Journal of Advanced Concrete Technology(2024 - 2025)
Statistical Perspective to Time-dependent Pull-out Behavior of Discrete Fibers: A Review
Kanazawa T.; Hashimoto K.; Park K.; Takahashi H.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.23, pp.99-115, 2025, .
(https://doi.org/10.3151/jact.23.99)
Abstract
Few studies have examined the statistical uncertainty which has been found by experimentation in mechanical interaction between discrete fibers and a cement-based matrix. This review work includes not only existing test results showing considerable fluctuation particularly in post-peak behavior, but also statistical and probabilistic approaches to account for that fluctuation. Our emphasis is on time-dependent behaviors such as pull-out creep and loading rate effects because of their remarkable scatter, which might hinder further research progress (e.g., difficulty separating true mechanical response from statistical variation). Potential sources of statistical fluctuation are identified using non-destructive measurements: X-ray computed tomography and acoustic emission techniques. Along with the observational evidence, fracture mechanics is effective at reinforcing the physical importance of probabilistic approaches such as a Markov chain. The necessity of a probabilistic perspective of cumulative damage processes is addressed because the viewpoint provides a common theoretical basis between time-dependent and stress-dependent pull-out processes. Copyright c 2025 Japan Concrete Institute.
Impact of Aggregate Physical Properties on the Compressive Strength of Concrete
Maruyama I.; Sugimoto S.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.23, pp.223-243, 2025, .
(https://doi.org/10.3151/jact.23.223)
Abstract
Understanding the role of aggregates in the compressive strength of brittle composites is crucial for optimizing construction material usage. In this study, we employed the rigid-body-spring-network model validated with experimental data. Through uniaxial compression loading tests on concrete, considering Youngfs modulus and compressive strength of the coarse aggregate as variables, we elucidated how the coarse aggregatefs physical properties influence concrete's compressive strength, illustrated using a straightforward diagram. When the coarse aggregatefs Young's modulus is lower than the mortar's, the stress transfer path within the mortar bends and cracks more rapidly, significantly lowering strength. Conversely, if the coarse aggregatefs Youngfs modulus exceeds that of the mortar, stress becomes concentrated in the aggregate, and the crack of the coarse aggregate governs the failure of concrete. c 2025 Japan Concrete Institute. All rights reserved.
Impact of Fuel Consumption by Traffic on the CO2 Balance of Pavements
Shinmi T.; Kawai K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.23, pp.138-151, 2025, .
(https://doi.org/10.3151/jact.23.138)
Abstract
Pavement?vehicle interaction affects vehicle fuel consumption, and reducing fuel consumption lowers CO2 emissions. Therefore, replacing asphalt pavements, which result in greater vehicle fuel consumption, with concrete or composite pavements when repairing pavement may reduce CO2 emissions for vehicle driving. This paper proposes a calculation method for CO2 emissions considering fuel consumption reduction by pavement?vehicle interaction and evaluate the difference in environmental impact among pavement types. We consider the reduction in CO2 emissions from cars as an environmental contribution by concrete or composite pavement, and we propose an evaluation method to introduce the reduction into the calculation of CO2 emissions throughout the life cycle of the pavement. We also introduce the effect of environmental temperature on CO2 emission reductions into the evaluation method. The results show that concrete and composite pavements have higher CO2 emissions than asphalt pavements throughout the life cycle of the pavement. Nevertheless, the reduction in CO2 emissions owing to the lesser fuel consumption by cars in concrete and composite pavements is significant, and CO2 emissions of concrete and composite pavements, including the effect of reduced fuel consumption, may be less than CO2 emissions of asphalt pavements, especially in cold areas. Copyright c 2025 Japan Concrete Institute.
Effect of NBO/T of Biomass Ash on Compressive Strength of Hardened Cement: New Insights from Evaluation of Pore Structure and Hydration Products
Takagi R.; Hayashi T.; Kamimura K.; Saito T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.23, pp.50-63, 2025, .
