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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from publisher, newspaper, foundation, etc.  Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.conbuildmat.2024.135655

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

DOI： https://doi.org/10.14250/cement.77.44

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

DOI： https://doi.org/10.14250/cement.77.222

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

DOI： https://doi.org/10.14250/cement.77.62

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

<p>In this paper, ¹H-NMR Relaxometry is applied to carbonation phase and analyzes changes of chemically bound water content, mobile water content, and total water content in hardened cement paste with the progress of carbonation. The results showed that calcium hydroxide and C-S-H were carbonated at 20℃ and 85％RH. From the measurement of transverse relaxation time T₂ by CPMG method, it was confirmed that the transverse relaxation time of Interlayer and Gel pore increased with carbonation. There was a positive correlation between carbonation degree of calcium hydroxide calculated by thermogravimetric/differential thermal analysis and decreasing of chemically bound water measured by Solid echo method, confirming that chemically bound water in calcium hydroxide changed to mobile water due to carbonation. Regarding mobile water, the water content of Gel pore increased and that of Interlayer decreased in C-S-H during the initial stage of carbonation.</p>

DOI： 10.14250/cement.77.44

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

<p>In order to visualize liquid water movement in concrete, changes in the state of concrete when water is immersed on one surface against concrete in a dry state were visualized using a digital image correlation method that can detect minute deformations on the surface of the object. By obtaining the change over time of the principal strain distribution from the amount of deformation, deformations showing drying shrinkage and swelling caused by liquid water penetration in the cement paste section were visualized. Deviations from the linear relationship between water absorption and depth of penetration and the square root of time, indicating liquid water penetration into cementitious materials, were confirmed, indirectly indicating that water movement causes water absorption and swelling of the cement paste, even in concrete aggregate scale analysis.</p>

DOI： 10.14250/cement.77.222

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

<p>In this study, we focused on the structural changes and phase composition of Calcium aluminate silicate hydrate （C-A-S-H） before and after carbonation to confirm its transformation by carbonation in the medium humidity range and its subsequent change after contact with liquid water. Based on the results of NMR, SEM-EDS analysis, and liquid phase composition analysis of the synthesized C-A-S-H, the structure was identified from the Ca/Si, Al/Si, H/Si, and Na/Si ratios and a schematic model was presented. After carbonation, the formation of vaterite, calcite, and aluminosilicate gel were confirmed. Unlike synthetic vaterite, vaterite of carbonated sample did not undergo a phase transition at 450℃. Thermogravimetric analysis demonstrated that carbonated sample’s vaterite undergoes a phase transition at 450-600℃. The vaterite underwent a phase change after immersion in the liquid phase and was confirmed to be all calcite. The aluminosilicate gel was found to have compositions of Al/Si＝0.16, Ca/Si＝0.09, and Na/Si＝0.09.</p>

DOI： 10.14250/cement.77.62

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nucengdes.2023.112602

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Building Engineering  

Expansive additives have been used in concrete to compensate for shrinkage and to induce chemical pre-stress. The cement paste incurs internal expansive stress owing to the formation of confined portlandite and ettringite crystals in the pore network, resulting in expansion at the macroscale. In this study, a poromechanical model was designed to model the expansion of cement paste and concrete due to the formation of such expansive hydrates. The effective expansive stress on the cement paste was calculated considering the volume of the hydrates derived from the hydration model and tangent poroelastic properties estimated using a micromechanical scheme. Experiments were performed to measure the expansion of the cement paste and concrete with different amounts of expansive additives under stress-free and restraint conditions. The model predictions were compared with the experimentally measured expansion, which confirmed the rationality of the model for estimating free expansion. Finally, the extension of the current modeling framework to estimate the restrained expansion of concrete is deliberated. The proposed multiscale model can be employed by the engineers to estimate the expansion of cement paste and concrete with EA and provide insights to estimate the amount of EA required for a given application.

DOI： 10.1016/j.jobe.2023.107554

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Concrete Institute  

<p>This paper reviews numerical studies on the effect of expansion and damage due to alkali-silica reaction (ASR) on the mechanical performance of concrete and reinforced concrete at the structural scale level. Previous research on model development that has focused on the performance of RC members or structures is collected and summarized based on how they operationalize expansion progress. The models can be divided into three categories: models that receive the target expansion amount as an input value, models that use expansion curves, and models that calculate the increase in free expansion by considering the kinetic process of ASR. The aim of the model development can be related to either the deformation of the member or the load capacity for static or dynamic load actions. Expansion transfer under confined conditions is characteristic of the ASR problem, and the methods to model expansion transfer are accordingly summarized. Various considerations concerning the effect of ASR expansion and associated damage on the concrete constitutive laws are also studied. Expansion transfer under multi-axial stress states can be accurately reproduced by the modeling of expansion redistribution and volumetric expansion reduction under stress conditions. There are diverse methods to model the resultant deterioration of mechanical properties, but the primary method is by reducing the strength and elastic modulus according to empirically determined relationships. The ideal modeling approach is still under discussion because the effect of the anisotropic cracking state on the anisotropic mechanical response still requires further study. Finally, current problems of assessment of ASR-damaged concrete structures were discussed, and the significance of the causal correlation between macroscopic expansion behavior and microscale factors was suggested.</p>

DOI： 10.3151/jact.21.655

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Expansion of concrete due to expansive additives (EAs) is greatly affected by the degree of external restraints in the form of reinforcements and supports. Furthermore, the presence of anisotropic restraints influences concrete expansion in different directions. In this study, a chemo-mechanical model was developed to estimate concrete expansion under the framework of poromechanics. The volume of expansive hydrates was obtained from the hydration model, which was used for estimating the stress on the cement paste using poromechanical formulations. An external non-isotropic state of stress affects the orientation of crystal precipitating inside the pores of the cement paste. Thus, anisotropy in concrete expansion due to external stress was considered by maintaining the chemo-mechanical equilibrium of crystals of expansive hydrates, which was reflected in the poro-elastic constants utilized to estimate the stress at the cement paste scale. Poroelastic coefficients were estimated using a micromechanical scheme reflecting the effect of crystal orientation. Dedicated experiments were performed to comprehend the anisotropic expansion of concrete under anisotropic external restraint conditions. Finally, the applicability of the model was verified by comparing the expansion in different directions estimated from the model and experiments performed in this study with available literature data. Thus, the developed chemo-mechanical model could benefit practitioners and engineers in evaluating the expansion behavior of restrained concrete for a given application.

DOI： 10.1016/j.cemconcomp.2023.105126

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

DOI： 10.14250/cement.76.238

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

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Expansive additives in higher dosages induce chemical prestress in concrete by imparting higher early-age expansion. However, induced stress and concrete expansion can vary significantly, depending on different restraint conditions. In addition, concrete expansion can be highly anisotropic depending on the nature of external restraints and boundary conditions. Experimentations have been performed to study the effect of uniaxial (anisotropic) restraint on the concrete expansion (in both restraint and stress-free directions) and induced prestress. A higher degree of restraint resulted in a substantial decrement in the longitudinal expansion. In contrast, expansion in the stress-free (lateral) direction was not much affected by the restraint in other direction. As a result, an overall decrement in the volumetric expansion was observed with an increase in the reinforcement ratios. Stress induced in concrete due to the restraint expansion in the longitudinal direction was found to be higher for a higher reinforcement ratio. Data provided from the current work can be used for the comprehensive modelling of expansive concrete under external restraints.

