Radiological behaviour of pigments and water repellents in cement-based mortars

Abstract The use of admixtures in mortars to improve both their physical-chemical and ornamental features has become increasingly common in recent years. The varying origin and composition of these products, some sourced from waste produced in other industries, poses the question of whether they modify the activity concentration index (ACI) of the construction materials to which they are added. Seven pigments, some of natural and others of artificial origin, and two water repellents were characterised both chemically and radiologically in this study. Neither the synthetic pigments nor the water repellents exhibited significant radiological content. The pigments based on Fe2O3 of natural origin had detectable activity concentrations of naturally occurring radionuclides from the 238U series. Those levels were attributable to the raw material used, namely the bauxite red mud generated in aluminium production. In addition to Si, Al, Fe, Ca, Ti and Na as majority elements, this sludge also contains traces of K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S and As, among others, including naturally occurring uranium. The public and occupational radiological risk due to exposure to pigment-modified construction materials were consequently assessed. Neither the doses for the public at large and for workers were found neither to be significant nor constitute any perceptible hazard, essentially in light of the small amounts of pigment used to prepare mortars.