One of the methods for improving the durability of reinforced concrete structures is the use of stainless steel bars. However, when stainless steel bars and carbon steel bars are used in combination in a reinforced concrete structure, there is concern about galvanic corrosion of carbon steel bars. Since there are not many studies dealing with galvanic corrosion of stainless steel bars and carbon steel bars in concrete, in this study, solution experiments and concrete experiments were conducted using specimens that reproduced galvanic corrosion of dissimilar metals. The relationship between the factors affecting corrosion and the corrosion rate of reinforcing bars was evaluated. As a result, in the solution experiment, the corrosion current between dissimilar metals tended to increase due to the increase in chloride concentration and cathode area. In concrete experiments, an increase in corrosion current was observed due to an increase in cathode area, especially when carbon and stainless steel bars were in a chloride attack environment. However, when only stainless steel bars were in a chloride attack environment, the effects of galvanic corrosion of dissimilar metals were not observed. In addition, the behavior of galvanic corrosion could be expressed by calculating the corrosion current density from the polarization curve of the steel bar.

In this study, we attempted to use Machine Learning to predict the visual judgment of material segregation of High-fluid concrete using the materials and concrete formulation as features. Random Forest and LightGBM, a type of ensemble learning, were used to obtain feature importance. Furthermore, Logistic Regression, a type of statistics and Machine Learning, was performed using these features of high importance in Machine Learning. Using Logistic Regression, we proposed a prediction formular for visual material segregation judgment and the prediction performance of the proposed prediction formula was evaluated.

This study discussed the effect of mix proportions on the passing velocity through obstacle and aggregate ratio before and after passing through obstacle with focusing on mechanically-compacting flowable concrete. The results clarified that as the ratio of sand to cement in the concrete increased, passing velocity through obstacle decreased whereas aggregate ratio before and after passing through obstacle increased and as unit aggregate volume in the concrete increased, passing velocity through obstacle and aggregate ratio before and after passing through obstacle decreased. It can be also found out that the effect of aggregate type on the passing velocity through obstacle and aggregate ratio before and after passing through obstacle was obvious for the concrete with appropriate fresh properties, and the shape of aggregate had a greatly effect on passing velocity through obstacle, and both the shape and fineness modulus of aggregate had a greatly effect on aggregate ratio before and after passing through obstacle. Moreover, in case of mix proportions that differ only aggregate types, the concentration of aggregate volume with consideration of the space for rotation during vibration, estimated by solid contents in aggregate in this research, is useful to evaluate the order of unit aggregate volume in the concrete that passing velocity through obstacle became almost all zero.

In this study, the hydration reaction between cement and volcanic glass powder （VG）and its hydrates were clarified, assuming the use of VG as a substitute for silica fume （SF）, which is often used in ultra-high-strength concrete. Furthermore, the relationship between the pore structure formed by the hydrates and the compressive strength development was also examined. As a result, the following findings were obtained. The total pore volume of the cement hardened body mixed with VG reached a minimum and the compressive strength peaked when the admixture ratio was 25％. On the other hand, in the case of SF, the total pore volume was at its minimum and the compressive strength peaked when the admixture ratio was 20％. As the admixture ratio of both VG and SF increased, the amount of C-S-H formation increased and the pore volume decreased due to the pozzolanic reaction, resulting in an increase in compressive strength. The peak admixture ratio of the pozzolanic reaction was 25％ and 20％, respectively. The C-S-H produced when the VG admixture ratio was below 30％ had a higher percentage of high-density C-S-H compared to SF, and the percentage of low-density C-S-H increased rapidly when the admixture ratio reached 30％. The amount of C-S-H produced when the VG admixture ratio was 30％ increased over that at the VG admixture ratio was 25％, but the amount of pores increased. However, the compressive strength when the VG admixture ratio was 30％ was similar to that at the VG admixture ratio was 25％. Based on the analysis of pore size distribution volume and C-S-H density, it was inferred that this was caused by an increase in the amount of pores in the gel porosity region due to the formation of more low-density C-S-H.

At present, thermal power generation accounts for about 70％ of domestic power generation in Japan, and a large amount of CO₂ emissions are regarded as a problem. Therefore, integrated coal gas combined cycle （IGCC）, which has improved the efficiency of coal-fired power generation, is drawing attention. IGCC has confirmed high power generation efficiency and CO₂ emission reduction effect, but one of the issues is the treatment and utilization of integrated coal gasification combined cycle （IGCC slag） emitted as a by-product. In order to solve this problem, in this study, we evaluated the mechanical performance and durability of high-strength mortar using IGCC slag.

