Journal of Advanced Concrete Technology
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Volume 15 , Issue 8
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Scientific paper
  • Satoshi Komatsu, Akira Hosoda
    Volume 15 (2017) Issue 8 Pages 368-380
    Released: August 24, 2017
    JOURNALS FREE ACCESS

    In this research, to clarify the time-dependent deformational behavior of RC beams with flexural cracks generated at an early age, continuous flexural loading of RC beams was conducted, and the effects of shrinkage property, age of cracking, and environmental conditions were experimentally investigated. A calculation method of total crack width utilizing the results of numerical simulation was proposed. Using this method, tensile deformation of RC beams at an early age was analyzed.

    The results of this study demonstrated that compressive deformation of concrete due to drying creep causes a significant increase in the tensile stress of reinforcement. Especially under high compressive stress/strength ratio, large creep deformation, which might be due to micro-cracks generated at ITZ between the cement paste and aggregate, should be properly considered in numerical simulation. Furthermore, deterioration of the bond between compressive reinforce-ment and the surrounding concrete might be another reason for the large creep deformation.

    Moreover, it was assumed that concrete between flexural cracks generated at a very early age could deform with less bond deterioration following the deformation of tensile reinforcement. This might be due to the generation of mi-cro-cracks at ITZ between the cement paste and aggregate, which might prevent internal cracks around reinforcement leading to deterioration of the bond.

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  • Ryota Kurihara, Nobuhiro Chijiwa, Koichi Maekawa
    Volume 15 (2017) Issue 8 Pages 381-396
    Released: August 24, 2017
    JOURNALS FREE ACCESS

    Gradual decay of natural frequency of reinforced concrete (RC) buildings is computationally investigated in view of the long-term moisture loss and associated shrinkage of concrete. The thermo-hygral analysis for RC lifetime over sev-eral decades is applied with monitoring data of existing multi-story buildings and nuclear power plants in service. The reduced natural frequency is numerically reproduced with delayed cracking near junction planes between structural members of different dimensions in multi-story buildings and dispersed cracks close to the surfaces of RC thick walls of nuclear power plants. In order to quantitatively clarify the impact of drying shrinkage, both sealed and open boundary conditions for moisture migration are assumed at simulation. It is also confirmed logically that the rate of decay for the natural frequency of the middle story RC building is faster because of the small thickness of walls, slabs and columns compared to structural members of nuclear power plants.

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  • Takeru Kanazawa, Yasuhiko Sato, Tomomasa Mikawa
    Volume 15 (2017) Issue 8 Pages 397-406
    Released: August 31, 2017
    JOURNALS FREE ACCESS

    This study presents a new bond model based on the deterioration mechanisms observed during uniaxial tensile tests of reinforced concrete prismatic specimens subjected to freeze-thaw cycles. The test results demonstrated that the bond stress reduced, even though the specimens were exposed only to temperature fluctuation without the damage in concrete cover. The proposed model considers the bond deterioration mechanism caused by the temperature fluctuation in addition to the damage in concrete cover. Finally, the proposed model shows good agreement with the test results regardless of the dominant deterioration mechanism.

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  • Xun Han, Xuehui An, Koichi Maekawa
    Volume 15 (2017) Issue 8 Pages 407-425
    Released: August 24, 2017
    JOURNALS FREE ACCESS

    A new method for predicting the water absorption process of unsaturated cementitious composites is proposed, and its functionality is experimentally verified. The mechanism of the capillarity on water absorption process is mathematically termed by a slip boundary condition of micro-flow of pore water, and employed to an unsaturated water permea-tion on the scheme of multi-scale modeling. The rapid sorption just after the exposure to condensed water is fairly simulated owing to the non-local formulation of hygro-gradient, which simply represents the thermodynamics of non-equilibrated states in dry pores. The proposed model of complexity of micro-pore connection is examined in terms of the initial water content, porosity and saturation of micro-pore structure and volume ratio of aggregate. It is further examined in terms of the intrinsic hydraulic profile by using the Boltzmann’s transform.

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  • Akira Hatanaka, Yogarajah Elakneswaran, Kiyofumi Kurumisawa, Toyoharu ...
    Volume 15 (2017) Issue 8 Pages 426-439
    Released: August 31, 2017
    JOURNALS FREE ACCESS

    The purpose of this study is to determine the tortuosity of cementitious materials containing blast furnace slag (BFS). Furthermore, the influence of tortuosity on multi-species transport into these materials is studied. The porosity and diffusivity of calcium silicate hydrate (C-S-H) were predicted using a three-dimensional spatial distribution model, which were then fitted to Archie’s law to determine tortuosity. The tortuosity increased with the slag replacement ratio, suggesting that the diffusion path for ions becomes complicated and lengthy due to slag addition. Thermoporometry was used to determine the pore size distribution of hydrated slag-blended cement. A partial replacement of ordinary Portland cement (OPC) with BFS modified the mineralogy (especially in the types of C-S-H), resulting in changes to the pore structure. The determined tortuosity and porosity were used in a reactive transport model to predict multi-species transport. Experimentally measured and simulated chloride profiles were in good agreement for hydrated OPC and slag-blended cements exposed to sodium chloride solutions. The causes for the low penetration rate of chloride in slag-blended cementitious materials are discussed considering their pore structure and surface electrical properties. The role of tortuosity on Cl-/OH- for the evaluation of chloride induced corrosion was also discussed.

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