Cement Science and Concrete Technology
Online ISSN : 2187-3313
Print ISSN : 0916-3182
ISSN-L : 0916-3182
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Displaying 1-50 of 62 articles from this issue
Cement Chemistry
  • Kazuho SUZUKI, Tsuyoshi SAITO, Kunio MATSUI, Tatsuhiko SAEKI
    2021 Volume 75 Issue 1 Pages 2-9
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper reports on the evaluation interlayer structural of 1.1nm Tobermorite by the isosteric heat of water adsorption calculated from low-pressure water vapor adsorption isotherms. The results show the relationship between a sharp increase in the adsorbed volume at low pressure (P/P0=1×10-3) and high regularity of (002) reflection in 1.1nm Tobermorite. This observation means that the adsorption in the range of relative pressure 2×10-4~3×10-3 is occurring for interlayer space of 1.1nm tobermorite, and the dependence was confirmed by the measurements with different adsorption temperatures. These results indicate that a micropore potential is formed inside the 1.1nm interlayer. It also suggests that the rate of increase of the isosteric heat of water adsorption from coverage 0.5~1 was higher associated with the uniformity of adsorption sites inside the interlayer.

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  • Tsuyoshi SAITO, Yosuke MITSUMORI, Kazuho SUZUKI, Kunio MATSUI
    2021 Volume 75 Issue 1 Pages 10-17
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The purpose of this study is to consider the effects of curing temperature on the crystal structure of C-(A)-S-H and Al-tobermorite. In this study, γ-Al2O3 was added to the starting Ca and Si sources, and the samples were cured under various conditions. As a result, it was confirmed that 1.4nm tobermorite was formed by curing of the Al-free samples at 40℃ for 28 days. In addition, the addition of Al to the 1.4nm tobermorite under the formation process indicated the possibility of Al-substituted 1.1nm tobermorite formation even under 40℃ temperature conditions. Furthermore, it was confirmed that the peaks of Al at the pairing site in C-A-S-H and Al-substituted 1.1nm tobermorite appeared at different positions, according to 27Al{1H}DD/CP MAS NMR measurements.

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  • Kyosuke TAKAHASHI, Tsuyoshi SAITO, Kazuho SUZUKI, Ryosuke HAYASHI
    2021 Volume 75 Issue 1 Pages 18-25
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The purpose of this study was to understand the effects of the coexistence of C-A-S-H, and differences in curing water, sulfate ion source, and curing temperature on the formation of ettringite and thaumasite in the presence of carbonate ions, especially in the presence of monocarbonate. The necessary materials were reacted as a reaction suspension, and the ettringite and thaumasite formation behaviors were investigated. Results show that the secondary formation of ettringite was promoted by the coexistence of C-A-S-H, and the effect of Al supply from Q2 (bridging site) in C-A-S-H was considered to be significant in terms of Al substitution site. In addition, the formation of thaumasite was suppressed by the effect of Na in seawater. Furthermore, it was confirmed that ettringite was decomposed into AFm phase under both temperature and pH conditions.

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  • Tsuyoshi SAITO, Kazuho SUZUKI, Kunio MATSUI, Tatsuhiko SAEKI
    2021 Volume 75 Issue 1 Pages 26-33
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper reports on the structural evaluation of C-S-H with a high Ca/Si molar ratio by the isosteric heat of water adsorption calculated from low-pressure water vapor adsorption isotherms. As a result, a sharp increase in the adsorbed volume at P/P0=2×10-4 is more pronounced in 1.1nm Tobermorite that has high regularity of (002) reflection and decreases with decreasing crystallinity. The results indicate that the adsorption near P/P0=2×10-4 is occurring for the interlayer space. Also, the rate of increase in the isosteric heat of adsorption and the maximum heat value of adsorption decreased with the decrease in the number of adsorption (silica) sites in the C-S-H interlayer.

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  • Mamiko UMETSU, Daisuke KUROKAWA, Taiichiro MORI, Etsuo SAKAI
    2021 Volume 75 Issue 1 Pages 34-41
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper discusses CO2 absorption and carbonation of hardened normal (N), moderate (MPC) and low heat Portland (LHC) cements. Calcite, vaterite and gel phase are produced in carbonated all cements. Si rich gel phase is produced in carbonated samples and Ca/Si of carbonated products analyzed by SEM-EDS is varied. Ettringite (AFt) is decomposed in all carbonated cements, but AFt is reproduced by reaction of gel phase and SO3 in carbonated MPC and LHC containing rich rate of SO3/Al2O3 compared with N. The reaction of belite is accelerated but the reaction rate of alite is not changed in carbonated samples. Total CO2 absorption measured by total carbon analyzer (TC) is larger than that of measured by thermal gravity (TG). This is related to calcium carbonate. Absorption of CO2 in hardened cements is range of 25 to 30mass% measured by TC. Temperature of weight loss of TG is determined by DTG. About 10-20% of CO2 is fixed as compounds other than calcium carbonate.

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  • Shota KONDO, Tsuyoshi SAITO, Kazuho SUZUKI, Tatsuhiko SAEKI
    2021 Volume 75 Issue 1 Pages 42-49
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper reports the hydration of cementitious materials using synthetic C3S and calcined kaolinite. A result shows that a pozzolanic reaction occurred from the early hydration stage, and C-S-H and stratlingite were formed as the main hydrates. The silicate chain of the formed C-S-H consisted of Q1 and Q2, and a part of the pairing site (Q2) and the bridging site (Q2) were substituted with four-coordinated Al. The bridging site (Q2) was also substituted with 6-coordinated Al. Furthermore, structural analysis of the stratlingite formed in this system showed that crystallization proceeds by the formation of an interlayer in addition to the main layer of stratlingite and that the growth of the interlayer increases in the order of Q2 connected to Al and Q2 not connected to Al.

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  • Masaki SATO, Hiroyuki SANGO
    2021 Volume 75 Issue 1 Pages 50-57
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    For alumina cement, the effects of temperature and humidity and the problem of crystal transition are of concern as major factors affecting the long-term strength. On the other hand, it has been reported that the strength of alumina cement exposed for a long period of time decreases due to crystal transition and then increases again. It has also been reported that significant carbonation has been observed. In this study, we paid particular attention to the carbonation and investigated and discussed the strength improvement of alumina cement paste by carbonation. The results showed that the compressive strength increased with the progress of carbonation up to 28 days of age, and the carbonation reached the whole extent. The alteration of the paste was considered to be due to the increase of amorphous material with the decomposition of crystalline hydrate by the progress of carbonation reaction.