To detect the internal deterioration in the concrete covered with carbon fiber reinforcement polymer （CFRP） sheets, this study developed a non-destructive test using electrical impedance variation and phase transition. The study considered a hypothesis that the concrete exhibits inductive, capacitive, and resistance properties depending on the frequency and permittivity of the applied voltage. Deterioration damage, such as cracks inside the concrete, is a type of air layer that causes polarization. The magnitude of polarization is expressed by the relative permittivity. The relative permittivity of concrete is about 6-10, and the relative permittivity of air is 1. In the case of cracks, which are a type of air layer, occurring inside the concrete, the apparent relative permittivity decreases. Changes in the relative permittivity of concrete can be captured by measuring the impedance and phase angle. The study conducted a freeze-thaw test using CFRP-covered concrete specimens. Furthermore, the study examined the frequency characteristics of impedance and phase under AC voltage with frequency ranging from 1MHz to 8MHz. The impedance and phase were measured using a probe with two electrode terminals. These frequency properties were evaluated by an impedance analyzer, which was controlled by a computer. The test results confirmed that the capacitive phase property of damaged concrete altered to exhibit inductive characteristics in the range of 2 to 4MHz. The fundamental test revealed that the internal damages of the CFRP covered concrete are detected by measuring a frequency at the impedance local maximum value and the phase transition property.

In this study, experimental investigations were conducted regarding an ultimate strength of continuous fiber reinforced concrete beams using CFRP rods and meshes. As a result, it was experimentally confirmed that the ultimate strength of the beam increases significantly by using CFRP rods and meshes as rebar replacements, and that the shear strength of the beams can be estimated with relatively reasonable accuracy according to the structural design formula in the design and construction guideline of continuous fiber reinforced concrete and AIJ standard for structural calculation of reinforced concrete structures.

The purpose of this study is to investigate the effect of mix proportioning factors and age on the electrical resistivity of polymer-modified mortars using redispersible polymer powder for repair work of reinforced concrete structures. Polymer-modified mortars using the redispersible polymer powder and various types of fine aggregates are prepared with fine aggregate-cement ratios of 1, 2 and 3, polymer-cement ratios of 0, 5, 10 and 15％, or polymer contents of 0 and 4.56％. The polymer-modified mortar specimens are cured under 2d-wet＋5dwater＋21d-dry condition for 28d. The cured specimens are stored under dry condition up to the age of 182d. The electrical resistivity and apparent water retention of the specimens are measured at the age of 28, 56, 91 and 182d. As a result, the electrical resistivity of the polymer-modified mortar is increased with an elapsing the age. However, the specimens give the almost constant value of the apparent water retention proposed in this study at the age of 182d. The electrical resistivity of the polymer-modified mortars at the age of 182d is larger than the electrical resistivity of the unmodified mortars, and increased with an increase in the polymer-cement ratio and the fine aggregate-cement ratio. The lesser effectiveness of the types of polymer and fine aggregate on the electrical resistivity of the polymer-modified mortar is recognized as compare to the effectiveness of the fine aggregate-cement ratio.

The influencing factors on drying shrinkage strain of cement mortar containing redispersible polymer powder （RPCM） are investigated by a drying shrinkage test with prism specimen which size is 40×40×160mm. The test conditions of temperature and humidity are 20±2℃ and 55±5％R.H., respectively. Two types of polymers polyacrylic ester polymer and vinyl acetate-vinyl versatate-acrylic acid polymer are used, and the content of these polymers are 0, 5 and 10％ by weight of cement. Results show that the higher the air content due to polymer, the higher the drying shrinkage strain. The ultimate strain is higher with the decrease of volume of fine aggregate or the increase of water-cement ratio. And the influence of polymer-cement ratio is different with type of polymer. Therefore, an estimating equation for ultimate strain of RPCM is constituted with corrected strain data by air content. That equation is consisted of a function of fine aggregate volume, water-cement ratio and polymer-cement ratio, and it was found that the proposed equation for drying shrinkage strain of RPCM can express the experimental data.