DOI： 10.1016/j.conbuildmat.2022.129330

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pergamon-elsevier science ltd  

This study aimed to develop a numerical method to evaluate thermal cracking, in terms of pa-rameters such as thermal crack width and crack spacing, on massive reinforced concrete (RC) wall structures externally restrained by a base structure. The existing experimental study was inves-tigated using the rigid body-spring model (RBSM) with new constitutive laws developed for this objective. Thermal cracks, which localized and propagated throughout the wall thickness, were successfully reproduced, and the good agreement with the experiment indicated the capability of the proposed numerical method. The time-dependent cracking behavior and the impacts of fac-tors affecting thermal cracking, which are difficult to investigate experimentally, are discussed.

DOI： 10.1016/j.engfracmech.2022.108800

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pergamon-elsevier science ltd  

The drying process of pure C3S paste with a water to binder ratio of 0.55 under different relative humidity conditions was monitored using proton nuclear magnetic resonance relaxometry. The desorption isotherm of the interlayer water was obtained experimentally. The relationship between the interlayer water content and T-2 value of the interlayer water defines the surface relaxation time, which provides quantitative data regarding the adsorbed water. According to the fast exchange model, the surface area at the sealed condition was 630 m(2)/g-calcium silicate hydrate (C-S-H), and it decreased during drying, which was associated with an increase in chemically bound water. The ratio of the decrease in the interlayer surface area to the increase in chemically bound water was 5400 m(2)/g. Based on this value, the total surface area of C-S-H was calculated to 830 to 921 m(2)/g-C-S-H.

DOI： 10.1016/j.cemconres.2022.106762

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

There has been a recent trend in Japan toward using precast segments to reduce the burden on construction sites and improve productivity. In large-scale precast segment structures such as bridges, the deformation of precast segments must be controlled during yard storage. This paper uses the multi-scale integrated chemo-hygric computational system (DuCOM-COM3) developed and extended by our group to numerically evaluate dimensional stability during yard storage of precast concrete with fly ash for a large-scale precast segmental bridge. To demonstrate the sensitivity to deformation behavior, simulations are conducted under three hypothetical cases of outdoor air temperature, outdoor air humidity, and temperature at the top surface of the segment, including the harsh temperature conditions expected in the Shikoku region. In the sensitivity analysis using the climatic conditions obtained from the field monitoring data as input, the reproducibility of the surface temperature and shrinkage of the concrete segment is improved by introducing the absorption of shortwave radiation by solar radiation on the segment top surface as an input parameter in the simulation.

DOI： 10.3151/jact.20.200

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Concrete Institute  

For safe disposal of the large volume of concrete waste generated during the decommissioning of the Fukushima Daiichi Nuclear Power Station (F1NPS), the state of Cs and Sr contamination in concrete waste must ideally be estimated in advance during waste disposal planning Cs and Sr are primarily adsorbed by calcium silicate hydrate (C-S-H) in cementitious materials. However, the amount of adsorption varies greatly with the Ca/Si mole ratio (C/S ratio) of C-S-H and with the presence or absence of coexisting elements, both of which vary according to interactions with the environment. This study attempted to model on the results of experiments on Cs and Sr adsorption by synthetic C-S-H with varying C/S ratios. Furthermore, for verifying whether the model can be applied to F1NPS, the results calculated by the model were compared with the experimental results for Cs and Sr adsorption on cement paste subjected to environmental conditions (carbonation, leaching, and presence or absence of coexisting elements (Na, K)). It was confirmed that the present model is overall able to reproduce Cs and Sr adsorption behavior on cement paste, considering changes due to environmental conditions.

DOI： 10.3151/jact.19.1061

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN CONCRETE INST  

Decommissioning of the Fukushima Daiichi Nuclear Power Station (F1NPS) in a proper manner requires assessment of the contamination levels and mechanisms for contamination in the concrete structures. Between January 2018 and March 2020, Japan's Ministry of Education Ministry of Education, Culture, Sports, Science and Technology (MEXT) conducted a project called "The Analysis of Radionuclide Contamination Mechanisms of Concrete and the Estimation of Contamination Distribution at the Fukushima Daiichi Nuclear Power Station". In this review, we outline the results of this study. The experimental results from the first project indicate that concrete carbonation, Ca leaching, and drying conditions affected the adsorption behaviors of Cs and Sr and therefore, their penetration depths. Additionally, the studies showed that a-nuclides precipitated on the surface of the samples because concrete causes a high pH. A reaction transport model was developed to assess further the adsorption characteristics of Cs and Sr in carbonated cement paste and on concrete aggregates. The model used real concrete characteristics from the materials used at F1NPS and historical boundary conditions at the site, including radionuclide concentrations and penetration profiles within the turbine pit wall. Capillary water suction resulting from dried concrete was evaluated by considering structural changes in cement hydrates using X-ray CR and H-1-NMR relaxometry.

DOI： 10.3151/jact.19.950

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The role of a shrinkage reducing agent (SRA) in the hardened cement paste during a first desorption process was investigated by measuring the small-angle X-ray scattering (SAXS). Fractal disc analysis and Guinier approximation were adopted to interpret the SAXS profiles. We experimentally confirmed that the presence of SRA molecules mitigated the piling of calcium-silicate hydrate (C-S-H) sheets, which could be monitored by the increase in the thickness of the disc, representing the agglomeration of C-S-H sheets. In addition, the basal spacing of C-S-H did not change during the drying. By contrast, the diameter of the discs monotonically decreased and showed a similar trend to that of samples lacking SRA. Based on these findings, we concluded that SRA molecules were on the surface of the C-S-H sheets and mitigated the piling, facilitating water removal from the C-S-H agglomeration in the RH range of 80-40%.

DOI： 10.1016/j.cemconres.2021.106429

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan concrete inst  

To decommission of the Fukushima-Daiichi nuclear power plant after the reactor accident, it is important to estimate the distribution of radionuclide contamination in the concrete for key elements such as Cs and Sr. A reaction transport model will be developed for these calculations. However, for a realistic model, the behaviors of Cs and Sr penetration in concrete must be experimentally investigated. A part of the results of a MEXT project called "The Analysis of Radionuclide Contamination Mechanisms of Concrete and the Estimation of Contamination Distribution at the Fukushima Daiichi Nuclear Power Station" are presented in this technical report. From our penetration analyses, the behaviors of neither Cs nor Sr were affected by each other. Additionally, the apparent diffusion coefficients of Cs and Sr were not significantly affected by the concentration or the presence of clay in the mortars. The penetration depth of Sr was smaller than that of Cs, and fly ash blended cement increased the resistance to penetration compared with ordinary Portland cement. Carbonation in the mortar samples increased the adsorption of Cs especially. Sr interacted with cement hydrates more than with clays. In oven-dried mortars, under the condition of water suction, the presence of clay retarded Cs penetration but had no effect on Sr. When the mortars were carbonated and oven-dried, the interactions between the solid phase and Cs or Sr took hours at least to complete.

