Cement with supplementary materials
Concrete is the most widely used construction material worldwide; its key ingredient is Portland cement (PC). In order to create a more sustainable process and product, it has become common practice to replace the maximum amount possible of cement used in concrete with more environmentally friendly substitutes. The replacement of cement can be partial such as in blended cements like CEM II where PC clinker quantity is greater than 65% by weight with one or two additions. The most common cement additives include fly ash (FA), ground granulated blast-furnace slag (GGBFS) and silica fume (SF).
Fly ash from coal-fired electric power stations is considered a pozzolan, which requires calcium hydroxide (Ca(OH)2) that is produced during the hydration of cement in order to react. The addition of fly ash leads to lower heat of hydration, improves the durability of the cement composite, and increases the concrete strength due to pozzolanic and filler effects that are notable at late ages. Slag comes from the iron manufacturing industry that has hydraulic properties; therefore, it would start to react from the time of setting. The presence of slag reduces the heat of hydration, and leads to a positive refinement of mortar and concrete microstructure. Consequently, the addition of FA and GGBFS reduces the permeability of concrete and improves their resistance to aggressive environments.
Binary, ternary, and quaternary (depending on the number of compositions) binders are currently being developed in order to meet the requirements of strength and durability demanded by the concrete market. Furthermore, the incorporation of these additions to cement has been found to be a very interesting way to immobilize heavy metals and radioactive waste. The immobilization capacity of heavy metals in cementitious mixtures produced with Portland cement, siliceous fly ash, fluidized bed combustion ash and granulated blast furnace slag was studied by Giergiczny et al. [J. Hazard. Mater. 160 (2008) 247-255], where Pb, Cu, Zn, Cd and Mn presented a high level of immobilization (99.9%) in mortars manufactured with 85% slag and 15% Portland cement, while Cr showed a lower degree of immobilization, which ranged from 86% in mortars based on 20% Portland cement, 30% combustion ash and 50% slag to 93.3% in Portland cement mortars. On the other hand, the sorption of radionuclide ions such as 137Cs+ and 90Sr2+ was studied in ternary mortars (65% slag and 5% silica fume) [Li et al. Cem. Concr. Res. 65 (2014) 52-57]. The Cs/Sr sorption capacity tended to increase due to the incorporation of Al into calcium silicate hydrate (C-S-H) structure from the ternary samples. Yoon et al. [Cem. Concr. Res. (2020) 106089] reported that the substitution of 70% slag increased the retention of Co2+ in the cement matrix, due to the enhanced Co uptake by the layered double hydroxide phases and by the refined pore structure of the slag-blended cement.
In the literature, some works can also be found [Bagosi et al. Cem. Concr. Res. 29 (1999) 479-485; Faiz et al. J. Mater. Environ. Sci. 6 (2015) 289-296] where Portland cement has been used to immobilize radioactive waste using ionic resins, but further research is required and therefore, one of the purposes of this Project is to study binary or ternary cements as possible immobilization matrices of nuclear grade ionic resins.