(https://doi.org/10.3151/jact.23.50)
Abstract
This study investigated the physical properties of hardened cement incorporating biomass ash (BA), considering the effect of the ratio of nonbridging oxygen atoms to tetrahedral-forming ions (NBO/T), a chemical indicator of ash. The reactivity of fly ash (FA) exhibited strong positive correlation with NBO/T, which can also serve as a reactivity indicator for other supplementary cementitious materials like slag. Chemical analysis revealed that BA possesses properties of both FA and blast furnace slag. During curing, the number of voids corresponding to small and large gel pores, formed by coagulated C?S?H, increased significantly, with sizes reaching tens of nanometers. Fourier transform infrared and aluminum nuclear magnetic resonance analyses showed that cement incorporating BA had higher compressive strength than coal ash-based cement, with higher contents of ettringite, C?A?S?H, and monosulfate after 28 days. This was attributed to the distinct compositions of coal and BA, alongside the usage of seawater and gypsum. Moreover, BA further enhanced the compressive strength owing to the influence of hydration products, including C?S?H. This positive correlation between NBO/T of BA and the compressive strength of the cured material suggests that NBO/T can serve as an indicator for estimating cement blending strength. This paper is the English translation from the authorsf previous work [Takagi, R., Hayashi, T., Kamimura, K. and Saito, T., (2023). gEffect of NBO/T of biomass ash on compressive strength of hardened cement.h Cement Science and Concrete Technology, 77, 153-162. (in Japanese)]. c 2025 Japan Concrete Institute.
Effect of Wet?dry Cycles and Water-to-cement Ratios on Cement Paste Carbonation
Zhao Z.; Oh D.; Kitagaki R.; Zheng T.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.23, pp.205-222, 2025, .
(https://doi.org/10.3151/jact.23.205)
Abstract
Cement production is associated with significant energy consumption and CO2 emissions, whereas concrete waste from demolition and renovation has the potential for CO2 absorption. This study investigated the effects of relative humidity and water-to-cement (w/c) ratio on the carbonation of hardened cement pastes with w/c ratios of 0.4, 0.5, and 0.6. Thermogravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy were used to analyze the carbonated samples, which were exposed to five different constant humidity conditions and underwent five types of wet?dry cycles. The results indicated that higher w/c ratios increased the hydration degree and pore formation, facilitating CO2 diffusion and promoting carbonation. Wet?dry cycles enhanced pore generation and calcium silicate hydrates (C-S-H) decomposition through shrinkage and deformation during the drying process. In addition, the minimum and maximum humidity of the wet?dry cycles influenced the formation of vaterite and amount of vaterite converted to calcite. The highest CO2 uptake after 14 days for WC06-40100 with a w/c ratio of 0.6 exhibited twice that of RH40 and 22% higher than that of RH80 on day 14. Moreover, the amount of CO2 uptake under RH40-100 for 28 days was approximately 17% of the annual CO2 emissions from cement production. c 2025 Japan Concrete Institute. All rights reserved.
Freeze-thaw Resistance of Concrete using Ground Granulated Blast-furnace Slag and Blast-furnace Slag Sand in Salt Water
Ayano T.; Fujii T.; Okazaki K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.253-266, 2024, .
(https://doi.org/10.3151/jact.22.253)
Abstract
The freeze-thaw resistance of concrete is significantly lower in salt water than in fresh water. Concrete deteriorates through repeated freezing and thawing, but in salt water, freezing alone leads to destruction. This paper investigated the effect of calcium hydroxide in concrete on the failure of concrete under such low temperatures. Calcium hydroxide precipitates at the transition zone between aggregate and cement paste due to the hydration of cement. The lower the temperature and the higher the concentration of salt water, the more calcium hydroxide dissolves. From concrete, more calcium hydroxide is eluted in salt water than in fresh water. This accelerates the deterioration of mortar and concrete due to freeze-thaw action. Mortar and concrete using ground granulated blast-furnace slag produces less calcium hydroxide. In mortar and concrete using blast-furnace slag sand, calcium hydroxide precipitated around the aggregate reacts with cement paste and blast-furnace slag sand to modify the transition zone. From these results, it was clarified that concrete using blast-furnace slag exhibits high freeze-thaw resistance even in salt water. Copyright c 2024 Japan Concrete Institute.
Numerical analysis of flow and segregation of self-consolidating concrete during casting of reinforced elements
Chen W.; Li Z.; Shi C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.735-750, 2024, .
(https://doi.org/10.3151/jact.22.735)
Abstract
It is well known that whether self-consolidating concrete (SCC) can be self-consolidated mainly depends on its flowability and segregation resistance. The shape and grading of coarse aggregate (CA) particles, as well as the arrangement of reinforcing bars, are two of the main factors influencing these properties. In this study, we developed a new meshless particle method that can reflect the influences of CA shape and rebar on concrete flow and segregation behavior during casting reinforced elements. Fresh concrete was represented by irregular CA particles and spherical mortar particles. CA particles were formed by small elementary particles (EP) to have their actual sizes and shape index. Then, the flow and segregation behaviors of two kinds of concrete in an L-shaped box with rebars were investigated experimentally and numerically, respectively. As a result, compared to the original double-phase & multi-particle (DPMP) method, the proposed numerical method improves the simulation accuracy by approximately 30% for flow behavior, and 20% for segregation behavior, respectively, during casting reinforced SCC using crushed stone as CA with poor shape, however, shows only a slight improvement when simulating the flow and segregation behaviors of SCC using artificial aggregate as CA with nearly spherical shape. Copyright c 2024 Japan Concrete Institute.
