• Computers and Concrete
• /
• 제16권6호
• /
• pp.865-880
• /
• 2015

Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete's resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.

• Corrosion Science and Technology
• /
• 제3권3호
• /
• pp.118-126
• /
• 2004

The correlation between sensor output and corrosion rate of reinforcing steel was evaluated by laboratory electrochemical tests in saturated $Ca(OH)_2$ with 3.5 wt.% NaCl and confirmed in concrete environment. In this paper, two types of electrochemical probes were developed: galvanic cells containing of steel/copper and steel/stainless steel couples. Potentiodynamic test, weight loss measurement, monitoring of open-circuit potential, linear polarization resistance (LPR) measurement and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of steel bar embedded in concrete. Also, galvanic current measurements were conducted to obtain the charge of sensor embedded in concrete. In this study, steel/copper and steel/stainless steel sensors showed a good correlation in simulated concrete solution between sensor output and corrosion rate of steel bar. However, there was no linear relationship between steel/stainless steel sensor output and corrosion rate of steel bar in concrete environment due to the low galvanic current output. Thus, steel/copper sensor is a reliable corrosion monitoring sensor system which can detect corrosion rate of reinforcing steel in concrete structures.

• 방사성폐기물학회지
• /
• 제14권1호
• /
• pp.11-19
• /
• 2016

This paper focuses on the estimation of durability and service-life of reinforced concrete structures in Wolsong Low- and intermediate-level wastes Disposal Center (WLDC) in Korea. There are six disposal silos located in the saturated environment. The silo concrete is degraded due to reactions with groundwater and chemical attacks, and finally it will lose its properties as a transport barrier. The infiltration of sulfate and magnesium, leaching of potassium hydroxide, and chlorine induced corrosion are the most significant factors for degradation of reinforced concrete structure in underground environment. From the result of evaluation of the degradation time for each factor, the degradation rate of the reinforced concrete due to sulfate and magnesium is $1.308{\times}10^{-3}cm/yr$, and it is estimated to take 48,000 years for full degradation while potassium hydroxide is leached in depth of less than 1.5 cm at 1,000 years after the initiation of degradation. In case of chlorine induced corrosion, it takes 1,648 years to initiate corrosion in the main reinforced bar and 2,288 years to reach the lifetime limit of the structural integrity, and thus it is evaluated as the most significant factor.

• 한국초등과학교육학회지:초등과학교육
• /
• 제30권3호
• /
• pp.305-314
• /
• 2011

In this study, the analogies on saturated solution generated by elementary school teachers were analyzed in their numbers, materials, and types aspects. The results were also compared with those of general and science-gifted elementary students. A test on the self-generating analogies on the target concept was administered to 111 elementary school teachers, 60 fifth graders at four science-gifted education institutes and 91 fifth graders at three elementary schools. The results revealed that the teachers made more analogies than the general and science-gifted students. In general, both the teachers and the students tended to make the analogies using the materials in family, riding, digestive, and school situations. However, there were a little difference between the teachers and the students in the cases of the analogies using other situations including body/physical activity. Similarly to the cases of the students, the teachers made more functional analogies than structural or structural/functional ones and did more concrete ones than abstract ones. However, they made more verbal, artificial, and enriched analogies than the students. They also made more highly systematic analogies than the general students, and did less ones than the science-gifted students. Educational implications of these findings are discussed.

• 한국초등과학교육학회지:초등과학교육
• /
• 제29권2호
• /
• pp.219-232
• /
• 2010

In this study, we investigated and compared the types of analogy generation processes and the perceptions of analogy generation on saturated solution of fifth grade scientifically-gifted and general elementary students. After the instruction of self-generating analogies on 'saturated solution' concept for two classes, 12 scientifically-gifted and 8 general elementary students were interviewed to explore their analogy generation processes and the perceptions of the abilities required in the processes, the conditions of good analogies, and the advantages/disadvantages of analogy generation. The results revealed that their analogy generation processes were classified into three types. The scientifically-gifted students generated the analogies in more systematic and efficient ways and had better understanding of the important parts in the processes than the general elementary students. They also suggested more concrete and various ideas about the conditions of good analogies. Many scientifically-gifted and general elementary students thought that analogy generation would have positive influences on the developments of the cognitive aspects such as various higher-level thinking abilities and understanding of science concepts as well as the affective aspects such as science learning motivation and interest. Educational implications of these findings are discussed.

