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

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EFFECTS OF LIMESTONE AGGREGATE DERIVED FROM CORALS ON PROPERTIES OF SELF-COMPACTING CONCRETE MIXED WITH SEAWATER

Hiroshi TAKENAKA, Osamu TANIGUCHI, Ryoichi TANAKA, Kazuhide YONAMINE, Toru YAMAJI, Osamu KIYOMIYA
Volume 76 Issue 4 Pages 255-269, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_255/_article/-char/en

Abstract:
Experimental studies were conducted on fundamental properties, shrinkage properties, thermal properties, and wear properties of self-compacting concrete mixed with seawater and limestone aggregate derived from corals assuming use on isolated islands. As a result, the concrete using this aggregates with many voids had excellent fluidity, moderate segregation resistance, and the same strength development as when using ordinary aggregates. In addition, shrinkage and thermal expansion coefficient were smaller than that of concrete using ordinary aggregate. Furthermore, even when coral aggregate was used, abrasion resistance of concrete equivalent to that when using ordinary aggregate could be secured by setting the water cement ratio and unit coarse aggregate volume small.

MAINTENANCE OF NORTH BREAKWATER DOME IN WAKKANAI PORT USING DETERIORATION MAPPING

Kazuya HASE, Hiroshi YOKOTA, Yasuhiko SATO
Volume 76 Issue 4 Pages 270-282, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_270/_article/-char/en

Abstract:
TWakkanai Port, located in the northernmost part of Japan, has a breakwater called “North Breakwater Dome, ” which is reminiscent of ancient Greek architecture. Construction of the North Breakwater Dome was completed in 1936, and an overall rehabilitation was conducted from 1978 to 1981. Currently, the deterioration of the dome is becoming apparent. We examined the remedial measures for deterioration, but the issues were to devise a method for assessing the performance of reinforced concrete members and a reasonable repair method. This is because the inspection range is very large, and the structure of the Dome is a civil engineering heritage. To solve the issues, we devised the deterioration mapping that is created by subdividing of large inspection areas, and by grading into five grades of deterioration based on damage. By using deterioration mapping, it is possible to quantitatively grasp damages in large areas, to quantitatively understand the corrosion state of reinforced concrete members, and to implement reasonable repair on an unit area basis. This paper discusses the effectiveness of the deterioration mapping using the case study of the North Breakwater Dome maintenance.

IMPROVEMENT OF DETECTION ACCURACY FOR VOIDS IN PC DUCT BY WIDE-RANGE ULTRASONIC TEST (WUT) CONSIDERING THE IMPACT OF REFLECTION WAVE FROM END-FACE

Kuniharu FUKUSHIMA, Takanori KINOSHITA, Mikio HARA, Isamu YOSHITAKE
Volume 76 Issue 4 Pages 283-292, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_283/_article/-char/en

Abstract:
 Non-destructive tests with ultrasonic waves are often used to examine grouting conditions in tendon-duct of post-tensioned prestressed concrete bridges. Wide-range ultrasonic testing (WUT), a kind of the NDT technique, has an advantage that it is applicable even in relatively thick PC girders. WUT is often employed in box-girders of PC bridge because the grout inspection can be conducted at the inner space of the girder without a scaffolding. WUT analyses the reflection ultrasonic waves and evaluates voids from the observed high-frequency waves. The observed ultrasonic waves include reflection waves from the end-face of girder in addition to the reflection waves from the voids. It is well known that the former reflection waves are generally greater than the latter. The influence of reflection waves from the end-face should be evaluated properly to detect the voids of PC duct. To improve the accuracy of void detection by WUT, this study aims at examining the influence of reflection waves from the duct and the end-face. The study conducted the fundamental experiment using 4 test specimens: A) concrete embedding a void-duct; B) concrete embedding a grout-filled duct; C) plain concrete of 240 mm thick; and D) plain concrete of 135 mm thick. The paper reports the influence of reflection waves from the end-face on the void detection of WUT.