Effect of Fly Ash Content on Rheological Properties of Self-compacting Geopolymer Mortar
Ghafoor M.T.; Fujiyama C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.103-114, 2024, .
(https://doi.org/10.3151/jact.22.103)
Abstract
This study is a continuation of the published research studies relevant to self-compacting geopolymer mortar (SCGM) prototype using fly ash. The aim of this study was to investigate the effect of fly ash quantity on the rheological properties of SCGM. The flow properties include relative flow area (Gm) and relative funnel speed (Rm) is determined with the variation of fly ash to sand ratio (FA/S), volume of water to powder ratio (Vw/Vp), and superplasticizer to powder ratio (Sp/P). The test results exhibited that the increase in FA/S from 0.5 to 1.0 positively affected the Gm and Rm of SCGM. The maximum Gm of 10.90 and Rm of 1.43 were obtained for the SCGM mix having FA/S of 1.0, Vw/Vp of 1.02, and Sp/P of 3%. Overall, test results exhibited that with an increase in FA/S comparable flow properties of SCGM were achieved even at lower Vw/Vp and Sp/P. The recommended boundary for SCGM is proposed by comparing the experimental test result of this study with previous studies. c 2024 Japan Concrete Institute.
Extraction of Carbonation Rate from Depth Profile of Concrete Carbonation by using Pseudo-analytical Solution of Two-component Reaction-diffusion Equation
Ichikawa T.; Haga K.; Yamada K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.139-148, 2024, .
(https://doi.org/10.3151/jact.22.139)
Abstract
The accurate numerical solution of a one-dimensional two-component reaction-diffusion equation including a second-order chemical reaction between concrete constituents and carbon dioxide to generate carbonated products was approximated by a simple analytical function which was given as a function of the effective diffusion coefficient of CO2, the rate constant of CO2 absorption, and parameters determined by the initial and the boundary conditions of the system. The pseudo-analytical solution thus obtained showed that the depth profile of carbonation shifts in parallel with square-root of time, and the rate constant of carbonation is determined from the location where the amount of the carbonated product is a half of the maximum amount. Comparison of the pseudo-analytical solution with an observed depth profile of concrete carbonation makes it possible to directly extract the rate constant of concrete carbonation that is necessary for predicting the future progress of the carbonation. Copyright c 2024 Japan Concrete Institute.
Structural Performance of RC Members Affected by Alkali?silica Reaction According to Crack Patterns
Joo H.E.; Takahashi Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.455-470, 2024, .
(https://doi.org/10.3151/jact.22.455)
Abstract
The structural performance of reinforced concrete (RC) members affected by alkali?silica reaction (ASR) is difficult to predict because of the multi-scale phenomena. Recent structural tests reveal that the performance of RC members also depends on ASR-induced crack patterns, including localized cracks and dispersed microcracks. Additionally, microscopic factors, such as crack-filling by gel and presence of microcracks, are relevant. To explore this in detail, a computational system for finite element analysis of ASR-damaged RC members was developed. This study numerically investigated the structural behavior of ASR-affected RC members based on localized/dispersed crack patterns and microscopic factors. The applicability of the developed computational system was verified by comparing the analysis results with experimental data. The analysis results showed that ASR-damaged RC members with dispersed microcracks exhibited highly ductile behavior, while those with localized cracks failed in shear. This is because the dispersed crack pattern prevents the shear crack propagation and enhances the mechanical contribution of gel filling cracks, while the localized ASR cracks facilitate critical crack propagation, leading to failure, and minimize the gel-filling effect. Through the analytical investigations, it was found that the localized ASR cracks can result in significant loss of structural performance; thus, this study recommends the assessment of structural capacity of RC members in the case where the localized cracks were observed. Copyright c 2024 Japan Concrete Institute.
Development of Silicate-Based Surface Impregnation Solution with High Permeability for Restoration of Degraded Concrete
Kitada T.; Li Z.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.294-310, 2024, .
