Journal of Advanced Concrete Technology(2022 - 2023)
Thermal Expansion of Cement Paste at Various Relative Humidities after Long-term Drying: Experiments and Modeling
Aili A.; Maruyama I.; Vandamme M.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.151-165, 2023, .
(https://doi.org/10.3151/jact.21.151)
Abstract
The coefficient of thermal expansion (CTE) of cement paste is an essential parameter for estimating cracks of cement-based structures, including under normal operating conditions. The CTE of low-heat Portland cement pastes dried for a long term at various relative humidities were measured by applying trapezoidal temperature history. The measured CTE was a convex function when displayed versus relative humidity and was highest at the relative humidity of 58%. At the relative humidity of 11%, the CTE was similar to the one of the fully dried sample. Based on a drying shrinkage model in the literature that classifies pore water as free liquid water and adsorbed water, we computed pore pressure change and corresponding strain, from which the CTEs were estimated. The microstructural rearrangements of cement paste due to long-term drying were taken into account by obtaining pore size distributions from water vapor sorption isotherm. The CTEs predicted with the model agree well with the measured ones. Copyright c 2023 Japan Concrete Institute.
Study on Mix Proportion Design Procedure for Super-high Cementitious RCC with Stone Powder Replacement
Aosaka Y.; Tsutsui S.; Miki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.123-135, 2023, .
(https://doi.org/10.3151/jact.21.123)
Abstract
Super-high cementitious roller-compacted concrete (SHCRCC) that have unit cementitious materials content of 220 kg/m3 or higher can be recognized as "construction friendly RCC". In this study, the proposition of how to reduce construction costs without sacrificing the workability was investigated. To solve the issue, mix proportions replacing the high volume of cementitious materials, cement, and fly ash with stone powder (SP) were surveyed. Based on exhaustive investigations, it was found that the mix proportion can be realized with sufficient tolerance of workability. In the proposed mix proportion, the cementitious materials replaced with SP up to about 100 kg/m3 provide a large paste volume of 240 to 260 L/m3. In addition, it was verified that the SP plays a sufficient role as an alternative to cementitious materials since the compressive and tensile strengths of the RCC, and the watertightness and bond strength at lift joints are the same as, if not better than high cementitious RCC (HCRCC). Reducing cementitious materials also helps to control the temperature rise of the RCC. In the case of a large-scale RCC dam of 150 m in height and 2 million m3 volume with 5 zones, it is found that a cost reduction is about 25 to 30% for cementitious materials and chemical admixture, and a placement speed is about 20% faster than that of medium cementitious RCC (MCRCC) thanks to a large workability margin. c 2023 Japan Concrete Institute. All rights reserved.
Wet-carbonation-based Mineral Extraction and CO2 Sequestration Using Concrete Waste Fines at a Low Temperature
Bui N.K.; Kurihara R.; Wang W.; Kanematsu M.; Hyodo H.; Takano M.; Hirao H.; Noguchi T.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.166-188, 2023, .
(https://doi.org/10.3151/jact.21.166)
Abstract
This study investigates the wet carbonation of concrete fines with CO2 and natural air gas bubbling in a carbonation system at low temperatures. After the air- and CO2-wet carbonations, the properties of a solution and hydrated cement paste powder are determined. In the air and CO2-wet carbonations, more Ca is extracted into the solution at a low temperature of 5C. This high Ca concentration in the solution through air-wet carbonation primarily originates from the portlandite and unhydrated phases of the cement paste. Even in solutions with high pH values, the rehydration process and C?S?H decomposition occur simultaneously in air-wet carbonation. Moreover, CO2-wet carbonation indicates that the decalcification of C?S?H occurs rapidly, even in the presence of portlandite. Air-wet carbonation presents a potential method for the direct air capture of CO2 using concrete waste fines in a short period. Copyright c 2023 Japan Concrete Institute.
Stress-bearing Mechanism of Concrete Damaged by Delayed Ettringite Formation under Compressive Stress with Various Loading Patterns
Fujishima M.; Miura T.; Kawabata Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.294-306, 2023, .
