Cement Science and Concrete Technology
Online ISSN : 2187-3313
Print ISSN : 0916-3182
ISSN-L : 0916-3182
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Cement Chemistry
  • Yosuke MITSUMORI, Tsuyoshi SAITO, Fukumasa KATO, Tatsuhiko SAEKI
    2019 Volume 73 Issue 1 Pages 2-9
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The purpose of this study is to consider the effects of addition of Al and Mg on the formation and crystal of tobermorite. The samples were synthesized in different conditions of curing (autoclave curing or hydration curing at 80℃) and additional materials (gehlenite, akermanite, and gehlenite-akermanite) which are known as industrial by-products. Therefore, this study will contribute in terms of developing sustainable society. As a result, 1.1nm tobermorite which was including Al was generated by addmixing gehlenite or gehlenite-akermanite under high pressure and high temperature condition (autoclave curing). In addition, the large amount of Al in gehlenite or gehlenite-akermanite replaced Si at bridging site in 1.1nm tobermorite. Furthermore, the interlayer spacing of 1.4nm tobermorite got narrower to 1.1nm without strong drying after 80℃ hydration. This was due to replacing Si to Al in gehlenite, and SiO4 tetrahedra at bridging site was tied together and interlayer spacing got narrower. This result is great step to realize a material design to produce 1.1nm tobermorite in concrete at low temperature. On the other hand, the amount of 1.1nm tobermorite increased by admixture akermanite under high pressure and high temperature condition. But akermanite was hard to react at low temperature condition such as 80℃.

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  • Fukumasa KATO, Tsuyoshi SAITO, Kunio MATSUI, Tatsuhiko SAEKI
    2019 Volume 73 Issue 1 Pages 10-17
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In this paper, the effect of drying condition on the structural change of Mg and alkali added 1.4nm tobermorite was examined through measuring the samples which were dried at RH=11-88% for a long time, after hydration at 80℃. As a result, at RH=11%, 1.4nm tobermorite was well-crystalized and its strcture was stabilized, which was unstable under high RH condition. Furthermore, the N2 sorption isotherm of the samples suggested that meso- and macropore structure of pretreated samples were completely different by conditions of long-term drying, even though XRD showed no significant differences. Besides, under 80℃ hydration, formation of 1.4nm tobermorite might be promoted by Mg, which is considered to be bridged the Si chain between the 1.4nm tobermorite layers.

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  • Ryosuke HAYASHI, Tsuyoshi SAITO, Kennosuke SATO, Tatsuhiko SAEKI
    2019 Volume 73 Issue 1 Pages 18-25
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    Sulfate attack is known as one of the deterioration phenomena of concrete structures. According to previous researches, it has been suggested that the presence of carbonate ion may promote secondary ettringite formation and expansion;however, the details of this hypothesis have not been confirmed by experiments. The purpose of this research is to examine the effects of mixing amount of monocarbonate and curing temperature on thaumasite and ettringite formation. Synthesized monocarbonate and the materials required for thaumasite formation were mixed with deionized water in order to hydrate in the suspension, after which the solid phases after hydration were analyzed. As a result, when a mixture of portlandite, calcium carbonate, amorphous silica, gypsum and a large amount of monocarbonate was mixed and hydrated at 5, 20, 40℃, the amount of secondary ettringite formation was increased with the rise of curing temperature. In particular, the amount of secondary ettringite formation was increased significantly when a large amount of monocarbonate was mixed. It was suggested that the secondary ettringite formation from monocarbonate is strongly affected by the dissolution of CH and the formation of C-A-S-H in the suspensions.

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  • Etsuo SAKAI, Mamiko UMETSU, Nobukazu NITO, Ryuichiro KUGA
    2019 Volume 73 Issue 1 Pages 26-31
    Published: March 31, 2020
    Released: March 31, 2020
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    The authors have been reported that the strength of fly ash cement can be improved and obtained the same strength of ordinary Portland cement by using of high alite cement adjusting alite contents and free-CaO and addition of small amount of limestone powder. This paper discusses the hydration and hydrated products of this improved fly ash cement (AFC) compared with ordinary Portland cement (N) and generally fly ash cement (NF). The reaction rate of fly ash (FA) or alite measured by XRD and selective dissolution method, and hydrated products was analyzed by SEM-EDS or solid state-NMR. The reaction rate of FA in hardened AFC is larger than that of FA in hardened NF. AFm is observed in hydrated N or NF. In hydrated AFC, AFt is also detected in addition of monocarbonate. The effect of LSP is observed at long term curing sample. Ca/Si ratio of calcium aluminous silicate hydrates (C-A-S-H) in hydrated samples are decreased and Al/Si ratio of C-A-S-H is increased by adding of FA. Bridge of AlO4 and SiO4 is increased by adding of FA, compared with the hydrated N. But this value of hydrated AFC is smaller than that of hydrated NF.

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  • Yuta NAKAGAWA, Daisuke KUROKAWA, Shunichiro UCHIDA, Hiroshi HIRAO
    2019 Volume 73 Issue 1 Pages 32-37
    Published: March 31, 2020
    Released: March 31, 2020
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    The quality of cement changes depending on storage condition such as temperature and humidity. In this study, the influence of storage condition on cement characteristics and properties were evaluated. The cement was stored in four conditions which differed from each other in temperature and humidity. Two characteristics were measured:the mass ratio of hemihydrate to gypsum and hemihydrate (ratio of hemihydrate) and the sample’s weight loss up to 500℃, which is not due to dehydration of gypsum. Moreover, the sample’s properties such as compressive strength and setting time were measured. In high humidity condition, cement absorbed moisture resulting in weight loss increase. Because of this, the compressive strength decreased and the setting time was delayed. In low humidity and high temperature condition, the weight loss did not change but the ratio of hemihydrate increased. This caused delay of the setting time. In low humidity and low temperature condition, characteristics and properties did not change.

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  • Seishi GOTO, Junya NAKAMURA, Takeshi IYODA
    2019 Volume 73 Issue 1 Pages 38-43
    Published: March 31, 2020
    Released: March 31, 2020
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    The carbonation process of concretes had been discussed by taking accounts of mass, reactivities with CO32- and particle sizes of CH and C-S-H. It was assumed that the reactivity of CH with CO32- is only a little higher than that of C-S-H, and the particle diameters are 30μm for CH and 30nm for C-S-H. And also, it is assumed that the rate of carbonation of particle system obey Jander’s rule when they are in the liquid with constant concentration. When the rate of supply of CO32- is lower than the rate of carbonation obeyed Jander’s rule, the amounts of carbonation should be equal to that of CO32- supplied. When the amounts of CO32- supplied becomes more than that obeyed Jander’s equation, the process may move to next step. Owing to these ideas how the accelerating condition affects to the rate of carbonation had been discussed. As a result, following results were obtained;1. the reaction ratio of CH at the carbonation front will differ with the accelerating condition. 2. The color of the carbonation zone will be pink due to the accelerating condition. 3. The coefficient of carbonation will depend on the amounts of C-S-H and CH with a weight.

