The physical and thermal properties of concrete under high temperature are obtained in order to provide reference data for material models necessary to evaluate the structural integrity of steel plate concrete containment vessels (SCCV) under accident conditions. Various parameters, such as temperature, heating duration, temperature history (heating, cooling, and the post-cooling process), water binder ratio, cement type, and aggregate type, are considered. Data on the temperature dependence of physical properties (compressive strength, elastic modulus, strain at compressive strength, splitting tensile strength) and thermal properties (thermal expansion strain, specific heat, thermal conductivity) are obtained from concrete of the same mix proportion. The effects of the variables on the properties of concrete are clarified, and the differences between test results and existing codes, such as the Eurocode, are highlighted.
The objective of this research is to establish proper modeling of FEM simulation for early thermal stress in second lining concrete of NATM tunnels. The proposed model was verified by field measurements. Stresses at the crown and at the sides close to the invert of the second lining were investigated using the established FEM model. First, a simulation scheme was proposed considering thermal behaviors in detail and was sufficiently verified using tunnel monitoring data obtained from a previous study. It was observed that accurate modeling was indispensable for the variation of air temperature and for thermal properties of waterproofing membrane to obtain dependable temperature simulation results. Second, appropriate modeling for several kinds of joints and important inputs related to early thermal stress such as effective Young’s modulus, autogenous shrinkage development, and setting of hardening time were proposed. Simulation results of structural strain and stress were verified by measurement data in a recently constructed tunnel. Slight difference between simulation results and measurement might be partially due to the material model idealizations and due to the structural imperfections in actual structures. From the stress distributions extracted from the simulation re-sults, it was observed that the crown cracks might be non-penetrating cracks and the cracks close to invert might be penetrating cracks.
Present study aims on evaluating the seismic performances of existing Masonry Infilled Reinforced Concrete (MIRC) buildings commonly found in many South and Southeast Asian countries utilizing appropriate masonry properties in Applied Element Method (AEM) models. First, masonry constituents and masonry composite properties were deter-mined for different masonry meshes through extensive parametric studies verified through the experimental results of masonry prisms under uniaxial compression and half scaled masonry infilled RC frames under in-plane cyclic load. Next, the established infill properties were utilized for time history dynamic analysis of an existing 8-storied MIRC building for different AEM models including soft story, retrofitted soft story, infills in all floors and bare RC frames ne-glecting stiffness contribution of infills. The analytical results revealed: 1) the unpredicted soft story column failure compared to the similar bare RC frame, 2) the inability of infills to improve the seismic performance of the surrounding RC frames, 3) the effectiveness of steel plate jacketing for preventing soft story failure and, 4) the effect of the exist-ence of overhead water tanks on the alteration of seismic behavior of RC buildings.
This work reports on the development of microstructural and mechanical properties of mortar cubes under the synergetic action of stray current and various environmental/curing conditions. The study refers to specimens cured for 24h only, followed by a 112 days period of partial or full submersion in water or alkaline medium. Additionally, equally prepared mortar specimens were tested in sealed conditions. The outcomes for submerged and saturated conditions were compared to sealed conditions. Three current density regimes were employed i.e. 1 A/m2, 100 mA/m2, and 10 mA/m2, simulating different levels of stray (DC) current environment. The highest level of 1A/m2 was also comparable to stray current densities, as measured in field conditions. The tests were designed in a way, so that the effects of diffu-sion-controlled transport (ions leaching due to concentration gradients), were distinguished from migration-controlled ones (ion/water transport in stray current conditions). Mechanical, microstructural and electrical properties were moni-tored throughout the test. For water-conditioned specimens, the stray current was found to accelerate degradation pro-cesses. This was reflected by decreased compressive strength, reduced electrical resistivity and increased porosity of the matrix. The results were attributed to leaching-out of alkali ions due to concentration gradients, where except diffusion, migration took place i.e. the leaching-out effect was accelerated by water and ions migration in conditions of stray cur-rent flow. In contrast, stray current flowing through mortar in sealed conditions (as well as through mortar in alkaline medium) resulted in increased compressive strength and electrical resistivity. These were accompanied by densification of the bulk matrix and reduced porosity. It can be concluded that for a cement-based material at early hydration age, both positive and negative effects of stray current flow can be expected. The level and direction of these effects are dependent on the external environment and the current density levels, where stray currents above 100 mA/m2 and in conditions of concentration gradients with the external medium, would lead to more pronounced negative effects on microstructural and micromechanical performance.
In this paper, the starting materials necessary for producing magnesium oxychloride cement (MOC) were produced from dolomite ore using leaching-carbonation-evaporation-pyrohydrolysis processes. The influences of the molar ratio of MgO/MgCl2 (Mx) and H2O/MgCl2 (Hy) on the properties of the MOC (cured for 7 days) were determined using physico-mechanical methods. SEM and XRD analyses were conducted to determine the change of phase and microstructure of the selected 7-day MOC depending on the production conduction. The experimental results show that the best mix proportion of 7-day MOC was found to be M6.06H14 and its thermal conductivity, flexural strength, and compressive strength values were found to be 1.202 W/mK, 4.22 MPa, and 87.7 MPa, respectively. The water resistance of the MOC was improved by a small amount of H3PO4 (4% of MgO by weight). Consequently, if MOC is produced from dolomite, high-purity synthetic aragonite and CO2 would be obtained as byproducts, which are strongly demanded.
The electrical resistivity of concrete is an important value for designing electrochemical anti-corrosive methods or a durability indicator of reinforced concrete structures. It is well known that the four-probe method (the Wenner method) can be useful one for non-destructive evaluation of electrical resistivity. However, it has been pointed out that the measured results must be identified as an apparent value including the effect of water content gradient in concrete. In order to consider the engineering property of apparent electrical resistivity, this study evaluated the water content gra-dient dependency of the measured results by experimental approach and numerical analysis with FEM. As a result, this study explained the mechanism about the probe spacing dependency of apparent electrical resistivity of concrete with water content gradient in depth direction. Moreover, it was pointed out that the apparent electrical resistivity of con-crete with water content gradient was correlated with the electrical resistivity at a depth about equal to the probe spac-ing, and measuring apparent electrical resistivity does not necessarily mean that the four probe method can evaluate the electrical resistivity of the immediate surface of concrete in dry conditions. In addition to this, it was recommended to compare the apparent electrical resistivities measured by several distance of the probe spacing in order to clarify the presence or absence of the effect of the water content gradient in concrete.
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