(https://doi.org/10.3151/jact.22.294)
Abstract
In this study, for developing a silicate-based surface impregnation solution with high permeability to repair degraded concrete from the surface to the interior, experiments were conducted to investigate the effect of blending sodium hydroxide (NaOH) on the permeability of the lithium silicate solution (LS) that is one of generally used silicate surface impregnation materials. The high permeability of the modified LS solution, composed of LS, NaO, and water, was confirmed by solution immersion test using several grades of concrete and heated concrete with different strengths, and by ICP-AES analysis. Appropriate NaOH blend significantly increased the penetration of LS into concrete. The appropriate NaOH blends and the mechanisms of increasing permeability were investigated by the setting time test of fresh pastes of modified LS solution and unheated or 650 C-heated Portland cement paste powders, and the SEM-EDS, XRD, TG-DTA analyses of hardened pastes. As a result, when NaOH is blended in an amount such that the Na/Si molar ratio of NaOH-modified LS solutions is in the range of 0.5-1.25, they have high permeability. The addition of NaOH reduces the solubility of Ca(OH)2, being a hydrate of Portland cement (PC), and therefore delays the calcium silicate formation between Ca(OH)2 and LS. This delay prevents the penetration path of LS from being quickly blocked by calcium silicate, thus LS permeability is improved. However, the addition of excessive NaOH destroys other hydrates of PC to dissolve Ca ions, instead increasing the calcium silicate formation. In addition, the blend of NaOH would increase the alkalinity of neutralized concretes. c 2024 Japan Concrete Institute.
Performance Recovery of Fire-damaged Concrete by Impregnation of NaOH-added Lithium Silicate
Li Z.; Kitada T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.751-768, 2024, .
(https://doi.org/10.3151/jact.22.751)
Abstract
When concrete is subjected to the elevated temperatures of a fire, cracking occurs and the mechanical performance and durability deteriorate. Current crack repair methods using epoxy or polymer cement cannot repair microscopic damage and cannot restore the performances of whole concrete. There is no effective method to promote the recovery of concrete properties after fire. In this study, the authors proposed to use a highly permeable and alkaline silicate surface impregnation solution (NW-LS) to repair fire-damaged concrete, which is composed of sodium hydroxide (NaOH), lithium silicate (LS) and water and can penetrate in the inside of concrete. The concretes used in the experiments had the compressive strengths of 24.4 to 60.0 MPa before heating, and were heated at different temperatures (300, 500, 650 C) and then cooled in water or air. The changes in the performances, chemical compositions, and internal structure of the concretes after repairing were investigated in detail. The experimental results indicate that the repair densified the internal structure of heated concretes by the reaction between the silicate of the solution and the Ca(OH)2 of the heated concretes, and greatly increased the compressive strength, carbonation resistance, and freezing-thawing resistance of the heated concretes. In addition, the alkalinity of heated concrete was restored by the NW-LS solution. Copyright c 2024 Japan Concrete Institute.
Cold-sintered Carbonated Concrete Waste Fines: A Calcium Carbonate Concrete Block
Maruyama I.; Bui N.K.; Meawad A.; Kurihara R.; Mitani Y.; Hyodo H.; Kanematsu M.; Noguchi T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.406-418, 2024, .
(https://doi.org/10.3151/jact.22.406)
Abstract
Cementitious materials generally have large carbon footprints because of the high CO2 emitted during Portland cement production. This is because limestone is used as an essential CaO resource, and its decomposition by calcination emits CO2. From this perspective, the concrete in urban buildings can be considered an urban mine of CaO resources. In this study, we propose obtaining a solidified product by crushing all the waste concrete, carbonating it, pressurizing it with a calcium bicarbonate solution, and drying it. The experimental results show that the bicarbonate solution, high-temperature conditions, and extended loading period produce a higher strength. In addition, neck growth at the contact surfaces of the carbonated concrete fines was confirmed using scanning electron microscopy. Consequently, the proposed method indicates that the hardening mechanism is the cold sintering of calcium carbonate on the surface of fine-carbonated concrete particles. This method allows the developed blocks to be used semi-permanently with relatively low energy consumption through repeated crushing and re-pressurization. Copyright c 2024 Japan Concrete Institute.
Development of a Large-scale Thermogravimetry and Gas Analyzer for Determining Carbon in Concrete
Maruyama I.; Noritake K.; Hosoi Y.; Takahashi H.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.383-390, 2024, .