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  • Shuya OSAKI, Daiki ATARASHI, Hyeonjin SONG, Yuhji SUDOH
    2019 Volume 73 Issue 1 Pages 44-51
    Published: March 31, 2020
    Released: March 31, 2020
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    In order to investigate the effect of calcium nitrite addition on the hydration reaction of blast furnace slag, Ca(OH)2-blast furnace slag paste was prepared and compared with the effect of gypsum addition. At the same time, the effect of calcium nitrite on the hydration of blast furnace cement was also examined. In the case of addition of gypsum, the reaction was stagnant after 14 days, and AFt was confirmed as the main hydration product. By contrast, The hydration reaction of blast furnace slag was continuously promoted by calcium nitrite addition and formed AFm(NO2). The amount of C-S-H production also increased. The hydration reaction of blast furnace slag and base cement in blast furnace cemente is promoted by calcium nitrite, therefore, it is considered that calcium nitrite can be expected as an activator for blast furnace cement.

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  • Etsuo SAKAI, Yukiko UEDA, Yutaka AIKAWA, Nobukazu NITO
    2019 Volume 73 Issue 1 Pages 52-58
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    This paper discusses the influence of calcium nitrite and diethanol-propanolamine (DEIPA) on the strength and the hydration reaction of high volume slag cement (HVBFSC) containing 60% blast furnace slag (BFS), 5% anhydrite and 30% ordinary Porltand cement (OPC). By adding of combination with calcium nitrite and DEIPA, the compressive strength of HVBFSC mortars are increased in each curing time. In this case, the initial hydration of BFS is accelerated and on the hydration of OPC is also promoted at late stage in the hydration of HVBFSC. The effect of calcium nitrite and DEIPA on the early hydration of HVBFSC is analysis by modified Tomosawa Motel of hydration. By adding of DEIPA or combination of DEIPA and calcium nitrite, diffusion coefficient in modified Tomosawa model is increased, water can be moved easily through the hydrated layer formed surround BFS compared with the case of no addition. Hydrated products are not changed by addition of these additives and CH, CSH and AFt and small amounts of AFm are produced. By adding of calcium nitrite and DEIPA, AFt is mainly produced.

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  • Hyeonjin SONG, Daiki ATARASHI, Yoshifumi HOSOKAWA, Miho MIYAKAWA
    2019 Volume 73 Issue 1 Pages 59-64
    Published: March 31, 2020
    Released: March 31, 2020
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    In this study, it investigated that the effects of three types alkanolamine (TIPA, DEIPA, MDEA) on the early hydration reaction of FA cement, in order to development of FA cement that improved early strength. As a result, loss on ignition and heat of hydration was increase in FA cements with all alkanolamine, and reaction ratio of C4AF in clinker mineral was greatly increased. However, it was confirmed that the influence of the alkanolamine on the hydration reaction of C3S and FA was not almost. In addition, the formation of AFm as a hydration product of FA cement with alkanolamine is faster than no addition. Early strength of FA cement is expected to increase, beacuse of cement of hydration reaction in FA cement with three types alkanolamine is increased, and hydration reaction of FA is not inhibited.

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  • Etsuo SAKAI, Mamiko UMETSU, Kazuki MATSUZAWA, Ryuichiro KUGA
    2019 Volume 73 Issue 1 Pages 65-70
    Published: March 31, 2020
    Released: March 31, 2020
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    This paper discusses the chemical and physical properties of fly ash (FA) treated by electrostatic belt separation method. Hydration of FA cement containing treated FA is also investigated. Chemical composition and mineral composition of treated FA are not changed compared to original or untreated FA. But loss on ignition of treated FA is drastically decreased by separation method. The fluidity of paste with superplasticizer can be improved by using of treated FA containing less than 1% unburned carbon. The reaction of cement in FA cement with treated FA is accelralated The reaction rate of treated FA is larger than that of original FA. Type of FA such as FT or F is not influenced on calcium aluminate hydrates.

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Properties of Hardened Cement and Mortar
  • Yuya SUDA, Jun TOMIYAMA, Tsuyoshi SAITO, Tatsuhiko SAEKI
    2019 Volume 73 Issue 1 Pages 71-78
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    It is important to assess the durability of concrete structures due to their long-term service. Carbonation, one of the dominant forms of deterioration of concrete structures, is influenced by various conditions, such as concrete materials, mixture, temperature and relative humidity (RH). The effect of humidity on carbonation is well known;carbonation rate and carbonation shrinkage are most effective under intermediate humidity. The effect of carbonation on concrete involve the dissolution of hydration products, mainly portlandite and calcium silicate hydrate (C-S-H), and the precipitation of CaCO3 in pore solution. However, the effects of RH on the carbonation reaction of hydration products have not been clarified.
    The purpose of this study was to investigate the effect of RH on the carbonation of hydration products. Ordinary Portland cement-paste samples were exposed to accelerated carbonation under 3%-CO2 concentration at different RH conditions (RH85%, RH66%, RH43% and RH11%) and the temperature at 20℃. Thermogravimetric, differential-thermal and X-Ray-diffraction-Rietveld analysis were used to quantify the amount of portlandite and CaCO3 polymorphs. Change in the carbonation shrinkage over time under different RH conditions, was also measured. Experimental results show that calcite was the dominant mineral among the CaCO3 polymorphs under the condition of RH66%, whereas aragonite and vaterite were mainly present CaCO3 polymorphs in carbonated cement paste under RH43%. Change in the carbonation shrinkage over time differed by RH conditions, although the amount of CaCO3 was the same. There were major changes in carbonation rate of C-S-H and portlandite under different RHs. Results indicate that carbonation level of C-S-H under RH43% is higher than that under RH66% and RH85%. Thermodynamic modeling was performed to demonstrate how carbonation shrinkage is affected by carbonation behavior of C-S-H under different RH conditions.