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  • Daiki ATARASHI, Natsuki YOSHIDA, Toru KINOSE, Jo ADACHI
    2021 Volume 75 Issue 1 Pages 58-65
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, we discussed the influence of heating atmosphere on the chemical changes, such as crystal phase and carbonation of hardened cement paste. The decomposition of hydration products was accelerated by heating and related to the decrease of compressive strength of mortar. β-C2S and C4AF were reproduced under heating condition at 800℃. And we also investigated the change in crystal phase of cement paste under high temperature condition by using high temperature XRD in-situ analysis. In the case of heating with N2, Ca(OH)2 in hardened cement paste changed to CaO at 400~500℃. However, in the case of heating with CO2, Ca(OH)2 in hardened cement paste changed to CaCO3 at 400~500℃. We can observed the decomposition of Ca(OH)2 to CaO and reproduction of CaCO3 with CO2 gas by TG-DTA analysis. And CaO was directly reacted with CO2 under this reaction. It is considered that this result is related to the carbonation of concrete under fire damage.

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  • Shin-ichi IGARASHI, Soshi YAMASHITA, Keigo YUGAMI
    2021 Volume 75 Issue 1 Pages 66-73
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The surface density of air voids was evaluated from the records of linear traverse measurement. The entire volume of the protected paste region was estimated by the product of the surface density and the assumed thickness of the protection from the surface of air voids. The volume fraction of the protected volume to the entire cement paste matrix was defined as the coverage ratio. If the thickness of the protected volume is assumed 0.2mm, which has been generally recognized as an upper limit of the spacing factor for moderate exposure of concrete, the coverage ratio is greater than 80% in the concrete with adequate air contents. The protected paste region was also evaluated using 2D images of air voids. The distribution of those air voids identified in the images was considered as planar point processes. The paste region including the points was divided according to the algorithm for Dirichlet tessellation. Each polygonal tile surrounding a point representing air void was regarded as an area to be protected by the void. A histogram of the areas of those tiles was obtained, and the sizes of the tiles were compared with the protected area fraction estimated from the assumed thickness of protection and the surface density. If the thickness was assumed 0.2mm for the protected area, most of the tiles were covered with the protected areas provided by air voids. The sizes of protected paste volume inferred from the Dirichlet tessellation were comparable with that estimated by the surface density of air voids. In other words, when a distance comparable with the allowable spacing factor is assumed, the cement paste matrix around random air voids is almost covered with the protected region.

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  • Takayasu ITOH, Daiki ATARASHI, Soya HARADA, Masashi OSAKI
    2021 Volume 75 Issue 1 Pages 74-81
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This study investigated mechanism of acceleration of slag reaction by the addition of calcium sulfate (CS) and calcium nitrite (CN) using laboratory-made slags with different Al2O3 contents analyzed by XRD, 27Al-MAS NMR and SEM-EDS. In the case of CS addition, the initial reaction of slag was promoted by Ettringite(Et)formation. However, as diffusion of ions would be suppressed by Et and Monosulfate (Ms) formed on the slag surface, the degree of the long-term reaction of slag was almost same as that without CS. On the other hand, in the case of CN addition, NO2 ion increases the solubility of slag and AFm (Ni) nitrite is formed away from the slag surface. As a result, diffusion of ions is not inhibited on the slag surface and the slag reaction ratio can be significantly increased.

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  • Takayasu ITOH, Daiki ATARASHI, Soya HARADA, Masashi OSAKI
    2021 Volume 75 Issue 1 Pages 82-89
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This study investigated the effect of the simultaneous addition of gypsum (CS) and calcium nitrite (CN) on hydration reaction and strength development of low-basicity (about 1.6) CaO-MgO-Al2O3-SiO2 glass and blast furnace slag. When CN and CS were added to the low-basicity slag, the solubility of Al from the slag increased by CN addition and the amount of Ettringite (Et) increased significantly by the reaction between CS and dissolved Al. As a result, the heat liberation of hydration and the combined water of the low-basicity slag with CN and CS increased to those of the high basicity slag with CS. However, as the excess formation of Et reduces the long-term strength, the amount of gypsum should be minimized when CN is added to slag.

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  • Jo ADACHI, Daiki ATARASHI, Satoshi FUJIWARA, Nobukazu NITO
    2021 Volume 75 Issue 1 Pages 90-96
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, we investigated the influence of anhydrite fineness on the initial strength development property and the hydration of blast furnace slag cement. Compared to adding anhydrite with a low degree of fineness, the strength development of blast furnace slag cement improved up to 3 days by addition of anhydrite with a high degree of fineness. However, the strength development of the cement decreases at 7 days. From the results of the hydration reaction analysis, the improvement of strength development of blast furnace slag cement up to 3 days is due to the acceleration of alite reaction by anhydrite with a high degree of fineness. And, the decrease of strength development of the cement with high fineness degree anhydrite at 7 days is due to the delay in the reaction of the aluminate phase and the production of ettringite.

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  • Hiroshi KADOTA, Yuka YOSHIDA, Masaaki MATSUSHIMA, Kenichi SHIMOSAKA
    2021 Volume 75 Issue 1 Pages 97-104
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    Aiming at the practical productivity and strength of sulfated slag cement, we examined various inorganic chemicals as activator that enhances the strength, and researched on the effect of combination of specific activators. Disodium hydrogenphosphate, magnesium chloride, magnesium carbonate, magnesium sulfate, calcium chloride and calcium nitrite improved the compressive strength of sulfated slag cement. Furthermore, a remarkable synergistic effect on the strength was obtained by the combination of activators with different activating age. Sulfated slag cement activated by the combination of calcium chloride or calcium nitrite and disodium hydrogenphosphate showed almost the same compressive strength with ordinary Portland cement at the age of 28days.

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  • Shota UMEKI, Ippei MARUYAMA
    2021 Volume 75 Issue 1 Pages 105-112
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, experiments were conducted over a period of one year using hardened ordinary Portland cement with fly ash substituted at 0, 7, and 14%. Microstructural changes of fly ash particles during pozzolanic reaction and precipitated C-A-S-H were observed using FE-SEM. The relationship between the water vapor and nitrogen specific surface areas and the pozzolanic reaction was summarized, and the water vapor BET surface area increased and the nitrogen BET surface area decreased as the pozzolanic reaction progressed. This indicates that the C-A-S-H produced by the pozzolanic reaction decreases the LD C-S-H, which is as dense as the HD C-S-H.

