title: Influence of the porosity on the ²²²Rn exhalation rate of concrete.
abstract: The composition of 23 concrete mixtures was varied in five separate series to evaluate the influence of porosity on the ²²²Rn exhalation rate. In each series, a range in porosities is obtained by varying (1) the amount of cement, (2) type of cement (Portland or blast furnace slag cement), (3) the amount of water at a fixed cement level, (4) addition of an air entraining agent, or (5) the amount of recycled aggregates. The porosities ranged from 1% to 16%. The ²²²Rn exhalation rate is normalized to the ²²⁶Ra activity concentration and expressed as the ²²²Rn release factor to eliminate the effect of differences in ²²⁶Ra activity concentrations among the various concrete mixtures. Since most ²²²Rn originates from the cement, a ²²²Rn release factor based on the amount of ²²⁶Ra introduced by the cements appeared to be more adequate. Although the methods to attain the porosities in the concrete mixtures differ widely, this cement-related factor corresponds well with the capillary porosity of the mixtures. Since the water-to-cement ratio of the fresh paste is a good indicator of the capillary porosity, this is the guiding factor in the fabrication of concretes low in ²²²Rn exhalation. The lower the water-to-cement ratio, the less capillary pore area will be available from which ²²²Rn can emanate from the mineral matrix into the pore system. The good correlation between the cement-based ²²²Rn release factor and literature data on the internal capillary pore area support the results of this study.
authors.affiliation: Nuclear Research and consultancy Group, PO Box 9034, 6800 ES Arnhem, The Netherlands. p.dejong@nrg.eu
authors.forename: Peter
authors.initials: P
authors.lastname: de Jong
authors.forename: Willem
authors.initials: W
authors.lastname: van Dijk
authors.forename: Mario
authors.initials: M
authors.lastname: de Rooij
mesh_terms: D000388:Air; D003252:Construction Materials / Q000032:analysis*; D007700:Kinetics; D016062:Porosity; D011851:Radioactivity; D011886:Radon / Q000032:analysis*; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D011886:Radon