EVALUATION ON PERFORMANCE OF EPOXY RESIN FOR CRACK INJECTION OF CONCRETE IN COLD ENVIRONMENT

Isao NAITO, Hiroshi YOKOTA
Volume 76 Issue 4 Pages 293-305, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_293/_article/-char/en

Abstract:
To quantitatively evaluate the performance of epoxy resins for crack injection in cold environment, we performed injection tests using cylindrical specimens with controlled crack widths during which the changes in viscosity and temperature of the epoxy resins were measured during the injection. This paper presents the results of the areal rate into a crack under various temperatures and injection rates. As a result, the injection performance of epoxy resins depends on the environmental temperature inside the crack because the resin changes its temperature very little due to its chemical reaction in low temperature environments. In addition, the injection areal rate has a correction with the environmental temperatures of 5°C or less. From this correlation, it is possible to quantitatively evaluate the injection performance of epoxy resin for crack injection in cold environment at the design stage.

DEFORMATION OF CEMENT PASTE AND HYDRATES UNDER HIGH-PRESSURE TRIAXIAL TEST CONDITIONS

Yuya SAKAI, Shin-ichi UEHARA
Volume 76 Issue 4 Pages 306-314, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_306/_article/-char/en

Abstract:
 In this study, triaxial tests were performed on compacts of leached/unleached cement paste, calcium hydroxide, and synthesized C-S-H to understand the deformation mechanisms of cement paste and concrete under high pressure and also the mechanism of higher strength and density development of crushed concrete through compaction when the concrete powder is wet. It was found that compact of calcium hydroxide significantly reduced strength and stiffness when it was wet. The synthesized C-S-H reduced the stiffness under high confining pressure, but the effect of moisture was small compared with that of calcium hydroxide. Based on the obtained results, the process of the strength gain of crushed concrete through compaction is explained as follows: C-S-H, which deformed easily, was squeezed out, the calcium hydroxide structure was formed, and the structure deformation occurred readily when the concrete was wet. These findings are useful for understanding the deformation mechanisms of ordinary concrete and cement paste.

ESTIMATION OF HYDROTHERMAL CONDITION IN CONCRETE MANHOLE FOR INFORMATION NETWORK BY INTEGRATED HEAT TRANSFER ANALYSIS OF SOIL AND STRUCTURES

Kazuaki WATANABE, Takumi SHIMOMURA, Norihiro FUJIMOTO, Hisatoshi KASAHARA, Takanobu SUZUKI
Volume 76 Issue 2 Pages 65-77, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/2/76_65/_article/-char/en

Abstract:
An integrated heat transfer analysis of manhole and soil was conducted to predict hydrothermal condition and condensation in manhole, which affects deterioration process of manhole for information network. It was verified that time-dependent change of temperature in manholes in various region in Japan can be simulated. Based on the results of heat transfer analysis, occurrence of condensation was predicted. Water content was calculated by moisture transfer analysis in concrete, in which capillary suction of condensed water. It was clarified that condensation likely occur in manhole in winter and accordingly water content in concrete become higher in winter, which might accelerate corrosion of reinforcement in concrete.

PROPOSAL OF A COMPLETELY NON-DESTRUCTIVE EVALUATION METHOD OF CORROSION RATE OF REINFORCING STEEL INSIDE CONCRETE STRUCTURE

Toshinori KANEMITSU, Shimpei ONO
Volume 76 Issue 4 Pages 315-331, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_315/_article/-char/en

Abstract:
It is essential to develop an inspection method capable of diagnosis for corrosion of reinforcing steel inside the concrete structure since the aging of reinforced concrete (RC) structures is in progress. However, in the conventional methods, it is necessary to partially destroy the existing structure to measure the corrosion rate of the reinforcing steel. In this work, to develop a non-destructive method to measure the corrosion rate of the steel inside the existing structure using a four-probe AC impedance method, the impedance is measured for mortar and concrete specimens. Also, current dispersion analysis clears the change of the measurement value depending on the probe distance and the rebar depth.  As a result, we succeeded in proposing a condition capable of applying the method and an index capable of converting into a corrosion rate under the condition. It is shown that we can set a measurement condition according to a targeted concrete structure and evaluate the corrosion rate of the reinforcing steel using the non-destructive method.