(https://doi.org/10.3151/JACT.21.294)
Abstract
The involvement of expansion cracks in reducing compressive properties was experimentally evaluated. Concrete specimens deteriorated by delayed ettringite formation were subjected to three loading patterns (monotonic, stepwise cyclic and sustained loadings) and digital image correlation was performed to observe the behavior of expansion cracks during compressive loading. As a result, while significantly large plastic deformation was generated in the pre-peak, the reduction in compressive properties was hardly influenced by the loading patterns. The elastic strain, obtained from the loading hysteresis, increased linearly until a maximum load was reached. Consequently, two possible stress-bearing mechanism of concrete damaged by delayed ettringite formation under compressive stress was proposed to explain the development of elastic and plastic strains and the reduction in the compressive property. Copyright c 2023 Japan Concrete Institute.
Effect of Original Mix Proportion on Rapid Removing of Attached Mortar for Recycled Concrete Aggregate Through a Freeze-thaw Approach
Gong F.; Wang Z.; Yang L.; Wu Q.; Ning Y.; Zeng Q.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.477-491, 2023, .
(https://doi.org/10.3151/jact.21.477)
Abstract
The fundamental reason to the unsatisfied performance of recycled aggregate concrete (RCA) is the existence of attached mortar in recycled concrete aggregate. A new physical method to remove the attached mortar is proposed in this study, which is a multiple process based on freeze-thaw cycles (FTCs). This study adopts the freeze-thaw modification technology and explores its efficiency in treating RCA with different strength and water to cement ratio. The effectiveness of such modification method is also evaluated, where the results show that for w/c=0.68, 10-15 freeze-thaw cycles are needed, for w/c=0.54, 15-20 FTCs are required and for w/c=0.38, 20-25 cycles are necessary. The mechanical properties of unmodified recycled aggregate concrete (RAC) are related not only to the strength of the parent concrete, but also to the content of attached mortar of recycled concrete aggregate and its durability which is further related to the water-cement ratio (w/c). On the other hand, modified recycled aggregate concrete (mRAC) could achieve satisfied mechanical properties and long-term properties as using natural aggregate concrete (NAC). Copyright c 2023 Japan Concrete Institute.
Crack Resistance under Compressive Stress of Concrete Made Using Granulated Blast-furnace Slag Sand
Hashimoto R.; Onoue K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.17-24, 2023, .
(https://doi.org/10.3151/jact.21.17)
Abstract
Cyclic loading tests are conducted for four cases with upper-limit stress ratios of 35%, 50%, 65%, and 80% in order to investigate the crack resistance under compressive stress of concrete made using granulated blast-furnace slag sand (BFS), obtained from three steelworks in Japan. Mountain sand is used as a natural aggregate for comparison and the energy for crack nucleation and propagation is derived for each type of concrete. It is found that BFS concrete generally has a lower crack propagation energy and a higher strain recovery rate than concrete made using natural aggregate. Within the scope of the study, BFS concrete is deemed to possess adequate resistance with respect to concrete crack propagation, regardless of the type of BFS used. This paper is an English translation of the authors' previous work [Hashimoto, R. and Onoue, K., (2022). gCrack resistance of concrete using granulated blast-furnace slag sand under compressive stress.h Proceedings of the Japan Concrete Institute, 44, 338-393. (in Japanese)]. Copyright c 2023 Japan Concrete Institute.
Physicochemical Analysis of Chloride Diffusion and Adsorption in Water-saturated Concrete: Theory and Measurement
Ichikawa T.; Haga K.; Yamada K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.218-233, 2023, .
(https://doi.org/10.3151/jact.21.218)
Abstract
The theory of ionic diffusion in water-saturated concrete accompanying ion exchange with mobile or immobile adsorbed ions was constructed by using the general theory of diffusion and the condition of electrical neutrality. Analysis of the diffusion profile of chloride (Cl-) ions in concrete with the theory revealed that adsorbed Cl- ions in AFm and C-S-H are as mobile as free Cl- ions in the pore solution, so that the adsorption does not retard the ingress of Cl- ions. The existing test methods for determining the effective or apparent diffusion coefficient of Cl- ions were evaluated on the bases of the present theory and new experimental findings. It was revealed that steady-state electrochemical methods such as NTBUILD-355 and ASTM C1202 are not suitable for determining the diffusion coefficient, because the steady state methods expel preexisting diffusible ions which strongly affect the diffusion of Cl- ions. Moreover, the steady state methods overestimate the diffusion rate because the methods assume that adsorbed Cl- ions are immobile. The electrochemically- accelerated method NT BUILD 443 is also unsuitable for the diffusion test, because the acceleration is induced by the electro-osmotic flow of the external solution into concrete. The present diffusion theory necessitates the effective selfdiffusion coefficient of not only Cl- ions but also all the other diffusible ions in concrete. A simple method of determining the effective self-diffusion coefficients of arbitrary ions in concrete from the diffusion profile of Cl- ions was presented. c 2023 Japan Concrete Institute.
