Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
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Scientific paper
  • Hue Thi Nguyen, Hiroshi Masuya, Tuan Minh Ha, Saiji Fukada, Daishin Ha ...
    2018 Volume 16 Issue 8 Pages 317-332
    Published: August 17, 2018
    Released: August 18, 2018
    JOURNALS FREE ACCESS

    The Shinmiya Bridge was completed in October 1988 in Ishikawa, Japan. This was the first prestressed concrete bridge in Japan, and the world, to utilize carbon-fiber-reinforced plastic (Carbon Fiber Composite Cable, CFCC) tendons in its main girders to counteract salt damage. To investigate and clarify the serviceability and durability of the main girders after a long period of service in a corrosive environment, two full-scale PC test girders were fabricated and placed next to the main girders in the same conditions at the time of the original construction from 1988. One of them was used for a destructive test in 1994. In this study, another test specimen exposed to a severe environment for 30 years was subjected to a destructive bending test and CFCCs taken out from the test girder were analyzed via mechanical and chemical tests. The suitability of the CFCC and durability of the main girder were confirmed. In addition, a numerical model was proposed to predict the behavior of a main PC girder using a finite element analysis program called DIANA. The influences of the input data from the experiment, the decrease in material properties, and the bond-slip model were studied in the simulation.

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  • Nguyen Trong Lam, Shingo Asamoto, Kunio Matsui
    2018 Volume 16 Issue 8 Pages 333-342
    Published: August 17, 2018
    Released: August 18, 2018
    JOURNALS FREE ACCESS

    We investigated the microstructure and shrinkage behavior of autoclaved aerated concrete (AAC) from several manufacturers in Vietnam comparing with Japanese AAC. Three types of Vietnamese AAC and one type of Japanese AAC were used for powder X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, and shrinkage tests. The experimental results show that the main hydration products of AAC that used fly ash as silica materials is semicrystalline calcium silicate hydrate, while the ones of others are tobermorite; but the tobermorite crystals of AACs from some manufacturers in Vietnam are disordered structures and lack of interlocking among tobermorite crystals. The pore size distribution of all Vietnamese AAC are single peak, whereas Japanese AAC is bimodal. The pore distribution characteristics of AACs significantly influenced their shrinkage behavior and the shrinkage of Vietnamese AAC is higher than that of Japanese AAC at intermediate relative humidity (RH). The capillary tension is the principle shrinkage mechanism for AAC materials at high RH (above about 65%) to cause local minimum shrinkage of Japanese AAC at high RHs, while the change in surface free energy is dominant at low RH conditions.

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  • Quang Dieu Nguyen, Mohammad Shakhaout Hossain Khan, Arnaud Castel
    2018 Volume 16 Issue 8 Pages 343-357
    Published: August 17, 2018
    Released: August 18, 2018
    JOURNALS FREE ACCESS

    In this paper, various engineering properties of both fresh and hardened concrete with various limestone and calcined clay contents are investigated. Two concrete grades were considered: 50 MPa or 30 MPa average 28 days compressive strength. A low grade calcined clay was used with about 50% amorphous phase.

    A reduction in concrete workability was observed with the increase in General Purpose (GP) cement substitution. Superplasticiser was required to obtain a slump equivalent to that of reference GP cement concrete. With 15% GP cement replacement rate, the 28 days compressive strength achieved was superior to that of reference grade 50 MPa concrete, reaching 58 MPa. However, the average 28 days compressive strength reduced significantly with 30% and 45% GP cement replacement, reaching about 35 MPa. Considering concretes with similar 28-day compressive strength, results showed that the 7-day compressive strength was only marginally affected by the limestone and calcined clay substitu-tion. Mercury intrusion porosimetry results revealed that incorporating calcined clay and limestone led to significant refinement of the porosity: increase in the quantity of pores inferior to 0.01µm and reduction in the quantity of coarse pores (with size > 0.1 µm).

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