STUDY ON THE RELATIONSHIP BETWEEN MASS TRANSFER RESISTANCE AND APPEARANCE ALTERATION OF ACTUAL STRUCTURES BY AIR PERMEABILITY TECHNIQUE

Ryota HAYASHI, Hirotaka HAZEHARA, Masashi SOEDA, Sakura FUKAMI
Volume 76 Issue 4 Pages 332-348, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_332/_article/-char/en

Abstract:
The purpose of this study was to clarify the relationship between air permeability and mass transfer resistance of concrete subjected to various deterioration factors. This was done by analysing cores collected from actual structures and the relationship between air permeability and the progress of deterioration was studied.  Experiments were carried out and it was observed that the air permeability coefficient of the deteriorated part was clearly larger than the healthy part. It was also estimated that the higher the air permeability and the larger the oxygen supply amount, the sooner the deterioration such as peeling occured. Rebar corrosion progressed rapidly due to the effects of deterioration factors like the CO2, chloride ions and water ingress. Therefore, in the environmental range of the actual structure studied this time, it was suggested that the damage could be quantitatively assessed by measuring the air permeability coefficient using core at any given location.

EVALUATION OF PUNCHING SHEAR RESISTANCE OF RC SLABS WITH PYRAMID SHELL MODEL

Kazunori FUJIKAKE, Tadasu ITAGAKI, Shinpei IKEDA, Tomoyuki TOGO, Keigo TAKEUCHI
Volume 76 Issue 4 Pages 349-359, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_349/_article/-char/en

Abstract:
 The aim of this study was to find out the punching shear failure mechanism of RC slabs through experimental investigation and nonlinear finite element analysis. In the nonlinear finite element analysis, 3D Nonlinear Cementitious 3 constitutive model was specifically applied to concrete material to express the stress – strain relationship of concrete subjected to triaxial compressive stress states. As a result, it was found that triaxial compressive region was formed in the vicinity of the loading plate, and the compression failure of concrete in this region caused punching shear failure of the RC slab. Therefore, a pyramid shell model was proposed based on the load bearing mechanism formed around the vicinity of the loading plate. Finally, the evaluation formula for the punching shear resistance derived from this pyramidal shell model was in good agreement with the previous experimental results.

EVALUATION OF BENDING PERFORMANCE OF ARAMID SHORT FIBER REINFORCED CONCRETE EXPOSED IN ENVIRONMENTS OF DIFFERENT TEMPERATURE WATER AND AIR

Atsushi HOKURA, Shinichi MIYAZATO, Shuhei OKAMURA, Daishi YOSHIMOTO, Hiroshi KURAKATA
Volume 76 Issue 4 Pages 374-385, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_374/_article/-char/en

Abstract:
Although the mechanical performance just after the production of short fiber reinforced concrete has been clarified, the evaluation of the mechanical performance after being exposed for a long time in view of the influence of water has not been made. Therefore, in this study, the bending strength and bending toughness of aramid short fiber reinforced concrete after exposure in water and air at different temperatures were evaluated. As a result, 1) The mechanical performance after exposure in water decreases with time as the exposure temperature is higher, while the mechanical performance after exposure in air is kept. 2) The mechanical performance after exposure for 100 years in water at 20°C was estimated by exposure for 1 month to 3 years in a high temperature water environment. 3) When bundled-type short fibers were mixed, it is expected to retain mechanical performance of 90% or more of the initial value even if exposed to water at 20°C for 100 years.

CONSTRUCTION OF EVALUATING EQUATION FOR CAPACITIES OF BEAM ACTION IN SHEAR RESISTANCE MECHANISMS OF RC BEAMS BASED ON STRESS TRANSFER ALONG INCLINED CRACK PATHS

Yuta YAMADA
Volume 76 Issue 4 Pages 386-402, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_386/_article/-char/en

