Concrete Research and Technology

Study on Accurate Calculation Method for Shear Strength of Reinforced Concrete Deep Beam

Reiko Seki, Koichi Matsumoto, Tadayoshi Ishibashi, Masashi Kobayashi

2012 Volume 23 Issue 2 Pages 49-58
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.49

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Shear strength obtained by the conventional evaluation method changes discontinuously at the shear span ratio of 2.0. This causes a discrepancy in the cross-section shape of a structure with shear span ratio around 2.0. As a possible solution to the above problem, the authors have introduced a new evaluation method for the shear strength of wall-type pier regarded as a deep beam. The contribution of shear reinforcing bars obtained by the truss theory and the diagonal compression failure strength of web concrete were taken into account in the new evaluation method. The purpose of this study is to demonstrate the applicability of this new evaluation method for a variety of beam specimens.

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A Study on the Effect of Bleeding on Freeze and Thaw Resistance of Concrete

Noboru Sakata, Takumi Sugamata, Daisuke Hayashi, Jiro Sakue

2012 Volume 23 Issue 2 Pages 59-69
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.59

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A study on the effect of bleeding on the freeze-thaw resistance of concrete was conducted. The greater the amount of bleeding was, the worse the freeze-thaw resistance of the concrete became when changing the amount of bleeding through the partial substitution of limestone powder for fine aggregate or blending of two fine aggregates. Both the pore size distribution as measured by the mercury intrusion technique and the Vickers hardness of the transition zone around the coarse aggregate were insusceptible to the effect of bleeding in test pieces of φ100×200 mm, while the greater the amount of bleeding was, the bigger the air-void spacing factor became. It is assumed that the bleeding flow promotes defoaming and coalescence of the air voids entrained by the AE agent. Using the buoyancy method (Air Void Analyzer system), it was determined that the greater the amount of bleeding is, the higher the air void spacing factor tends to become in the first 1 to 3 hours after mixing, owing to the time dependence of the critical air void spacing factor of fresh concrete.

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Properties of Blended Cement Concrete Cured for 45 Years

Yasutomo Ueki, Yusuke Ohtsuka, Shinya Hiramoto, Yasuhiro Dan

2012 Volume 23 Issue 2 Pages 71-79
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.71

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This study reports on the properties of several types of blast-furnace slag (BFS) cement concrete and BFS cement concrete with fly ash (FA) substitution, as measured using specimens cured in water for 45 years. Ca leaching around the surface area of the specimens was confirmed, but compressive strength tended to develop with increases of BFS ratio in the case of long-term curing. In the case of BFS cement with 30% FA substitution, the compressive strength was higher than BFS cement after 10 years. This suggests that adding FA improves the long-term compressive strength of BFS cement. Vaterite produced on the surface area of the specimens containing FA was found to improve Vickers hardness by filling in micropores of the binder.

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Development of Loading Devices for Uniaxial Tension on Strain Hardening Cementitious Composites

Takatsune Kikuta, Hirozo Mihashi, Hiroshi Akita

2012 Volume 23 Issue 2 Pages 81-90
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.81

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Strain-Hardening Cementitious Composites (SHCC) show very ductile behavior under tensile stress. These excellent new materials can be used to make very ductile as well as very durable structural members. To further the application of this new type of material to structural members, it is essential to assess more properly its tensile mechanical performance using suitably sized specimens. The test methods proposed so far, however, are limited to either uniaxial tension tests using rather small and thin geometries, or an indirect assessment using bending tests. The purpose of the present study is to develop loading devices for uniaxial tension tests on specimens of SHCC with the section size of 100x100 mm². The effectiveness of the developed loading devices is examined through a series of experiments. Furthermore, the influence of the boundary conditions is critically discussed.

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Study of the Vapour Phase Diffusivity in Hardened Cement Pastes Based on Water Adsorption Isotherms

Hideyuki Utsumi

2012 Volume 23 Issue 2 Pages 91-97
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.91

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The characteristics of moisture diffusivity, which change depending on the water content, were examined based on the water adsorption isotherms of hardened cement pastes optimized by the BSB model. The maximum value of moisture diffusivity occurs in the monolayer adsorption state, regardless of material age or water cement ratio, and it decreases as the amount of monolayer adsorption increases. The mechanism of moisture diffusivity in hardened cement pastes can be split into two factors. One addresses the interaction effects between the surface of specimens and moisture becoming the driving force of adsorption before the monolayer adsorption state is reached. The other addresses the geometrical effects related to the diffusion pathway in the adsorbed state beyond the monolayer adsorption state.

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Feasibility Studies on a Connection for Steel Structures Using Steel Fiber Reinforced Cementitious Composite

Yusuke Tanabe, Yuji Ishikawa, Eiji Fujii, Masahito Ohno

2012 Volume 23 Issue 2 Pages 99-110
Published: 2012
Released on J-STAGE: May 15, 2012

DOIhttps://doi.org/10.3151/crt.23.99

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This paper describes feasibility studies on a connection for free-form steel structures using FRCC (Fiber Reinforced Cementitious Composite). Firstly, basic material characteristics of high-strength mortar reinforced with two different kinds of steel fibers are investigated through material bending tests. Then the bending characteristics of a connection consisting of FRCC, stud-welded rebars and rebar mesh are investigated through cyclic bending tests. Following verification of the accuracy of FEM analysis by simulating the bending test, the combined bending and axial force capacity of the connection is estimated by analysis to determine the connection's scope of application.

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