DOI： 10.3151/jact.19.756

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Language：English   Publishing type：Part of collection (book)   Publisher：CRC Press  

Japan Nuclear Energy Safety Organization (JNES) has published an aggregate test method so-called as JNES flow (the method mainly composed of international methods RILEM AAR 3 and RILEM AAR 4) and alkali-silica reaction (ASR) diagnosis method. In this research, we conducted the RILEM methods using Japanese aggregates, which were international aggregate test methods that were considered to be highly reliable. Especially, we evaluated the suitability of various RILEM aggregate testing methods for Japanese aggregates with regard to methods for detecting reactivity of late expansive aggregates, which have been reported in recent years. Furthermore, for the ASR diagnostic method that emphasizes the petrological evaluation test after collecting concrete cores samples, various test specimens with different stages of deterioration were produced, and the core appearance observation and polarization microscope observation were performed on the collected core samples. We also conducted observations using a film scanner and evaluated the applicability of the proposed ASR diagnostic method to Japanese aggregates. Based on the above, an example of the alkali aggregate reaction test flow of concrete structures effective for reactive aggregates were proposed through comparison among various domestic and international aggregate test methods. Furthermore, an example of the alkali aggregate reaction diagnosis flow of concrete structures was proposed by conducting tests with several methods using cores which were sampled from the concrete specimens and the concrete structures.

DOI： 10.1201/9780429279119-362

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN CONCRETE INST  

This experimental and numerical study aims to evaluate the penetration depth of contaminated water in the concrete structures involved in the Fukushima Daiichi nuclear powerplant. The influence of the mortar mixture on water absorption was investigated by varying the composition: mortars containing aggregates from river sand and crushed limestone sand were compared, and 15% of the cement in the mixture was substituted with fly ash. The effect of temperature in nuclear conditions is also significant; therefore, water uptake at temperatures of 20 and 60 degrees C was considered. Finally, pre-drying conditions were studied by drying the sample at two different conditions: at 105 degrees C and at 40% RH (relative humidity) and 20 degrees C. Water uptake was monitored using x-ray computed radiography in combination with mass measurements. In all cases, anomalous sorption, or a nonlinear relationship between penetration depth and the square root of exposure time was observed, with the sorption curves showing bimodal behavior. The aggregate type had no significant effect on the water uptake results. However, the samples containing fly ash clearly had lower water uptake rates, which can be explained by the differences in the calcium silicate hydrate (C-S-H) structures. With increasing temperature, the penetration was slightly accelerated at the beginning of the experiment, with the rate of penetration then decreasing rapidly. The densification of C-S-H at higher temperatures could contribute to this phenomenon. Microstructural rearrangements can also explain why the highest uptake rates occurred for samples that were exposed to severe drying conditions (105 degrees C). The experimental results were consistent when the microstructural rearrangement was considered, further confirming these conclusions.

DOI： 10.3151/jact.19.168

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

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This study aims to develop an analytical tool to predict the expansion of Hauyne and free-lime based expansive additives in RC structures. Hydration of species was based on the multi-component heat of hydration model which incorporates referential heat rate at a certain temperature and thermal activities following Arrhenius' law of chemical reaction. All other time-dependent properties of concrete such as elastic modulus, temperature, pore pressure, creep, moisture status, total porosity of interlayer, gel and capillary pores are computed internally based on the micromodels of materials inside the system. Coupling this material information with poromechanics, volumetric change generated by cement hydration and shrinkage is systematically included in the modelling of concrete mechanics, which deals with macroscopic structural responses based on the space-averaged constitutive laws on the fixed four-way cracked concrete model. Finally, the models are then verified with experimental results that could prove the models’ capability in predicting the amount of expansion under various replacement ratios.

DOI： 10.1007/978-3-030-72921-9_18

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN CONCRETE INST  

During sorption, the microstructural evolutions of two different cement pastes (with water-to-cement ratios of 0.40 and 0.55) are studied via proton-nuclear-magnetic-resonance relaxometry. The water uptake test is performed for samples dried at 105 degrees C under three different temperatures of 20 degrees C, 40 degrees C, and 60 degrees C for the first twenty-six days of sorption. It is observed that the water went first to the larger pores before migrating to the finest ones. This behavior is accelerated with increasing temperature. The rate of water exchange between fine and large pores is estimated and found to increase with temperature for both studied mixtures. The activation energy corresponding to this water movement is calculated and found to be higher for the lowest water-to-cement ratio, owing its finer microstructure. Finally, the activation energy related to the local water transport in re-distribution from large pores to fine pores is calculated and found to be inferior to the experimental results, which can be explained by the dynamic microstructure not being considered in the classical theories.

DOI： 10.3151/jact.18.588

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Ultra-High Performance Fibre-Reinforced Cementitious Composites (UHP-FRCC) show excellent mechanical performances in terms of strength, ductility, and durability. Therefore, these cementitious materials have been successfully used for repairing, strengthening, and seismic retrofitting of old structures. However, UHP-FRCCs are not always environmental friendly products, especially in terms of the initial cost, due to the large quantity of cement that is contained in the mixture. Different rates of fly ash substitute herein part of the cement, and the new UHP-FRCCs are used to retrofit concrete columns to overcome this problem. To simulate the mechanical response of these columns, cylindrical specimens, which are made of normal concrete and reinforced with different UHP-FRCC jackets, are tested in uniaxial compression. Relationships between the size of the jacket, the percentage of cement replaced by fly ash, and the strength of the columns are measured and analyzed by means of the eco-mechanical approach. As a result, a replacement of approximately 50% of cement with fly ash, and a suitable thickness of the UHP-FRCC jacket, might ensure the lowest environmental impact without compromising the mechanical performances.

DOI： 10.3390/ma12234010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN CONCRETE INST  

The Fukushima-Daiichi nuclear power station accident in East Japan in 2011 released radioactive cesium (r-Cs) into the surrounding environment. In addition to the major contamination of soil and vegetation, surrounding concrete structures have also been contaminated. Understanding the contamination characteristics is important for the decontamination or disposal of offsite and onsite concrete structures. However, r-Cs contamination of actual concrete has not been extensively investigated. In this paper, the r-Cs contamination characteristics of actual concrete are introduced on the basis of several field surveys and analysis of concrete samples taken from actual contaminated structures in the Fukushima prefecture. As no dissolution to water was detected, the surface contamination was safely removed by water-jet abrasion. However, in KCl solution, significant dissolution of r-Cs was detected. A contamination depth analysis was performed by quantitative r-Cs concentration mapping based on beta-ray radiography using imaging plates. In many cases, such as roadside gutter cover plates, r-Cs was located on the surface without significant penetration into the concrete. However, in cases such as degraded concrete, deeper penetration up to several millimeters deep was observed. In cracked concrete, the r-Cs penetrated at least 10 cm, with the contamination level decreasing one order of magnitude in the first 1 cm.

