Hydroxyapatite coatings on cement paste as barriers against radiological contamination

A novel method for precipitating hydroxyapatite (HAp) onto cement paste is investigated for protecting concrete infrastructure from radiological contamination. Legacy nuclear sites contain large volumes of contaminated concrete and are expensive and dangerous to decommission. One solution is to 'design for decommissioning' by confining contaminants to a thin layer. Current layering methods, including paints or films, offer poor durability over plant lifespans. Here, we present a mineral-HAp-coated cement, which innovatively serves as a barrier layer to radioactive contaminants (e.g. Sr, U). HAp is shown to directly mineralise onto a cement paste block in a layer several microns thick via a two-step process: first, applying a silica-based scaffold onto a cement paste block; and second, soaking the resulting block in a PO₄-enriched Ringer's solution. Strontium ingression was tested on coated and uncoated cement paste (~ 40 × 40 × 40mm cement, 450 mL, 1000 mg L^- 1 Sr) for a period of 1-week. While both coated and uncoated samples reduced the solution concentration of Sr by half, Sr was held within the HAp layer of coated cement paste and was not observed within the cement matrix. In the uncoated samples, Sr had penetrated further into the block. Further studies aim to characterise HAp before and after exposure to a range of radioactive contaminants and to develop a method for mechanical layer separation.