Concrete Journal
Online ISSN : 2186-2753
Print ISSN : 0387-1061
ISSN-L : 0387-1061
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Volume 53, Issue 10
Displaying 1-19 of 19 articles from this issue
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  • Outline of JIS for Polypropylene Short Fibers for Concrete
    S. Sogo, M. Hayakawa, Y. Muroga
    2015 Volume 53 Issue 10 Pages 861-866
    Published: 2015
    Released on J-STAGE: October 01, 2016
    DOIhttps://doi.org/10.3151/coj.53.861
    JOURNAL FREE ACCESS
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    In recent years, the applications of short polypropylene fibers for concrete structures have been increasing for purposes such as the prevention of fall out of concrete pieces from structures and of concrete spalling due to fire exposure. Based on the background, on March 20, 2015, the Japanese Industrial Standard for polypropylene short fibers was established for users and manufacturers. This report provides an overview of the published standard for polypropylene short fibers and difficulties in establishing the standard. This report also introduces the characteristics such as fiber types, linear density, the quality and the effect of the use of fibers in concrete.
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  • Development of Durability Enhancement Technique for Concrete by Continuous Drain-Moist Curing
    T. Usui, S. Miyahara, J. Sakamoto, T. Kishi
    2015 Volume 53 Issue 10 Pages 867-873
    Published: 2015
    Released on J-STAGE: October 01, 2016
    DOIhttps://doi.org/10.3151/coj.53.867
    JOURNAL FREE ACCESS
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    With the aim of developing a technique that improves the durability of concrete through curing, a curing method that allows, through the use of a newly developed special form, the discharge of excess water and air bubbles from concrete immediately after it has been placed, and moist curing through rapid water supply after it sets, as a continuous operation without demolding. Along with establishing standard construction methods through trials using large members simulating wall rails, durability tests were performed, confirming various curing effects such as reduction of surface air permeability, inhibition of carbonation, and inhibition of chloride ingress. Further, the effects of this technique in actual structures were demonstrated through application to RC bridge wall rails. This paper reports also on the study of new methods for supplying water to further expand the range of applications of the proposed curing technique.
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  • Improved Properties and Micro-Structural Analyses on the Concrete Mixed by SEC Method
    R. Shionaga, K. Toda, Y. Ito, H. Takahashi
    2015 Volume 53 Issue 10 Pages 874-881
    Published: 2015
    Released on J-STAGE: October 01, 2016
    DOIhttps://doi.org/10.3151/coj.53.874
    JOURNAL FREE ACCESS
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    Concrete manufactured using the SEC method─a two-stage mixing method in which primary mixing using primary water is followed by secondary mixing using secondary water─exhibits less bleeding and higher strength after curing. The SEC method was found to enhance filling ability under vibration of concrete in the fresh state, and to contribute to the reduction of variations in strength properties as well as the reduction of shrinkage cracks after curing. To elucidate the mechanism behind such performance improvements, microstructural analyses using SEM and EPMA were conducted for the quantitative evaluation of the reaction rate of cement in the paste and the transition zone at the cement-aggregate interface. As a result, the SEC method was found to contribute to the reduction of average thickness of the transition zone around aggregate. Further, reduction of transition zone thickness was determined to be linked to higher density, and thus durability, of concrete.
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