Abstract:
This paper proposes an evaluating equation to estimate capacities of beam action in shear resistance mechanisms of reinforced concrete (RC) beams for construction of simplified theoretical evaluating equations of the shear capacity. The fundamental equation was derived by the assumption that plane sections remain plane and by equilibrium conditions of the free body in the beam action which was separated by formulized inclined crack paths based on elastic solutions inside the vertical stress non-predominant region. The crack opening model, shear transfer model and tension softening model along the inclined crack paths were proposed based on direct shear experiments by using plain concrete specimens whose heights were 65 mm to 800 mm. The evaluating equation for capacities of beam action was constructed by applying these models based on the direct shear experiments. The static loading experiments and finite element (FE) analyses for RC beams whose shear span ratios were 1.0 to 3.0, and whose effective depths were 200 mm to 1600 mm were conducted to verify accuracies of the evaluating equations. As a result of the experiments and FE analyses, it was indicated that when the load carrying mechanism transition region was relativity small, the ratios of capacity of beam action for shear capacity were approximately same values independently of magnitude of its capacities, and that the ratios were governed by the shear span ratios. It was made clear that the evaluating equation could be evaluate for the ratios of estimated value for observed value with following accuracies: the averaged value was 1.0, the standard deviation was 0.10, and the coefficient of variation was 10.0 %.

DURABILITY EVALUATION WITH WHEEL RUNNING TESTS AND COMPUTATIONAL SIMULATIONS ON PRECAST PC SLAB WITH HALF RIGID JOINT UNDER THE NEGATIVE BENDING MOMENT

Shinichiro KITA, Nobuaki SAKURAI, Koichi MAEKAWA
Volume 76 Issue 4 Pages 403-420, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_403/_article/-char/en

Abstract:
Wheel running tests have been conducted on precast PC slabs jointed with only fillers under the maximum negative bending moment assumed on the intermediate support of actual plate girder bridge. Constant repetitive moving load of 250kN was applied on Slabs jointed with polymer cement mortar and epoxy resin mortar, and these specimens showed interfacial fracture with smaller number of cycles than expected. Meanwhile, tensile fatigue tests have been also conducted on two kinds of fillers, and the different S-N curves were observed between the fillers and concrete.  Considering the above tests, computational simulations have been conducted. Firstly, the history of the stress on the interference of joints until initial damage was investigated by reproducing wheel running tests. Secondly, the actual durability of slabs jointed with the fillers was evaluated by parametric analysis with negative bending moment and repetitive moving load.

INFLUENCE OF VIBRATION ON FRESH CONCRETE FLOW VELOCITY

Kazuaki NISHIMURA, Yoshitaka KATO
Volume 76 Issue 4 Pages 421-431, 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/4/76_421/_article/-char/en

Abstract:
Various ideas have been proposed on the mechanism of flow of fresh concrete by vibration compaction, but unclear points still remain. Therefore, the objective of this research is to investigate the influence of vibration compaction on the flow behavior of fresh concrete. First, the flow velocity of fresh concrete under vibration compaction was formulated, and the effect of vibration compaction on fresh concrete was grasped by the experimental results. As a result, it was found that the apparent yield stress of fresh concrete decreased with vibration compaction, and the flow velocity of fresh concrete increased. In addition, the apparent yield stress of fresh concrete under vibration compaction was considered to be determined by the flow resistance of gravel, the blocking of gravel, and the acceleration of vibration waves.

RELATIONSHIP BETWEEN SHEAR FORCE AND SLIP OF REINFORCING BAR IN A JOINT INTERFACE OF HALF PRECAST RC STRUCTURE

Ryosuke TAKAHASHI, Hiroshi SHIMA, Satoshi MATSUOKA, Satoshi TSUCHIYA
Volume 77 Issue 1 Pages 1-14, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/1/77_1/_article/-char/en

Abstract:
Precast concrete structure increases because of its advantages such as enhancement of the productivity. Analysis by using finite element method has a possibility to make evaluation and design of precast concrete structure more reasonable. A reliable dynamic model of joint interface between precast concrete and site concrete is required for the analysis. This paper focuses the joint interface connected by deformed reinforcing bars. Experiment of element specimens representing the interface are conducted and numerical model for a relationship between shear force and shear displacement of the interface is proposed. Deformation of the reinforcing bar is regarded as combination of two arcs and established bond - slip models of the reinforcing bar are applied in the model. A simpler model for application to FE analysis, that is a bilinear slip - strain relationship based on the experimental curve, is also proposed.