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  • Mamiko UMETSU, Yutaka AIKAWA, Ryuichiro KUGA, Etsuo SAKAI
    2021 Volume 75 Issue 1 Pages 113-119
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper discusses the hydration and hydrated products of fly ash cement containing high C3S cement (H) or ordinary Portland cement (N) and small amount of limestone powder at 30℃. Hydration of these cement was simulated by modified Tomosawa model. The reaction of FA is determined by selective dissolution method. The reaction rate of FA in FA cement with H is larger than that of FA in FA cement with N. Based on the simulation analysis of the reaction of FA, it is estimated that the formed reaction layer surrounding FA in FA cement with H is not densely compared with the case of FA cement with N. Hydrated products of these cement are C-S-H, calcium hydrate (CH) and ettringite (AFt) and monocarbonate (MC). Chemical composition of C-S-H is determined by SEM-EDS method. Al/Si in C-S-H of both cements is not changed, Ca/Si of C-S-H in FA cement with H is slightly larger than that of FA cement with N. The chemical composition of C-S-H in FA cement is effected by the composition of glass phase in FA.

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  • Masahito TADA, Ryuichiroh KUGA, Shunichiroh UCHIDA, Nobukazu NITO
    2021 Volume 75 Issue 1 Pages 120-127
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In order to enhance both durability issues and early age strength, improved early age strength development of fly ash cement (AF) was studied with increasing the amount of alite, f.CaO content and surface area compared to Ordinary Portland Cement (OPC). In this paper, the early age strength under steam curing condition of AF as precast concrete product was studied. The long-term hydration by selective dissolution method, Quantitative X-Ray Diffraction, and SEM-EDS was investigated. The experimental results showed that the compressive strength of AF just after demolding was about 4N/mm2 which is higher compared to OPC under the same curing conditions. The reaction of clinker and fly ash were enhanced under steam curing conditions compared to sealed ones at long-term ages. Therefore, it seems that AF shows not only higher early age strength compared to OPC and common fly ash cement but also the resistance to alkali silica reaction about the same as the common fly ash cement under air curing which is the practical use as precast concrete product. Moreover, it was found that Ca/(Si+Al) ratio of C-S-H was similar in both the AF paste and fly ash cement containing OPC (FB) paste at 182 days and was about 1.4.

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Properties of Hardened Cement and Mortar
  • Kennosuke SATO, Shigehiko SAITO
    2021 Volume 75 Issue 1 Pages 128-135
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The present study experimentally examined the sulfate ion sorption and elution characteristics of calcium-silicate-hydrate (C-S-H) and the chemical changes associated with it such as changes in solid phase compositions and chemical bonds at the atomic level. The sulfate ion sorption test was carried out under 20℃ or 60℃ using synthesized C-S-H having different C/S ratios and solutions in which the sulfate ion concentrations were adjusted with sodium sulfate or potassium sulfate. Subsequently, the elution test was performed. The amount of sulfate ion sorption was found to increase with increasing of C/S ratios, regardless of whether sodium sulfate or potassium sulfate was used. The sulfate ions sorbed on C-S-H were fixed as gypsum under the condition of high sulfate ion concentration using sodium sulfate, and as syngenite under the condition of high sulfate ion concentration using potassium sulfate. The sulfate ions were sorbed to C-S-H even when the sulfate ion concentration was low;however, above mentioned minerals were not formed. It was also found that the sulfate ions sorbed on C-S-H can be eluted in both cases when they are fixed as gypsum or syngenite and when they are not fixed as minerals under the condition of low sulfate ion concentration.

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  • Yukiko NISHIOKA, Tetsurou MATSUSHITA, Masarou KOJIMA, Yuki NAITO
    2021 Volume 75 Issue 1 Pages 136-143
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, the effects of curing temperature and amount of retarder on setting characteristics, hydration heat generation, hydration products, and compressive strength were examined using mortar mixed in a high temperature environment assuming the hot season. As a result, it was shown that the addition of the retarder broadens the hydration curve and promotes the hydration reaction after the third peak of the hydration curve, and that the addition of the retarder at 38℃ enhances the strength. Similarly, mercury intrusion tests, low-temperature DSC, and SEM observations were carried out using cement paste mixed in a high-temperature environment, and it was clarified that the continuity of macropores was improved by curing at 70℃, and that the pore diameter shifted to the smaller one by increasing the amount of retarder, and that the gel pore was changed by the retarder.

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  • So GOTO, Shota UMEKI, Ryo KURIHARA, Ippei MARUYAMA
    2021 Volume 75 Issue 1 Pages 144-151
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, nitrogen sorption using ordinary/low heat Portland cement paste, was conducted to understand the microstructural changes of C-S-H during first drying and re-humidifying processes. As a result, the mineral composition of cement affected the pore structure of C-S-H during the first drying process, but not during the re-humidifying process. The irreversible shrinkage of cement is due to pores of 1-5nm, and different pore structure changes were observed in pores of 5-15 and 15-100nm for ordinary/low heat Portland cement with different shrinkage strain.

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  • Miki SEGAWA, So GOTO, Ryo KURIHARA, Ippei MARUYAMA
    2021 Volume 75 Issue 1 Pages 152-159
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, the microstructural changes due to humidity control conditions were investigated by water vapor adsorption tests and 1H-NMR Relaxometry measurements in low heat Portland cement based HCP subjected to long-term RH conditioning at 11, 33, 40, 50, 75, and 95% relative humidity. Although the values of moisture content and specific surface area differed greatly depending on the measurement methods, decreasing trend in response to drying was confirmed in both methods. Specific surface area for each method was different depending on their assumed pore shapes. Water vapor sorption see the outside of the aggregated structure of C-S-H, while the 1H-NMR relaxometry see overall structure of C-S-H, but the changes in the specific surface areas of both methods attributed to the shrinkage of C-S-H due to drying.

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  • Mariko SUZUKI, Shin NAMBU, Kento KOIDE, Takeju MATSUKA
    2021 Volume 75 Issue 1 Pages 160-165
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, the production method of urea-containing mortar that is effective in reducing the drying shrinkage was investigated from the length change rate measurement. The preparation of urea-containing mortar was the three methods;the first one was used urea solution as the mixing water, the second one was used urea solution as the curing water and the third one was used fine aggregate soaked in urea solution. As a result, the most effective method for reducing the dry shrinkage of mortar was to change the curing water to urea solution. Furthermore, in this paper, the advantages and problems of each urea-containing mortar are summarized.