• Computers and Concrete
• /
• 제4권4호
• /
• pp.273-284
• /
• 2007

The paper considers a theoretical model for the study of the process of transfer of sulfate ions in saturated porous media - mineral composites. In its turn, the model treats diffusion of sulfate ions into cement based composites, accounting for simultaneous effects such as filling of micro-capillaries with ions and chemical products and liquid push out of them. The proposed numerical algorithm enables one to account for those simultaneous effects, as well as to model the diffusive behavior of separate sections of the considered volume, such as inert fillers. The cases studied illustrate the capabilities of the proposed model and those of the algorithm developed to study diffusion, considering the specimen complex configuration. Computations show that the theoretical assumptions enable one to qualitatively estimate the experimental evidence and the capabilities of the studied composite. The results found can be used to both assess the sulfate corrosion in saturated systems and predict and estimate damage of structures built of cement-based mineral composites.

• Computers and Concrete
• /
• 제4권2호
• /
• pp.157-166
• /
• 2007

The paper considers a theoretical model to study sulfate ion diffusion in saturated porous media - cement based mineral composites, accounting for simultaneous effects, such as filling micro-capillaries (pores) with ions and chemical products and liquid push out of them. Pore volume change and its effect on the distribution of ion concentration within the specimen are investigated. Relations for the distribution of the capillary relative radius and volume within the composite under consideration are found. The numerical algorithm used is further completed to consider capillary size change and the effects accompanying sulfate ion diffusion. Ion distribution within the cross section and volume of specimens fabricated from mineral composites is numerically studied, accounting for the change of material capillary size and volume. Characteristic cases of 2D and 3D diffusion are analyzed. The results found can be used to both assess the sulfate corrosion in saturated systems and predict changes occurring in the pore structure of the composite as a result of sulfate ion diffusion.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2016년도 춘계 학술논문 발표대회
• /
• pp.134-135
• /
• 2016

This study aims to compare relative moisture content and gravity moisture content in calculating the rational percentage of moisture content. High-strength concrete, which is made of blast-furnace slag and silica fume, was used as the compound for this study, and the specimens were made into a saturated condition through the vacuum suction. According to the results of this study, all specimens were completely dried when they were under the temperature of 105℃ for more than 31 days. They were fully saturated after 72 hours through vacuum suction. In addition, relative moisture content responded more sensitively to moisture content than gravity moisture content did, so it can be concluded that relative moisture content is better in calculating the rational percentage of moisture content.

• Computers and Concrete
• /
• 제16권5호
• /
• pp.669-682
• /
• 2015

Degradation of reinforced concrete (RC) structures due to chloride penetration followed by reinforcement corrosion has been a serious problem in civil engineering for many years. The numerical simulation methods at present are mainly finite element method (FEM) and finite difference method (FDM), which are based on mesh. Mesh generation in engineering takes a long time. In the present article, the numerical solution of chloride transport in concrete is analyzed using radial point interpolation method (RPIM) and element-free Galerkin (EFG). They are all meshless methods. RPIM utilizes radial polynomial basis, whereas EFG uses the moving least-square approximation. A Galerkin weak form on global is used to attain the discrete equation, and four different numerical examples are presented. MQ function and appropriate parameters have been proposed in RPIM. Numerical simulation results are compared with those obtained from the finite element method (FEM) and analytical solutions. Two case of chloride transport in full saturated and unsaturated concrete are analyzed to test the practical applicability and performance of the RPIM and EFG. A good agreement is obtained among RPIM, EFG, and the experimental data. It indicates that RPIM and EFG are reliable meshless methods for prediction of chloride concentration in concrete structures.

• Computers and Concrete
• /
• 제15권1호
• /
• pp.37-54
• /
• 2015

In general, cracks significantly deteriorate the in-situ performance of concrete members and structures, especially in urban metro tunnels that have been embedded in saturated soft soils. The microcapsule self-healing method is a newly developed healing method for repairing cracked concrete. To investigate the optimal microcapsule parameters that will have the best healing effect in concrete, a 3D analytical probability healing model is proposed; it is based on the microcapsule self-healing method's healing mechanism, and its purpose is to predict the healing efficiency and healing probability of given cracks. The proposed model comprehensively considers the radius and the volume fraction of microcapsules, the expected healing efficiency, the parameters of cracks, the broken ratio and the healing probability. Furthermore, a simplified probability healing model is proposed to facilitate the calculation. Then, a Monte Carlo test is conducted to verify the proposed 3D analytical probability healing model. Finally, the influences of microcapsules' parameters on the healing efficiency and the healing probability of the microcapsule self-healing method are examined in light of the proposed probability model.