J-Stage (Journal of JSCE in Engish)
J-Stage (Journal of JSCE (E2 Division) in Japanese)

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FLEXURAL STRENGTHENING EFFECT OF PRE-TENSIONED UFC PANEL ON REINFORCED CONCRETE BEAMS

Pornpen LIMPANINLACHAT, Koji MATSUMOTO, Takuro NAKAMURA, Katsuya KONO, Junichiro NIWA
Vol. 4, No. 1, p.181-196, Journal of JSCE (in English)

Abstract:
Recently, various strengthening methods have been utilized to enhance the structural performance and extend the life cycle of RC structures. However, the existing strengthening methods still have some drawbacks especially in the durability aspect. In this study, with the outstanding properties of UFC (i.e., high strength, ductility, and durability), a new flexural strengthening method using precast UFC panels was used to strengthen the RC beams. However, to obtain greater strengthening effect and durability, PC strands were pre-tensioned to the panel and this panel was subjected to a heat curing procedure to supplement a hydration procedure and eliminate the effect of shrinkage. Using this novel technology, this research was conducted to investigate the flexural enhancement and corresponding behavior of RC beams strengthened by pre-tensioned UFC panel. Five pre-tensioned UFC panels and eight strengthened RC beams were prepared and investigated using the bending test. Two different experimental parameters, i.e., prestressing level and amount of PC strands, were used. The undercut anchor bolts were applied for sufficient bonding between interfaces. The bending results of panels were investigated to compute the exact prestressing level in order to determine the calculation of prestressing losses. The results of the strengthened beams revealed that the pre-tensioned UFC panel drastically enhanced the loading capacity of RC beams, and each variable parameter affected the different structural characteristics. To ensure compatibility along a cross-section of the strengthening system, the compatibility along panel specimens and strengthened RC beams was investigated. Finally, the strain compatibility was satisfied at the mid-span of beams where the calculation of load-carrying capacity in strengthened beams could be carried out by using conventional flexural section analysis.

FUNDAMENTAL STUDY ON THE PRACTICAL APPLICATION OF SELF-COMPACTING CONCRETE USING SEAWATER AND UNWASHED SEA SAND

Takahiro SAKAI, Toru YAMAJI, Osamu KIYOMIYA
Vol. 72, No. 3, p.196-213, Journal of JSCE (Division E2) (in Japanese)

Abstract:
The influence of NaCl on initial strength enhancement effect of concrete using seawater as mixing water is dominant, which is the main component of seawater. The initial hydration of the C3S is promoted by NaCl. Compared with the case of using tap water, it was confirmed that the formed tissue is denser. Previously, self-compacting concrete using sea water and unwashed sea sand for urgent restoration works as well as for construction work at isolated islands and other similar region where fresh water is not sufficient was developed. In this study, strength, drying shrinkage and thermal properties of concrete with sea water and unwashed sea sand are experimentally examined. It is found that initial strength development increased as compared with the control concrete made of tap water and land sand. Drying shrinkage strain and autogenous shrinkage strain of concrete were almost equal or higher than the control concrete, but the improvement of crack resistance was observed. Furthermore, in regard to the thermal properties, the rate of temperature rise due to the accelerated hydration reaction and the coefficient of thermal expansion was slightly larger. Considering these properties, the proposed concrete can possibly be used for un-reinforced concrete application.

TENSILE FRACTURE ANALYSIS OF FIBER REINFORCED CEMENTITIOUS COMPOSITES WITH REINFORCING BAR AND FRACTURE BEHAVIOR EVALUATION FOCUSING ON BRIDGING FORCE

Hiroki OGURA, Minoru KUNIEDA, Hikaru NAKAMURA
Vol. 72, No. 3, p.249-267, Journal of JSCE (Division E2) (in Japanese)

Abstract:
This paper introduces the results of tensile fracture analysis of Fiber Reinforced Cementitious Composites (FRCC) with reinforcing bar by means of meso-scale analysis concerning discretized short fibers. The effects of fiber volume fraction, steel reinforcement ratio, bond characteristic between steel reinforcement and FRCC, and fiber distribution on the tensile fracture are numerically investigated. The analytical result shows that there are cases in which cracks were localized in post-yield range of reinforcing bars. The localization mechanism was numerically explained and method for inhibiting the localization was demonstrated by focusing on the amount of bridging forces of fiber and steel bar. In the case of Strain Hardening Cementitious Composites (SHCC), it was clarified that the usage of steel reinforcement is effective to enhance strain capacity.