Impact of Radiation-induced Expansion of Aggregate on Structural Performance of Hollow Cylindrical RC Member
Kambayashi D.; Maruyama I.; Kontani O.; Sawada S.; Ohkubo T.; Murakami K.; Suzuki K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.536-554, 2023, .
(https://doi.org/10.3151/jact.21.536)
Abstract
Reinforced concrete (RC) hollow cylindrical members were numerically investigated to understand the impact of the radiation-induced volume expansion of aggregates on the seismic performance of the member. The rigid body spring network model was used in this analysis, and the proposed constitutive laws and used parameters were validated by comparing two horizontal loading experiments for two RC members: a reference experiment and one in which a temperature gradient developed in wall of the members. The resultant volume expansion of concrete was confirmed. After validating the methodology, different degrees of aggregate expansion strain were applied to the aggregate elements considering the reduced temperature and neutron fluence distribution inside the wall, assuming the real size of the biological shielding concrete. The RC members were then loaded horizontally. It was confirmed that the stiffness and maximum bearing capacity decreased slightly with an increase in the neutron fluence, and the deformation at the maximum bearing capacity increased slightly. Based on the rigid body spring network model calculation results, a simplified analytical model that can reproduce the shear deformation?horizontal load relationship was proposed based on the model proposed by Inada (1987). c 2023 Japan Concrete Institute. All rights reserved.
Tension Stiffening Affected by Radiation-induced Volume Expansion of Aggregate
Kambayashi D.; Maruyama I.; Kontani O.; Sawada S.; Ohkubo T.; Murakami K.; Suzuki K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.351-366, 2023, .
(https://doi.org/10.3151/jact.21.351)
Abstract
The tension stiffening behavior of reinforced concrete (RC) prisms, affected by the aggregate volume expansion induced by neutron irradiation, were numerically investigated using a rigid body spring network model. First, the model was validated by comparison with the uniaxial tension test results of wet- and dry-cured (with volume contraction of concrete) RC prisms. Subsequently, different degrees of expansion strain were applied to the aggregate elements in the RC prism model and the uniaxial tension loading was simulated again. Tension stiffening decreased under larger radiation-induced volume expansion of the aggregate owing to the corresponding decrease in the concrete tensile strength with increasing damage, this behavior changed considerably according to the restraint condition. Indeed, the Youngfs modulus of the restrained concrete after aggregate expansion was larger than that of the unrestrained concrete after aggregate expansion. However, the compressive stress in the concrete after aggregate expansion was effectively transmitted to the rebar during uniaxial tension loading; this behavior indicated that RC could maintain its integrity under uniaxial tension even after 0.5% aggregate linear expansion. c 2023 Japan Concrete Institute. All rights reserved.
Applicability of Deformation Indices Reasonably Evaluating Load Carrying Capacity and Failure Mode of Full-Scale RC Members Subjected to Bilateral Loads
Komatsu S.; Miyagawa Y.; Matsuo T.; Hata A.; Shimabata T.; Nakamura H.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.421-435, 2023, .
(https://doi.org/10.3151/jact.21.421)
Abstract
In this paper, the applicability of two deformation indices related to displacement of concrete members proposed by the authors has been verified for full-scale RC members with shear or bending failure under bilateral loads. These two indices, namely "thickness increment of RC member" assuming out-of-plane shear failure, and a newly proposed index, "relative displacement on compressive edge in RC member", which assumes in-plane shear failure and out-of-plane bending failure, are mainly discussed in this paper. As a result, it was revealed that the deformation indices could estimate the failure mode of RC columns with shear failure or bending failure under horizontal bilateral loads. In addition, it was confirmed that one of the indices reached the limit value at about 90% or more of the maximum load, and that the element size dependence was small. It was also found that this index can reasonably evaluate the load carrying capacity as much as or better than the existing strain indices. Copyright c 2023 Japan Concrete Institute.
Micro- and Macro-scale Mechanical Properties of Meta-cherts as Concrete Aggregates
Maekawa K.; Wang W.; Samouh H.; Ishikawa S.; Kontani O.; Ohkubo T.; Murakami K.; Suzuki K.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.284-293, 2023, .