KINEMATIC MODEL COMBINED WITH FREEZE-THAW DEPTH FOR SHEAR-CRITICAL RC BRIDGE PIER

Takeru KANAZAWA, Yuji USHIWATARI
Volume 77 Issue 1 Pages 15-24, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/1/77_15/_article/-char/en

Abstract:
This study presents a kinematic model for shear-critical RC columns subjected to freeze-thaw action based on upper bound theorem. The developed model enables derivation of the shear resistance of damaged concrete when the displacement field is divided into undamaged and damaged zones based on freeze-thaw depth obtained from on-site inspections. The accuracy of the model is verified by comparing its predictions with an earlier published database on RC columns failing in shear after freeze-thaw exposure. The predicted shear strengths show good agreement with the test results within error of 20%. Thereafter, the current shear strength of an existing RC bridge pier with severe frost damage is analyzed by the model. Results demonstrate that the freeze-thaw depth may allow rational structural assessment.

EXPERIMENTAL STUDY ON SEISMIC BEHAVIOR OF ANCHORAGES EMBEDDED IN REINFORCED CONCRETE WITH FLEXURAL CRACKS

Seiji NAGATA, Toyofumi MATSUO, Hironori MOROZUMI, Keizo OHTOMO
Volume 76 Issue 3 Pages 209-228 , 2020, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/76/3/76_209/_article/-char/en

Abstract:
This paper deal with the strength and hysteretic behavior during an earthquakes associated with the anchorages considering the effects of flexural cracks developed in reinforced concrete. In the experiments, eight reinforced concrete specimens with four headed anchor bolts are used. These specimens include two types of anchorages depending on the failure modes: the bolt yield type and the concrete failure type. The Results of cyclic loading tests (static tests) show that the effects of the flexural cracks in the anchorage strength appears more obviously in the concrete failure type than the bolt yield type. However, the strength can be recovered by applying crack repair with the epoxy injection. In addition, a series of the shake table tests (dynamic tests) present that the nonlinear hysteretic behavior of the anchorages under the dynamic loads demonstrates well those under the static loads.

ESTIMATION OF CHEMICAL PRE-STRAIN AND CHEMICAL PRE-STRESS FOR CPC MEMBERS WITHOUT SYMMETRICAL AXIS IN CROSS SECTION

Kentaro SUHARA, Yukikazu TSUJI, Chunhe LI, Tatsuya NISHIZAKI, Kazuma IGARASHI, Mineki KOZU
Volume 77 Issue 2 Pages 25-36, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/2/77_25/_article/-char/en

Abstract:
Precise practical estimation of the expansive strain distribution in cross-sectional dimension is important for effective use of CPC(Chemically pre-stressed concrete) members, but previous studies have reported only the expansive strain distribution of CPC members having symmetrical arrangement of reinforcing bars and cross-sectional dimensions. In this study, we report the estimation method and the experimental results of the expansive strain distribution of CPC members with non-symmetrical rebar arrangement in T-shaped and L-shaped cross sections. The value of the expansive strain estimated by the proposed cross-sectional analysis from the expansive strain of the JIS specimen is goodly corresponded with the experimental value using the Work-done concept.

STUDY ON EVALUATION METHOD OF CO2 ABSORPTION AND PHYSICAL PROPERTIES OF CEMENTITIOUS MATERIALS WITH CARBONATION CURING

Takeshi TORICHIGAI, Kosuke YOKOZEKI, Ichiro YOSHIOKA, Minoru MORIOKA
Volume 77 Issue 2 Pages 37-54, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/2/77_37/_article/-char/en

Abstract:
The amount of CO2 absorbed in cementitious materials using blast furnace slag and γ-2CaO·SiO2 partially instead of cement and carbonation curing was evaluated by various analytical methods. As a result, it was shown that inorganic carbon analysis is more suitable than thermal analysis to evaluate the amount of CO2 absorption in concrete. In addition, it was shown that the concrete using blast furnace slag and γ-2CaO·SiO2 can absorb large amount of CO2 during carbonation curing. Furthermore, it was confirmed that porosity and compressive strength of the concrete equal to or higher than those of ordinary concrete can be obtained by improving the reaction of blast furnace slag due to the high temperature during carbonation curing and densifying the pore structure due to carbonation of γ-2CaO·SiO2.