DOI： 10.3151/jact.17.659

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本コンクリート工学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN CONCRETE INST  

Alkali release from aggregates is considered to cause expansion due to the alkali-silica reaction (ASR), owing to the increase in the hydroxide ion concentration (namely pH) of the pore solution. However, a direct validation of this assertion has not yet been made. In this research, the effects of the type of soak solution, which might better mimic the composition of the pore solution, on the behavior of alkali release from aggregates are investigated through immersion tests of aggregates. More importantly, accompanying ions dissolved from the aggregates are also measured in order to determine the mechanism for the increase in hydroxide ion concentration of the pore solution. The test results show that this increase can barely be observed, despite a considerable amount of alkalis being released. The results critically question the conventional view that alkali released from an aggregate serves to accelerate the ASR.

DOI： 10.3151/jact.16.61

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

Ultra High Performance - Fiber Reinforced Cementitious Composites (UHP-FRCC) has successfully developed in the last decades. They show excellent mechanical properties and durability, due to the highly dense microstructure produced by extremely low water/binder ratio and large amounts of cement. Thus, replacing part of the cement content with High Volume Fly Ash (HVFA) could be an effective way to improve also the ecological properties of UHP-FRCC. Indeed, most of the carbon footprint of cement-based composites is caused by the CO2 production of cement manufacturing. On the other hand, HVFA tends to reduce the mechanical properties of UHP-FRCC, especially at the early age. To evaluate the effect of some cement replacement (20, 50 and 70% by weight), a series of uniaxial compression and tensile tests have been performed and described in this paper. At the same time, through the Eco-Mechanical Index (EMI), ecological performances are evaluated on the basis of the measured mechanical properties. As a result, the application of UHP-FRCC in full-scale structures (e.g., composite concrete columns) is really convenient in the presence of HVFA, although the material properties (the compressive strength, in particular) show an opposite trend.

DOI： 10.1007/978-94-024-1194-2_29

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Meso- and micro-scale structural changes in matured hardened cement paste dried slowly for 1.5 years at different relative humidities (RHs) are evaluated by small-angle X-ray scattering profiles covering a q range of 0.017 nm(-1)-30 nm(-1) with a fractal disc-shaped particle analysis and Guinier approximation. The fractal disc-shaped particle analysis revealed that calcium-silicate-hydrate (C-S-H) agglomerations are very thin (similar to 2.5 nm) and of relatively large width (similar to 35 nm) under high RH conditions. However, the agglomerations are segmented (in width) into similar to 10 nm below an RH of 40%. The Guinier approximation found the possibility that the scattering profiles in the range of 2 nm(-1)-8 nm(-1) correspond to a spacing between C-S-H monolayers and it showed stepwise changes at 40%-50% RH. The stepwise behavior of the distance between C-S-H monolayers may explain a kink in water vapor desorption at around 40% RH. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.cemconres.2016.10.002

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Ultra-high-performance fiber-reinforced cementitious composite (UHP-FRCC) has been successfully developed over the last decade. UHP-FRCC shows very high strength and high durability because of its very low water binder ratio and dense microstructures. Moreover, by incorporating a combination of steel and mineral fibers with different sizes in the mixture design, UHP-FRCC also exhibits high ductility and high energy absorption capacity, even under uniaxial tensile stress. The high ductility of UHP-FRCC materials shows strain hardening behavior with multiple cracking after the occurrence of the first crack. While extensive research on the tensile and bending behavior of this composite under short-term loading is reported, only limited results can be found on time-dependent behavior of UHP-FRCC under sustained long-term loading, which is strongly related to the situation of real structures. This paper presents experimental results concerning the time-dependent behavior of cracked UHP-FRCC specimens under sustained bending load. In bending creep test, sustained load with 50 % of the pre-cracking load was applied to a pair of prismatic specimens of 50 x 100 x 400 mm under a 4-point bending setup. The performance of UHP-FRCC is compared with those of conventional fiber reinforced cementitious composites(FRCC) using steel and synthetic fibers, which are investigated within the Round Robin Test (RRT) organized by RILEM TC 261-CCF. The results showed that UHP-FRCC exhibited smaller creep deformation at the sustained loading condition than the conventional FRCC, even when the initial deformation of the UHP-FRCC is much larger than the conventional FRCC. Cracking pattern, in terms of crack width and number of cracks, was also studied in both composites under sustained loads. As a result, the superior resistance of UHP-FRCC was obtained with respect to conventional FRCC.

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Ultra-High-Performance Fiber-Reinforced Cementitious Composite (UHP-FRCC) shows very high strength and durability due to its very dense microstructure. While extensive research on the tensile and bending behavior of this composite under short-term loading has been reported, limited results are available on the time dependent behavior of UHP-FRCC under sustained loading, which are strongly related to the real-life-structures. This paper presents experimental results concerning creep behavior of cracked UHP-FRCC specimens under sustained tensile and bending loads up to 28 days. Under uniaxial tension, the load is applied to dog-bone type specimens. In the case of bending creep test, a sustained load is applied to a pair of prismatic specimens in a 4-point bending setup. The results show that UHP-FRCC exhibits low creep deformation under both these loading conditions. Furthermore, deflection hardening behavior lasts under Cracking behavior in terms of crack width and number of cracks under sustained loads in both composites is also studied and their comparisons are presented in the paper.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Cement Association  

<p>Although it is apparent that the deterioration due to alkali silica reaction is caused by the expansion produced by alkali-silica gel generated by the reaction between alkali and some reactive silicious minerals in alkali-reactive aggregate, there is still controversial for the mechanism of alkali-silica gel staying in the reactive aggregate and producing the expansion pressure and cracks in the concrete. Therefore, this paper tried to identify the mechanism of expansion pressure through some simplified element test using highly reactive andesite, which focuses on alkali-silica gel leaching / staying in the reactive aggregate. A series of experiments, the fluorescent observation of the alkali-silica gel distribution appeared on the cut surface of the reactive aggregate, which immersed into some kind of alkali solutions, hardened gypsum pastes or hardened cement pastes and the crack distribution in the cut surface of the cement paste matrix was carried out. As a result, the alkali-silica gel leached out and did not stay in the reactive aggregate without dense hardened cement paste matrix around. Furthermore, the alkali-silica gel in the dense hardened cement paste seems leach gradually from the reactive aggregate into hardened cement paste matrix without any visible cracking and this trend should be accelerated in case of high temperature or high water to binder ratio.</p>

DOI： 10.14250/cement.71.272

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For the purpose of performance evaluation of an existing reinforced concrete member, a chemo-thermo-hygro model to predict the spatial and temporal changes of physical properties of concrete in the member, named the "Computational Cement-Based Material Model (CCBM)", was proposed. This proposed simulation model includes models of rate of hydration of cement minerals, phase composition, and resultant properties of cement paste (i.e., compressive strength, Young's modulus, Poisson's ratio, thermal expansion coefficient, autogenous shrinkage, drying shrinkage, heat capacity, heat transfer coefficient, water vapor sorption isotherms, and water transfer coefficient). Furthermore, the model for compressive strength of concrete considered the variation in cement paste strength due to its colloidal features as well as micro-defects produced around aggregate due to differences in volume between aggregates and mortar upon heating and drying. The concrete properties of spatial distribution and temporal changes were evaluated by coupling these models with heat and water transport. Validation of these models was achieved by using existing experimental data. Using this CCBM, a thick concrete wall made with moderate Portland cement with a water-to-cement ratio of 0.55 under one-sided heating was simulated and potential problems that can arise during an integrity evaluation were discussed. If the required compressive strength, which was assessed within 91 days of placement, remains unchanged, an additional hydration process can build an adequate strength margin to overcome the risk of strength reduction due to heat and drying. However, in the case that the required strength is increased due to a re-evaluated risk, such as the magnitude of an earthquake, performance evaluation is not trivial as the core sample taken from the side where the execution of sampling is possible could exhibit a greater strength than the average strength of the target concrete member. Therefore, numerical evaluation might aid in this kind of situation.