(https://doi.org/10.3151/JACT.21.284)
Abstract
This paper presents the measurement of the tensile strength, Young's modulus, and linear coefficient of thermal expansion in a meta-chert. Two areas are targeted in this aggregate - a white area where quartz grains are densely compacted and a gray area where the quartz grains are coarser. The macro- and micro-scale data are compared. Young's modulus is not significantly different between macro-scale compression and micro-scale tension loading in the white region. Macro-scale splitting and micro-scale direct tensile strengths exhibit similar bimodal behavior due to the failure mechanisms of these two distinct areas. The macro- and micro-scale coefficients of thermal expansion are similar for the gray region, reflecting the quartz nature. Conversely, the micro-scale coefficient of thermal expansion of the white area shows a different behavior. Copyright c 2023 Japan Concrete Institute.
Pullout Tests on Concrete Breakout Strength of Headed Reinforcement Bars Embedded in Roof Exterior Beam-Column Joints
Mohsuni H.; Matsui T.; Sanada Y.; Sakuta J.; Kiyohara T.; Kim Y.; Adachi T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.392-404, 2023, .
(https://doi.org/10.3151/jact.21.392)
Abstract
Recently, the use of headed bars as mechanical anchorage in reinforced concrete beam-column joints has increased rapidly. This type of anchorage is used for T-shaped beam and exterior column joints at middle floors and for L- and T-shaped beam-column joints at the rooftops of buildings. However, few experimental data are available regarding the anchorage capacity of headed bars embedded in L-shaped beam-column joints. Nine pullout tests are conducted to investigate the anchorage capacity of headed bars embedded in L-shaped beam-column joints. Parameters affecting the anchorage capacity, such as the diameter, embedment length, location of the headed bars, and the number of supplementary bars are considered. The anchorage capacity of the headed bars is evaluated using empirical formulas proposed by Kubota and Murakami and a formula for concrete cone failure. The failure behavior of the specimens is concrete failure with cracks propagating in the diagonal direction at the maximum applied load. The anchorage capacity increases with the embedment length and diameter of the headed bars, number of supplementary bars, and concrete area. For most specimens, the Kubota and Murakami formulas overestimate the anchorage capacity, whereas formula for concrete cone failure yields lower anchorage capacities as compared with the test results. Copyright c 2023 Japan Concrete Institute.
Flexural Behavior of Precast Concrete Slab Connections using Loop Steel Bars and Mortar
Nguyen Q.-T.; Maki T.; Mutsuyoshi H.; Ishihara Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.436-449, 2023, .
(https://doi.org/10.3151/jact.21.436)
Abstract
Loop reinforcements are commonly used to connect precast concrete elements. However, the strength of the connection in the case of short overlapping lengths and mortar joints has not been discussed extensively in previous studies. Moreover, proposed equations tend to overestimate the flexural capacity of the connection. In this study, six specimens with vertical loop steel bars and mortar joints were tested. The variables were the overlapping length, bending diameter, and distance between the loop bars in a pair. The findings indicated that reducing the overlapping length and bending diameter decreased the flexural strength of the loop joint. Further, the distance between the loop bars had a negligible effect on the bearing capacity but a significant impact on the ductile performance. Three-dimensional finite element analyses were conducted to predict the mechanical behaviors of the loop connection. The numerical simulation corroborated the experiment results in terms of the load-deflection behavior and reinforcing bar strains. Finally, empirical equations were proposed to predict the flexural strength of multiple vertical loop connections. Copyright c 2023 Japan Concrete Institute.
Terahertz (THz) Wave Imaging in Civil Engineering to Assess Self-Healing of Fiber-Reinforced Cementitious Composites (FRCC)
Nishiwaki T.; Shimizu K.; Tanabe T.; Gardner D.; Maddalena R.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.58-75, 2023, .
(https://doi.org/10.3151/jact.21.58)
Abstract
Although numerous studies have proven the effectiveness of self-healing technologies in concrete, its practical application is limited to only few trials. One of the reasons lies in the lack of self-healing in-situ non-destructive evaluation methods as opposed to invasive and extensive laboratory testing. In this study, a novel Terahertz (THz) wave imaging technique is proposed as a simple, non-destructive, and non-contact measurement methodology to quantitatively evaluate the self-healing effectiveness of cementitious materials. Experiments were conducted in fiber-reinforced cementitious composites (FRCC), which confirmed self-healing performance based on a combination of stimulated autogenous and autonomous healing by using supplementary cementitious materials (FRCC), and PVA fibers; the self-healing index was also calculated by using novel THz wave measurement and compared with existing evaluation methods. Simultaneously, sorptivity test and microstructural characterization on damaged and healed specimens were conducted as the conventional methods. As a result, the proposed THz imaging successfully quantified the self-healing performance on cementitious samples. Also, a correlation between the recovery rate (cracked/healed) measured by sorptivity test and THz wave imaging was defined. Copyright c 2023 Japan Concrete Institute.