A STUDY ON THE CORRELATION BETWEEN THE REINFORCING ERAS AND EFFECTS OF CARBON FIBER SHEET REINFORCEMENT METHODS FOR RC SLABS OF ROAD BRIDGES USING LIGHTWEIGHT AGGREGATES

Kazuhito UCHIUMI, Masaaki HAMANO, Shigeyuki MATSUI, Kota YAMAGUCHI, Nobuyuki TANAKA
Volume 77 Issue 2 Pages 55-64, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/2/77_55/_article/-char/en

Abstract:
The carbon fiber grid bonding methods with reinforcing effects certified by the wheel load running tests conducted on ordinary RC slabs, are often adopted for anti-aging reinforcement of lightweight RC slabs using lightweight aggregates. In order to verify its applicability, the wheel load running tests were conducted for lightweight RC slabs without and with reinforced by the carbon fiber grid bonding methods. In addition to the abovementioned test results, this paper examines the reinforcing eras and effects in comparison with the fatigue damage situations of the existing lightweight RC slabs. As a conclusion, there are certain reinforcing effects of the carbon fiber grid bonding method for lightweight RC slabs, and the acquired correlation between the reinforcing eras and effects suggests that reinforcing should be implemented before crack density increases.

SITE IMPLEMENTATION REPORT OF CAST-IN-SITU PRESTRESSED CONCRETE ROAD BRIDGE DECK USING BOTH EARLY-HIGH-STRENGTH PORTLAND CEMENT AND FLY ASH

Naoki SAKAKIBARA, Shota TOMIZUKA, Atsushi YOSHIDA, Takuya MAESHIMA, Yasuhiro KODA, Ichiro IWAKI
Volume 77 Issue 2 Pages 65-77, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/2/77_65/_article/-char/en

Abstract:
In order to ensure the durability of cast-in-situ prestressed concrete road bridge deck in an environment where deicing salt is sprayed, we examined the workability of fly ash concrete on the premise of local production for local consumption and implemented it on highway road bridge. As the evaluation procedure of fly ash concrete, 1) laboratory test, 2) workability confirmation test using site mock up deck, 3) laboratory test for problem solving from the workability confirmation of site mock up deck, 4) actual concrete mixing plant test for final confirmation were conducted. And the mix proportion of fly ash concrete that satisfies the required performance for construction on site was decided from the evaluation procedure. As a result, it was found that the loss of slump and air content during transporting from ready-mixed concrete factory to site was remarkable in the fly ash concrete using both early-high-strength Portland cement and fly ash. Therefore, at the time of mixing fly ash concrete at the ready-mixed concrete factory, it is decided that properly setting the amount of increase in slump and in air content in anticipation of the slump and air content of arrival time at the site is needed. In addition, since the fresh properties such as slump and air content after pumping fly ash concrete in the implementation work were good, it was clarified that fly ash concrete can be applied to cast-in-situ prestressed concrete road bridge deck.

PENETRATION OF CHLORIDE IONS INTO HARDENED CEMENT CONSIDERING MULTIPLE IONS IN SEAWATER

Satoko NAOMACHI, Yoshitaka KATO
Volume 77 Issue 3 Pages 78-91, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/3/77_78/_article/-char/en

Abstract:
To understand the effects of multiple ions in seawater on the penetration of chloride ions and the alteration of the solid phase of hardened cement, immersion tests were conducted with four different solutions. In the case of mortar, chloride penetration was accelerated in NaCl+MgSO4 solution and suppressed in artificial seawater, as indicated by the results of the immersion test for 1736 days. This was thought to be due to the influence of aragonite brucite gypsum, and ettringite formed, and leaching of CSH on the mortar surface. For concrete, the results of 1008 days of immersion test showed that regardless of the type of immersion solution, there was no portlandite in the area up to 10 mm of the concrete, suggesting that changes in the pore structure due to leaching affected the penetration of chloride ions.

