Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
ISSN-L : 1346-8014
Volume 22, Issue 3
Displaying 1-6 of 6 articles from this issue
Scientific paper
  • Muhammad Talha Ghafoor, Chikako Fujiyama
    2024 Volume 22 Issue 3 Pages 103-114
    Published: March 09, 2024
    Released on J-STAGE: March 09, 2024

    This study is a continuation of the published research studies relevant to self-compacting geopolymer mortar (SCGM) prototype using fly ash. The aim of this study was to investigate the effect of fly ash quantity on the rheological properties of SCGM. The flow properties include relative flow area (Gm) and relative funnel speed (Rm) is determined with the variation of fly ash to sand ratio (FA/S), volume of water to powder ratio (Vw/Vp), and superplasticizer to powder ratio (Sp/P). The test results exhibited that the increase in FA/S from 0.5 to 1.0 positively affected the Gm and Rm of SCGM. The maximum Gm of 10.90 and Rm of 1.43 were obtained for the SCGM mix having FA/S of 1.0, Vw/Vp of 1.02, and Sp/P of 3%. Overall, test results exhibited that with an increase in FA/S comparable flow properties of SCGM were achieved even at lower Vw/Vp and Sp/P. The recommended boundary for SCGM is proposed by comparing the experimental test result of this study with previous studies.

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  • Chi Zhang, Koki Yamaoka, Takashi Fujinaga, Yuping Sun
    2024 Volume 22 Issue 3 Pages 115-127
    Published: March 12, 2024
    Released on J-STAGE: March 12, 2024

    Six square steel tube-encased concrete (SC) columns confined by bolted circular thin steel tube were fabricated and tested under cyclical reversed lateral load to investigate their structural behavior. The primary experimental variables included the axial load ratio, the grade of the encased square steel tubes (FB rank and FC rank), the infilling of concrete into the encased steel tube, and the thickness of outer circular bolted thin steel tubes. Experimental results revealed that confinement by the bolted circular thin steel tube with outer-diameter-to-thickness ratio of 189 could ensure sufficient ductility to the SC columns, and the bolted thin steel tube did not rupture until the drift angle of about 0.09 rad. Furthermore, a simple evaluation method for the ultimate flexural strength of SC column section was proposed along with a numerical analytical method to predict the overall behavior of SC columns. The proposed methods can take the confinement effect by the bolted circular steel tube into consideration. Fairly good agreement between the experimental results and the calculated ones verified the reliability and accuracy of the proposed methods.

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  • Kazuya Ohyama, Soshi Yamashita, Shin-ichi Igarashi
    2024 Volume 22 Issue 3 Pages 128-138
    Published: March 09, 2024
    Released on J-STAGE: March 09, 2024

    Paste volumes protected by air voids against frost attacks were estimated using Dirichlet tessellation tiles. Each tile was regarded as an area protected by air voids. The characteristic distance was defined by the largest tile size to reach a cumulative area fraction of 0.95. The significance of this distance was verified by a Monte Carlo test for the simulation of random point patterns. Comparing the characteristic distance and conventional spacing factor, the latter corresponds to the actual distance required for protecting the local region with the highest vulnerability to frost attack. The tessellation model provides the protection characteristic distance without overlaps even in the region of clustered air voids.

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  • Tsuneki Ichikawa, Kazuko Haga, Kazuo Yamada
    2024 Volume 22 Issue 3 Pages 139-148
    Published: March 21, 2024
    Released on J-STAGE: March 21, 2024

    The accurate numerical solution of a one-dimensional two-component reaction-diffusion equation including a second-order chemical reaction between concrete constituents and carbon dioxide to generate carbonated products was approximated by a simple analytical function which was given as a function of the effective diffusion coefficient of CO2, the rate constant of CO2 absorption, and parameters determined by the initial and the boundary conditions of the system. The pseudo-analytical solution thus obtained showed that the depth profile of carbonation shifts in parallel with square-root of time, and the rate constant of carbonation is determined from the location where the amount of the carbonated product is a half of the maximum amount. Comparison of the pseudo-analytical solution with an observed depth profile of concrete carbonation makes it possible to directly extract the rate constant of concrete carbonation that is necessary for predicting the future progress of the carbonation.

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  • Hu-zhi Zhang, Yi-jun Kang, Li-kun Li, Jian-qun Wang
    2024 Volume 22 Issue 3 Pages 162-177
    Published: March 29, 2024
    Released on J-STAGE: March 29, 2024

    To better utilize topology optimization theory to assist in designing reinforced concrete (RC) D-region members, a novel application mode, the Genetic Bi-directional Evolutionary Structural Optimization (GBESO) method based on Finite Element Analysis (FEA) with discrete models is proposed. Correspondingly a design method for reinforcement layout of RC D-region members is also derived. Non-linear FEA verification is conducted on numerical examples involving deep beams with openings. The results demonstrate that the GBESO algorithm exhibits better global optimization capacities compared to Evolutionary Structural Optimization-type (ESO-type) algorithms. It also provides rebar topologies that are more in line with the optimization objective, bringing lower steel consumption and higher rebar utilization rates. Moreover, by introducing inclined rebar to the members, their shear strength is enhanced to a level comparable to the flexural one, significantly improving ultimate load-bearing capacity, elastoplastic deformation capacity, and better ductility compared to empirical method.

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Technical report
  • Xiaofeng Han, Lixiao Zhao, Xiaoguang Sun, Li Tian, Zhenxing Du, Pengg ...
    2024 Volume 22 Issue 3 Pages 149-161
    Published: March 26, 2024
    Released on J-STAGE: March 26, 2024

    Steam curing is a widely used technique for producing precast concrete components in practical engineering. Chloride attack is a main factor that leads to the corrosion of rebars in concrete structures, which significantly affects the durability and safety of concrete structures in marine environments. In this paper, XRD, LF-NMR, 29Si NMR, and 27Al NMR were used to investigate the microstructure evolution of steam-cured concrete and standard-cured concrete. Then, the steam-cured and standard-cured concrete were subjected to actual marine exposure tests to explore the microstructure evolution of concrete and the chloride erosion behavior in the tidal zone. The results showed that steam-curing can increase the average molecular chain length (MCL) and polymerization degree of C-(A)-S-H, promote the transformation of silicon-oxygen tetrahedral dimer to polymer, and increase the Q2/Q1 value of steam-cured concrete to twice that of standard-cured concrete. Compared to standard-cured specimens, steam-cured concrete specimens had significantly more harmful pores and multi-harmful pores. With the increase of exposure time to the marine environment, the depth of the convection zone inside the concrete did not change significantly, however, the peak value of chloride concentration increased gradually. The addition of SCMs to steam-cured concrete reduced the content of free and total chloride, which was well explained by microscopic tests. The concentration of chloride on the surface and chloride diffusion coefficient of steam-cured concrete showed a quadratic function relationship with the increase of slag content, and an exponential decay relationship with the content of fly ash.

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