A Micromechanics-based Study on Cracking Characteristics of Engineered Geopolymer Composite
Ohno M.; Li V.C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.271-283, 2023, .
(https://doi.org/10.3151/JACT.21.271)
Abstract
This study aims at experimentally and analytically characterizing cracking characteristics of Engineered Geopolymer Composites (EGCs) and at identifying optimal combinations of micromechanical parameters for enhancing the composite tensile performance. Fly ash-based EGCs with different volume fractions of polyvinyl alcohol fibers are investigated. The number of cracks and residual crack widths are measured for EGC specimens uniaxially loaded to 1% and 2% tensile strain. The observed crack patterns are analyzed by a micromechanics-based model that relates matrix, fiber, and interface properties to the macroscopic composite behavior. The experimental results demonstrate the lognormal distributions of crack widths and more tightly controlled cracking compared to Engineered Cementitious Composites. The simulated fiber bridging stress-crack opening relationship (Ð-Â relationship) suggests that relatively high chemical bond and low frictional bond lead to the tight crack width. The simulation results also suggest that the first-cracking strength and the subsequent micro-cracking stress during the hardening stage should be below the analytical Ð-Â curve peak. Higher chemical bond is beneficial for meeting these conditions, but if it is too high, fiber rupture dominates over pull-out, which lowers the complementary energy. Lower frictional bond or slip-hardening coefficient can suppress the fiber rupture tendency. Copyright c 2023 Japan Concrete Institute.
Analysis of Non-uniform Local Strain in Corroded Reinforcing Bar in Concrete using Digital Image Correlation
Peng H.; Avadh K.; Nagai K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.42-57, 2023, .
(https://doi.org/10.3151/jact.21.42)
Abstract
Change in the mechanism of post corrosion bond behavior was investigated in a previous experimental study by analyzing the deformations in concrete using digital image correlation (DIC). Using their DIC data, this study focuses on the local strain non-uniformity in reinforcing bar during the uniaxial tensile test due to the effect of rib height reduction and corrosion layer. The results show that, the local strain below the rib tip is higher than that below the flat part between ribs, due to compressive stress resulting from mechanical interaction at the rib tip. Furthermore, the non-uniformity in local strain is less pronounced in highly corroded reinforcing bar because less compressive stress is transferred due to gentler rib slope. In highly corroded reinforcing bar, the appearance of non-uniformity in local strain is delayed since the accumulated corrosion product on the reinforcing bar surface delays the mechanical interaction and stress transfer between the concrete and the reinforcing bar. Copyright c 2023 Japan Concrete Institute.
Effect of Bond Property Between CFRP Bar and Concrete on Nonlinear Behavior of Circular CFRP Reinforced Concrete Beams
Rabotovao M.A.; Miki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.380-391, 2023, .
(https://doi.org/10.3151/jact.21.380)
Abstract
Carbon fiber reinforced polymer (CFRP) bars present advantages over conventional steel rebars such as non-corrosiveness and relatively high tensile strength. CFRP bars cannot directly substitute steel rebars as the main reinforcement for concrete structures due to a lack of understanding of the behavior of CFRP-reinforced concrete (RC) members. This research investigates the effect of surface characteristics of deformed FRP bars on the bond between FRP bars and concrete. Moreover, the research aims to understand how the bond property of FRP bars affects the behavior of CFRP RC beams under shear load. An analysis was conducted for a better understanding of this matter by producing different bond models with a reproductive pull-out test that takes into consideration the surface characteristics aspect of the FRP bar. The structural analysis for CFRP RC beams using the proposed bond models was conducted. It was observed that surface characteristics of CFRP rebars affect the bond-slip curves in a way that the ribbed type presents higher bond strength and greater shear stiffness modulus than the dented type. In addition, the analysis for CFRP RC beams using a ribbed bond model tends to generate steeper diagonal cracks leading to the shear failure in the CFRP RC beams. Copyright c 2023 Japan Concrete Institute.
