Monitoring cement hydration using radon exhalation method: Fid-Bau Portal

Monitoring cement hydration using radon exhalation method

Kovler, K.

Different mechanisms influencing radon exhalation rate from cement and hydration products are analyzed. The experiments with cement pastes with water/cement ratio of 0.33 cast and hydrated in hermetically closed desiccators are described. The radon concentration above the surface of specimens was measured by continuous radon monitor. Dramatic increase of the radon exhalation rate to ~0.5 mBq kg^-1 s^-1 was observed in a few hours after mixing with water. The test results showed a correlation between radon exhalation rate and deliberation of hydration heat and changing air relative humidity during the period of time associated with setting. Analysis of the literature data shows that heating of the materials weakens physical adsorption of radon gas atoms on newly formed solid surfaces and can enhance the radon exhalation rate by several times. However, the performed experiment shows that the radon exhalation rate increases much higher, and then decreases again, when the system starts consolidating. The curing temperature changed in the tests from 20 deg C to 60 deg C accelerated the setting process by a few hours, but did not result in changing the maximum exhalation rate too much. A dramatic growth of radon exhalation rate when cement sets can be explained mainly by two phenomena: (a) intensive formation of microstructure with an extremely high specific surface area, while porosity is still high; and (b) 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.