A comprehensive model to describe radiolytic processes in cement medium

Basic mechanisms controlling the radiolysis in cementitious matrices are reviewed in the specific context of the gamma irradiation, in closed system without upper vapour space, at 25 °C, with a pore solution representative of a Portland cement paste. A general survey of data corresponding to each phenomenological area is given, particularly with a list of reactions for alkaline medium and a revised description of equilibria related to calcium hydroxide. Simulations as a function of dose rate, liquid saturation in the porosity or initial amount of H2 are carried out with the CHEMSIMUL code. They show the existence of several ways in the radiolysis regulation involving calcium peroxide octahydrate precipitation, a law of mass action through the bulk general system, or the particular activation of an Allen’s type chain reaction. This latter seems faster in alkaline medium (pH > 13) where radicals H and OH are, respectively, replaced by e aq - and O−. Excepted when a strong reducing agent is initially present, O2 is normally produced by radiolysis and CaO2 · 8H2O cannot be responsible of its disappearance.