To develop a new post-reinforcing method, the authors study RC beam repaired by UHPFRC with an embedded CFRP rod. The CFRP rod was used for flexural reinforcement and UHPFRC was for both flexural and shear reinforcement. Therefore, the effects of flexural and shear reinforcement of the RC beam were the main foci of the study. In this study, FEM analysis was made focusing on the process of bond splitting failure and cracking to reveal the cause of the experimental results. As a result, the following conclusions were derived. 1） The FEM result obtained by incorporating the bond-slip model of the CFRP rod showed a good agreement with the experimental load-displacement relationship, 2） The bond-slip models of the CFRP rod significantly affected the load capacity of the RC beam, 3） Experimental and FEM results indicated that the horizontal shear failure of the CFRP rods occurred after the bond splitting failure of the one.

This paper reports on the phase transformation of C-A-S-H/N-A-S-H blends and the structural characterization of C-A-S-H and zeolites formed in this process. C-A-S-H/N-A-S-H blend gels were prepared with different Si/Al and Ca/Si ratios and characterized by X-ray diffraction （XRD）, fourier transform infrared spectroscopy （FT-IR） and magic angle spinning nuclear magnetic resonance （MAS NMR）. The results showed that when the Al content in the blend gels was high, zeolite with a high Si/Al composition ratio is formed, and when Ca is added, C-A-S-H is formed immediately after gel mixing, but then the zeolite phase is gradually formed. On the other hand, when Al content in the blend gel was low, C-A-S-H became the main phase even with a small addition of Ca. Furthermore, FT-IR spectra may provide insight into the formation behavior of C-A-S-H and the relationship between the Ca/Si ratio and the amount of Al in solid solution in C-A-S-H.

An inorganic carbon analyzer （coulometer） was used to measure the amount of fixed carbon in the carbonated paste. Since the coulometer has a limited track record and few facilities for its use, a reliability evaluation using reagents and a study of its use with test specimens were also conducted. As a result, the coulometer was tested three times, and the average value was found to be within ±2％ error. Coulomter, thermal analysis, and X-ray diffraction were also used to analyze the distribution of fixed carbon dioxide content in the partially carbonated paste. The results showed that about half of the maximum fixed amount of carbon dioxide was fixed even around the depth of neutralization with phenolphthalein, and that carbon dioxide was fixed even at unneutralized positions.

In this study, wet and dry carbonation treatment of cement paste fine powder and recycled fine powder made from concrete was carried out, and calcium carbonate and CO₂ sequestration quantity were examined. In the wet treatment, only calcite was formed in the calcium carbonate, while in the dry treatment, vaterite and a small amount of aragonite were also formed. It was shown that vaterite aragonite and calcite could be separated and evaluated by dynamic TG, and that the calcium carbonate content could be measured accurately. It was also found that the calcium content of cement in recycled fine powder was higher when hard sandstone was used as coarse aggregate than limestone, and that the fixation potential of CO₂ was higher.

This study examined the effectiveness of accelerated carbonation using an externally heated rotary kiln for efficient CO₂ uptake in recycled concrete aggregates. As a result, accelerated carbonation treatment was shown to be effective in promoting CO₂ uptake of recycled concrete aggregates. Also, scale-up tests showed that operation at 500kg/h scale was stable, indicating the feasibility of process construction. Moreover, the amount of hexavalent chromium elution did not increase with accelerated carbonation, indicating that environmental safety is not a problem. It was confirmed that the modified CBR satisfied the quality standard for upper layer roadbed material and the high temperature （120℃） carbonated recycled concrete aggregates had sufficient performance as a roadbed material. These results indicate that recycled concrete aggregates treated by accelerated carbonation can be recycled as roadbed material.

Coal gasification slag, by-product of combined cycle coal gasification combined cycle power generation, is expected to be used as a fine aggregate for concrete. Although a number of experimental studies have been conducted as a fine aggregate for concrete, there have been few experimental studies on the chemical properties of slag. We attempted to elucidate the silicate structure of coal gasification slag by combining the examination of insoluble residues by dilute hydrochloric acid solution, measurement of siloxane chain length distribution by trimethylsililation method, and solid-state NMR. Contrary to the expectation that the silicate structure of slag is mostly composed of amorphous phase, mainly glass phase similar to fly ash, some slag with high CaO/SiO₂ molar ratio was found to be composed of siloxane oligomer with relatively short chain length similar to blast furnace slag.