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  • Yuqi REN, Ippei MARUYAMA, Atsushi TOMOYOSE, Ryo KURIHARA
    2021 Volume 75 Issue 1 Pages 166-173
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    Volcanic glass powder can be used as a pozzolanic material. Unlike fly ash from industrial waste, it is a sustainable material from volcanic activities. With the publication of JIS A 6209 “Volcanic glass powder for use in concrete”, volcanic glass powder started to be used in construction industry. Hydration process of individual cement clinker of ordinary Portland cement and pozzolanic reaction of volcanic glass powder were studied in this research. The water to binder ratio is constant at 0.4 and other parameters of the present study are volcanic glass powder replacement ratio (0%, 10%, 20%), and curing temperature (20, 40, 60℃). XRD/Rietveld analysis and Thermogravimetric analysis were used to obtain the degree of hydration. Selective dissolution method was performed to get the degree of reaction of volcanic glass powder. The pozzolanic reaction of volcanic glass powder was clarified by the difference in the measured portlandite amount and estimated portlandite amount. On the basis of the experimental results, the effect of temperature and volcanic glass powder replacement ratio on the hydration of individual clinker was evaluated. Volcanic glass powder showed high reactivity in the present study. A model of volcanic glass powder reaction rate was proposed based on the model of hydration made by Parrot.

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  • Kiyofumi KURUMISAWA
    2021 Volume 75 Issue 1 Pages 174-180
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The physical properties of the blast furnace slag composite with the inorganic salt were investigated. The compressive strength was initially increased by adding an inorganic salt. The drying shrinkage tended to differ depending on the type of inorganic salt added, and the initial shrinkage with the sulfate-based salts was lower than that without salt. On the other hand, it was shown that the shrinkage increased in the initial stage with nitrite and calcium chloride, but did not increase significantly thereafter. The diffusion coefficient also tended to differ depending on the type of the inorganic salt to which it was added, and the diffusion coefficient of specimen with inorganic salt tended to be higher than that without salt. It was considered that this was because the addition of the inorganic salt produced an aluminate-based hydrate, which reduced the amount of anions such as chloride or iodine adsorbed in specimen. It was shown that the amount of adsorption is the dominant factor on the diffusion performance of blast furnace slag composite.

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  • Jihoon KIM, Yu YAMAZAKI, Ryoma KITAGAKI, Yukio HAMA
    2021 Volume 75 Issue 1 Pages 181-187
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The microstructural changes of ordinary cement and blast furnace cement paste under repeated dry and wet environments were investigated by 29Si MAS NMR, MIP and 1H NMR relaxometry. Under dry conditions of 50℃ and 11%RH, the cement paste usually causes coarsening of capillary pores due to compression of the C-S-H layer, and this is difficult to recover due to rewetting. Like ordinary cement paste, the blast furnace cement paste also has an increase in capillary pores due to drying, but the pores recover to a certain extent by rewetting. This behavior may be due to the difference in chemical composition between ordinary cement and blast furnace cement, such as an increase in the average chain length of C-S-H and resistance to compression of the C-S-H layer due to the inclusion of Al2O3.

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  • Yosuke ITO, Shinji KAWABE, Hiroto TERANISHI, Yuta INOUE
    2021 Volume 75 Issue 1 Pages 188-194
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In order to prevent communication failure caused by interference between devices that use electromagnetic waves such as wireless LAN in buildings, electromagnetic wave absorbers are required on the walls and floors of buildings. In the case of a wide range of electromagnetic frequencies, a narrow-band absorber that absorbs electromagnetic waves only in a specific frequency band cannot prevent communication problems, so a broadband absorber is required.To solve this problem, a broadband electromagnetic wave absorber has been studied by using a mortar made of electric furnace oxidizing slag, which has high density and complex permittivity, and styrofoam beads, which have lower density than electric furnace oxidizing slag (hereinafter referred to as beads slag mortar) as aggregate. The beads slag mortar becomes a wide band electromagnetic wave absorber in which the electric furnace oxidizing slag and styrofoam beads are separated by vibrating when uncured, and the complex relative permittivity and complex relative permeability gradually increase from the direction of electromagnetic wave incidence to the bottom of the mortar, like a multi-layered electromagnetic wave absorber. This wide band electromagnetic wave absorber can be manufactured easily and inexpensively because it can be manufactured with the general equipment used for mortar fabrication.
    In this study, the area occupied by the electric furnace oxidizing slag per unit cross-sectional area of the specimen and the return loss of the specimen are measured in order to clarify the effect of water cement ratio and vibrating time of beads slag mortar on the separation of beads and electromagnetic wave absorption performance. As a result of the measurement of the area occupied by electric furnace oxidizing slag per unit cross-sectional area, it was found that the electric furnace oxidizing slag and styrofoam beads of the beads slag mortar flowed as the mortar was vibrated, and the beads slag mortar flowed more easily even with a short vibrating time as the water cement ratio increased.
    From the measurement of the return loss, it was found that the electromagnetic wave absorption performance of the beads slag mortar increased with the increase of the water cement ratio and the increase of the vibrating time until the two layers separated and peaked.

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Testing and Evaluation of Concrete
  • Masaya TAKEDA, Toshikatsu SAITO, Katsunori DEMURA
    2021 Volume 75 Issue 1 Pages 195-201
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The purpose of this study is to investigate the coefficient of admixture for granulated blast-furnace slag and fly ash in an estimation formula for static modulus of elasticity of porous concretes. The porous concretes using the crushed hard sandstone and limestone as coarse aggregates with the different static modulus of elasticity and the cement mortars using the blast-furnace slag cement type B or fly ash type Ⅱ added ordinary portland cement as binders are prepared with the percentage of the target voids of 10, 20 and 30%, water-binder ratios of 25.0%. The porous concrete specimens are cured under 20℃ moist for 1d and 20℃ water for 27, 55 or 83d, and subjected to the voids , compressive strength and static modulus of elasticity tests at the age of 28 and 56 and 84d. The compressive strength and static modulus of elasticity of the porous concretes are discussed in detail. As a result, the coefficients of admixture for granulated blast-furnace slag of 0.95 and fly ash of 1.1 are determined for the following estimation formula for the static modulus of elasticity of the porous concrete in the previous study.
    Ek1×k2×17.1×(γ/2.1)1.5×(fc/20)(1/1.4), where, E:static modulus of elasticity (GPa),fc:compressive strength (MPa), γ:mass of unit volume (t/m3), k1:coefficient of type of coarse aggregate, k2:coefficient of admixture.
    It is concluded from this study and the previous studies that the above mentions formula is applicable for estimating the static modulus of elasticity of the porous concretes. The coefficients of type of coarse aggregate of 1.0 for the crushed hard sandstone and 1.2 for the limestone, the coefficient of admixture of 0.95 for the silica fume and the granulated blast-furnace slag and 1.1 for the fly ash can be used for the estimation formula. The values of these coefficients are same as the coefficients used for the New-RC formula for estimating the static modulus of elasticity of the ordinary concrete standardized by Architectural Institute of Japan.