Fire Spalling Behavior of Various Polymer Modified Mortars under Ring Restraint
Sugino Y.; Ozawa M.; Sukekawa M.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.367-379, 2023, .
(https://doi.org/10.3151/jact.21.367)
Abstract
Polymer modified mortar (PMM) is indispensable for repairing and reinforcing concrete structures owing to its excellent adhesion to concrete, compactness, and workability. However, PMM tends to spall when exposed to high temperatures because it contains organic polymers. In this study, a ring-restrained heating test was performed on normal cement mortar and PMM mixed with three types of polymers to investigate the factors that affect fire spalling, such as differences in fire spalling magnitude, restraint stress, and water vapor pressure. Furthermore, a tensile strain failure model based on thermal stress theory was used to evaluate temporal changes in fire spalling depth. Copyright c 2023 Japan Concrete Institute.
Cyclic Behavior of Steel-Concrete Composite Dowel by Clothoid-Shaped Shear Connectors under Fully Reversed Cyclic Stress
Suzuki A.; Hiraga K.; Kimura Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.76-91, 2023, .
(https://doi.org/10.3151/jact.21.76)
Abstract
Recently, novel types of shear connectors have been investigated enthusiastically in Europe. Among the new connector geometries, clothoid-shaped shear connectors are used practically for bridge engineering. Although various schemes for evaluating mechanical performance can be used, they were established based on the pushout test database. During their time of use, the concrete slab is expected to be subjected to fully reversed cyclic stress during an earthquake. The stress history thereby differs from those of standard pushout tests, resulting in the discrepancy from the evaluation equations. To address this concern through this study, cyclic loading tests were conducted, imposing compressive and tensile stresses cyclically. A comprehensive experiment using 14 specimens with various influential parameters revealed the cyclic behavior and stress transfer mechanism. The results confirmed that the mechanical capacity of a composite dowel with a clothoid-shaped shear connector is dependent on the stress orientation. Furthermore, the applicability of earlier evaluation formulae was clarified based on established knowledge of experimentally obtained data. Because the necessity for reflecting the stress history was demonstrated, this research newly presents a formula for evaluation of the ultimate shear strength and load-displacement relation. c 2023 Japan Concrete Institute. All rights reserved.
Characterisation of gOne-parth Ambient Cured Engineered Geopolymer Composites
Teo W.; Shirai K.; Lim J.H.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.204-217, 2023, .
(https://doi.org/10.3151/JACT.21.204)
Abstract
Engineered geopolymer composites (EGC) recently emerged as a promising alternative to resolve traditional concrete's CO2 emission and brittleness. It features a cementless-based solution and possesses pseudo-strain-hardening (PSH) behaviour with high tensile ductility. There are two main obstacles associated with the use of geopolymer: firstly, the handling of user-hostile alkaline solutions and secondly, the necessity of heat curing. This paper aims to summarize the findings on the development and characterization of an ambient cured gone-parth EGC under the influence of various parameters, namely binder proportion between fly ash (FA) and ground granulated blast furnace slag (GGBS), quartz powder/binder ratio, alkali activator/binder ratio and water/binder ratio. Fresh and mechanical properties consisting of compressive strength, uniaxial tensile performance, and microstructure analysis were conducted. The results obtained indicate that increased FA content favours the attainment of PSH behaviour of the composite due to low matrix fracture toughness and fibre-matrix interfacial bond strength. Low water content and increased alkali activator content would greatly enhance the matrix toughness and fibre-matrix interfacial bond strength. The addition of quartz powder may favour strength attainment, but excessive quantities may have unfavourable consequences on the PSH behaviour. Copyright c 2023 Japan Concrete Institute.
Development of Mesoscale Simulation Approach of Concrete Material and Structural Behavior with Physical Damages with RBSM
Ueda T.; Wang Z.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.492-522, 2023, .
