Title:
Mechanisms of Radon Exhalation from Hardening Cementitious Materials
Author(s):
Konstantin Kovler
Publication:
Materials Journal
Volume:
105
Issue:
4
Appears on pages(s):
404-413
Keywords:
humidity; hydration; microstructure; porosity; portland cement; radioactivity; radon exhalation; temperature
DOI:
10.14359/19903
Date:
7/1/2008
Abstract:
The hardening of portland cement was monitored by the radon exhalation method. Three stages were distinguished on the time dependence of radon concentration: Stage I--dormant period, Stage II--intensive microstructural transformations, and Stage III--densification and drying of the structure. Radon exhalation is especially sensitive to the initial set when the radon flux starts growing quickly. The sharp increase of radon flux is explained by a synergy of the following main effects: 1) quick microstructural formation while porosity is still high; 2) intensive flow of water, which traps radon from the newly formed solid surfaces of C-S-H to the sample surface and enhances radon emanation power; and 3) high evaporation rate from the surface, as a result of hydration heat. A weakened physical adsorption of radon gas on the solid surfaces due to the hydration heat cannot be neglected, although this mechanism does not seem to be decisive.