial residues into valuable construction materials such as inorganic polymers (IPs). These IPs can often be developed from both a single residue stream (e.g. metallurgical residue) or a combination of residue streams (typically amorphous/non-crystalline), mixed with an activating solution (e.g. Na-, K- hydroxides and silicates). The superior properties of IPs over OPC-based structures (fire resistance, chemical resistance, etc.) have led to different studies for their application as an immobilisation matrix for hazardous and radioactive substances 1-4 . The effectiveness in immobilising elements such as cesium (Cs) and strontium (Sr) has been proven in several studies 1-3 . However, the effect of the introduced elements on the properties of the IP-matrix has been studied to a much lesser extent 5,6 . Also, due to high variability in precursor compositions and the differences between high-Ca and low-Ca IP strength development, the conclusions of these studies cannot easily be generalised. This study focusses on the effect of Cs + and Sr 2+ on the setting time, strength development, and microstructure of IPs developed from ground granulated blast-furnace slag (GGBFS). Materials and Methods The chemical composition of the GGBFS was analysed by X-ray fluorescence spectroscopy (Philips PW 2400). For producing IPs, GGBFS was used as precursor and NaOH as activating solution. GGBFS was milled to a Blaine-value of 5430 ± 40 cm²/g (EN 196-6) and the concentration of the solution used was 6 mole NaOH/L. IP-pastes were produced by mixing GGBFS with the activating solution at a liquid-over-solid ratio (L/S) of 0.37. This was chosen based on preliminary tests and allowed to attain pastes fluid enough for casting. Cs + and Sr 2+ were added (in the form of CsNO3 and Sr(NO3)2) to account for 0, 0.5, 1 and 2 wt% of the final IP-mass (Table 1). The pastes with Sr(NO3)2 were less fluid, thus a slight increase in the L/S ratio (Table 1) deemed necessary. The resulting pastes were cast in 20 x 20 x 80 mm³ moulds and covered