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Properties of Concrete
  • Takuya OHNO, Yuji MITANI, Ippei MARUYAMA
    2021 Volume 75 Issue 1 Pages 202-209
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    In order to control shrinkage cracks of concrete structures more accurately, it is required to predict shrinkage strain of concrete member size. However, predictions under real environments where different specimen size and temperature and humidity change have not been fully investigated. In this study, Ordinary Portland cement and blast furnace cement type B concrete with different volume to surface ratio were studied in this research. The samples were investigated the relative humidity and shrinkage strain inside the concrete under 20℃ environment under 60%RH condition and an indoor exposure where only temperature and humidity change while not affected by sunlight, rainfall, wind, etc. As a result, in the range of volume to surface ratio of 100mm or less, the test specimens in the indoor exposure environment had a slower evolution of shrinkage strain compared to the one of 20℃ environment under 60%RH condition and the shrinkage strain in the indoor exposure environment was about 5 to 15% smaller at the drying period of 364 days than in the environment under the condition of 60%RH at 20℃. Shrinkage strain in the indoor exposure environment were about 5 to 15% smaller than that of 20℃ environment under 60%RH condition in the drying period of 364 days. Moreover, it was confirmed that the behavior of shrinkage strain in a real environment where temperature and humidity change can be predicted by applying the monthly average value or annual average value of the relative humidity around the specimen to the existing prediction formula.

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  • Yoshitaka MATSUURA, Masaki WASHIZU, Takuya MAESHIMA, Ichiro IWAKI
    2021 Volume 75 Issue 1 Pages 210-217
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    Aiming to establish the use of coal gasification slag fine aggregate (CGS) which has become a new JIS standard material as a slag aggregate for concrete, the quality of CGS due to the type of coal, and the effect of the CGS mix ratio on the fundamental properties of concrete were investigated. As a result, the investigations confirmed that the amount of bleeding increased and the early age strength slightly decreased with increasing CGS mix ratio. However, at long-term age, the studies suggested that the transition zone may be densified by pozzolanic reaction of CGS itself, which may have a positive effect such as an increase in long-term strength and an improvement in chloride penetration resistance.

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  • Takeshi IGAI, Tatsuhiko SAEKI, Tsuyoshi SAITO
    2021 Volume 75 Issue 1 Pages 218-224
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    Three-component concrete, in which silica fume is mixed with blast furnace slag cement, has been reported that chloride penetration resistance is greatly improved. In this study, the characteristics of Three-component concrete were investigated. It was laboratory tests and actual structure tests were conducted on coastal structures. As a result, it was confirmed that the compressive strength, static modulus of elasticity, and electrical resistivity of concrete increased at 3 years. In addition, the higher the proportion of blast-furnace slag, the larger the carbonation coefficient.

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Durability
  • Luge CHENG, Ippei MARUYAMA
    2021 Volume 75 Issue 1 Pages 225-232
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, the effects of relative humidity (RH) and temperature on the corrosion rate of rebar in chloride contaminated mortar were evaluated. Electrochemical characteristics including electrical resistivity of mortar and corrosion rate of rebar under different RH and temperature conditions were measured. Higher RH and temperature conditions lead to the decrease of electrical resistivity of mortar. Increasing RH increases the corrosion rate by develop more channels to transfer hydroxyl ions from cathode to anode. The increase of temperature up to a threshold value of 40℃ or 45℃ accelerates the corrosion rate. When the temperature is over such a threshold value, a continuous attenuation of corrosion rate occurs. In addition, the sensitivity of the effect of temperature on corrosion rate evolution is higher under high RH range than which under low RH range. The possible causes of such phenomenon are analyzed.

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  • Takahiro HARIGAI, Konosuke TAKAHARA
    2021 Volume 75 Issue 1 Pages 233-239
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The rebar corrosion limit of concrete using silica fume mixed cement and ordinary portland cement was evaluated by the autoclave method. In this study, corrosion grade of rebar, ratio of corrosion area of rebar, chloride ion diffusion coefficient, bound chloride ion ratio and total pore volume were measured. Concludingly, the concrete using silica fume mixed cement indicated high rebar corrosion resistance in range of W/C ratio 13 to 17% even with chloride ion contents 1.5kg/m3. While, the concrete using ordinary portland cement improved rebar corrosion resistance due to decrease of W/C ratio and indicated high rebar corrosion resistance with chloride ion contents 0.4kg/m3 at W/C ratio 35%.
    In addition, the chloride ion diffusion coefficient tended to decrease as W/C ratio decreased. The total pore volume of mortar also decreased as W/C ratio decreased. Therefore, decreasing the total pore volume by reducing W/C ratio or using silica fume was considered that the environment around the rebar was less likely to corrode because the movement of deterioration factors that corrode rebar was suppressed by the densification of the hardened cement structure. The bound chloride ion ratio of cement paste using ordinary portland cement was higher than silica fume premix cement in the sealed curing.

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  • Takumi TANAKA, Toshikatsu SAITO, Katsunori DEMURA, Masaru KAKEGAWA
    2021 Volume 75 Issue 1 Pages 240-246
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This paper deals with the effect of the application quantity of water-absorption-controlling material on adhesive strength properties and carbonation resistance of polymer-modified mortar coated concretes. Two types of the polymer-modified mortar are prepared with the polymer-cement ratios of 0 and 5% as coating mortars. The base concrete surface is treated by the water-absorption-controlling materials with the application quantity of 20, 25 and 30g/m2 as solids. Then the base concretes are coated by the polymer-modified mortars with coating thickness of 2.5mm, and cured under prescribed conditions for 28d. The adhesive strength of the coated polymer-modified mortar is measured with failure modes. The polymer-modified mortar coated concrete specimens are stored in the carbonation chamber with 30℃, 60%(RH) and CO2 concentration of 60%. After the coated polymer-modified mortar layer is completely carbonated, the carbonation depth of the base concretes are measured at storage periods of 28, 56 and 84d. As results, the adhesive strength of the polymer-modified mortar and carbonation resistance of the base concrete are improved by applying the water-absorption-controlling material to the base concrete. The adhesive strength and the carbonation resistance are increased with increasing the application quantity of the water-absorption-controlling material. The polymer-modified mortar layer still inhibits CO2 penetration after the layer is completely carbonated. Such carbonation resistibility of the polymer-modified mortar layer and by the application of the water-absorption-controlling materials improve the carbonation resistance of the base concrete coated with the polymer-modified mortar.

