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Modeling of Mechanical Properties of Concrete Mixed with Expansive Additive
Hyeonggil Choi,Takafumi Noguchi 한국콘크리트학회 2015 International Journal of Concrete Structures and M Vol.9 No.4
This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.
Park, Sun-Gyu,Noguchi, Takafumi,Kim, Moo-Han Korea Concrete Institute 2006 International Journal of Concrete Structures and M Vol.18 No.e2
This paper shows a study of the efficiency of expansive additive and shrinkage reducing admixture in controlling restrained shrinkage cracking of high performance concrete at early age. Free autogenous shrinkage test of $100{\times}100{\times}400mm$ concrete specimens and simulated completely-restrained test with VRTM(variable restraint testing machine) were performed. Creep and autogenous shrinkage of high-performance concrete with and without expansive additive and shrinkage reducing admixture were investigated by experiments that provided data on free autogenous shrinkage and restrained shrinkage. The results showed that the addition of expansive additive and shrinkage reducing admixture effectively reduced autogenous shrinkage and tensile stress in the restrained conditions. Also, it was found that the shrinkage stress was relaxed by 90% in high-performance concrete with and without expansive additive and shrinkage reducing admixtures at early age.
Phan, Quy Thanh,Noguchi, Takafumi Sustainable Building Research Center 2010 International journal of sustainable building tech Vol.1 No.2
After the collapse of Can Tho Bridge, a severe accident with 54 people dead and 80 injured, the risk assessment of sustainable concrete structures for Vietnam construction industry becomes an extremely important subject. In spite of many accidents in construction, there is still no research in the risk management of construction industry in Vietnam. Based on the situation, "Development of Risk assessment system for Sustainable Concrete Structures with Construction Management in Vietnam" has been conducted. The first survey was conducted with the cooperation of experienced person who has responsibility in construction-related companies in Vietnam. In order to collect actual data concerning the cause, the type and the probability of various incidents, the repair cost after the failure occurrence and the proactive cost with purpose of incident prevention to prolong the life of concrete structures and reduce the life cycle cost in Vietnam. As a result of this investigation, Event Tree Analysis (ETA) is used to classify and evaluate the damage form, identifying the occurrence probability and the cost of loss. This research estimates 26 types of failure (hazards) which might be occurred in concrete construction, based on the assumption that hazard occurred dependently. Based on ETA, each failure is disposed into 4 cases. Some case of risk curves are used to identify and evaluate the sequence of events in the failures. By this result, construction companies in Vietnam have been aware of preventing construction failure that might be occurred. Comparison was made between the results in Vietnam and those in Japan to find out appropriate measures to minimize the risk in concrete construction.
Lim, Young-Chul,Noguchi, Takafumi,Cho, Chang-Geun Elsevier 2018 CEMENT AND CONCRETE COMPOSITES Vol.90 No.-
<P><B>Abstract</B></P> <P>Concrete resistivity in reinforced concrete structures is used as an indicator of durability related to the corrosion risk. This study aims to develop a quantitative analysis method of geometric effects of nearby reinforcement in the electrical resistivity measurement. The A-REM proposed in this study is a mathematical model to enable analysis of not only concrete (or mortar) and reinforcement resistivity, but also of geometric effects such as rebar diameter, cover depth, electrode interval, and the spatial relationship between the rebar and electrodes. The effect of nearby reinforcement on the electrical resistivity measurement was presented to be obtained from the apparent resistivity rate (AR rate) calculated by the A-REM. The A-REM for the estimation of the nearby reinforcement effects was verified by comparing the apparent resistivity values obtained from mortar specimens having different reinforcement diameters and cover depths. The result shows that the calculated values of the A-REM are correlated with the experimental values of apparent resistivity.</P>
Lim, Young-Chul,Noguchi, Takafumi,Lee, Han-Seung The Iron and Steel Institute of Japan 2009 ISIJ international Vol.49 No.1
<P>This study aims to formulate a resistivity model whereby the concrete resistivity expressing the environment of steel reinforcement can be directly estimated and evaluated based on measurement immediately above reinforcement as a method of evaluating corrosion deterioration in reinforced concrete structures. It also aims to provide a theoretical ground for the feasibility of durability evaluation by electric non-destructive techniques with no need for chipping of cover concrete. This Resistivity Estimation Model (REM), which is a mathematical model using the mirror method, combines conventional four-electrode measurement of resistivity with geometric parameters including cover depth, bar diameter, and electrode intervals. This model was verified by estimation using this model at areas directly above reinforcement and resistivity measurement at areas unaffected by reinforcement in regard to the assessment of the concrete resistivity. Both results strongly correlated, proving the validity of this model. It is expected to be applicable to laboratory study and field diagnosis regarding reinforcement corrosion.</P>
Tae, Sung-Ho,Noguchi, Takafumi,Ujiro, Takumi Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.10
<P>Reinforced concrete specimens were prepared by embedding 10 types of Cr-bearing reinforcing bars having different Cr contents and supplying saltwater from the upper surfaces to allow chloride ions to penetrate into concrete, thereby forming macrocells, with the aim of developing Cr-bearing rebars having corrosion-preventing properties required under macrocell-corrosion conditions due to differences in the chloride concentrations. The time-related changes in the macrocell corrosion current density, soluble chloride ion content of concrete, and half-cell potential were then measured during corrosion-accelerating test up to eight months. Also, the corrosion area and corrosion loss of anodic and cathodic bars were measured at the end of the 8-month corrosion-accelerating test to investigate the corrosion-inhibiting property of Cr-bearing rebars in macrocell corrosion environments due to chloride ion concentration in concrete.As a result, the Cr content required for corrosion inhibition was found to be more than 7% in macrocell corrosion environments with a difference in soluble chloride ion concentrations of not more than 2.4 kg/m<SUP>3</SUP>.</P>
Corrosion Resistance of Cr-bearing Rebar in Concrete with Chloride Ion Content
Tae, Sung-Ho,Lee, Han-Seung,Noguchi, Takafumi,Ujiro, Takumi,Shin, Sung-Woo The Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.7
<P>As a fundamental study on the performance of Cr-bearing rebars in steel reinforced concrete structures exposed to corrosive environments, The test specimens were made by installing 8 types of rebars in concretes with a chloride ion content of 0.3, 0.6, 1.2, 2.4 and 24 kg/m<SUP>3</SUP>. Corrosion accelerated curing were then conducted with them. The corrosion resistance of Cr-bearing rebars was examined by measuring crack widths, half-cell potential, corrosion area and weight loss after 155 cycles of corrosion- accelerating curing.The results of the study showed that the corrosion resistance increased as the Cr content increased regardless of the content of chloride ions, and that the Cr-bearing rebars with a Cr content of 5% and 9% showed high corrosion resistance in concretes with a chloride ion content of 1.2 and 2.4 kg/m<SUP>3</SUP>, respectively.</P>