(https://doi.org/10.3151/jact.21.492)
Abstract
This paper introduces the development of mesoscale modeling approach with Rigid Body Spring Model (RBSM) for concrete with damages for the multi-scale modeling of concrete and concrete structures with damages. The development works have been conducted by the team, including the authors, at Hokkaido University. The mesoscale modeling is with the generic model applicable for various damage/deterioration. The main concept for the mesoscale modeling is explained first with the literature review to show the necessity of the mesoscale modeling. As the simulation results, macroscale stress-strain relationships and crack propagation in compression and tension under static, sustained, and cyclic loadings, mesoscale damage evolution under freeze thaw cycles (FTCs), and FTCs combined with fatigue loadings and the resulting macroscale stress-strain relationships under compression and tension, and macroscale chloride diffusion of concrete with frost damages are presented. Using the numerical parametric study with the mesoscale simulation, the macroscale stressstrain relationships in compression and tension of concrete with frost damages are presented and applied to the macroscale FEM analysis for concrete beam with frost damage. The analytical results show the applicability of this multi-scale modeling approach. Meanwhile, the remaining tasks for the developed mesoscale modeling approach with RBSM are summarized, which are development of 3D models, extension of generic mesoscale model to other damage/deterioration cases, interface model between concrete and reinforcement, model for materials other than cement concrete, microscale modeling of materials, multi-field analysis, modification of the inaccuracy with modeling by RBSM as well as the experimentation in mesoscale. Copyright c 2023 Japan Concrete Institute.
Space Averaging of Electric Field accompanying Corrosion of Reinforcement and its Verification by Pseudo-Concrete
Wang Z.; Maekawa K.; Gong F.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.25-41, 2023, .
(https://doi.org/10.3151/jact.21.25)
Abstract
This paper aims to verify a space-averaged electric filed simulation, where the whole surfaces of reinforcing bars are blended into the 3D finite volume for identifying the electric potential to drive the macro-cell corrosion of structural concrete. Experimental verification is conducted with transparent pseudo-concrete, which has chemical pore-solutions similar to those of concrete, and with which the location of anodic poles accompanying brownish rusts and the cathodic ones surrounded by hydrogen bubbles may be visually identified. The proposed electro-chemical analysis platform to be integrated with ion transport and equilibrium is adopted for full consistency with dispersed reinforcing bars. Global macro-cell corrosions of tunnel mockup and reinforcement layers induced by electric current leakage are verified quantitatively with dispersed multi-ion concentration as well as corrosion profile. Copyright c 2023 Japan Concrete Institute.
Cyclic Behavior of Interfaces for Seismically Retrofitted RC Buildings
Yamada T.; Takase Y.; Abe T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.92-106, 2023, .
(https://doi.org/10.3151/jact.21.92)
Abstract
In seismically retrofitted reinforced concrete (RC) structures, new members are connected to existing members using interfaces with roughened surfaces and post-installed dowel bars. During an earthquake, the interfaces are subjected to cyclic shear and normal stresses. Therefore, the structural design of interfaces is essential. In a previous study, normal and shear loads were applied to interface specimens. Moreover, a shear strength estimation method was proposed; however, the cyclic behavior was not discussed. This paper presents a cyclic model of the roughened surface in retrofitted RC structures. First, an envelope model was constructed using the previous shear strength estimation method and Saenz model, a constitutive law of concrete. Subsequently, the cyclic rules were modeled. Moreover, a previous dowel model was incorporated into the proposed cyclic model to estimate the test results. Finally, the proposed model provided reasonably estimated test results; the average ratio of the test results to the model results was 1.04. In addition, as  increased, the effect of the dowel bar intensified in terms of shear. Copyright c 2023 Japan Concrete Institute.
Evaluation of Bond Repair Effect for Ultra-high-strength Concrete Specimens by Neutron Diffraction Method
Yasue A.; Kobayashi K.; Yoshioka M.; Noma T.; Okuno K.; Tanaka S.; Hirata Y.; Oh-Oka T.; Kimura Y.; Nagai T.; Shobu T.; Nishio Y.; Kanematsu M.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.21, pp.337-350, 2023, .
(https://doi.org/10.3151/jact.21.337)
Abstract
The purpose of this study was to evaluate the use of resin injection to repair cracks in ultra-high-strength concrete (UHSC) members. As a preliminary step, the applicability of the neutron diffraction method (NDM) to investigate the effect of repairs in UHSC specimens was examined. The experimental results showed that the NDM can measure stresses in rebars in UHSC and normal concrete specimens. Therefore, in this experiment, the NDM was used to measure the bond performance of repairs with epoxy resin around the slit in normal concrete and UHSC specimens and examine the effect of repair on the UHSC specimens. Displacement around the slit was measured using a PI-shape displacement transducer. The evaluation confirmed that the bond performance of the repaired area was recovered by resin injection regardless of the concrete strength. In addition, the displacement around the slit was smaller for the injected specimens than the noninjected specimens. These experimental results clarified that by injecting resin, the same bond repair effect could be obtained in UHSC and normal concrete specimens. c 2023 Japan Concrete Institute.
