Dedicated cement compositions were formulated to enable the incorporation of large volume fractions of red mud in alkali activated cements, taking into account the role of the aluminosilicate phase in the processes of hydration and hardening. High volume red mud alkali activated cements were synthesized using a proper combination of red mud, low basic aluminosilicate compounds with a glass phase (blast-furnace slag) and additives selected from high-basic Ca-containing cements with a crystalline structure (Portland cement). Compressive strength of the cements under study is 30-60 MPa (tested in mortar). The microstructure of the hardened cement paste and the role of red mud in the structure formation process were investigated. In addition to the use of red mud in cement, its use as an aggregate in concrete was studied to enable the use of larger quantities in the final concrete. In concrete road bases, the use of red mud can reach even 90% by mass. Since enhanced concentrations of naturally occurring radionuclides can be present in red mud this aspect was investigated to make sure that these materials are safe to use from a radiological point of view. Highlights  High volume red mud alkali activated cements and concretes have high strength.  Hydration products are low-basic CSHs and alkaline ferro-and aluminosilicates. From radiological safety, concretes with 90% can be used for road construction.

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Minimizing harmful effects to the environment in waste-management practices requires continuous innovation. This is especially important in the field of radioactive waste management. Alternatives to the commonly used ordinary Portland cement matrices are being increasingly studied for improved immobilisation purposes. The development of inorganic polymers (IP) from industrial residues has been successfully studied for the immobilisation of caesium (Cs +) and strontium (Sr 2+). However, knowledge of the effect of these introduced elements on the IP-matrix is scarce, especially considering that studied effects are dependent on the IP-precursor characteristics and the form in which the Cs + and Sr 2+ are introduced. In this study, IPs containing varying amounts of CsNO3 and Sr(NO3)2 were developed to study the effect of the introduced elements on the IP-characteristics. IPsamples were developed from ground granulated blast furnace slag (GGBFS) and 6 M NaOH activating solution. Cs + and Sr 2+ were added to account for 0.5, 1 and 2 wt% of the total IP-mass. Throughout the entire study, Cs +-addition showed no significant effects on the studied parameters. Calorimetric results showed that Sr 2+ severely affects reaction kinetics, consuming hydroxide ions necessary for the alkali activation reaction. Sr 2+-addition also caused a severe decrease in compressive strength, increased calcium leaching, and decreased sodium and hydroxide leaching. Micro-chemical analyses showed that Cs + is almost fully incorporated in the formed IP-matrix, while Sr 2+ mainly precipitates as Sr(OH)2 in concentrated regions throughout the IP-structure. The findings presented in this paper give insights on the effect of contaminant elements on the immobilizing matrix.

This study characterises the naturally occurring radionuclide (NOR) contents of a suite of secondary raw materials or industrial residues that are normally disposed of in landfills or lagoons but now are increasingly used in green concretes. This includes ashes from a variety of industrial processes and red mud from aluminium production, as well as air pollution control residue and cement kiln dust. The chemical composition of the samples was determined with X-ray fluorescence spectroscopy (XRF). The Ra-226, Th-232 and K-40 activity concentrations were obtained by gamma spectrometry, and the results were compared with recently published NOR databases. The correlation between the NOR contents and the main chemical 2 composition was investigated. The radioactive equilibrium in the U-238 chain was studied based on the determination of progeny isotopes. The most commonly used calculation methods (activity concentration index and radium equivalent concentration) were applied to classify the samples. The radon exhalation rate of the samples was measured, and the radon emanation coefficient was calculated. Significant correlation was found between the NORs and certain chemical components. The massic exhalation demonstrated a broad range, and it was found that the emanation coefficients were significantly lower in the case of the residues generated as a result of high-temperature combustion processes. The results showed a weak correlation between the Ra-226 concentration and the radon exhalation. This emphasizes that managing the Ra-226 content of recycled material by itself is not sufficient to control the radon exhalation of recycled materials used in building products. The investigated parameters and their correlation behaviour could be used to source apportion materials found during the process of landfill mining and recovery of material for recycling.

One of the major challenges for the nuclear industry is the safe and sustainable immobilisation of radioactive wastes (RAW). Currently, the most commonly used immobilisation matrices for low and intermediate level wastes are based on ordinary Portland cement. For the more difficult to immobilise nuclides, such as caesium (Cs +) and strontium (Sr 2+), researchers have been studying alternative immobilisation matrices, of which alkali-activated materials (AAM) are a very promising option. However, the differences in precursor compositions and the use of different types of activating solutions make it difficult to fully understand the effects of precursor composition on the immobilisation of introduced nuclides. Therefore, six different compositions of laboratorysynthesized Ca-Si-Al slags were developed to serve as precursors for low-alkaline AAMs to study their immobilisation behaviour. Immobilisation capacities up to 97.6 % Cs + and 99.9 % Sr 2+ were achieved with 1 wt% waste loading when leaching for 7 days at 20 °C in Milli Q water. Cs + immobilisation is higher at lower Si/Al and Ca/(Si+Al) ratios. Immobilisation of Sr 2+ is higher at a lower Ca/(Si+Al) ratio and independent of Si/Al ratio. The results of this study offer a deeper understanding of the immobilisation behaviour of AAMs and can encourage further research and application of AAMs for RAW immobilisation.