Radiological characterisation of alkali-activated construction materials containing red mud, fly ash and ground granulated blast-furnace slag

Abstract

Poor storage of industrial wastes has been a cause of land contamination issues. These wastes or by-products have the potential to be used as secondary raw materials in construction, promoting the concept of a circular economy that will avoid land contamination. Here we evaluate radiological environmental impacts when wastes that contain elevated levels of naturally occurring radionuclides (NORs) such as red mud, fly ash and ground granulated blast furnace slag are made into ‘green cements’ such as geopolymers or alkali-activated materials (AAMs). During the study, three AAM concrete and mortar series with various mixing ratios were prepared and investigated. The NOR content, I-Index, radon emanation and exhalation of the precursor waste materials and their cement products were measured and calculated and the strength of the cement products was compared. The emanation and the exhalation properties were calculated for the final products, weighing the data of the components as a function of their mixing ratio. The I-index alone suggested that the AAMs would be suitable products. AAMs containing ground granulated blast furnace slag exhibited the lowest radon exhalation and higher compressive strength, while the fly ash and red mud AAMs had increased final radon exhalation. In the case of fly ash, alkaline activation of fly ash dramatically increased the radon exhalation; the highest measured fly ash exhalation was 1.49 times of the theoretically calculated exhalation value. This highlights the increased risk of using fly ash as a component in AAMs and the need to carry out testing on the final products as well as individual secondary raw materials.