Speaker
Description
The use of supplementary cementitious materials (SCMs) is one of the most used ways to reduce CO2 emissions associated to the production of Portland cement. However, many of these SCMs are Naturally Occurring Radioactive Materials (NORM), which present naturally occurring radionuclides. Radon emission from these types of materials, together with radon infiltration from the ground through them, is one of the main sources of indoor radon. Radon transport through any material is regulated by its radon diffusion coefficient, D, hence playing an important role when trying to mitigate radon accumulation indoors. Current methodologies developed to determine D can be difficult to apply. ISO 11665-13 imposes restrictive conditions on the experimental system and requires the application of numerical methods. In this work, a new algorithm and its software were developed to complement the ISO. The algorithm solves for the physical governing equations and finds the value of D that best fits the data by minimising the differences between the predicted and experimental concentrations. Two sets of seven cement pastes, with different quantities of additives and cured for 2 and 28 days, respectively, were used to test the algorithm, resulting in a total of 14 samples. A validation procedure was developed for internal validation, and results were compared with the literature for external validation. The radon properties of the cement pastes were studied in function of the technical properties to determine their suitability as building and insulating materials against radon. The D of the pastes changed by an order of magnitude between those with a 2-day curing time and those with a 28-day curing time, the latter being less permeable to radon. In addition, there was a decrease in D as the percentage of superplasticiser admixture increased, due to the reduction in the porosity of the final pastes and the reduction in radon permeability. In conclusion, the methodology for radon diffusion coefficient measurement was tested and validated satisfactorily and, with his application, it was found that different characteristics of the cement paste production, which influence the final microstructure, can produce cements containing NORM material with radon permeabilities low enough to be used as a barrier against radon.