(https://doi.org/10.3151/jact.22.383)
Abstract
One carbon neutralization measure applied in the concrete sector is the use of artificial carbonate in concrete for immobilization. This CO2 reduction technology corresponds to the CO2 emitted during concrete production. When considering the marketability of these technologies, especially for newly developed products in the carbon market, it is essential to quantify the amount of CO2 fixed as inorganic carbonate. Additionally, as a representative test specimen for concrete containing aggregate, a S100 ~ 200 mm cylinder specimen is conventionally used for physical property evaluation. To evaluate the amount of CO2 fixed in one batch of concrete, a mass far from that of the conventional chemical analysis sample may need to be analyzed. Therefore, in this study, we investigated a pulverization process for concrete analytical materials. We also propose a new analytical apparatus that can be used to measure large cylinder specimens. Experimental results showed that the newly developed analyzer, equipped with a mass balance and CO2 and H2O gas analyzer for large cylinders, exhibited excellent analytical variability and measurement speed performance. It was also inferred that the homogenization process is necessary to grind the entire cylindrical concrete specimen into a fine powder and homogenize it to improve the representativeness of the concrete. c 2024 Japan Concrete Institute. All rights reserved.
Estimation of the Protected Paste Volume by Spatial Tessellation Associated with the Point Pattern of Air Voids
Ohyama K.; Yamashita S.; Igarashi S.-I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.128-138, 2024, .
(https://doi.org/10.3151/jact.22.128)
Abstract
Paste volumes protected by air voids against frost attacks were estimated using Dirichlet tessellation tiles. Each tile was regarded as an area protected by air voids. The characteristic distance was defined by the largest tile size to reach a cumulative area fraction of 0.95. The significance of this distance was verified by a Monte Carlo test for the simulation of random point patterns. Comparing the characteristic distance and conventional spacing factor, the latter corresponds to the actual distance required for protecting the local region with the highest vulnerability to frost attack. The tessellation model provides the protection characteristic distance without overlaps even in the region of clustered air voids. c 2024 Japan Concrete Institute.
Suppression of Segregation and Effective Utilization of Residual Concrete Containing Excess Water by Adding Paper Sludge Ash
Onoue K.; Atarashi D.; Tabata K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.784-796, 2024, .
(https://doi.org/10.3151/jact.22.784)
Abstract
Unused residual concrete, retaining an excess water post-washing, is typically discharged at ready-mixed concrete plants, where it undergoes segregation into concrete debris and sludge. The significant expense incurred in managing concrete sludge disposal presents a pressing challenge. This study focuses on the high water absorbency of paper sludge ash (PSA) to develop a novel technology aimed at reducing excess water content in residual concrete. This is achieved by directly adding PSA into the drum of an agitator truck and agitating, thereby minimizing segregation. Laboratory experiments conducted with simulated residual concretes demonstrate that as the PSA-to-excess-water ratio increases, there is a corresponding reduction in slump value and amount of bleeding, coupled with an increase in compressive strength. Additionally, an equation is proposed for estimating excess water content in residual concrete using a time-domain-reflectometry, facilitating the calculation of PSA amount required on-site. The efficacy of the proposed equation is substantiated through demonstration experiments conducted at a ready-mixed concrete plant, affirming the significant property enhancement facilitated by PSA in residual concrete. c 2024 Japan Concrete Institute.
Development of Post-installed Headed Bars Embedded into Grouted Holes with Enlarged Ends
Ousalem H.; Horiuchi G.; Hamada A.; Takatsu H.; Idosako Y.; Masuda H.; Hiroshima Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.62-76, 2024, .
(https://doi.org/10.3151/jact.22.62)
Abstract
To secure good quality post-installed anchors with a relatively short anchorage length and sufficient pull-out/shear resistance, an anchoring method with enlarged diameter at the end of drilled holes has been developed. Anchors were provided with head plates and fixed into the enlarged holes using non-shrinkage high-strength cementitious grout. Pull-out and shear preliminary tests were conducted to investigate the behavior and evaluate the strength of such anchors set in concrete. Furthermore, an evaluation method, based on the Japanese recommendations for design of composite constructions, was proposed. The evaluated pullout and shear capacities of all tested anchors designed to fail by steel yielding ensured sufficient safety margin as to test results, whereas those of some anchors designed to fail by concrete cone breakout should be reduced. c 2024 Japan Concrete Institute.
Assessment on Bond Strength of CFRP Sheet Bonded to Concrete Focused on Sheet Stiffness
Ozaki M.; Sato Y.; Yoshida E.; Takeuchi A.; Yamada Y.; Nagashima F.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.190-206, 2024, .
(https://doi.org/10.3151/jact.22.190)
Abstract
In previous studies on the bond behaviors of FRP sheets attached to concrete, specimens for bond tests that contained FRP sheets with relatively low stiffnesses were used. However, in actual strengthening design, high stiffnesses of FRP sheets are required because the scale of the structure is very large. Therefore, in this study, bond tests were conducted using specimens with many different sheet stiffnesses and with polyurea resin. As a result, the bond strength increased as the stiffness increased with multiple CFRP sheets. Nevertheless, existing bond strength models overestimated the bond strength when the stiffness exceeded 200 kN/mm. In addition, 3D scanning measurements of patterned and indented concrete thin layers behind CFRP sheets revealed that the interfacial fracture energy was strongly related to the surface area of the concrete thin layer, not to the CFRP sheet stiffness or the resin properties. Copyright c 2024 Japan Concrete Institute.
