Characterization of radionuclides present in portland cement, gypsum and phosphogypsum mortars

Abstract

Portland cement is the main ingredient of concrete and various types of finishing materials. It is considered as the main and most consumed building material in the world, which is used for all type of construction including residential and commercial buildings, dwellings, offices, and industrial facilities. Portland cement is made from the chemical composition of major oxides, such as CaO, SiO2, Al2O3, and Fe2O3, and minor oxides, which include MgO, SO3 together with alkali oxides (K2O and Na2O) and other compounds such as P2O5, TiO2, MnO3, among others. Being produced from different type of natural raw materials, such as limestone, chalk, marl, clays, slags and shale among other, the manufacturing of Portland cement involves the crushing rocks, their mixture with different ingredients such as iron ore or/and fly ash, grounding, homogenizing of this mixture, and then its calcination and fusion at a temperature about 1450 °C. As result of such industrial process the Portland cement could contain rather significant quantity of natural radionuclides such as 226Ra, 232Th and 40K. The main purpose of present study was to characterize and quantify the concentration levels of 226Ra, 232Th and 40K in Portland cement, gypsum and phosphogypsum mortar samples from Brazil using gamma spectrometry. The radiological risk of studied building materials was evaluated by measurements of activity concentration of 222Rn exhaled by these materials into the air and calculating the values of the emanation coefficient (f), the radium equivalent activity (Raeq), absorbed gamma dose rate (Din), the annual effective dose (Ein), the alpha hazard index (Iα), the gamma hazard index (Iγ), as well as external hazard index (Hex) and the internal hazard index (Hin). Obtained values of hazard indexes were found below the recommended limits.