PREDICTIONAL METHOD FOR REBAR CORROSION DEGREE EXISTING CAVITY CAUSED BY REBAR CORROSION IN RC STRUCTURE

Hideki OSHITA, Takayumi IMAI, Syogo HAYASHI, Yoshihiro FUKUOKA
Vol. 72, No. 3, p.268-287, Journal of JSCE (Division E2) (in Japanese)

Abstract:
Simple modeling method of corrosion degree in rebar existing the cavity caused by the expansive stress in concrete due to the corrosion in rebar in RC structure is investigated. Employing the thermal on concrete surface by the thermography, heat stored in reinforcing steel-bar (rebar) due to electro-magnetic heating is applied to estimate qualitatively the thickness of cavity and the corrosion degree. The thickness of corroded layer in rebar is identified by the difference of the increased value of temperature on concrete surface between the measured value and the analyzed value assumed the rebar as non corroded state. On the other hand, the thickness of cavity is identified by the rate of the temperature increase on the concrete surface. An applicability of the analysis is demonstrated by the comparison between the analyzed and those measured value.

A STUDY ON MODELING OF CLIMATE CONDITIONS FOR DURABILITY EVALUATION OF CONCRETE STRUCTURES

Akihiko NAKAMURA, Mitsuo KUNICHIKA, Kei KAWAMURA, Hideaki NAKAMURA
Vol. 72, No. 3, p.288-303, Journal of JSCE (Division E2) (in Japanese)

Abstract:
Environment conditions are the external factor that affect the durability of concrete structures. Especially, early-age cracking such as thermal cracking and drying shrinkage cracking influences concrete durability. Therefore, it is important to understand this external factor accurately in order to evaluate the durability of a concrete structure. Meteorological conditions such as the ambient temperature and humidity are especially important in an external factor because meteorological conditions influence deterioration such as the crack and the steel corrosion. In this study, the seasonal fluctuation models of vapour pressure, ambient temperature and relative humidity were constructed by using the latest meteorological data.

EVALUATION OF RESISTANCE OF CONCRETE TO CHLORIDE INGRESS BY USING CHLORIDE PENETRATION DEPTH AFTER NON-STEADY-STATE MIGRATION EXPERIMENT

Eisuke NAKAMURA, Hiroshi MINAGAWA, Shintaro MIYAMOTO, Makoto HISADA, Hirohisa KOGA, Hiroshi WATANABE
Vol. 72, No. 3, p.304-322, Journal of JSCE (Division E2) (in Japanese)

Abstract:
An experimental study was conducted to develop an evaluation method for the resistance of concrete to chloride ingress by using chloride penetration depths measured with a colorimetric method after non-steady-state migration experiments. The evaluation method was quicker and simpler than other existing laboratory-accelerated tests because the non-steady-state chloride penetration depths were utilized to evaluate the resistance of concrete to chloride ingress. An appropriate procedure to determine the applied voltage and the testing period was proposed on the basis of the experimental results obtained by using mortar and concrete specimens. The movement of chloride during the non-steady-state migration experiments was also clarified by analyzing the tested specimens. The test results derived from the evaluation method were compatible with those given by the immersion test; both test results accurately indicated the improvement of the resistance of concrete to chloride ingress due to mixing supplementary cementitious materials. Moreover, the evaluation method was found useful for measuring the time-dependent development of the resistance of concrete to chloride ingress.

INVESTIGATION OF DETERIORATION OF CONCRETES AFFECTED BY FREEZE-THAW AND ASR IN HIGHWAY BRIDGES

Yoshiki TANAKA, Masahiro ISHIDA, Jun MURAKOSHI
Vol. 72, No. 3, p.214-233, Journal of JSCE (Division E2) (in Japanese)

Abstract:
The causes of deterioration observed in the concrete elements of two removed highway bridges were examined. One is decks taken from a 75-year-old reinforced concrete bridge showing numerous horizontal cracks. The other is an element cut out from the pier of a 47-year-old bridge, of which cracks and spalling along a water leakage from expansion joints were found on the side. The splitting of coarse aggregates was remarkably found along the cracks in both the elements. In each the concrete element, gravel containing reactive aggregates was used, and the several signs of alkali silica reaction (ASR) were recognized. In addition, since the bridges suffered from repeated freezing and thawing cycles and deicing salt used in winter, the effects of frost-induced deterioration were examined. From the results, it was found that the cracks and the necessary conditions for cracking were similar to those as exhibited in the initial symptom of D-cracking shown around joints in concrete pavements, so that the potential causes of the cracks might contain not only the ASR but also the splitting of the coarse aggregates due to the freeze-thaw action.

UPPER FILLER MATERIAL APPLIED IN CAVERN TYPE RADIOACTIVE WASTE DISPOSAL FACILITY

Shin-ichi TAKECHI, Toshiyuki SASAKI, Kosuke YOKOZEKI, Hiroshi SHIMBO, Yoshihiro AKIYAMA, Tsutomu YADA, Yukikazu TSUJI
Vol. 72, No. 3, p.234-248, Journal of JSCE (Division E2) (in Japanese)

Abstract:
As the upper filler concrete material applied in the cavern type radioactive waste disposal facility is poured just over the radioactive waste packages stored in the facility where the environment may be in a high temperature because of the decay heat, it is concerned that the filling efficiency and the hardening character of the filler may be affected by the temperature. As the construction of upper filler material is done under radiation condition, there are some issues as follows; the filler must be constructed by unmanned remote operation, the filler needs to keep a certain thickness to guarantee the shielding capacity, and so on. In this paper, we have designed the mix proportion of upper filler concrete through filling efficiency experiments simulating high-temperature environment, and have revealed the effect of the temperature on the hardening properties with high-temperature curing tests. Moreover, by doing a full-scale demonstration, we confirmed the feasibility of unmanned construction of upper filler concrete by pumping and movable bucket method.