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  • OTSUKA SAKATA HERLY NICOLAS, Kennosuke SATO, Shigehiko SAITO
    2019 Volume 73 Issue 1 Pages 79-86
    Published: March 31, 2020
    Released: March 31, 2020
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    The present study experimentally examined the relationship between the property of oxygen transport in hardened cement paste after sodium sulfate solution immersion and the change of hydration products. Oxygen diffusion coefficient, pore volume, pore distribution and phase composition of cement paste specimens exposed to sodium sulfate solution and ion exchanged water were acquired. As the result, the oxygen diffusion coefficient of the specimens after sodium sulfate immersion decreased compared to that of the specimens after ion exchanged water immersion. This decrease in the oxygen diffusion coefficient was considered to be caused by the complication of the pore structure of the hardened cement paste due to the decrease of pore volume (diameter > 20nm) when the specimens are immersed in sodium sulfate solution. And there was a certain correlation between the volume of C-S-H and ettringite and the pore volume (diameter > 20nm). It is one of the evident that the formation of ettringite reduced the pore volume (diameter > 20nm) and reduced the oxygen diffusion coefficient.

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  • Satoshi FUJIWARA, Taro KOSUGE, Masanori MARUOKA, Hiromi FUJIWARA
    2019 Volume 73 Issue 1 Pages 87-94
    Published: March 31, 2020
    Released: March 31, 2020
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    As a method of sulfuric acid resistance of a concrete structure, there is a method of using a sulfuric acid resistant cement-based material using blast furnace slag fine powder and pozzolanic admixture. On the other hand, sulfuric acid resistant cement-based materials are required to have an improved initial strength. Therefore, we examined sulfuric acid resistant cement-based materials using single micron blast furnace slag fine powder and fly ash. By using a single micron blast furnace slag ultrafine powder, the initial strength was improved with equivalent sulfuric acid resistance. Furthermore, the combination of blast furnace slag sand and blast furnace slag ultrafine powder significantly improved the sulfuric acid resistance.

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  • Katsunori DEMURA, Toshikatsu SAITO, Masaya TAKEDA
    2019 Volume 73 Issue 1 Pages 95-102
    Published: March 31, 2020
    Released: March 31, 2020
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    The purpose of this study is to investigate the effect of polymer content on resistance to water permeation and durability of polymer-modified mortars. Polymer-modified mortars using re-dispersible polymer powder and with fine aggregate cement ratio of 2 and 3, water-cement ratios of 45, 50, 55 and 60%, polymer contents of 0, 2, 4 and 6% are prepared, and cured under 2d-wet+5d-water+21d-dry or 2d-wet+26d-dry condition. Cured specimens are tested for water permeability, carbonation depth and chloride ion penetration depth. As a result, effective factors consist of water cement ratio, polymer content, air content and fine aggregate cement ratio water for the permeability, carbonation depth and chloride ion penetration depth of the polymer-modified mortar are proposed. Regardless of the type of polymer and curing condition, the good relationships are recognized for the water permeability, carbonation depth and chloride ion penetration depth of the polymer-modified mortars and the products of the those effective factors by the water permeability, carbonation depth and chloride ion penetration depth of unmodified mortar. The polymer content may be used as a new mix proportioning factor of the polymer-modified mortars.

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  • Yuya YAMADA, Kiyofumi KURUMISAWA
    2019 Volume 73 Issue 1 Pages 103-110
    Published: March 31, 2020
    Released: March 31, 2020
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    The use of blast furnace cement is being promoted to reduce CO2 emissions during cement production, but in cold climates such as Hokkaido region there is a concern that initial strength of blast furnace cement may decrease by using air entrained agent (AE) for improving freeze-thaw resistance and scaling may occur. However, increase with air content decrease compressive strength, although it is possible to take measures by mixing a novel accelerator using a combination of a polyol and a sulfate and a new frost damage inhibitor for concrete such as oil type as a new method that is independent of air content, it has not been investigated whether the combined use of these agents suppresses the development of initial strength. Moreover, the effect of combined use of accelerator and a frost damage inhibitor on the reaction of blast furnace slag is not clear. Therefore, in this research, we clarified the mechanism of the strength development of the hardened blast furnace slag cement using the frost damage inhibitor and the accelerator together by performing a strength test and phase composition analysis by XRD Rietveld method and SEM observation. As a result, it was found that the C3S and C3A reaction rate increased by the accelerator, and the frost damage inhibitor did not inhibit the reaction.

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  • Kiyofumi KURMISAWA
    2019 Volume 73 Issue 1 Pages 111-117
    Published: March 31, 2020
    Released: March 31, 2020
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    In cold region such as Hokkaido, when placing concrete in winter, it is necessary to carry out appropriate curing. However, blast furnace slag cement concrete requires longer curing than ordinary Portland cement concrete. Therefore, in order to increase the use of blast furnace cement for concrete production, it is necessary to improve initial strength development. The purpose of this study is to clarify the influence of hardening accelerator on the reaction of blast furnace slag powder. In this study, we focused on hardened blast furnace slag and calcium hydroxide to clarify the influence of accelerators. As a result, it was clarified that the initial strength enhancement of the sample mixed with nitrite-type accelerator was high. Moreover, it confirmed that the nitrite type-AFm was produced as a hydrate in sample with nitrite-type accelerator. Also, it was shown from the results of phase equilibrium model calculation that the volume of the hydrate did not change significantly.

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  • Kento ONOMOTO, Koji TAKASU, Hidehiro KOYAMADA, Hiroki SUYAMA
    2019 Volume 73 Issue 1 Pages 118-125
    Published: March 31, 2020
    Released: March 31, 2020
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    Effective utilization of fly ash as a by-product of coal-fired power plant is an issue. However, as the quality of fly ash fluctuates depending on the coal source, quality stabilization is required. Therefore, we studied development of quality stabilization technology for improving the quality by flotation method, and developed the unburned carbon removing device. Influence on hydration reaction and pore structure when curing temperature was changed was verified by cement paste with modified fly ash. The early age compressive strength increased with higher curing temperature, and there was no influence of fly ash. At long-term age, curing at 40℃ was promoted by the pozzolanic reaction to the greatest extent. And, Compressive strength showed higher strength of cement paste with fly ash. The relationship between the cumulative temperature and the compressive strength is difficult to estimate and evaluate the compressive strength at the cumulative temperature as the temperature curing becomes 80℃. Regarding the reaction rate of C3S, the modified fly ash showed the same level of reaction as Japanese Industrial Standard fly ash classII. However, the hydration rate of C2S of the modified fly ash was lower than the hydration rate of non-modified fly ash. The amount of calcium hydroxide was higher as the curing temperature was higher, and there was a difference from that without fly ash. The higher the curing temperature, the more pozzolanic reaction progressed at early age. The relationship between C-S-H and compressive strength was confirmed to increase in compressive strength with increasing C-S-H in a single specimen. If the kind of fly ash and curing temperature are different, amount of C-S-H is different even at the same level of compressive strength, so we could not estimate the strength. In the range of pore diameter 0.03~0.3μm, specimens with curing temperature 5, 20 and 40℃ increased with progression of the age. Whereas in the specimen 80℃ the specimens decreased. The influence of the amount of un burned carbon in fly ash is small on the pore structure.

