In this paper corrosion rate of steel reinforcements after carbonation of concrete was studied using AC impedance technique and weight loss measurements taking the effects of cement type, water to binder ratio, cover thickness,relative humidity and the like into account. Based on the study a corrosion rate eguation that includes the above factors and the relative humidity of 40 to 95% as variables was proposed by modifying Stern-Geary eguation. Ways of applying the eguation to the inside and outside environments of buildings were discussed, which resulted in a proposal of estimated corrsion rates after carbonation.
The main feature of a prestressed concrete containment vessel (hereinafter referred to as "PCCV") is that unbonded tendons, which are not bonded to the structure, are used because the tension of the tendon needs to be measured in periodical in-service inspection (hereinafter referred to as "ISI") to ensure that the performance of the power plant is maintained during the service life. This report describes the results of measurement of the tension of the tendon, which has been performed as an activity to maintain the PCCV in Ohi Nuclear Power Plant (hereafter referred to as Ohi "NPP") Units 3 and 4 of Kansai Electric Power in the past twenty some years since the construction of the PCCV, the changes in the standards and guidelines for the maintenance of the PCCV in Japan, as well as the discussion of non-destructive test-based methods for estimating the strength of high-strength concrete used for the PCCV and the development of a hydraulic shim-type load cell-based system for the measurement of the tension of the tendon, taking into account the ease of non-destructive testing, etc.
The critical amount of corrosion for initiating cracking along reinforcements was studied by wet and dry exposure tests and by RBSM analysis. The experiments showed that the critical amount of corrosion was in the range of 10 to 100 mg/cm 2 and was influenced by water-binder ratio of concrete, cover thickness and bar diameter. The results of the RBSM analysis showed similar tendencies with the experimental ones, when tension softening of concrete and crack development were taken into account. A modifying coefficient, however, was necessary for the critical values obtained by the two methods to coincide. Based on the results, some equations to express the critical amount of corrosion were proposed, taking water-binder ratio, cover thickness and bar diameter into account.
This paper describes the study on the appropriate test method of the dry density for the shielding concrete. A series of experiments was conducted based on the Latin square method considering cement type and test condition variability. The following conclusions can be drawn.1. The drying convergence time of a concrete specimen depends on the pre-curing period, the shape of the specimen and the drying temperature. The longer pre-curing period, larger specimen size and lower drying temperature make the drying convergence time longer.2. Although there are two judgment criteria for oven-dry condition of the concrete specimen and these two criteria influence the drying convergence time, these two criteria do not influence the dry density of the concrete specimen.
The carbonation rate coefficient of the medium heat Portland cement with fly ash was studied in both accelerated and natural exposure test conditions. The coefficient of the cement was higher than that of ordinary Portland cement (N cement) by 1.5 to 2.0 times under accelerated test conditions when water to binder ratio was 60%, but it was nearly the same with that of N cement under out door exposure test conditions. The cement factor (α2) of the cement was calculated to be 1.1 and the environment related factor (β3) was to be 3.5 according to the carbonation rate coefficient equations by the AIJ durability design recommendation.
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