Disappearance of oxygen in concrete under irradiation: The role of peroxides in radiolysis

Under irradiation, the interstitial liquid in concretes is affected by radiolysis. Normally produced with H-2 in alkaline medium, O-2 is not observed. It is shown that the disappearance of O-2 results not only from the fast reaction with the e(aq)(-) radical, which causes a negative redox potential, but also from peroxide trapping in CaO2. 8H(2)O, a highly insoluble phase whose solubility product is estimated at 2.8 x 10(-11). The disequilibrium that occurs in the redox sequence dioxygen (0) <-> superoxide (- 1/2) <-> peroxide (-1) is responsible for depleting most of the oxygenated species in the solution. CaO2. 8H(2)O is formed at the expense of calcium in solution, of portlandite, and of ettringite, but, being unstable, it disappears in the cement paste when H2O2 is no longer present in the medium. Consideration of the reaction between Ca(OH)(2) and H2O2 in the CHEMSIMUL kinetic code, which also highlights 0, consumption, seems to describe the long-term radiolysis of concrete accurately. (C) 1998 Elsevier Science Ltd.