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  • Yosuke ITO, Shinji KAWABE, Yuta INOUE, Haruki TAGUCHI
    2019 Volume 73 Issue 1 Pages 126-132
    Published: March 31, 2020
    Released: March 31, 2020
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    An electromagnetic wave absorber is effective to prevent electromagnetic wave interference between electromagnetic wave utilizing devices in building spaces. Mortar in which a part of the aggregate is replaced with electric furnace oxidizing slag (hereinafter referred to as slag mortar) has electromagnetic wave absorption performance and can be manufactured inexpensively compared to the conventional electromagnetic wave absorbers. However, it is difficult to design electromagnetic wave absorbers using slag mortar, because an effect of the amount of electric furnace oxidizing slag substitution on electromagnetic wave absorption performance is not systematically studied. In this research, the mechanism of electromagnetic wave absorption is clarified from the effect of the amount of electric furnace oxidizing slag substitution on the complex relative permittivity and the complex relative permeability. And we found a design method for slag mortar absorbing the electromagnetic wave of any frequency by adjusting the amount of electric furnace oxidizing slag substitution and the thickness of mortar.

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  • Yotaro INOUE, Hisahiro MATSUNAGA, Katsunori TAKAHASHI
    2019 Volume 73 Issue 1 Pages 133-140
    Published: March 31, 2020
    Released: March 31, 2020
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    Reinforced iron and steel slag hydrated matrix, which is consisting mainly of steelmaking slag as aggregate and ground granulated blast furnace slag as binder, were exposed in tidal zone of sea area for almost 10 years and various properties of them were examined. The average compressive strength of iron and steel slag hydrated matrix after 10 years exposure was 30.5N/mm2, which is about 1.5 times as high as same sample after standard curing for 28 days. Pore size was small at deeper area from surface. The average neutralization depth was 2.0-2.2mm, and the neutralization rate coefficient was smaller than that of ordinary Portland cement concrete and slag cement concrete exposed in sea area for long period. The apparent Cl diffusion coefficient was 0.052-0.060cm2/year, which was smaller than that of slag cement concrete exposed in sea area for long period. The corrosion degree of rebar was 0.174 mdd, which was small value. It is considered that the high blending ratio of ground granulated blast furnace slag within binder of iron and steel slag hydrated matrix influences long-term improvement of strength and seawater resistance. Generation of Friedel’s salt, and condensation of SO3 were confirmed, that are also confirmed in ordinary Portland cement concrete and slag cement concrete exposed in sea area for long period.

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  • Daiki SHIMAZAKI, Taiichiro MORI, Yukio SASAGAWA, Etsuo SAKAI
    2019 Volume 73 Issue 1 Pages 141-147
    Published: March 31, 2020
    Released: March 31, 2020
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    Calcium aluminate cement based on calcium aluminate is superior in early strength, fire resistance and chemical resistance compared to Portland cement. On the other hand, it has been pointed out that the conversion of hydrated products decreases the strength of concrete associated with the curing temperature. This study aims at examining into durability of Calcium aluminate cement concrete by drilled core specimens at 50 years in various placing conditions to see characteristics in terms of compressive strength, tensile strength Poisson’s ratio, depth of carbonation, and hydration state related. The Calcium aluminate cement concrete without fly ash shows lower compressive strength development in course of time and decreases strength drastically when it is placed in winter. On the other hand, it is proved that the Calcium aluminate cement concrete added fly ash highly develops strength and retains durability. It is considered that by mixing the fly ash, stable strutringite was generated, and the conversion was suppressed.

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Testing and Evaluation of Concrete
  • Daisuke SAWAKI
    2019 Volume 73 Issue 1 Pages 148-154
    Published: March 31, 2020
    Released: March 31, 2020
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    A method to detect water absorption controlling material on mortar for setting wall tiles by TG-MS was researched. TG-MS was executed on two types of water absorption controlling materials respectively composed primarily of ethylene-vinyl acetate copolymer (EVA) and acrylate-styrene copolymer (ASt), and their thermal decomposition characteristics were evaluated. A component with m/z of=60, which was considered to be acetic acid, was formed by thermal decomposition of the EVA type material. A component with m/z of=104, which was considered to be styrene, was formed by thermal decomposition of the ASt type material. These two components were found to be the characteristic components of each water absorption controlling material. Mortar samples were prepared by coating these water absorption controlling materials on mortar, and powders collected from the surfaces of these mortars were subjected to TG-MS. In the case of the ASt type material, styrene was also detected and it was determined to be the key component for detection of ASt type water absorption controlling material on a mortar. In the case of the EVA type material, acetone as well as acetic acid were detected and these two components were determined to be the key components for detection of EVA type water absorption controlling material on mortar.

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  • Soju KANAMORI, Toshikatsu SEKI, Shigeki SEKO, Kazuo YAMADA
    2019 Volume 73 Issue 1 Pages 155-162
    Published: March 31, 2020
    Released: March 31, 2020
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    In this study, as a fundamental study on the applicability of the aerial ultrasonic wave method for evaluating the aged deterioration of concrete buildings, the accuracy of internal evaluation for the cracks and poor filling areas affecting the corrosion of reinforced steel bars and PC steel bars in the concrete buildings were examined. The following results were obtained in this study. By applying the aerial ultrasonic wave method proposed in this study, it was possible to evaluate the projected area of the cracks projected on the concrete surface, the filling defect area more than 4.5mm width around reinforced steel bar and the location of sheath tube. However, it was difficult to evaluate the angle of cracks, the location of reinforced steel bar and the filling defect area of grout in sheath tube regardless of the evaluating indexs.

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  • Masaya TAKEDA, Toshikatsu SAITO, Katsunori DEMURA
    2019 Volume 73 Issue 1 Pages 163-169
    Published: March 31, 2020
    Released: March 31, 2020
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    The purpose of this study is to investigate the applicability of New RC equation of Architectural Institute of Japan (AIJ) for estimating the static modulus of elasticity of the ordinary cement concrete to the porous concrete. The porous concretes using cement mortar as a binder and two types of coarse aggregates with different static modulus of elasticity are prepared with the percentage of the target voids of 10, 15, 20, 25 and 30%, water-cement ratios of 22.5, 25.0 and 30.0%. 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, 56 and 84d. As a result, the static modulus of elasticity of the porous concretes having same compressive strength at each age is slightly improved by prolonging the age. However, the New RC equation of AIJ for estimating the static modulus of elasticity of the ordinary cement concrete is applicable to estimating the static modulus of elasticity of the porous concrete.