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A method for predicting volume changes of aggregate during variations in humidity and temperature was studied. Siliceous rock aggregates commercially available in Japan were sampled from various regions and subjected to XRD (X-ray diffraction) analysis, thermal analysis, and volume change experiments. Drying shrinkage strain and the thermal expansion coefficient of the aggregates were found to be related to their mineral composition and bound water content. Experiments confirmed that drying shrinkage was correlated with the chlorite and bound water content of the aggregate, and that thermal expansion coefficients were correlated with the aggregate's quartz content. (C) 2015 Elsevier Ltd. All rights reserved.

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Short-term length change isotherms (SLCIs) and water vapor sorption isotherms are useful to eliminate the effects of the colloidal features of C-S-H. SLCIs of hardened cement pastes initially conditioned by drying to equilibrium at different relative humidities (RHs) were measured over a complete RH loop between 5% and 98%. Based on the correlation between incremental thickness of adsorption and incremental strain from 40% to 98% RH, the basal spacing of C-S-H above 40% RH appears to increase further with increasing water vapor sorption. However, no correlation of these values was found from 5% to 40% RH and the basal spacing is considered stable in this domain. These properties of C-S-H are directly related to its isothermal volume change as a function of RH. It can be concluded that the dominant shrinkage driver above 40% RH is disjoining or hydration pressure and that below 40% RH is change in surface energy. (C) 2015 Elsevier Ltd. All rights reserved.

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Understanding changes in the strength and Young's modulus of concrete under long-term drying or heating less than or equal to 90 degrees C is crucial for managing the aging of industrial buildings. We collected experimental data on changes in the physical properties of concrete components, aggregates, cement pastes, and concretes containing different aggregates and mortar under different heating and drying conditions. The change in compressive strength of concretes under various drying or heating conditions was explained by the behavior of the cement paste matrix and damage accumulation caused by differences in volume changes between the aggregate and mortar. In contrast, the variation in the Young's modulus of concrete caused by the drying or heating conditions was mainly explained by the increase in the number of voids due to internal cracking in the concrete. (C) 2014 Elsevier Ltd. All rights reserved.

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The body of data about the reaction kinetics of cement has greatly grown in recent years, and in terms of techniques for the prediction of the resulting hydrate formation phases, databases contributing to thermodynamic equilibrium calculations have been developed and are growing increasingly sophisticated. On the other hand, though many studies on cement aim to contribute to concrete engineering and numerical model researchers have pointed out the necessity of shedding light on the relationship between the microstructures generated by hydration and physical properties, such data remains scarce. This study investigated Portland cements using two commonly used water-cement ratios and three types of mineral compositions in the material age range of up to one year. The phase composition in relation to cement hydration was determined by X-ray powder diffraction and Rietveld analysis. In terms of physical properties, compressive strength and Young's modulus were measured through loading tests, and Young's modulus and Poisson's ratio were also obtained from the ultrasonic pulse propagation velocity of longitudinal and transverse waves. Further, water vapor adsorption tests to shed light on moisture behavior were conducted, yielding the BET specific surface area. Thermal conductivity, an important determinant of thermal behavior, was measured using the transient hot wire method. On the premise of the application of these physical properties to numerical calculations, their correlation with the information obtained from the phase composition was considered, leading to the proposal of simple and relatively high-accuracy empirical formulas. Further, background information about raising the correlation of these empirical formulas was also discussed.

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This paper reports the microstructural changes and resultant bulk physical property changes in hardened cement paste (hcp) during the first desorption process. The microstructural changes and solid-phase changes were evaluated by water vapor sorption, nitrogen sorption, ultrasonic velocity, and Si-29 and (27)AI nuclear magnetic resonance. Strength, Young's modulus, and drying shrinkage were also examined. The first drying process increased the volume of macropores and decreased the volume of mesopores and interlayer spaces. Furthermore, in the first drying process globule clusters were interconnected. During the first desorption, the strength increased for samples cured at 100% to 90% RH, decreased for 90% to 40% RH, and increased again for 40% to 11% RH. This behavior is explained by both microstructural changes in hcp and C-S-H globule densification. The drying shrinkage strains during rapid drying and slow drying were compared and the effects of the microstructural changes and evaporation were separated. (C) 2014 Elsevier Ltd. All rights reserved.

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Cement pastes undergo elevated temperature histories due to hydration heat liberation at early ages. Thermal expansion coefficients of cement paste and concrete change with age, showing a decrease after mixing, a subsequent minimum and then a gradual increase. These changes contribute to thermal strain. In this study, effects of water-cement ratio and cement type on volume changes in early-age cement pastes were experimentally examined using a newly developed apparatus capable of simultaneously determining both thermal expansion coefficient and total strain of cement pastes. The dependence of the thermal expansion coefficient on hydration was affected by water-cement ratio, cement type, elevated temperature history and particularly by the free water content of the cement pastes, while the relationship between thermal expansion coefficient and free water content varied with water-cement ratio. A notable increase in thermal expansion coefficient at early ages was observed when water-cement ratio was low and alite content in cement was high. At a water-cement ratio of 0.30, low-heat Portland cement paste resulted in a small total strain while moderate-heat and ordinary Portland cement pastes showed larger strains. Because no particular difference was observed in the thermal strains, shrinkage in the low-heat Portland cement paste was attributed to autogenous strain. At a water-cement ratio of 0.40, self-desiccation had a significant influence upon autogenous shrinkage and dependence of thermal expansion coefficient on hydration, and the effect of the mineral composition of cements was notable. However, for cement pastes with a water cement ratio of 0.55, no significant effects of self-desiccation were observed, probably because considerable excess water was present.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Methods for assessing the soundness of concrete exposed to irradiation are being developed within the framework of a project of the Nuclear Regulation Authority (NRA) "Japan Ageing Management Program for System Safety". This paper presents the background of this project and recent research works. The major reason for deterioration of concrete under irradiation conditions is expansion of aggregate due to neutron and gamma-ray irradiation. Dislocation of atoms in covalent structures of aggregate minerals, and resultant lattice constant change and alteration to amorphous phase are produced by fast neutrons. In addition, through electronic exertion, some energy deposition is accumulated as permanent distortion/strain in atomic structures. Other effects are also summarized. We plan to conduct a neutron irradiation test from May 2013. In selecting mix proportions and concrete components for the irradiation test program, sample size as a function of capsule size and gamma-heating, cement type, and aggregate size and type are determined based on preliminary experiments.