In this study, the interlayer structure was evaluated by obtaining the water vapor adsorption isotherms from low relative pressure and the isotopic differential heat of adsorption calculated by the Clausius-Clapeyron equation for heat treated 1.4nm tobermolite, which was changed to 1.1nm, without Si-Q³ bond. The low crystallinity C-S-H was also evaluated using 1.4nm tobermorite with heat treatment as a comparison. As a result, characteristic bimodal peaks appeared in the heat of adsorption change in the low humidity range, and the behavior up to the first and second peaks were attributed to adsorption in the interlayer and on the outer surface of the interlayer, respectively. Also, the increase of the first peak in the heat of adsorption of 1.4nm tobermorite was attributed to the hydration of Ca^2＋ ions bridging the interlayer.

In this study, to investigate the effect of the addition rate of Ca/Si＝2.0 C-S-H and its carbonated samples to C₃S on the hydration acceleration effect, Ca/Si＝2.0 C-S-H synthesized by an original method based on complex polymerization and its carbonated samples were added to C₃S in different ratios. As a comparison, samples added with C-S-H with different Ca/Si ratios and structures were also prepared and discussed in terms of nucleation seeding. As a result, the induction phase was not observed only in the condition with C-S-H with a Ca/Si ratio of 2.0, and the acceleration phase was reduced to 4.5 hours, less than half of that with C₃S alone hydration at a 10％ addition rate. Although carbonation increased the specific surface area and reduced the particle size of all nucleating agents, they tended to be less effective in promoting hydration than before carbonation. This result supports Gartner's assertion that the hydration acceleration effect of C-S-H is due to the silanol group at the end of the silicate chain.

This paper investigates the Al substitution properties in C-S-H with a Ca/Si ratio of 2.0 obtained by hydrating highly reactive belite, and the regeneration of belite by re-calcinating. The results show that Al was incorporated bridging site in C-S-H with a Ca/Si ratio of 2.0 as 4- and 6-coordinated Al and that the basal spacing increased with an increase in the amount of substitution. On the other hand, belite was regenerated from C-A-S-H with a high Ca/Si ratio by calcinating at 800℃. The crystallite diameter and specific surface area of the regenerated belite were similar to those of the pre-hydrated belite, indicating that the formation of α’-C₂S was predominant over β-C₂S with increasing Al substitution. These results indicate that recyclable cement may sustain the regeneration cycle even if its key element, C-S-H with a Ca/Si ratio of 2.0, is altered by Al.

We conducted comparison test of cementitious materials as paste, mortar and concrete containing （a） natural limestone powder and （b） synthetic calcium carbonate powder made from Ca（OH）₂ which is by-produced when acetylene gas is manufactured as minor additional constituents respectively. The paste and mortar’s evaluations are conducted according to JIS R 5201：2015 and the test results are adapted to all the requirements of JIS R 5210：2019. The test result of the concrete containing （b） showed lower slump than （a）, however it was improved by optimizing addition of superplasticizer and the slump change over time was similar to the concrete containing （a）. The compressive strength development of （b） was mostly same level as （a）.

In this study, cementitious materials using calcined allophane were investigated. The results showed that the main components of the paste with 30％ of calcined allophane substituted for alite were CH, low crystalline C-S-H and stratlingite, and that the compressive strength was equivalent to that of a single phase of alite or a paste with 30％ of calcined kaolinite substituted for alite. The compressive strength of the paste was found to be equivalent to that of a single phase of alite or alite with 30％ calcined kaolinite. In addition, in the pastes with an increase of 70％ substitution of calcined allophane, the alite reacted completely, stratlingite became the main component and the compressive strength tended to be higher than in the pastes with 30％ substitution of calcined allophane.

Low alkalinity cement is considered desirable as cementitious materials applied for radioactive waste disposal facilities. We investigated optimum mix proportion of highly containing fly ash silica fume cement which is considered as one of the low alkalinity cements from the point of view of low alkalinity, compressive strength and economic efficiency. As a result, it was suggested that OPC：SF：FA＝36～40：12～16：44～48 is candidate for optimum mix proportion in this study. Therefore, we could suggest these mix proportion with economic advantages which had silica fume content reduced, having the required performance as low alkalinity cement equivalent to the conventional basic mix proportion.

Most of the previous studies on the propagation of acceleration inside fresh concrete have measured the acceleration in the filled sample or from outside the formwork, and there have been few cases where the acceleration of fresh concrete in flow during the compaction process has been measured. In this study, the acceleration on fresh concrete during compaction in mock up form was measured. With the measurement system developed in this experiment, the acceleration propagating inside the fresh concrete was able to measure on several places of the position at the same time and the existence of acceleration damping could be quantitatively determined. It was also found that the acceleration propagated into the concrete from the onsite vibrator was independent of the value of slump.