Applicability of XRD/Rietveld Analysis with an External Standard Method for the Quantification of Mineral Components in Carbonated Hardened Cement Paste
Saeki N.; Kurihara R.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.602-619, 2024, .
(https://doi.org/10.3151/jact.22.602)
Abstract
For the quantification of mineralogical components in cementitious materials using XRD, the external standard method, where the standard material is measured separately from the samples, has several advantages in avoiding artifacts arising from internally mixing the standard material. This method has been applied to the quantification of cement clinker and its hydration process, but rarely to its carbonation progress. In this study, we examined its applicability to carbonated cement pastes. By determining the H2O and CO2 amount contained in each sample, the mass attenuation coefficient was calculated, which enabled quantification using the external standard method. Four different standard materials were examined, among which ?-corundum was regarded as the most crystalline, and hence, most suitable. Comparing the obtained quantitative amounts of portlandite and calcium carbonate with those in the TG results and the calcium aluminate phases with those in 27Al NMR results, we demonstrated that the external standard method can accurately quantify the crystalline amount. Additionally, it was shown that the choice of the crystal structure of vaterite for Rietveld refinement has a significant influence on the quantification in Rietveld refinement. c 2024 Japan Concrete Institute. All rights reserved.
Influence of the Unit Content and Grading Distribution of Fine Aggregates on the Long-term Skid Resistance of Concrete Pavement
Senthilvelan J.; Izuo H.; Endo T.; Ueno A.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.431-444, 2024, .
(https://doi.org/10.3151/jact.22.431)
Abstract
This study analyzed the influences of the unit content (UC) and grading distribution (FM) of fine aggregates on the longterm skid resistance (SR) of concrete pavement. For this purpose, laboratory specimens using fine aggregates with varying UCs and FMs were made. This study used to measure the SR using a dynamic friction tester (DFT). Additionally, threedimensional (3D) profile data of the specimen surfaces were collected using a 3D laser profilometer after specific intervals of surface polishing. This study examined the characteristics of SR by surface amplitude indices at specific wavelengths. Furthermore, this paper presents an SR prediction model through multiple linear regression analysis using surface amplitude indices. The results revealed that a combination of micro- and macrotexture amplitude indices at specific wavelengths is suitable for expressing SR. This study also showed that both the UC and FM of fine aggregates have a significant influence on long-term SR. Furthermore, the evaluation of SR using the predicted indices showed the sharpness, shape, and roughness interaction at specific wavelengths with SR. This study recommends that road engineers use this information for better understanding. c 2024 Japan Concrete Institute.
Meso-scale Modeling of Anomalous Moisture Transport in Concrete Considering Microstructural Change of Cement-based Material
Srimook P.; Ogawa K.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.344-371, 2024, .
(https://doi.org/10.3151/jact.22.344)
Abstract
Moisture transport is the key phenomenon indicating the deterioration of the durability and structural performance of concrete structures. Although various studies have attempted to evaluate moisture transport in concrete, an anomalous behavior, which does not follow the root-t law compared to other porous material, was not explicitly taken into account. To quantitatively evaluate anomalous moisture transport, this study developed a couple of numerical methods between the truss-network model (TNM) and the rigid-body-spring model (RBSM) for this purpose. The colloidal behavior of calcium-silicate-hydrate (C-S-H), which is the major phase of cement-based material, was introduced to consider the anomalous behavior and mechanical response regarding the microstructural change of cement paste as well as cracks that significantly accelerate the moisture transport in concrete. The numerical results indicated that both microstructural change of cement paste and rapid absorption through cracks cause anomalous behavior. In addition, the numerical results suggest that volumetric change of cement paste should rely on water content related to the colloidal behavior of C-S-H in order to reproduce the realistic expansion and the closure of cracks during a rewetting process that affects structural performance and durability of concrete. Copyright c 2024 Japan Concrete Institute.
Case Study on the Effect of Mechanically-compacting Flowable Concrete with Low CO2 Emission on Productivity, Economic Efficiency, and Environmental Impact
Suzuki M.; Kato Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.576-587, 2024, .