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  • Shinya ITO, Akihiro HORI, Junya NAKAMURA, Takeshi IYODA
    2019 Volume 73 Issue 1 Pages 170-175
    Published: March 31, 2020
    Released: March 31, 2020
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    Physical properties and salt penetration behavior of concrete with chlorine immobilization material and expansive additive added were verified. It was confirmed that concrete to which chlorine immobilization material and expansive additive were added had no influence on mechanical properties compared with the case of no mixing. And when used in combination with an expansive additive, the expansion strain was introduced and it was confirmed that there was no effect on salt resistance if the expansion strain is within the proper range. As the penetration behavior of chloride ions, it was confirmed that penetration of chloride ions was suppressed by the addition of a chlorine immobilizing material in the immersion method similar to the natural state, but the penetration behavior was excessive in the accelerated test using electricity as a driving force. When converting from the effective diffusion coefficient by electrophoresis to the apparent diffusion coefficient, the necessity of newly setting the conversion coefficient was indicated in the material for chemically immobilizing ions such as the chlorine immobilizing material. In this paper, the relationship between the diffusion coefficient obtained by the apparent diffusion coefficient and electrophoresis in concrete using chlorine-immobilized material and expansive additive were examined, and shows the difference in the conversion coefficient as an example.

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  • Naoki SAKAKIBARA, Shota TOMIDUKA, Yasuhiro KODA, Ichiro IWAKI
    2019 Volume 73 Issue 1 Pages 176-183
    Published: March 31, 2020
    Released: March 31, 2020
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    In this study, we evaluated the quality and performance of fly ash concrete in which 20% mass of fly ash was used with regard to cement. In the mix proportion, mass of cement was stayed and fly ash was externally used as an admixture by replacing from aggregates. Fly ash used in this study was the coal ash which was classified as type Ⅳ fly ash, however a part of them has as good quality as type Ⅱ fly ash. As a result, it was confirmed that this fly ash can ensure the air entrainment of fly ash concrete without impairing fly ash concrete workability as a powder interpolating cement and fine aggregate. Based on this result, the quality range of fly ash controlled by type Ⅳ fly ash to be used was proposed for the practical application of ready-mixed concrete in the future. Furthermore, the applicability to actual cast-in-place prestressed concrete road bridge deck slab was examined. It was shown that the fly ash concrete having sufficient fresh concrete properties such as slump, air contents and bleeding ratio, and hardened properties such as design strength and required early stage compressive strength for introducing pre-stressing and having sufficient anti-chloride ingress performance and alkali silica reaction resistance can be produced.

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  • Yutaka IIZUKA, Motoyuki OKANO, Toshiya MORITA
    2019 Volume 73 Issue 1 Pages 184-191
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    With the objective of rationalizing the joint between precast membars, propose a restrained lap joint that has undergone a tensinle test with a focus on the lap length and pitch of the spiral reinforcement (the reinforcing bar ratio). Then, conducted bending and shear experiments on the members that had the joint fitted with the restrained lap joint. The results reverled that by setting the lap lengths of the main rebars with diameters of D25 and D13 to nine and eigth times that of the main bar diameter, resperctively, and a spiral-rebar reinforcing bar ratio of 6.2%, the connector exhibited performance similar that of an SD345 rebar joint. Further, it was revealed that the connected members that had a joint fitted with the connecter showed bending and shear performance equivalent to those of a monolithic members.

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Properties of Concrete
  • Yuya SAKAI, Shin-ichi UEHARA
    2019 Volume 73 Issue 1 Pages 192-199
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    Hardened cement paste is a brittle material but known to deform in a ductile manner under confining pressure. However, the mechanism involved in ductile deformation is not well understood. Classification of deformation mechanisms based on strain rate-differential stress relationships indicate that dislocation creep is a possible mechanism for ductile deformation but that the main hydrate of hardened cement paste is C-S-H, which is a gel material. In addition, dislocation cannot be defined in a gel material because dislocation represents a linear defect in a crystal material. In this study, scanning electron microscopy (SEM) observation and a stepwise creep test were conducted to understand the hydrates that govern the deformation of hardened cement paste under confining pressure. A sample prepared by mixing synthesized hydrates and commercial chemicals and compacting showed a different deformation behavior from that of the crushed and compacted cement paste sample. SEM observation of crushed and compacted cement paste revealed crystals of calcium hydroxide larger than 100μm. Compacts composed of cement paste powder with additional crushing or leaching of calcium with ammonium nitrate showed a different deformation behavior from that of cement paste. These results indicate that assembled calcium hydroxide plays a critical role in the deformation of cement paste under confining pressure and that the assemblage of calcium hydroxide was lost by additional crushing and leaching.

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  • Ryoichi ASHIZAWA, Toshiaki MIZOBUCHI, Hiroki IZUMI
    2019 Volume 73 Issue 1 Pages 200-207
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In the thermal stress analysis, the effect of creep is considered as an apparent instantaneous stiffness decrease using the effective Young’s modulus which is Young’s modulus multiplied by a reduction coefficient. However, the reduction coefficient is used same value regardless of the type of cement, the mix proportion of concrete, the temperature history, etc. In this study, the purpose is to evaluate the effect of concrete temperature on the reduction coefficient for Young’s modulus. We conducted experiment using thermal stress testing machine with temperature history as a factor, and obtained the reduction coefficient. As a result, it was confirmed that reduction coefficient for Young’s modulus shows different values depending on the temperature history. In addition, it was confirmed that the value was highly correlated with the rate of temperature rise, the maximum temperature, and the period of tensile stress.

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  • Shingo YOSHIMOTO, Tatsuo SHINMI, Hiroyoshi KATO, Takuya SEKI
    2019 Volume 73 Issue 1 Pages 208-213
    Published: March 31, 2020
    Released: March 31, 2020
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    Recently, global warming is a serious problem for environmental protection. In Japan, therefore, reduction of CO2 emission is an important task in any industries. It is demanded that approach to reduction of CO2 emission, Especially, in the large scale construction works. It is promoted to use blast furnace slag cement instead of ordinary portland cement because of a little amount of CO2 emission. However, there is a problem that blast furnace slag cement has lower initial strength than ordinary portland cement. This paper writes down of improvement method about initial strength development for blast furnace slag cement. In this study, we confirmed a strength property of the blended cement which mixed high early strength portland cement and blast furnace slag cement type B as initial strength improvement for blast furnace slag cement. As a result, we confirmed the water cement ratio of the blended cement that has the same compressive strength on 28days as ordinary portland cement. Furthermore, in the case of under 70% of mixing rates, initial strength development of blend cement which mixed high early strength portland cement and blast furnace slag cement type B is equal to or more than ordinary portland cement. In addition, reduction of CO2 emission effect was estimate by this test in comparison with ordinary portland cement, too.