DOI： 10.1115/POWER2013-98114

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DOI： 10.3130/aijs.78.1203

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Materials Science, Japan  

Hydrated hardened cement paste samples using white cement were cured under different relative humidity con- ditions. After 180-day drying, Adsorption and desorption isotherms as well as chemically bound water of cured hard- ened cement paste were measured. Based on the adsorption data, it was concluded that drying process has two dif- ferent effects on a sorption property. One effect was seen in drying process over 70%RH. Capillary pore with more than 2nm size was collapsed and amount of capillary condensation is decreased as it is dried in the lower relative humidity. The second effect was seen in drying process under below 60%RH. The vapor BET surface area was dra- matically decreased as cement paste cured in lower relative humidity. From the change of chemically bound water and vapor BET surface area, it was deduced that a reaction of silanol to siloxane bond in C-S-H poses decrease in vapor adsorption sites. © 2013 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.62.219

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Sustainable Construction Materials and Technologies  

Water vapor sorption isotherms, nitrogen sorption isotherms, and bending strength of cement paste cured with different relative humidity for 1 year are measured. Effect of drying on microstructure has two ways. One is nano-scale effect, in which nano-scale pore among globules is collapsed due to capillary tension or solution and re-precipitation cycle of C-S-H. The other one is atomic-scale effect, in which water adsorption sites are reduced due to drying by changing of other than Si network. From such effect, cement paste shows different nature of microstructure according to thermodynamic conditions, and resultantly, the physical properties are altered.

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3130/aijs.77.1819

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

Prediction system for compressive concrete strength in aged structural member is proposed. This system is composed of models of rate of hydration, cement paste phase composition, heat production, specific heat, compressive strength, vapor desorption isotherm, coupled heat and moisture Iransfer. Each model is verified through experimental data This system is aiming for the structural member which can not beaccessed or can not be evaluated by the core sample test. Using non-destructive data or quality conlrol sample's data, this system might illustrate the distribution and development of concrete staigth in structural member properly. From the calculation results for a concrete member exposed to high temperature condition, strength development as well as distribution is quite sensitive to the boundary condition, and this concludes that the evaluation of structural member under such special condition needs precise boundary conditions.

DOI： 10.3130/aijs.77.323

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DOI： 10.3130/aijs.77.153

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Structural and Construction Engineering  

Hydration process of many kinds of cement paste is investigated by powder X-ray diffraction (XRD)/Rietveld analysis. The parameters of the present study are type of cement (Ordinary Portland cement, Low heat cement, and Eco-cement), water to cement ratio (0.50, 0.35), and curing temperature (283, 293, 313K). In this contribution, reaction of aluminate phase (3CaO·Al 2O 3) and ferrite phase (4CaO·Al 2O 3· Fe 2O 3) are focused and evaluated. Experimental results show that the reaction of both aluminate phase and ferrite phase are affected by the temperature and presence of calcite. When system includes calcite, monocarbonate aluminate is mainly produced, rather than ettringite. And in the case of high curing temperature, Al 2O 3 is reacted as amorphous. Regarding ferrite phase, the reaction degree at the age of 1 year decrease as curing temperature increases, this can be presumed due to dense amorphous phase around cement minerals. Based on these experimental facts, simple hydration model is proposed to evaluate development of hydration degree of aluminate phase and ferrite phase.

DOI： 10.3130/aijs.76.1

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DOI： 10.3130/aijs.76.1737

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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DOI： 10.3130/aijs.76.1033

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DOI： 10.3130/aijs.76.865

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DOI： 10.3130/aijs.76.231

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3130/aijs.76.213

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this contribution, velocities of elastic wave and shear wave were obtained by ultrasonic pulse method with hardening cement paste and mortar whose water to cement ratio was 0.30, 0.40 and 0.55. And four classes（cement paste, 20%, 40%, 60%）of aggregate volume fraction ratio were prepared in each water to cement ratios. Then, Poisson's ratios and dynamic elasticity were calculated from experimental results of elastic wave, shear wave and bulk density at predefined concrete age. As a result, steep reduction of Poisson's ratio was observed in early age in all specimens, however, decreasing ratio was different from each aggregate volume fraction. And it was reported that this time dependent changes of Poisson's ratio made an influence to accuracy of composite model for predicting the dynamic elasticity in the case of the range over 40% volume fraction of aggregate. In that case, the estimated values were improved by taking time dependent changes of Poisson's ratio into consideration. On the other hand, the estimated value by Hashin - Hansen model of mortar whose volume fraction of aggregate was 60% showed much higher value than measuring. And this difference was considered to be occurred due to large amount of void content than that of lower volume fraction of aggregate.

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It is known that the evaluation of volume change of hardened cement paste is controlled the hydration force, which derived from the potential of hydroxyl group. And then, for the evaluation of volume change due to hardened cement paste drying, specific surface area of calcium silicate hydrate in the hardened cement paste, which affects statistical adsorption vapor thickness in the hardened cement paste, is focused. The synthesized calcium silicate hydrate（synthesized C-S-H）, which calcium to silicate molar ratio is 0.9, 1.1, 1.3, 1.5, is prepared. The specific surface area of each C-S-H, which pre-treated under degased and each temperature（30degC, 105degC, 150degC）, is measured by 20degC vapor adsorption isotherm and B.E.T theory. The H₂O/Si molar ratio of each C-S-H, which humidificated under each relative humidity（0％RH, 60％RH, 95％RH）, are measured by Thermal Gravity Analysis. Based on thermodynamic model of silanol group on the C-S-H by Nonat, the unit model of C-S-H, which has four silanol group（two variable -SiOH, a -SiOH, a -SiOCaOH） is proposed. the number of water molecule, which adsorbs on each silanol groups, is identified and the specific surface area model of C-S-H in adsorption process are proposed. The proposed model can predict the specific surface area of various C-S-H, which has various Ca/Si molar ratio or pretreated each temperature drying condition.

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Hydration pressure of hardened cement paste containing blast furnace slag with 30％ or 45％ replacement of base ordinary Portland cement with water to binder ratio of 0.40 and 0.55 was determined experimentally. The experimental study is composed of measuring adsorption and desorption isotherm, length-change isotherm, Young's modulus and Poisson's ratio, and density of hardened cement paste.<br/>It is experimentally confirmed that 1）the desorption isotherm of hardened cement paste containing blast furnace slag has the larger water content than those of hardened cement paste with Portland cement, 2）Drying shrinkage of hardened cement paste containing slag with a condition of W/B＝0.55 is larger than those of hardened cement paste with Portland cement especially in the range of relative humidity lower than 60％RH, 3）the drying shrinkage of hardened cement paste containing slag with a condition of W/B＝0.40 showed almost the similar amount compared to those of hardened cement paste with Portland cement.<br/>Based on the hydration pressure theory which is proposed by the first author is adopted to this experimental result, and, according to this result, it is presented that the surface of hardened cement paste containing blast furnace slag has the larger interaction with water than that of hardened cement paste with ordinary Portland cement.<br/>This is the main factor for that hardened cement paste with blast furnace slag exhibits the large drying shrinkage.