(https://doi.org/10.3151/jact.22.576)
Abstract
The authors are developing mechanically-compacting flowable concrete with low CO2 emission for rationalization, labor reduction in concrete work, and reduction of CO2 emissions. In this paper, as a case study on the application of developed concrete, a concrete mix and a combination of reinforcement materials that satisfy the design criteria strength and specified durability have been set, and their application in terms of productivity, economy, and environmental impact has been estimated. The desired improvement in productivity and reduction in CO2 emissions could be achieved, and the construction costs required to achieve these goals were generally understood. The CO2 price in CO2 emissions trading was calculated for each case, and it was shown that the CO2 price depends on the CO2 reduction measure. Copyright c 2024 Japan Concrete Institute.
Quantification of CO? in Cement Pastes with Different Degrees of Carbonation
Takahashi H.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.706-715, 2024, .
(https://doi.org/10.3151/jact.22.706)
Abstract
In the cement and concrete industries, technologies are being developed to reduce CO? emissions by fixing it as inorganic carbonates within cementitious materials. This study quantitatively analyzed the CO? content in cement pastes under different carbonation conditions using back-titration, thermogravimetry (TGA), and combustion-infrared absorption methods. The analysis of silica gel produced from the decomposition of C-S-H and gas components generated during the thermal analysis of carbonated samples allowed for an evaluation of the sample properties and an examination of the errors associated with each quantification method. Back-titration effectively decomposed carbonates and cement hydrates, accurately quantifying CO? regardless of the composition and amount of silica gel. In contrast, TGA tended to underestimate CO? as it failed to detect CO? derived from calcium carbonate polymorphs at lower temperatures. The combustion-infrared absorption method showed slightly higher CO? quantification compared to back-titration due to the influence of residual organic matter, and equipment without a desulfurization tube tended to quantify even more CO? Copyright c 2024 Japan Concrete Institute.
A Proposal of Maturity Function on the Strength Development of Concrete Below the Freezing Point
Taniguchi M.; Hama Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.311-326, 2024, .
(https://doi.org/10.3151/jact.22.311)
Abstract
Compressive strength development of concrete is essential for cold weather concreting. It is well known that the strength development of concrete at temperatures below the freezing point is much delayed, however, the evaluation method for sub-zero temperatures has not been shown clearly yet. Therefore, when the average outside air temperature is under freezing point the planning method for cold weather concreting is not clear. This study focused on the effect of temperature on the strength development of concrete under sub-zero conditions by conducting various experiments. As a result, a function is proposed to calculate the maturity below the freezing point. The proposed function could explain the strength development of the concrete exposure in winter. c 2024 Japan Concrete Institute.
Test Method of Segregation Resistance of High Fluidity Concrete Based on Numerical Simulation of Dynamic Segregation of Coarse Aggregate
Xu Z.; Li Z.; Liu J.; Chen W.; Liu J.; Han F.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.372-382, 2024, .
(https://doi.org/10.3151/jact.22.372)
Abstract
The workability of high fluidity concrete (HFC) also depends on its segregation resistance besides fluidity, and gap-passing ability, etc. Currently, there is a lack of easy, quantitative method for evaluating segregation resistance. Efficient assessment is crucial for construction applications of HFC. This paper aims to propose a simple test method for the segregation resistance of HFC on basis of the J-ring test that has been generally used for evaluating the fluidity and passing ability of HFC. Experiment and numerical simulation of J-ring test were conducted for HFCs with different fluidity and segregation resistance. The fresh concretes were treated as two-phase granular fluids of matrix mortar and coarse aggregate in simulation by a newly developed particle meshless method, called DPMP-MPS. The flow and segregation behaviors of the HFCs during J-ring test under different lifting speeds of slump cone were investigated. The numerical results demonstrate a close correlation between the final flow value to slump value ratio (SF-J/SL-J ratio) and the segregation resistances of HFCs. Consequently, the J-ring test can assess the segregation resistance based on the SF-J/SL-J ratio. Notably, it emphasizes that, for precise evaluation of HFC workability using the J-ring test, the lifting speed of the slump cone should fall within the range of 10 to 15 cm/s. Copyright c 2024 Japan Concrete Institute.
Damage Evaluation of Circular Tunnels Subjected to Local Deformation in Fault Crush Zones
Yamanoi Y.; Miyagawa Y.; Nagata S.; Sakashita K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.769-783, 2024, .
