Long-term Material Properties of a Thick Concrete Wall Exposed to Ordinary Environmental Conditions in a Nuclear Reactor Building: the Contribution of Cement Hydrates and Feldspar Interaction

Abstract

A variation of material properties with depth is observed in a massive, seismic-resistant internal wall of Unit 1 of the Hamaoka Nuclear Power Plant (NPP) 45 years after its construction. The maximum values are attained in the center of the structural element and gradually decrease towards the surface, while still well exceeding the required performance. It is found that this trend can be mostly attributed to the reaction between cement hydrates and rock-forming minerals of a feldspar group, which releases silica and alumina oxides into the pore solution, where they react with portlandite to form new hydrates. No evidence of expansive distress similar to the alkali-silica reaction (ASR) is found in the material, owing to this reaction. Possible implications for the aging management of existing concrete structures are discussed.