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  • Ryota HASHIMOTO, Kozo ONOUE
    2019 Volume 73 Issue 1 Pages 214-221
    Published: March 31, 2020
    Released: March 31, 2020
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    Recently, highly durable concrete using blast-furnace slag sand (BFS) has been extensively studied in Japan. Since BFS has a latent hydraulicity under alkaline conditions, when it is used as a raw material of concrete, it is expected that cracks of concrete are healed due to precipitation of hydration products. In the present study, crack healing properties of mortar using BFS by re-curing are experimentally investigated. Using prism specimens of 40×40×160mm with a water flow hole of φ6mm in its center, water flow tests are conducted to evaluate the degree of crack healing. The re-curing methods are in water and in saturated calcium hydroxide solution. Test results show that incorporating BFS with re-curing in saturated calcium hydroxide solution results in better crack healing properties of mortar specimens.

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  • Kazuya HONDA, Akihisa NAKAUE, Nobuo UEHARA, Masaaki HASHIBA
    2019 Volume 73 Issue 1 Pages 222-228
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The appearance is necessary to concrete structure, and brightness of precast concrete products is important quality. Purpose of this study is to reduce the difference of the brightness between precast concrete products, and stabilization of precast concrete product brightness. We considered influence of accumulated temperature until mold-demolding and the exposure environment to brightness of precast concrete product. It was confirmed that the exposure environment has a big influence on the brightness pf precast concrete product. But, in the case of over 600℃・h accumulated temperature until mold-demolding, the brightness of precast concrete product stabilizes irrespective of influence of expose environment.

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Durability
  • Syunichi OSHIMA, Naohide OMIZO, Shinichi MIYAZATO, Daichi KUROIWA
    2019 Volume 73 Issue 1 Pages 229-236
    Published: March 31, 2020
    Released: March 31, 2020
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    In this study, a water permeability test, determination of neutralization depth by sulfuric acid and amount of sulfate ion penetration, and measurement of the Vickers hardness were performed using mortar impregnated with two kinds of silicate-based surface penetrants in order to evaluate the influence of silicate-based surface penetrants on sulfuric acid degradation. The shape of the mortar impregnated with the surface penetrants was maintained after sulfuric acid degradation. It was suggested that the use of the sodium silicate-based surface penetrants was suppressed the water permeability, the neutralization depth by the acid, and amounts of sulfate ion penetration because of suppression of surface porosity due to the remain of insoluble salts on the mortar surface after the sulfuric acid degradation. The sulfuric acid degradation at pH 2 in this study condition did not greatly affected the Vickers hardness of mortar. Therefore, it was considered that the modification effect by silicate-based surface penetrants was maintained after sulfuric acid degradation. As the results, it was suggested that the surface penetrants had the sufficiently modification effect on mortar even after the sulfuric acid degradation.

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  • Tomohiko IGATA, Kiyoshi MURAKAMI, Koji TAKEDA, Manabu MATSUDA
    2019 Volume 73 Issue 1 Pages 237-243
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    This study aimed to develop a precast concrete mix which is excellent in sulfuric acid resistance. The experimental factors were the type of binder and aggregate, the combination of materials, the substitution ratio of admixture, the ratio of sand binder to the ratio of water binder, and the sulfuric acid immersion test was performed with a mortar specimen. As a result, the influence of the fine aggregate on the sulfuric acid resistance was larger than that of the binder, and the waste molten slag, limestone crushed sand and blast furnace slag fine aggregate suppress the permeation of sulfuric acid to the inside. In addition, the influence of the water binder ratio on the sulfuric acid resistance is that in the use of washed sea sand and limestone crushed sand in the fine aggregate, as the water binder ratio is smaller, the surface layer part peels off and the penetration of sulfuric acid into the inside progresses. In the blast furnace slag fine aggregate use formulation, a dense film was formed on the surface layer, and the penetration of sulfuric acid into the interior was suppressed as the water-bonding material ratio was smaller.

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  • Yuto TANAKADATE, Shunsuke HANEHARA
    2019 Volume 73 Issue 1 Pages 244-250
    Published: March 31, 2020
    Released: March 31, 2020
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    In recent year, concrete deterioration of surface due to scaling has been becoming heavier with increase of scattering amount of deicer in road structure. According to the previous researches which reported about characteristic of salt scaling, it is suggested that the freezing and thawing process of deicer solution on the concrete surface affects salt scaling. In order to elucidate the effect of the freezing and thawing process of the deicer solution on the scaling, we conducted repeated tests of temperature drop and temperature rise in various temperature ranges from -30 to -5 degrees centigrade below the freezing point of deicer solutions. The deicer solution was an aqueous solution of NaCl, KCl, CH3COONa and CH3COOK in this study. The results obtained that temperature range at which scaling occurs differs depending on the kind of deicer solution. In all deicer solutions, the temperature range at which scaling occurs is between the freezing point and the eutectic point of each deicer solutions. In this temperature range, deicer solution state is a mixture of pure ice and high-concentration deicer solution. On the other hand, scaling did not occur below the eutectic point of deicer solution, at which deicer solution state is a mixture of pure ice and crystal of deicer. Therefore, scaling occurs due to the phenomenon that part of high-concentration deicer solution freezes and thaws with temperature changing.

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  • Masahiro MIYAZONO, Toshiharu KISHI
    2019 Volume 73 Issue 1 Pages 251-258
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The mortar and concrete specimens given repetition dry-wet cycles were evaluated pore structure obtained through the MIP method and freeze-thaw resistance according to JIS A 1148. As a result, it was confirmed that the pore structure of the mortar and concrete specimen given repetition of dry-wet cycles increased the ratio of continuative pore volume. In addition, the specimens given repetition of dry-wet cycles before the test of JIS A 1148 was occurred surface deterioration more remarkably than the specimens which were given water curing or accelerated drying before the test of JIS A 1148. But, it was confirmed that the change of pore structure was reduced despite repetition of dry-wet cycles in case of carbonation curing or using admixture such as blast furnace slag or silica fume. also the surface deterioration for the test of JIS A 1148 was reduced.

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  • Tomohiko IGATA, Toshio URANO, Manabu MATSUDA, Kiyoshi MURAKAMI
    2019 Volume 73 Issue 1 Pages 259-265
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In the previous research, the authors clarified that blending using fly ash or ground granulated blast-furnace slag as an additive improves salinity permeation resistance compared to blending ordinary plain portland cement. In this report, with the aim of further improving salt resistance performance, special inorganic fine powders expected for high strength and high durability of concrete are used in combination with the preparation of the previous report, and salt penetration resistance is compared and evaluated. As a result, fixation of salt content was promoted by the use of the special inorganic fine powder, the apparent diffusion coefficient of chloride ions was lowered, and the improvement of salt resistance performance by the special inorganic fine powder was recognized.

