2017 Volume 71 Issue 1 Pages 240-247
In order to ensure long-term safety operation of nuclear power plants, it is necessary to evaluate the soundness of concrete used in the plants against various deterioration events. Irradiation environment is a particularly characteristic boundary condition of the materials for nuclear power plant, and consequently, it is important to grasp its deterioration mechanism.
The effect of gamma-ray irradiation on carbonation of cement paste using high early strength Portland cement was investigated. XRD/Rietveld analysis, TG-DTA, FT-IR, water vapor sorption and nitrogen sorption measurements were conducted on the samples with/without 60Co gamma-ray irradiation up to the dose about 50,000 kGy. As a result, the differences in carbonation under gamma-ray irradiation environment and non-irradiated environment were identified from the viewpoint of phase compositions and microstructure, as shown below.
From the experimental results, it was confirmed that large portion of C-S-H was carbonated and vaterite was mainly precipitated under gamma-ray irradiation, whereas calcite was mainly precipitated through the carbonation without irradiation.
In addition, from the viewpoint of microstructure, it was confirmed that the hardened cement paste carbonated under gamma-ray irradiation had less amount of cavitation in nitrogen sorption isotherm measurement at 77K than that carbonated without gamma-ray irradiation, and a sharp change of desorption amount around 40％ RH in water vapor sorption isotherm measurement by volume method at 293 K, which was originally confirmed in the hardened cement paste before irradiation. All these experimental facts suggest that the similar microstructure originated by non-carbonated C-S-H in hardened cement paste before irradiation was preserved under gamma-ray irradiation condition with forming vaterite through carbonation of C-S-H.