FATIGUE-BASED STRUCTURAL BEHAVIOR OF RC BRIDGE SLABS WITH DIFFERENT LOADING HISTORIES

Yoshisato HIRATSUKA, Mineo SENDA, Chikako FUJIYAMA, Koichi MAEKAWA
Vol. 72, No. 4, p.323-342, Journal of JSCE (Division E2) (in Japanese)

Abstract:
This paper discusses the path dependency of high cycle fatigue behaviors of RC bridge slabs under various loading histories in use of laboratory experiments and numerical behavioral simulation. A prototype standard RC slab and another two specimens, which were initially loaded statically in advance, were prepared for the subsequent wheel-type loading. All three of them were tested under a moving load of 160kN. Observed is the independency of the progressive mid-span deflection on the loading histories. Furthermore, the same trend is rather observed at a level of 220kN as well with another set of specimens of exactly the same shape and dimension. The observed phenomenon in the experiments was successfully simulated by direct path-integral 3D nonlinear FE analysis considering the varying boundary conditions from the preliminary loading state to the main one to introduce the high cycle fatigue damages.

SERVICEABILITY SIMULATION OF RC BRIDGE DECKS SUBJECTED TO COUPLED DRYING SHRINKAGE AND WHEEL-TYPE FATIGUE LOADS

Yoshisato HIRATSUKA, Koichi MAEKAWA
Vol. 72, No. 4, p.343-354, Journal of JSCE (Division E2) (in Japanese)

Abstract:
As moving load testing of RC slabs of highway bridges takes several months, drying shrinkage of concrete progresses concurrently with fatigue-induced damage during this time. Further, as actual bridges are placed in service after drying shrinkage has progressed to some extent, RC slab fatigue life test results do not correspond with the actual life of RC slabs in service. This study investigated the effect of the combined action of drying shrinkage and fatigue-induced damage by using multi-scale analysis based on thermodynamics. The increase in deflection under fatigue load was found to be the result of the combined action of shrinkage and load-induced fatigue damage, and the process by which damage progresses through their interaction was elucidated.

EFFECT OF BLAST-FURNACE SLAG FINE AGGREGATE ON IMPROVEMENT OF PROPERTIES OF HARDENED CONCRETE

Kazuhide SAITO, Ryo YOSHIDA, Chiaki YOSHIZAWA, Hidetaka UMEHARA
Vol. 72, No. 4, p.355-367, Journal of JSCE (Division E2) (in Japanese)

Abstract:
By replacing the blast furnace slag fine aggregate with natural fine aggregate, hardening properties improving effect, such as long-term strength enhancement, drying shrinkage reduction, and carbonation inhibition of concrete is known to be obtained. In this study, for the purpose of revealing the mechanism of hardening properties improvement of blast-furnace slag fine aggregate, we focused on the difference in particle size of the blast-furnace slag fine aggregate, and investigated the influence of each particle diameter on properties of hardened mortar. As a result, it was found that blast-furnace slag fine aggregate is effective in strength enhancement and drying shrinkage reduction as particle size is small, and particle size smaller than about 0.045 mm is more effective. Next, we confirmed the influence that content of the particle size smaller than about 0.045 mm gave to properties of hardened concrete. As a result, it was found that the compressive strength is remarkably enhanced, and effect on drying shrinkage and carbonation was small by adding about 5% of blast furnace slag powder as the particle size smaller than about 0.045mm.

DEFORMATION MECHANISM OF CEMENT PASTE AND EFFECT OF WATER

Yuya SAKAI, Toshiharu KISHI
Vol. 72, No. 4, p.368-379, Journal of JSCE (Division E2) (in Japanese)

Abstract:
Triaxial compressive tests were carried out at different confining pressure and water content to understand the deformation mechanism of hardened cement paste. Results showed that stress did not decrease up to 10% strain, and macroscopic damage was not observed when tested under a certain confining pressure. This confining pressure differed depending on moisture content. Stepwise creep tests were conducted, and the slopes of the obtained differential stress-strain rate curves in a double logarithmic chart were around three, indicating that deformation was caused by dislocation creep. A sample saturated with sucrose solution exhibited more brittle behavior after the peak stress as compared to the behavior of the sample saturated with tap water. The results indicated that the deformation of cement paste was probably affected by dislocation, mechanical twinning, and pressure solution. Those mechanisms can affect cement paste and concrete deformation under low confining pressures.