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  • Masato SAITO, Takehiro SAWAMOTO, Koichiro SHITAMA, Masanori HIGUCHI
    2019 Volume 73 Issue 1 Pages 266-271
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The properties of concrete surface which influence the durability of concrete structures will be greatly affected on mix proportions and curing conditions. In this study, the effects of nominal strength, type of cement, demolding timing and curing method on air permeability of concrete were investigated. As a result, curing method supplying water from outside of the concrete was most effective to do the coefficient of air permeability small in case of the normal portland cement. Curing method which didn’t make water dry from the concrete surface was effective to do the coefficient of air permeability small in case of the portland-blast furnace slag cement typeB. And then appropriate curing was effective for air permeability small than increase of concrete strength. Therefore, there was no clear correlation between the coefficient of air permeability and the concrete strength. However, there was correlation between the coefficient of air permeability and the sound speed of concrete surface. The coefficient of air permeability tended to be small that the sound speed of concrete surface became speedy. And the coefficient of air permeability tended to be small that the water content of concrete became high.

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  • Masumi INOUE, Heesup CHOI, Kunihiko HIRONO, Masanobu SUGIMOTO
    2019 Volume 73 Issue 1 Pages 272-278
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In this study, the authors aim to clarify the applicability of Al-Mg ally spraying rebar to reinforcement for concrete member. Corrosion resistance and bond properties of Al-Mg ally spraying rebar in concrete were examined. As a result, the corrosion resistance of Al-Mg spraying rebar in concrete depends on the type and quantity of sealing treatment. This experiment demonstrated that Al-Mg alloy spraying rebar using a predetermined amount of epoxy coating as a sealing treatment has a good corrosion resistance when chloride content around the reinforcing bar is high. And in the pull-out test, it was confirmed that Al-Mg alloy spraying rebar using epoxy coating has a good bond strength in concrete.

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  • Ichiro KURODA, Toshiyuki HORIGUCHI
    2019 Volume 73 Issue 1 Pages 279-286
    Published: March 31, 2020
    Released: March 31, 2020
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    Collision of rock pellets mixed in waterflows causes surface damage to concrete of the dams and the soil saving dams, and causes problems on the maintenance of these structures. Some experimental researches had been tried to grasp this phenomena up to now, but shapes of the rock pellets have not been considered in these past researches using with only ball shaped drop weights in the repeat collision tests. In this paper, repeat collison tests using with drop weights shaped in polyhedron with vertexes are carried out to estimate the effects of vertexes of rock pellets on the surface damages of the concrete by the impact loading. The cuboctahedron which is one kind of polyhedron with regular polygons is employed to shape the drop weights with vertexes to compare with the ball shaped drop weights. Ratio of loss volume per the kinetic energy increased by the vertexes of drop weight are discussed from the experimental results. In addition, effects of the drop weight mass and the dropweight height are discussed from a view point of the relationship between the loss volume on concrete surface and the kinetic energy of drop weights.

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  • Masahiko KISHIDA, Takumi MAEDA, Ichiro IWAKI, Toshiharu KISHI
    2019 Volume 73 Issue 1 Pages 287-294
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The internal voids of lightweight aggregate used for lightweight concrete slab are filled with water by the pre-soaking. Therefore, the frost damage resistance of the lightweight concrete slab is inferior compared to the concrete slab consist of generic aggregate. In order to examine the applicability of the lightweight concrete to cold regions, it was carried out freeze-thaw test in different concrete mix design of water-binder ratio. As a result, in the lightweight concrete type-2, it was not observed improvement in frost damage resistance due to an increase in air content of concrete. In case of the mix design for the cast-in-place concrete which of water-binder ratio is 37%, it was confirmed that the frost resistance of the concrete is improved due to eliminate moisture which is a factor in freezing expansion and reducing the saturation of aggregates by using both lightweight coarse aggregate and lightweight fine aggregate with low moisture containing state. On the other hand, in case of the mix design for the pre-cast concrete which of water-binder ratio is 25.5%, it was possible to secure the frost resistance by applying coarse aggregate with low moisture containing state. This was because the moisture content of lightweight fine aggregate is lowered due to supply the moisture inside lightweight fine aggregate to cement paste side.

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  • Akitaka KIUCHI, Tadashi ABE, Toshiaki SAWANO
    2019 Volume 73 Issue 1 Pages 295-302
    Published: March 31, 2020
    Released: March 31, 2020
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    This study is an experiment study about the dynamic influence in the load fluctuation to occur when a large vehicle passes an expansion joint. We were carried out wheel running fatigue tests by constant load and the vibration load using the RC slab test specimen. The experiment evaluated a fatigue resistance and an experiment impact coefficient. As a result, the fatigue life of vibration load applied load amplitude ±20% or ±30% of RC slab specimen was reduced by 60% or 90% compared to the fatigue life of RC slab specimen applied constant load. In addition, the experiment impact coefficient was far exceeding the impact coefficient specified of Specifications for highway bridges. It is thought that it is necessary to suppress deflection by increasing bending stiffness of RC slab near expansion joint and maintain expansion joint’s level difference according to fatigue life required by RC slab.

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  • Ryo KISHIRA, Takuya MAESHIMA, Yasuhiro KODA, Ichiro IWAKI
    2019 Volume 73 Issue 1 Pages 303-310
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In this study, alkali-silica reaction (ASR) deterioration in the RC road bridge deck under real environment was investigated experimentally. By constructing a full-scale RC deck on the steel main girder and exposing it outdoors, the environmental effects and the restraint by the main girder in the actual bridge were reproduced, and various measurements were carried out in the long term. As a result, the expansion amount had a periodic fluctuation due to the temperature dependence of ASR in the real environment, and the expansion start temperature tended to decrease as the deterioration progress. The occurrence of ASR gel and its composition were confirmed by polarization microscopy and SEM-EDS analysis. Furthermore, it was revealed that the various non-destructive tests were useful in evaluating the ASR deterioration on RC road bridge deck.

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Fiber Reinforced Concrete
  • Shintaro MORISHIMA, Makoto YAMAGUCHI, Soshiro SHIBUYA, Shinji KANEYASU
    2019 Volume 73 Issue 1 Pages 311-317
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The objective of this study was to investigate the possibility of improving the mechanical performance of SIFCON. Experimental investigations were conducted regarding the influences of various fiber types, 5 types of steel fiber and 4 types of synthetic fiber, on the fundamental mechanical properties of SIFCON. As a result, in case of SIFCON using steel fibers, the longer fibers length and the higher fiber volume fraction used, the higher flexural strength and toughness derived. In particular, high flexural strength of more than 70MPa was confirmed when used the ends-hooked steel fiber (diameter×length:0.9×0.6mm) with one hook bent at four points. Also, the influence of the ends hook shape on the flexural properties of SIFCON was small compared to the above two factors. Although the flexural strength and toughness of SIFCON with synthetic fibers were lower than that with steel fibers, it was confirmed that the flexural load bearing capacity of them increased up to relatively large deformation.