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  • Tetsu AKITOU, Mari KOBAYASHI, Keisuke TAKAHASHI, Toshinori KIMURA
    2021 Volume 75 Issue 1 Pages 247-254
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    In recent years, a large amount of seabed mineral resources have been found such as hydrothermal deposits, manganese nodules, cobalt rich crusts and rare earth mud exist on the deep seafloor near Japan, and resource development on the deep sea floor has attracted much attention. On the other hand, in order to achieve the Sustainable Development Goals, it is necessary to develop seabed resources in consideration of marine ecosystems.
    The authors have proposed eco-friendly mining methods that deep seafloor is covered by cement-based sealing compounds to suppress environmental disturbances associated with the development of seabed resources. Under such methods, cement is hydrated in-situ deep sea. Our previous studies have focused on sea water deterioration of fabricated specimens, and the deterioration and durability of cement-based materials casted and hardened on the deep seafloor have not been clarified. By the casting at deep sea, the materials may be contaminated by seawater and seabed sediments, which can affect the deterioration and durability.
    In this work, Portland cement-based sealing compounds were casted in-situ at deep seafloor at a depth of 1890m by using a remotely operated vehicle. The specimens were recovered after 217 days of exposure. The obtained X-ray diffraction and scanning electron microscopy-energy dispersive X-ray spectroscopy spot analysis data revealed that the significant calcium leaching occurred and carbonates such as hemicarbonate and monocarbonate were precipitated by the reaction with the seafloor sediment.

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  • Hiroki HONGO, Yoko ANDO, Runa KAWAJIRI, Kazuyuki TORII
    2021 Volume 75 Issue 1 Pages 255-262
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    Using concrete cores taken from the abutments of K and T bridges in Toyama Prefecture, the judgement of potential expansion capacity by accelerated expansion test in 1N-NaOH sol. was verified from the ASR reactivity of the used aggregate and the results of detailed texture observation of the concrete. Fine aggregates used in K bridge has a high content of andesite showing a high ASR reactivity and ASR-gel filled cracks were observed in andesite. By contrast, fine aggregates used in T bridge has a high content of rhyolitic welded tuff showing a low ASR reactivity and no cracks due to ASR were observed. As a result of the alkali solution immersion test, the concrete of K bridge was assessed as “harmful” and that of T bridge was as “innocuous”. From microscopic observations, it was considered that accelerated expansion in T bridge was not promoted due to original absence of cracks in concrete and the progress of carbonation in cement paste.

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  • Norihiro SUGAWARA, Shinichi MIYAZATO
    2021 Volume 75 Issue 1 Pages 263-269
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    In chloride attack, the passivation film of the rebar is destroyed and the corrosion progresses. In alkali silica reaction (ASR), the aggregate expands and cracks occur. This study evaluated the corrosion rate of the rebars in mortar with chloride ion and glass cullet, targeting the combined deterioration due to both chloride attack and ASR. That is, when the mortar was mixed, water containing sodium chloride aqueous solution was partially used. In addition, the glass cullet having reactivity was partially mixed with the land sand as a fine aggregate. Based on these procedures, specimens were deteriorated with independent chloride attack, independent ASR, or combined deterioration. The crack on the mortar was observed and the corrosion rate of the rebar was measured. In addition, the state of the passivation film was investigated from the anodic polarization curve, the amount of oxygen supply was investigated from the cathodic polarization curve, and the formation of an electric circuit was investigated from the mortar resistivity. These were evaluated comprehensively, and the influence of ASR on the corrosion rate was considered. As a result, it was clarified that the corrosion rate of the rebar in the mortar with ASR was high because oxygen was easily supplied through cracks.

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  • Tetsuji AKIYAMA, Toshiyuki KATSUHATA, Naruki KOYAMA
    2021 Volume 75 Issue 1 Pages 270-277
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The permeable form has the quality improvement effect of concrete surface layer. On the other hand, a wrinkle occurred at form setting works and might leave it and might be connected to aesthetic dirty at concrete surface. This cause is regarded as outputs to produce because the lack of permeable sheet hardness. Therefore we chose “permeable sheet having hardness that improved model” and in this experiment, a few kinds of different form materials were examined in the permeable form setting works and concrete aesthetic beauty and durability enhancement. As a result, slack and a wrinkle did not produce the sheet which we chose at the time of form setting works. And the durability enhancement of concrete surface layer using a permeable form having hardness is the same class in permeable form current model.

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  • Kousuke ONO, Tadashi ABE, Kazuhiko MINAKUCHI, Hiroshi ONISHI
    2021 Volume 75 Issue 1 Pages 278-285
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    Early cracking of the joint surface of the replacement slab has become a problem. As a solution to this problem, the authors propose replacement RC slabs with an adhesive applied to the joint surface as a method of ensuring the integrity of the joint surface of the slabs. This study verified a load-carrying capacity and fatigue durability that the running load test and the wheel load running fatigue test were conducted on a specimen with adhesive applied to the joint surface of replacement RC slabs. In addition, we also verified the suppression effect of the opening and closing width as an effect of applying the adhesive. As a result, whereas the maximum load-carrying capacity of the replacement RC slab in the running load test is not affected by the presence or absence of adhesive on the joint surfaces, the number of equivalent runs is improved by 1.2 times with applying adhesive to the joint surface of the replacement RC slab in the wheel load running fatigue test. In addition to the above, the behavior of the opening and closing width of the joint surface until it reaches the crack width of 0.2mm shown in the Bridge Inspection and Diagnosis Manual is different. While the opening and closing width of the joint reached 0.2mm at an early stage in the replacement RC slab that was directly concrete, it confirmed that the joint was closed until near failure by applying adhesive. In conclusion, the application of the adhesive to the joint surface of replacement RC slabs suppressed cracking of joint surfaces and improved fatigue durability of replacement RC slabs.

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High-strength Concrete and High-fluidity Concrete
Fiber Reinforced Concrete
  • Haotian LI, Ayumi SATOH, Kiyoshi MURAKAMI, Koudai KATA
    2021 Volume 75 Issue 1 Pages 286-293
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The authors study a new type of UHPFRC that is curable on construction site. This paper represents a new finding about an effect of the combined use of steel fibers with different lengths to the compressive and bending strengths, achieved from experiments in which specimens are made with UHPFRC that is curable on construction site. The results showed that the specimens made of UHPFRC with combined use of fibers with 6mm and 13mm in length had better bending strength, in comparison to the specimens with a single use in length of the fiber, in which all the volume fractions of fiber were the same (Vf=2.0%). But the compressive strength of the specimen was confirmed to be the same even when the length of fiber was single or combined. It was found that the high strength specimen with two lengths of the fiber had a larger number of the fiber that appeared on the cut surface than the specimens with a single length use of the fiber. Then, it is suggested that the number of the fiber had a positive effect on bending strength. Also, an experimental result is shown about the key issues of the binder component of UHPFRC for searching a best mixture, achieved from the specimens made of different ratio of blast furnace slag fine powder and gypsum in the binder component.