(https://doi.org/10.3151/jact.22.769)
Abstract
Tunnels that cross fault crush zones are subject to local deformation along these zones during earthquakes. Because the tunnel axis and the fault plane generally intersect in a three-dimensional manner, evaluating structural performance by using three-dimensional FEM is reasonable, and to this end selection of an appropriate damage indicator is required. To establish a damage evaluation method for the safety of tunnels subjected to local deformation, three-dimensional FEM analysis was carried out on previous loading experiments, the failure modes were analyzed, and the applicability of several damage evaluation indicators was verified. As a result, the damage to the tunnel in the model experiments was broadly classified into in-plane shear in the longitudinal section and out-of-plane shear in the longitudinal or transverse section. Performance evaluation using compressive damage indicators including minimum principal strain when the limit state of a tunnel is defined as the point at which the resistance to slippage in the crush zone is maximum was found to be feasible. Moreover, the results of the sensitivity analysis showed that evaluation based on the minimum principal strain is broadly applicable. Additionally, a limit value considering element size was proposed. c 2024 Japan Concrete Institute. All rights reserved.
Influence of Rebar Strength, Pre-treatment, and Measurement Method on Residual Stress Measurement using Portable X-ray Diffractometer
Yanagida R.; Fukada S.; Sasaki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.391-405, 2024, .
(https://doi.org/10.3151/jact.22.391)
Abstract
It is effective for the maintenance of existing structures to understand the current status, such as the residual stress of the materials used, and a portable X-ray diffractometer is used as a technique for measuring steel stress. Although measurement methods and pre-treatment for steel bars with low strength have been revealed, the influence of the strength on the X-ray stress measurement and the appropriate measurement method has not been clarified. In this study, residual stress measurements using the X-ray diffraction are performed on steel bars, the differences in the results for various steels with different strengths are discussed, and measurement conditions for accurate measurement are reported. In addition, the cause of the tendency of the X-ray stress measurement to be smaller than the actual increment value under high stress is investigated. The experimental results show that the appropriate measurement conditions vary depending on the rebar strength, and that the X-ray stress measurement under high stress also varies. The metallurgical structure of the steel was shown to be related to the cause of this phenomenon through microstructural observation and analysis of the deformation behavior. Copyright c 2024 Japan Concrete Institute.
Bond Strength of Post-installed Anchor Adhering to Damaged Concrete by Freeze-thaw Action
Yano Y.; Shiokoshi T.; Takase Y.; Ishida Y.; Abe T.; Takahashi M.; Ishigaki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.178-189, 2024, .
(https://doi.org/10.3151/jact.22.178)
Abstract
Reinforced concrete (RC) structures in cold regions are susceptible to surface deterioration due to freeze-thaw cycles (FTC). For sustainable development goals (SDGs) and a decarbonized society, damaged structures should be repaired and reinforced. Post-installed anchors are commonly used for seismic retrofitting and equipment fixation. However, research on the bond characteristics of damaged concrete is limited. Therefore, in this study, the bonding performance of adhesive anchors in damaged concrete was investigated. Liquid nitrogen was employed to subject the concrete surface to FTC subsequently, bond-slip tests were conducted with the degree of deterioration serving as a parameter. The results suggested, the bond strength decreased as the degree of damage increased. The reduction ratios of the post-installed anchor with epoxy and cement-based resins were almost identical. Furthermore, a bond strength equation was proposed by referring to the bond-slip model between the rebar and concrete (fib 1990). The test results were well predicted with a correlation coefficient of 0.94. This study is based on previous studies (Yano et al. 2022, 2023) but presents new findings. c 2024 Japan Concrete Institute. All rights reserved.
Structural Behaviors of Steel Tube-encased Concrete Columns Confined by Bolted Circular Thin Steel Tube
Zhang C.; Yamaoka K.; Fujinaga T.; Sun Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, pp.115-127, 2024, .
(https://doi.org/10.3151/jact.22.115)
Abstract
Six square steel tube-encased concrete (SC) columns confined by bolted circular thin steel tube were fabricated and tested under cyclical reversed lateral load to investigate their structural behavior. The primary experimental variables included the axial load ratio, the grade of the encased square steel tubes (FB rank and FC rank), the infilling of concrete into the encased steel tube, and the thickness of outer circular bolted thin steel tubes. Experimental results revealed that confinement by the bolted circular thin steel tube with outer-diameter-to-thickness ratio of 189 could ensure sufficient ductility to the SC columns, and the bolted thin steel tube did not rupture until the drift angle of about 0.09 rad. Furthermore, a simple evaluation method for the ultimate flexural strength of SC column section was proposed along with a numerical analytical method to predict the overall behavior of SC columns. The proposed methods can take the confinement effect by the bolted circular steel tube into consideration. Fairly good agreement between the experimental results and the calculated ones verified the reliability and accuracy of the proposed methods. c 2024 Japan Concrete Institute. All rights reserved.