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  • Kiyoshi MURAKAMI, Koji TAKEDA, Ayumi SATOH, Toshio URANO
    2019 Volume 73 Issue 1 Pages 318-324
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In this study for the purpose of calculating the ultimate strength in flexure of RC beams with SFRC, a method for replacing the tensile stress distribution in the cross section with an equivalent stress block was proposed considering the scale effect of the tensile softening curve of SFRC, and the application validity of this method was examined by the flexural testing result of the beam specimen. As a result, it was confirmed that a good correspondence was obtained between the experimental and analytical results as for the ultimate strength of the specimens.

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Repair and Strengthening
  • Soshiro SHIBUYA, Makoto YAMAGUCHI, Shintaro MORISHIMA, Mitsuhiro SHIGE ...
    2019 Volume 73 Issue 1 Pages 325-332
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The objective of this study was to develop a repairing technology for severely damaged reinforced concrete (RC) members. Therefore, crack injection repair with ultra-low viscosity epoxy resin was performed on RC beams in which tensile rebars yielded, and changes in flexural performance of RC beams due to repair was examined. Further, the temporal change in flexural performance of repaired RC beams under accelerated corrosive environment was also investigated. The results showed that it is possible to recover the flexural performance of the RC beams in which tensile rebars yielded to a level equal to that of the undamaged RC beams by applying this repairing method. The change in flexural performance of the repaired RC beams under the accelerated corrosive environment was similar to that of the undamaged RC beams, so that a good durability of repairing effect was confirmed.

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  • Takuya KONDO, Shin-ichi MIYAZATO, Hideki NISHINO, Katsunori YOKOI
    2019 Volume 73 Issue 1 Pages 333-339
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    The hardened cement in which the silicate type surface penetrants has reacted increases the strength of the area. A method of estimating the reforming depth using the Vickers hardness test has been proposed using this property. In this paper, the Vickers hardness test was carried out in the depth direction from the mortar surface, with the variation of water cement ration and the amount of penetrants related to the reaction of the silicate type surface penetrants as the test factor. And we examined the tendency. In mortars with high water cement ratio, the increase in Vickers hardness was small. And the tendency for the effect to become small was shown. Also, as the amount of penetrants increased, the reforming depth increased. However, the reforming depth of the mortar tended to be influenced by the density of the mortar. In addition, no clear increase in Vickers hardness was observed depending on the amount of the silicate type surface penetrants. This is considered to be due to the limited pore diameter reformed by the application of the silicate type surface penetrants. It is considered that the silicate type surface penetrants penetrates into the mortar while penetrating into the large void and causing a reaction in the small void.

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  • Norihiko KURIHARA, Takuya YOSHIDA, Taichi ENOMOTO, Satoru KOGA
    2019 Volume 73 Issue 1 Pages 340-347
    Published: March 31, 2020
    Released: March 31, 2020
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    In this study, bond and shear properties of bond surface jointed by chemical roughening method were investigated. As a result, the bond strength of the rough surface made by the chemical roughening method exceeded the NEXCO standard value of 1.5N/mm2. In addition, if the substrate material was ordinary concrete, the shear strength of the chemically rough surface was greater than that of the blasted surface. When evaluating the bond strength and shear strength of the bond surface, it was more accurate to use Rz JIS and Spc.

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  • Shohei UEMURA, Kiyoshi MURAKAMI, Ayumi SATOH, Seiichiro YAMAUCHI
    2019 Volume 73 Issue 1 Pages 348-354
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    In this study, in order to develop a CFRP rod/mesh embedded section thickening method for RC beams, we experimentally examined the bending/shear reinforcement effect of RC beams with CFRP rods/mesh. As a result, In the case of RC beams with bending and shear reinforcement by CFRP rod and mesh thickening, it was confirmed experimentally that a large increase in yield strength was obtained compared to ordinary RC beams. Moreover, as a result of examining by three-dimensional finite element analysis, the analysis result was able to reproduce the bending property of the experimental result. Furthermore, it was found from the analysis results that the adhesion constitutive law of CFRP rods greatly affects the increase and decrease of bending resistance of RC beams.

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  • Hirotaka NAKAJIMA, Tadashi ABE, Hiroyuki NOGUCHI, Keisuke SHIOTA
    2019 Volume 73 Issue 1 Pages 355-362
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    Two kinds of metal grid (expanded type and square cut type) has been developed as an alternative reinforcement bar used for steel fiber reinforced concrete (SFRC) upper surface thickness increased method of RC slab. We proposed upper SFRC surface thickness increased method using 2 kind of metal grid in combination with adhesive. In this study, the proposed method evaluated the fatigue durability of RC slab by the fatigue test under running wheel load. As result, the proposed method was controlled an increase of deflection and improves fatigue durability. In addition, reinforcement method with joint structure in thickness layer was having equivalent strengthen effect as the reinforcement method without joint structure. The joint structure was not a structural weakness point in this experiment. The reinforcement method with joint structure was improved fatigue durability of RC slab. Therefore, SFRC upper surface thickening reinforcement method can be arranged Metal-Grid within a thickness of 60mm, which is a pratical reinforcement method.

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Environment and Recycling
  • Yoshitaka IGAWA, Tsuyoshi SAITO, Kazuho SUZUKI, Yoshifumi HOSOKAWA
    2019 Volume 73 Issue 1 Pages 363-370
    Published: March 31, 2020
    Released: March 31, 2020
    JOURNALS FREE ACCESS

    This study focuses on highly reactive β-C2S and amorphous C-S-H with high CaO/SiO2 molar ratio(i.e. C/S ratio). Previous research suggests that highly reactive β-C2S have unique mechanisms of hydration due to its extremely large specific surface area. Following these suggestions, we examined hydration properties of β-C2S with high specific surface area and atomic-leveled homogeneity. This outstanding β-C2S were synthesized from unique technique based on “Complex polymerization method”. By using this, we succeeded to obtain highly reactive β-C2S even if initial C/S is below 2.0. Furthermore, amorphous C-S-H with high C/S ratio came out as a hydration product with almost no CH when C/S is above 1.5, which suggested regeneration cycle can be applied to concrete. Under other conditions, single-phased amorphous C-S-H with high C/S ratio were generated without CH. We concluded this C-S-H was consist mainly of fully hydrated CaOH ion-pairs, due to high pH value of aqueous phase.

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