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  • Hiroyuki NOGUCHI, Kazuhiko MINAKUCHI, Tadashi ABE, Toshiaki SAWANO
    2021 Volume 75 Issue 1 Pages 294-301
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, the axial compression loading tests were conducted with different spacing of tie bars and the synthetic surface shape of UFC panel using UFC・RC composite column members by focusing on the synthetic surface shape of UFC panel used as a permanent formwork type for a structural member. Axial compression loading experiments of a composite structure with different spacing of tie bars and the synthetic surface shape of UFC panel were verified by the effects on axial compressive properties and failure modes. As a result, the axial compressive load capacity and failure modes of RC column specimens and UFC・RC composite column specimens differed due to the difference in the spacing of tie bars. In addition, the shear resistance of the synthetic surface and the adhesion with a core-concrete were improved by increasing the concrete area ratio in the synthetic surface shape of UFC panel. Therefore, it became obvious that the composite structure resists axial compressive forces in an integrated manner due to the improved shear resistance and adhesion.

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Repair and Strengthening
  • Daigo SHIBATA, Makoto YAMAGUCHI, Yo MATSUKI
    2021 Volume 75 Issue 1 Pages 302-309
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The objective of this study was to obtain knowledge that contributes to the development of a performance recovery technology for severely damaged reinforced concrete(RC)members. The RC beams in which the tension rebars had yielded were repaired by injecting cracks using ultra-low viscosity epoxy resin, and the influence of the upward repair execution on their flexural performance and salt permeation resistance was experimentally investigated. The results showed that the flexural strength and toughness of the damaged RC beams can be recovered to the same level or higher than that of the undamaged RC beams by adapting this repair method, regardless of the direction of the repair execution. Further, it was also clarified that the salt permeation through cracks can be prevented well regardless of the direction of the repair execution.

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  • Yukihiro OKABE, Hirotaka HAZEHARA, Yuuji YAMADA, Kazunori ERA
    2021 Volume 75 Issue 1 Pages 310-316
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    This study is a verification of the rust preventive effect of Rebar when it is assumed that salt attack deterioration is injection into a concrete structure located in the incubation period to the progressive period. Another purpose was to clarify the long-term persistence of the rust preventive effect associated with the permeation of chloride ions over time after lithium nitrite injection method. Specifically, a specimen was prepared in which the amount of lithium nitrite injected was changed in concrete in which rebar having different degrees of corrosion were embedded in advance, which contained initial chloride ions to simulate salt damage. After that, the to grasp of the effect of the rebar protection by the natural potential and the polarization resistance value in the wet environment and the chloride ion environment, and the test of the dismantling measurement were performed to directly confirm the condition of the rebar.
    As a result, different corrosion rebar exerted a rust preventive effect by press-fitting lithium nitrite, and this persistence could be evaluated by NO2/Cl.
    In addition, even if the amount of lithium nitrite injected was increased, the rust preventive effect of the severely corroded rebar by salt attack, decreased due to the increase in chloride ions.
    Therefore, it is considered that the range of application of the long-term rust preventive effect obtained by the LINO2 injection method is the degree of corrosion in which the resistance value of the reinforcing bar is 70kΩ or less.

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  • Haotian LI, Ayumi SATOH, Kiyoshi MURAKAMI, Seiichiro YAMAUCHI
    2021 Volume 75 Issue 1 Pages 317-323
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    In this study, an experimental investigation was conducted regarding flexural and shear reinforcing effects of RC beams repaired with CFRP rod embedded. The cross-section restoration methods for these beams are as follows;One is a beam repaired by grout with CFRP rod and mesh embedded after chipping the cover concrete for one side of the beam and the other is a beam repaired by UHPFRC with CFRP rod embedded. As a result, it was experimentally confirmed that the ultimate strength of both beams was close to the strength calculated by flexural analysis based on the equivalent stress block method although the ultimate failure of both beams was caused by the bond splitting fracture of the rod.

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  • Haotian LI, Ayumi SATOH, Kiyoshi MURAKAMI, Seiichiro YAMAUCHI
    2021 Volume 75 Issue 1 Pages 324-331
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    For developing a new post-reinforcing method, the authors study RC beam thickened by UHPFRC with CFRP rod embedded. CFRP rod was used for flexural reinforcement and thickening UHPFRC was for both flexural and shear reinforcement. The effects of flexural and shear reinforcement of the RC beam were main foci of the study. In the previous paper, the experimental results were reported in which UHPFRC showed better load capacity and ductility than grouting material for the embedding material of CFRP rods. In this study, the aspects of bond fracture were searched in the RC beam thickened by UHPFRC with CFRP rod embedded after the load test, and also FEM analysis was made focusing on the process of bond fracture and cracking to reveal the cause of the experimental results. The observation study showed that the final fracture occurred from the bond splitting fracture around the rod. In FEM analysis, the load-displacement curve and fracture mode have good agreement with the test results. Also it is confirmed in FEM analysis that the improved bond strength due to the better constraining effects from UHPFRC caused a high bond stress even after debonding, which led a gradual decreasing of load after the peak load.

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  • Shunta SAKURAI, Naoki HORIKOSHI, Mitsuhiro MORI, Masayuki ISHII
    2021 Volume 75 Issue 1 Pages 332-339
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    There are many reports of various deformations and damages, such as cracks, deformation and flaking of the lining concrete in actual canal tunnel structures, and it is necessary to restore the function through repair and reinforcement. The authors developed an internal reinforcement method using CFRP strand sheets and ceramic mixed epoxy resin mortar for an agricultural canal tunnel lining where bending cracks were observed on the inner surface of the lining. Various elemental tests on the method were conducted, and it was confirmed that the method showed excellent long-term adhesion performance in water, water permeability and wear resistance in the environment of agricultural canal tunnels, which are in contact with water for a long time. In addition, in order to verify the reinforcement effect, two types of full-scale tunnel model specimens, one reinforced by this method and the other reinforced after cracks were generated in the plain concrete lining in advance, were fabricated, and loading tests were conducted on the specimens. As a result, although the initial stiffness was different, the two types of specimens show similar load bearing capacity and deformation performance in the ultimate state. Therefore, the effectiveness of this method as a reinforcement method for agricultural canal tunnels was confirmed.