INVESTIGATION OF TENSILE PROPERTIES AND RESTRAINED SHRINKAGE BEHAVIOUR OF UHPFRC USED FOR STRENGTHENING AND REHABILITATION OF STRUCTURAL MEMBERS

Tohru MAKITA, Yuji WATANABE
Volume 77 Issue 3 Pages 92-107, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/3/77_92/_article/-char/en

Abstract:
Ultra-High Performance Fibre Reinforced cementitious Composite (UHPFRC) is characterised by high compressive/tensile strength and very low permeability. Application of UHPFRC to structural members subjected to severe mechanical actions and environmental conditions, such as bridge decks, can take full advantage of these excellent properties. When UHPFRC is cast on existing structures, its shrinkage is restrained and tensile stresses are induced over the entire depth of the UHPFRC. Therefore, it is necessary to understand tensile properties and restrained shrinkage behaviour of UHPFRC for developing a method to strengthen and rehabilitate structural members with UHPFRC.  This paper presents results of direct tension tests and uniaxial restrained shrinkage tests of UHPFRC. UHPFRC mix used in the experimental tests is characterised by mortar matrix densified by ettringite (AFt) formation; thus, it is called “AFt-UHPFRC”. The direct tension tests are conducted for three UHPFRC mixtures and effects of wollastonite, fibre type and content, and curing conditions on tensile behaviour of the UHPFRC are discussed. The uniaxial restrained shrinkage tests are performed using a Temperature-Stress Testing Machine (TSTM) that allows investigating restrained shrinkage behaviour of cementitious materials from very early age. It is found that tensile creep significantly relaxes tensile stress due to restrained shrinkage and no microcracking occurs in UHPFRC under a full-restraint condition. Moreover, it is understood that although shrinkage strain of heat-cured UHPFRC is lower than that of UHPFRC without heat treatment, tensile stress induced due to restrained shrinkage is larger in heat-cured UHPFRC than UHPFRC without heat treatment.

BASIC STUDY ON BEHAVIOR OF BURIED FLEXIBLE PIPE UNDER APPLICATION OF INTERNAL LOADING METHOD

Koki OYAMA, Masahiro HYODO, Hidehiko OGATA, Masayuki ISHII, Kazuhiro UENO
Volume 77 Issue 3 Pages 108-118, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/3/77_108/_article/-char/en

Abstract:
The aim of this study is assessing behaviors of buried flexible pipes at applying the internal loading method (ILM) for evaluating the strength of these pipes. In this study, behaviors of buried and un-buried pipes were compared using a polyvinyl chloride (PVC) pipe and a fiberglass reinforced plastic mortal (FRPM) pipe. As a result, the relationships between load and deformation of buried pipes showed nonlinearity, in which deformation ratio increases with the increment of applied load. The curve lines were thought to be classified into two stages; before and after the occurrence of the small shear failure in back-filling soil. Because of the restraint by the backfilling soil, the inclination of load-deformation curves of buried pipes became larger for both kinds of pipes. The difference of inclination between buried and unburied pipes was larger with the PVC pipe whose ring stiffness is smaller than the FRPM pipe. In the circumferential direction on the outside of buried pipes, tensile strains accrued especially at both of top and bottom parts of it. On the contrary, compressive strains gradually increased at the four portions oblique to the loading axis. This result indicates that expansion of the diameters in oblique direction is restrained by backfilling soil around buried pipes.

DEVELOPMENT PROCESS AND APPLICABILITY OF A ULTRA-HIGH STRENGTH FIBER REINFORCED CONCRETE WITHOUT HEAT CURING

Koji TAMATAKI, Tomoaki ITO, Yoshikazu ISHIZEKI, Takayoshi HIRATA, Isamu YOSHITAKE
Volume 77 Issue 3 Pages 119-133, 2021, Journal of JSCE (Division E2) (in Japanese)

URL: https://www.jstage.jst.go.jp/article/jscejmcs/77/3/77_119/_article/-char/en

Abstract:
Production of ultra-high strength fiber reinforced concrete (UFC) generally requires heat-curing of high temperature. The UFC manufacturing at a site is often hard because of no heating equipment. The purpose of this study was to investigate proper materials and mixture for a UFC manufacturable under ambient temperature. In addition, to confirm the applicability of the developed UFC, the study conducted fundamental tests at a site by using the UFC supplied from a ready-mixed concrete plant. The study showed that a cement with a low C3A and high C3S content, water-binder ratios of 14% to 21%, and flow of 230mm to 290mm are suitable for the UFC without heat curing.