Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
ISSN-L : 1346-8014
Volume 17, Issue 10
Displaying 1-5 of 5 articles from this issue
Technical report
  • Bohao Wang, Feng Jin, Hu Zhou, Duruo Huang, Ning Liu, Wei Wang, Yiyang ...
    2019 Volume 17 Issue 10 Pages 559-570
    Published: October 05, 2019
    Released on J-STAGE: October 05, 2019

    This exploratory study investigated a new type of rock-filled concrete (RFC) named vibrated rock-filled concrete (VRFC). Different from the self-compacting concrete (SCC) used in traditional type of RFC, VRFC was built with ordinary pumping concrete (OPC) with the help of external vibration. The application of OPC further reduced the cement dosage and hydration heat of RFC, making it more widely applicable and environment-friendly without cost increase. It was proved that the fluidity of OPC could be significantly improved by external vibration, and the relationship between the flowing process and the mix proportion of OPC was also analyzed in the laboratory experiment. After verifying the feasibility of filling the rock voids with OPC in the laboratory, more than 700 m3 VRFC was constructed in the on-site experiment with roller compactors as the vibration source. Panoramic borehole color TV system and ultrasonic testing method were used to evaluate the quality of VRFC, and the influences of different parameters on the compactness as well as mechanical performance of VRFC were also analyzed.

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Scientific paper
  • Yasuo Wakabayashi, Yuichi Yoshimura, Maki Mizuta, Yoshie Otake, Yujiro ...
    2019 Volume 17 Issue 10 Pages 571-578
    Published: October 12, 2019
    Released on J-STAGE: October 12, 2019

    As a nondestructive measurement of chloride ion distribution in concrete is important from the viewpoint of preventive maintenance against chloride attack causing deterioration of many concrete structures, a diagnostic technique of a nondestructive measurement method using a neutron-captured prompt gamma-ray analysis (PGA) is being developed. As the first step of development, the γ-ray sensitivities of mortar samples with different chloride ion concentrations were determined experimentally by PGA using the RIKEN accelerator-driven compact neutron source. The results showed that the present detection system was sensitive to a chloride ion concentration of 1 kg/m3, which is lower than the marginal chloride ion concentration of 1.2 - 2.5 kg/m3 to incur corrosion. The time of flight measurement technique with pulsed neutrons was applied concerning the depth profile of chloride ion distribution in concrete.

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  • Yuta Yamada
    2019 Volume 17 Issue 10 Pages 579-591
    Published: October 19, 2019
    Released on J-STAGE: October 19, 2019

    This study investigated the effects of cracks along rebars in reinforced concrete (RC) beams with multiple holes inside the shear spans mainly based on nonlinear finite element (FE) analyses. The analytical parameters were the hole positions that increased the shear strengths of RC beams in static loading experiments, the crack positions, and the widths. As a result of the analyses, for beams with holes arranged from near the loading points toward the positions of tensile rebars at the mid-shear span with no stirrups, when the beams had a horizontal crack, the strengths increased to the flexural capacities. However, when the beam had vertical cracks, the strength decreased to 80% for beams without holes. Meanwhile, for beams with holes arranged from the bottom side of the loading points toward the mid-height with no stirrups, the strength increased to between 110% and 160% compared with beams without holes regardless of the crack positions. Moreover, the shear behaviors of the beams did not change when the equivalent crack width exceeded 0.3 mm for each case, and changes in the behaviors of beams with stirrups were negligibly small regardless of the hole positions. It was made clear that changes in the behaviors were caused by the contributions of arch mechanisms enhanced by localizations and expansions of the minimum principal stress distributions owing to the multiple holes.

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  • Yafen Zhang, Hiroshi Yokota, Yulong Zhu
    2019 Volume 17 Issue 10 Pages 592-602
    Published: October 26, 2019
    Released on J-STAGE: October 26, 2019

    The penetration of chloride ion leads to the corrosion initiation in reinforced concrete, which results in decreasing the durability of concrete. A theoretical diffusion-convection model describing the process of chloride ion penetration into concrete under external water pressure is described by considering multiple affecting factors such as unsaturated flow, fluid-solid coupling, and chloride binding. A numerical model of unsaturated concrete is built to simulate the coupled process. Based on this model, the classic expression of effective diffusion coefficient is modified by considering constrictivity factor, and the sensitivity analysis is carried out on five sets of parameters (i.e., effective diffusion coefficient, saturated permeability, van Genuchten parameters, initial saturation, and binding capacity parameters) aiming at evaluating the robustness of the model. The simulation results show that the multi-mechanism penetration model is computationally feasible, and the multiphysics coupling model can well reproduce the chloride ion transfer process in a microscopic perspective. Furthermore, the sensitivity analysis results indicate that the parameters governing moisture transport process are more sensitive to the prediction of the chloride ion penetration into undersea tunnel concrete.

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  • Chengyou Wu, Kejia Luo, Huifang Zhang, Hongfa Yu
    2019 Volume 17 Issue 10 Pages 603-615
    Published: October 26, 2019
    Released on J-STAGE: October 26, 2019

    Magnesium oxysulfate (MOS) cement is lightweight, offers fire resistance, and has good aesthetics. Although the addition of citric acid improves the cement’s late strength, the concomitant retardation of hydration of MOS by citric acid results in slow setting and low early strength. This may in return decrease the production efficiency of MOS cement products. In this study, 5•1•7 phase (5Mg(OH)2•MgSO4•7H2O) seed crystal (SC) is used as a modifier that works as a seed nucleus and accelerates the hydration of MOS cement in the early stages, in the absence or presence of citric acid. The effect of SC on compressive strength, setting time, and volume change is investigated in detail. X-ray diffraction, scanning electronic microscopy, hydration-heat release rate, and mercury intrusion porosimeter are performed to explain the influence mechanism of SC on the performance of the MOS cement. The results revealed that the in situ formation and growth of the new 5•1•7 phase crystals on the SC surface by the addition of SC can significantly accelerate the setting, improve the 12 h and 28 d compressive strengths, and reduce shrinkage of MOS cement without or with 0.05% citric acid.

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