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  • Yasukuni YOSHIOKA, Tadashi ABE, Kazuhiko MINAKUCHI, Noritaka MOROHASHI
    2021 Volume 75 Issue 1 Pages 340-347
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    This study is an experimental study on the reinforcement technology for RC columns damaged by deterioration over time and environmental factors. In the experiment, 2 kinds of specimens are prepared. Axial loading tests are conducted to damage the specimens. The authors proposed a method of repair and reinforcement damaged concrete column members by combining an adhesive-applied increasing thickness method using metal-grid expanded type and a crack repair method. The proposed repair and reinforcement method were used resin injection to repair cracks, installed with metal-grid expanded type, sprayed with epoxy adhesive then increased thickness with non-shrink mortar at 40mm. The results showed that the proposed reinforcing method improved a load-carrying capacity of RC columns and increased the strengthening effect by more than 2.0 times. It is considered that the axial compressive load capacity was properly shared between vertical bar and tie bar of metal-grid expanded type. Accordingly, the proposed repair and reinforcing method are considered to be practical as the reinforcement technology for damaged concrete bridge piers (RC columns).

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Environment and Recycling
  • Yu GOTO, Takumi UEHARA
    2021 Volume 75 Issue 1 Pages 348-355
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
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    The amount of waste gypsum board, which is one of the controlled industrial wastes, is increasing year by year, and there is an urgent need to take measures due to concerns about the tightness of the final disposal site. Waste gypsum board was treated as controlled industrial waste in 1999, and there is concern that there will be a shortage of controlled final disposal sites. In this study, waste gypsum board powder (hereinafter referred to as recycled gypsum powder), which is obtained by crushing, separating, and heating waste gypsum board, is kneaded into cement mortar. The applicability as a material or an admixture was considered. Although the strength of mortar mixed with recycled gypsum powder decreases, the results show that it is possible to control the strength decrease to some extent by using fly ash and blast furnace slag fine powder together. Since gypsum has swelling properties, the length of mortar mixed with regenerated gypsum powder was changed between wet and dry states, and the effect of mixing was clarified from experiments. Based on these results, the use of recycled gypsum powder was considered. Although the activity of recycled gypsum powder cannot be expected, it is desired to develop applications as bulk materials and backfill materials by paying attention to the feature of reducing shrinkage performance.

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  • Tsukasa NISIMOTO, Yu GOTO, Takumi UEHARA
    2021 Volume 75 Issue 1 Pages 356-363
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    Waste gypsum board is treated as managed industrial waste, and its use due to recycling is low, so there is an urgent need to consider new effective use destinations from the viewpoint of future disposal site limits and treatment costs.
    In this study, from the viewpoint of processing cost, we focused on the recycled dihydrate gypsum powder obtained by crushing and separating waste gypsum board. Focusing on the expansion promoting action of regenerated gypsum powder, the possibility of effective use as a filler by mixing with air mortar was examined. From experiments, it was clarified that the air mortar mixed with dihydrate regenerated gypsum powder satisfies the set target values in terms of the general required performances of lightness, fluidity, and strength characteristics. The air mortar mixed with dihydrate regenerated gypsum powder satisfies a wet density of 0.5 to 1.3g/cm3, a flow value of 180±20mm, and a compression strength of 1.0N/mm2 or more. A mixture of recycled dihydrate gypsum powder can carry more air than the base. Furthermore, as a material for studying new effective use destinations, the relationship between the amount of air contained and the compressive strength was quantified. The air mortar mixed with the recycled dihydrate gypsum powder exhibits the same strength as the base having the same amount of air when the content of air increases to about 50%.

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  • Hiroto MAWATARI, Tsuyoshi SAITO, Kazuho SUZUKI, Tatsuhiko SAEKI
    2021 Volume 75 Issue 1 Pages 364-371
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    In this study, we attempted to evaluate the structure of C-A-S-H, whose structure is unknown, from the differences in the products and the characteristics of their formation under different conditions by simultaneous formation of C-A-S-H and zeolite, which have many structural similarities. phase in the liquid phase under varying amounts of Si, Al, Ca, and Na, and to evaluate the structure of C-A-S-H. The results showed that zeolitic products were mainly observed under the zeolite-dominated condition with high Al content, but the amount of products decreased in proportion to the Ca content, indicating the possibility of C-A-S-H formation. On the other hand, in the case of the C-A-S-H dominant condition with high Si content, the formation of C-A-S-H was observed even with a small amount of Ca, and the formation of C-A-S-H, which is close to the crystal structure of tobermorite, tended to become dominant as the amount of Ca was increased.

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  • Misato TAKEUCHI, Makoto YAMAGUCHI
    2021 Volume 75 Issue 1 Pages 372-379
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    To contribute to the development of a water purification system that uses porous concrete (PoC) and water-extracted plants together, as a first step, experimental investigations were conducted on the growth of the water-extracted plants planted in PoC by hydroponics. As the water-extracted plants, Lythrum anceps and Cyperus alternifolius L., which are considered to be suitable species in terms of water purification, were adopted in this study. We produced PoC with reduced alkaline elution by carbonating its cement paste layer. As a result of the planting tests, it was confirmed that hydroponics of the above-mentioned water-extracted plants using the PoC planting base is sufficiently possible, although it is not as good as the culture soil.

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  • Eiichi KATSUBE, Daiki ATARASHI, Eiji SUNADA, Hiroyuki HASHIDA
    2021 Volume 75 Issue 1 Pages 380-387
    Published: March 31, 2022
    Released on J-STAGE: March 31, 2022
    JOURNAL FREE ACCESS

    Countermeasures against sludge water containing cement have become an urgent issue at ready-mixed concrete manufacturing plants. In this study, we conducted a demonstration test at three ready-mixed concrete manufacturing plants with different environmental temperatures regarding the high utilization of sludge water, which uses a solid in sludge water whose hydration reaction is suppressed by a condensation-delaying component as a binder. As a result, the concrete produced by substituting 6% of the unit cement amount with the solid in the flange water in which the hydration reaction was suppressed showed the same physical characteristics as the concrete with the standard composition and the influence of environmental temperatures was not observed. Furthermore, as a result of estimating the amount of CO2 reduction, it was shown that the power consumption of the equipment for manufacturing ready-mixed concrete and the amount of CO2 generated from the fuel consumed by the truck agitator may be offset by the high utilization of sludge water.

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