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For the evaluation of strength development with or without elevated temperature due to heat of hydration, specific surface area of hardened cement paste, which affects the strength of hardened cement paste, is focused. The hardened cement paste（hcp）of water to cement ratio of 55％ and 40％ with 20℃ constant temperature and maximum 60℃ temperature as mass concrete temperature history is prepared. The amount of C-S-H and CaO/SiO₂ molar ratio of C-S-H are identified by XRD/Rietveld analysis and phase composition model, and at the same time, specific surface area is measured by moisture sorption isotherm and BET theory. Additionally, specific surface area of hardened cement paste is compared to that of synthesized C-S-H. As a result, 1）when the hcp is subjected to elevated temperature history in early ages, the development of specific surface area of hardened cement paste increase rapidly in early age but het a peak, 2）CaO/SiO₂ molar ratio decreases rapidly in early age but increases gradually in a long term, 3）specific surface area of C-S-H in hardened cement paste for CaO/SiO₂ molar ratio is higher than synthesized C-S-H, and 4）specific surface area of hardened cement paste with/without elevated temperature history can be evaluated by the amount of C-S-H in hardened cement paste with a single curve.

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Mechanism of moisture sorption hysteresis of hardened cement paste is discussed in this paper. Firstly, cement paste with three type of cement and two different water to cement ratioes are tested for sorption isotherm. There exist the hysteresis in the range lower than 30％Rh. This phenomena is not common for normal porous materials. It is experimentally found that the adsorption isotherm as well as desorption isotherm is on the B.E.T plot, and the surface area calculated B.E.T theory from adsorption process and those from desorption process has the linear relationship. This results implies that, in the process of sorption isotherm test, some reproductive chemical reaction occur. Secondly, hysteresis experiment in high relative humidity of hardened cement paste is conducted. The experimental data in re-adsorption process shows convex downwards. This decrease in water content with increase in relative humidity indicates that the surface area of hardened cement is decreased. The two experimental data showed the evidence that the chemical reaction of hydrate occurs behind the desorption or adsorption process. In order to confirm this reaction, IR spectra and NMR spectra of synthesized C-S-H under different relative humidities, i.e. 95％RH, 60％RH, 0％RH（＝105℃-dry for 24hours）were measured. According to the experiment, the Si network is increased even in the drying process from 95％ RH to 60％ RH. This reveals that the C-S-H or hardened cement paste is not the stable substance in desorption or adsorption process with regard to water.

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Expansive additives are being widely used as shrinkage reducing/compensating admixture to reduce the early-age cracking and chemical prestressing. Such expansive additives influence the composition of cement hydration products and mechanical properties (stiffness and strength) of the cement and concrete, which ultimately affects the early age deformation. In the current study, the EMM-ARM (Elastic Modulus Measurement by Ambient Response Method), is used because of its ability to continuously monitor cement's real-time stiffness development paste with expansive additives. Stiffness development of the cement paste with expansive additives is captured in the unrestrained condition by allowing the free expansion during the stiffness measurement. An expansive additive, based on free lime, with a 10% (by weight) cement replacement ratio is studied in the current work. Results from the EMM-ARM are compared to the elastic modulus measurement from the compression testing of cylindrical specimens, and the mechanisms of expansive action on the microstructure in early-age are discussed.

DOI： 10.1007/978-3-030-72921-9_26

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Language：Japanese   Publisher：Japan Cement Association  

<p>Although it is apparent that the deterioration due to alkali silica reaction is caused by the expansion produced by alkali-silica gel generated by the reaction between alkali and some reactive silicious minerals in alkali-reactive aggregate, there is still controversial for the mechanism of alkali-silica gel staying in the reactive aggregate and producing the expansion pressure and cracks in the concrete. Therefore, this paper tried to identify the mechanism of expansion pressure through some simplified element test using highly reactive andesite, which focuses on alkali-silica gel leaching / staying in the reactive aggregate. A series of experiments, the fluorescent observation of the alkali-silica gel distribution appeared on the cut surface of the reactive aggregate, which immersed into some kind of alkali solutions, hardened gypsum pastes or hardened cement pastes and the crack distribution in the cut surface of the cement paste matrix was carried out. As a result, the alkali-silica gel leached out and did not stay in the reactive aggregate without dense hardened cement paste matrix around. Furthermore, the alkali-silica gel in the dense hardened cement paste seems leach gradually from the reactive aggregate into hardened cement paste matrix without any visible cracking and this trend should be accelerated in case of high temperature or high water to binder ratio.</p>

DOI： 10.14250/cement.71.272

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Other Link： https://www.aij.or.jp/paper/detail.html?productId=415001

Language：Japanese   Publisher：Architectural Institute of Japan  

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Other Link： https://www.aij.or.jp/paper/detail.html?productId=419156

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Language：Japanese   Publisher：公益社団法人 日本コンクリート工学会  

DOI： 10.3151/coj.51.291

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Aging of calcium silicate board is discussed in the present contribution. Recently, the fall of sealing which is composed of calcium silicate board has been reported at times. The mechanism of aging phenomena of calcium silicate board is not wholly understood. For this reason, the chemical analysis and physical property experiment on the aged and newly provided material are conducted and comparison of those results is made. It is experimentally confirmed that tobermorite in calcium silicate board can be carbonated and resultantly it causes decreasing of density, increasing of water vapor BET surface area and water penetration rate, and decrease in strength. The weight of calcium silicate board per strength can be dropped as it is about 12.5% of original value. It is expected that relatively high water content enhances carbonation rate because carbon dioxides dissolves in it and makes carbonic acid. Therefore, it is strongly recommended that calcium silicate board is only used in the drying condition.

DOI： 10.3130/aijs.78.1203

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Prediction system for compressive concrete strength in aged structural member is proposed. This system is composed of models of rate of hydration, cement paste phase composition, heat production, specific heat, compressive strength, vapor desorption isotherm, coupled heat and moisture transfer. Each model is verified through experimental data. This system is aiming for the structural member which can not be accessed or can not be evaluated by the core sample test. Using non-destructive data or quality control sample's data, this system might illustrate the distribution and development of concrete strength in structural member properly. From the calculation results for a concrete member exposed to high temperature condition, strength development as well as distribution is quite sensitive to the boundary condition, and this concludes that the evaluation of structural member under such special condition needs precise boundary conditions.

DOI： 10.3130/aijs.77.323

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Language：Japanese   Publisher：Architectural Institute of Japan  

The discusser wants the authors to answer or explain the following points:<br>1) The authors' discussion does not include a result of concrete specimen whose maximum curing temperature is 90°C and autogenous shrinkage attained the same amount as the specimens experienced lower maximum temperature history.<br>2) The proposed theory does not based on the experimental or theoretical results in some parts.<br>3) Several references are not suitable in the context of authors' story.

DOI： 10.3130/aijs.77.509

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Language：Japanese   Publisher：Architectural Institute of Japan  

It is strongly needed to predict and reduce the amount of concrete shrinkage. Prediction of hardened cement paste needs the information of specific surface area, volumetric water, and bulk modulus when it is based on the theory of hydration pressure. For this purpose, it is important to evaluate the water vapor BET surface area and find the way to predict this value. In this study, the specific surface area of various cement paste was determined by water vapor adsorption isotherm and B.E.T theory and chemically bound water of hardened cement of those was determined by thermal gravity analysis. Based on these data, the unique relationship between chemically bound water at the state of 11%RH condition and BET specific surface is found regardless of cement types.

