Concrete Research and Technology

A Fundamental Study on Modeling Prediction of Deterioration of Concrete Exposed to Very Low Temperature

Takuya OBARA, Kenji OGAWA, Ichiro IWAKI, Takashi MIURA

2003 Volume 14 Issue 2 Pages 1-10
Published: May 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.2_1

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It is known that concrete exposed to repeated cycles of cooling from ordinary temperature to very low temperature below -20°C induces severer deterioration than that cooled to -20°C, which is the standard temperature for any general study of frost damage. By considering the behavior of water in the pores of cement paste matrix, the model to predict and quantify such deterioration is necessary. In this study, a simple dilation model was formulated based on the behavior of pore water during the cooling process. A new index of deterioration, other than relative dynamic modulus of elasticity, was also proposed. It was found that the index calculated from this model corresponds well to that obtained from experimental data of various mixture proportions and cooling conditions.

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Analytical Accuracies of Maximum Strengths of Reinforced Concrete Framed Shear Walls by Macroscopic Models.

Makoto MOCHIZUKI, Norikazu ONOZATO, Masao TAKEHARA, Yukichi KANEHIRA

2003 Volume 14 Issue 2 Pages 11-22
Published: May 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.2_11

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In this paper the analytical accuracies of theauthors' three macroscopic models, which are referred to the original, the simplified, and the elasto-plastic models, for evaluating the maximum strengths of RC framed shear walls are discussed. The analyses using these three macroscopic models were executed for twenty fourspecimens selected by JCI committee for verification of the existing macroscopic models, eighty nine specimens selected by Dr.Naganuma for verification of his finite element method model, and five hundred and eighteen specimens conformed to the criteria established by the authors, conducted in Japan since 1970. And their results were compared with the observed maximum strengths in experiments. The comparisons show that the analytical accuracies of the authors'three macroscopic models are excellent for large range of the various parameters of the specimens.

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Estimation of the degree of hydration in cement pastes by the SEM-BSE image analysis

Shin-ichi Igarashi, Akio Watanabe, Mitsunori Kawamura

2003 Volume 14 Issue 2 Pages 23-29
Published: May 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.2_23

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The process of the formation of constituent phases in cement pastes with various water : cement ratios were quantitatively analyzed by the SEM-BSE image analysis. The proportions of each phase obtained by the analyses were compared with those calculated based on Powers' model. It was found from the comparisons thatthe volume fractions of constituents obtained by the image analysis at a certain degree of hydration were consistent with those estimated from Powers' model. The gel-space ratios were also calculated based on the degree of hydration of cement obtained by the image analysis. The development of strength in cement pastes was reasonably explained by the gel-space ratio theory.

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Model for the Skeleton Curve of Square CFT Beam-Columns

Go NAKAMURA, Takashi FUJINAGA, Isao MITANI, Yasuhiro OHTAN

2003 Volume 14 Issue 2 Pages 31-41
Published: May 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.2_31

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The objective of this study is to propose the skeleton curve model of the square CFT beam-columns, that is simple, easy to use and represent the actual behavior appropriately. In this study, we gave attention to tne change of the bearing axial load of steel pipe and filled concrete, and examined by conducting the elasto-plastic analysis to define the tendency of the bearing axial load. The skeleton curve model of steel beam-columns and concrete beam-columns were assumed respectively, which considered the bearing axial load. The skeleton curve model of square CFT columns is proposed by superposing the model of steel beam-columns and concrete beam-columns. Proposed model estimated the test results (Diameter-to-thickness ratio (D/t : 33-44), strength of concrete (F_c : 30, 60MPa), axial load ratio (n : 0.2-0.7), yield stress of the steel (_sσ_y : 400MPa)) generally.

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Influence of Preparation Method on Performance of Expansive Additve Containing Free-lime, Hauyne and Anhydrite.

Minoru MORIOKA, Etsuo SAKAI, Masaki DAIMON

2003 Volume 14 Issue 2 Pages 43-50
Published: May 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.2_43

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The authors examined the influence of the preparation method of free lime-hauyne-anhydrite system expansive additive on its performance. The result showed that even though the same composition of additives were used, the expansive additive that was prepared by dispersing the above three compounds into clinker had more excellent expansion performance than the expansive additive that was prepared by mixing the same three compounds. In addition, if the preparation condition was different, the compressive strength when the same rate of expansion was given showed a large difference. It was considered that these phenomena were originated from differences in the reaction velocity of free lime and formation mechanism of ettringite.

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