2019 Volume 17 Issue 12 Pages 673-685
Hardened cement pastes (HCP) with different water contents were irradiated with gamma rays under different temperatures and irradiation dose rates. The relationship between the quantity of hydrogen gas produced and the water content as well as the stability of HCP under gamma irradiation was evaluated. It is experimentally confirmed that hydrogen gas was mainly produced from the evaporable water. The G value of the hydrogen production assuming the radiation energy absorbed by the total water composed of chemically bound water (CBW) and evaporable water was ranging from 0.03 to 0.42. The G value of the hydrogen production for CBW was ranging from 0.03 to 0.07, which were an order of magnitude smaller than that of the bulk water (0.45).
Assuming that the radiation energy on evaporable water is used for the formation of hydrogen, it is experimentally confirmed that, in case of low dose rate, the G value tended to converge to a constant value when the evaporable water exceeded a certain value, while, in case of high dose rate, the G value increased as evaporable water increased. However, the G values of all cases grew with increasing evaporable water content and exceeded the G value of the bulk water (0.45). The CBW was not susceptible to gamma irradiation. Only 2 to 3% of the CBW was estimated to be decomposed by 200 MGy of gamma irradiation.