DOI： 10.3130/aijs.77.1819

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Language：Japanese   Publisher：Architectural Institute of Japan  

In this paper, total strain and time dependent change of thermal expansion coefficient (TEC) under temperature history of cement paste with W/C=0.3,0.4,0.55 whose binder is normal Portland cement, moderate Portland cement and low heat Portland cement were investigated. In all conditions, a rapid reduction of TEC was observed in very early age and TEC showed the local minimum value around 12-18hour. After that, it gradually increased with reduction of moisture content. During that term, low heat cement could reduce this increment of TEC under high temperature history. This time dependent change of TEC could produce shrinkage as thermal strain with temperature dropping. The amount of this thermal strain is relatively large, and in the case of W/C = 0.4, low heat cement shows lower thermal strain.

DOI： 10.3130/aijs.77.153

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The effect of elevated temperature history due to heat of hydration on physical properties and hydration system in the cement paste were investigated. The elevated temperature in early ages is known to cause stagnation of strength development. Therefore, the degree of hydration of each mineral component as well as hydrates is determined by X-ray/Rietveld analysis and cement paste properties, namely, the degree of hydration of each mineral, the amount of calcium hydroxide, chemically bound water, water content, density of hardened cement paste and mechanical properties were investigated. As a result, compressive strength, young's modulus, and shear modulus of hardened cement paste, regardless of W/C differences, can be evaluated with gel/space ratio of hardened cement paste with a single curve.

DOI： 10.3130/aijs.76.213

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Publisher：Architectural Institute of Japan  

Hydration process of many kinds of cement paste is investigated by powder X-ray diffraction (XRD)/Rietveld analysis. The parameters of the present study are type of cement (Ordinary Portland cement, Low heat cement, and Eco-cement), water to cement ratio (0.50, 0.35), and curing temperature (283, 293, 313K). In this contribution, reaction of aluminate phase (3CaO•Al₂O₃) and ferrite phase (4CaO•Al₂O₃•Fe₂O₃) is focused and evaluated. Experimental results show that the reaction of both aluminate phase and ferrite phase is affected by the temperature and presence of calcite. When system includes calcite, monocarbonate aluminate is mainly produced, rather than ettringite. And in the case of high curing temperature, Al₂O₃ is reacted as amorphous. Regarding ferrite phase, the reaction degree at the age of 1 year decrease as curing temperature increases, this can be presumed due to dense amorphous phase around cement minerals. Based on these experimental facts, simple hydration model is presented to evaluate development of hydration degree of aluminate phase and ferrite phase.

DOI： 10.3130/aijs.76.1

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Publisher：Architectural Institute of Japan  

Young's modulus, Poisson's ratio, and bulk modulus of hardened cement under controlled different relative humidities were measured by ultrasonic method as well as direct tensile loading test. It was experimentally confirmed that Young's modulus, Poisson's ratio, and bulk modulus of hardened cement paste decreased as decrease in equilibrium relative humidity especially in the range above 40%RH. And in the range below 40%RH, experimental results of direct tensile loading test showed the decrease in Young's modulus and Poisson's ratio while the experimental results of ultrasonic test showed slight increase of Young's modulus and almost constant behavior of Poisson's ratio. For the decrease of Young's modulus and Poisson's ratio can be explained by the reduction of load-bearing water in the hardened cement paste due to drying, and slight increase under 40%RH by ultrasonic test can be explained by the increase of Si-O network of C-S-H due to drying.

DOI： 10.3130/aijs.76.231

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Publisher：Architectural Institute of Japan  

Water transfer behavior in hardened cement paste is evaluated. For evaluation of water transfer, mass loss of specimens over time is measured and Boltzmann's method is applied to measured data. At the same time, desorption isotherm of hardened cement paste is evaluated. Using the diffusion coefficient for nominal water content and desorption isotherm, water conductivity for chemical potential of water in hardened cement paste is derived. Nine hardened cement paste specimens, which have different porosity, are tested and using these data, predicting model of water conductivity is proposed.<br> The proposed model needs the properties of hardened cement, such as, maximum water content at 20°C degree, water vapor BET surface area, and water content for predicting the water conductivity. According to the simulated results, the temperature dependency of water conductivity is obvious. Evaluation of temperature dependency of water conductivity is remained to be future issue.

DOI： 10.3130/aijs.76.1737

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Publisher：Architectural Institute of Japan  

Adsorption and desorption isotherm model of hardened cement paste under 20 °C is proposed. Adsorption and desorption isotherm of hardened cement paste with different water cement ratio, temperature history, and different degree of hydration were experimentally studied. Based on the experimental data, following characteristics were derived: 1) BET surface are of adsorption process and desorption process has linear relationship, 2) Relationship between statistical thickness of adsorption and relative humidity is identical in the range below 40%RH, 3) t-curve can be derived from the relationship between statistical thickness of adsorption and relative humidity, 4) difference between statistical thickness of adsorption and t-curve has a linear relationship between Kelvin radius, 5) virgin desorption curve value less than 40%RH has similar value of those of desorption curve after drying pre-treatment, 6) virgin desorption curve has a linear relationship with relative humidity. Based on these experimental points, empirical adsorption model is proposed.

DOI： 10.3130/aijs.76.1033

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Publisher：Architectural Institute of Japan  

Relationship between surface area of hardened cement and cement hydration was evaluated. Hydration process was evaluated by powder X-ray diffraction/Rietveld analysis, on the other hand, surface area of hardened cement paste is determined by water vapor adsorption isotherm and BET theory. Based on the experimental data, the surface area of hardened cement paste has strong correlation with the amount of C-S-H in hardened cement. The surface area by vapor adsorption is very sensitive to the sample preparation and therefore, correlation between surface and amount of C-S-H is different when the pre-drying condition is differed.

DOI： 10.3130/aijs.76.865

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Publisher：Architectural Institute of Japan  

Relationship between surface area of hardened cement and cement hydration was evaluated. Hydration process was evaluated by powder X-ray diffraction/Rietveld analysis, on the other hand, surface area of hardened cement paste is determined by water vapor adsorption isotherm and BET theory. Based on the experimental data, the surface area of hardened cement paste has strong correlation with the amount of C-S-H in hardened cement. The surface area by vapor adsorption is very sensitive to the sample preparation and therefore, correlation between surface and amount of C-S-H is different when the pre-drying condition is differed.

DOI： 10.3130/aijs.76.865

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Publisher：Architectural Institute of Japan  

Adsorption and desorption isotherm model of hardened cement paste under 20 °C is proposed. Adsorption and desorption isotherm of hardened cement paste with different water cement ratio, temperature history, and different degree of hydration were experimentally studied. Based on the experimental data, following characteristics were derived: 1) BET surface are of adsorption process and desorption process has linear relationship, 2) Relationship between statistical thickness of adsorption and relative humidity is identical in the range below 40%RH, 3) t-curve can be derived from the relationship between statistical thickness of adsorption and relative humidity, 4) difference between statistical thickness of adsorption and t-curve has a linear relationship between Kelvin radius, 5) virgin desorption curve value less than 40%RH has similar value of those of desorption curve after drying pre-treatment, 6) virgin desorption curve has a linear relationship with relative humidity. Based on these experimental points, empirical adsorption model is proposed.

DOI： 10.3130/aijs.76.1033

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Event date： 2011.2

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Event date： 2010.7

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Event date： 2010.2

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Event date： 2010.2

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Event date： 2009.7

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