Effects of the Mineral Composition of Cement on the Temperature Dependency of Strength Development
Taniguchi M.; Katsura O.; Sagawa T.; Hama Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.117-126, 2022, .
(https://doi.org/10.3151/jact.20.117)
Abstract
The use of low heat Portland cement has been promoted in recent years. However, there is no general method to predict the strength development of the concrete using cement that is composed of a wide range of minerals and the application of the 'maturity method (accumulated temperature)" has proved difficult for low heat Portland cement. Therefore, the authors consider the application of the equivalent age to predict the strength development of concrete using various type of cement. The strength development of mortar using cement that is composed of a wide range of minerals under different curing temperatures are then examined. As a result, the temperature dependency of strength development of various cements is explained by the equivalent age. The values of the apparent activation energy of cement are dependent on its mineral composition. This paper is the English translation from the authors' previous work. c 2022 Japan Concrete Institute. All rights reserved.
Review of Performance Assessment for Engineered Barrier Systems to Support Future RD&D of Radioactive Waste Management in Japan
Abe T.; Iida Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.236-253, 2022, .
(https://doi.org/10.3151/jact.20.236)
Abstract
This paper is a state-of-the-art report on the performance assessment of cementitious and related materials as components of engineered barrier systems for radioactive waste management. In this paper, (1) the concept of safety functions is reviewed as the engineering background of discussion, (2) an overview of the postclosure performance assessment for Belgian low- and intermediate-level short-lived radioactive waste disposal is provided, and (3) a modeling methodology for engineered barrier systems is analyzed using the concept of gmandala for durability mechanicsh. According to these works, authors present technical suggestions for technical stakeholders of Japanese low-level radioactive waste disposal. Copyright c 2022 Japan Concrete Institute
Study on Application of Class C Fly Ash for RCC dam in Nam Ngiep 1 Hydropower Project in Lao PDR
Aosaka Y.; Yamamoto T.; Tsutsui S.; Miki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.30-42, 2022, .
(https://doi.org/10.3151/jact.20.30)
Abstract
The Nam Ngiep 1 (NNP1) Hydropower Project in Lao PDR has constructed a 167 m-high roller compacted concrete (RCC) dam. Class C fly ash (FA) procured from the Mae Moh coal-fired power plant in Thailand has been selected as a supplemental cementitious material for the NNP1 RCC dam, to control hydration heat generation and improve workability. Though rarely used globally for RCC, it was found that the Class C FA was acceptable for the NNP1 RCC because it did not undergo a large temperature rise in its early age and because of the relatively high compressive strength of the concrete as the age in the medium-term and long-term as compared with general features of the concrete with Class C FA. To clarify the reaction mechanism for Class C FA, factors affecting the above features of Class C FA are analyzed and evaluated by observing FA particles and concrete core specimens of NNP1 RCC through a variety of devices, including Field Emission-Electron Probe Micro Analysis (FE-EPMA). This paper clarifies the reaction mechanism of the concrete with Class C FA and demonstrates its applicability for RCC dam and other structures. Copyright c 2022 Japan Concrete Institute
Current State of Knowledge on Bare High-Nickel Type Weathering Steel Towards the Application as Concrete Reinforcement
Benito E.K.D.; Ueno A.; Fukuyama T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.313-327, 2022, .
(https://doi.org/10.3151/jact.20.313)
Abstract
The principal issue facing reinforced concrete (RC) structures is the cost of failure due to corrosion and aging of steel reinforcements. High-Ni weathering steel (WS) is presently one of the most viable materials seen to address this issue. It is considered a cheap alternative to heavily alloyed stainless steels and also offers significantly better corrosion resistance than carbon steels (CS). This paper reviews the history and development of high-Ni WS around the world. The authors traced in detail how its protective rust layer forms under aggressive marine atmosphere in comparison to conventional Cr-type WS and CS. Synthesis of multiple studies reveals their differences in terms of rusting mechanism, corrosion products, and microstructural characteristics. It became apparent, however, that there exists a vast gap in our understanding of high-Ni WS in the context of RC structures. Some of the unresolved issues identified from literature are: (1) compositional difference of rusts that form in atmosphere and concrete; (2) long-term behavior; (3) lack of parameters necessary for service-life prediction; and (4) required concrete conditions for rust development. Information derived from these research gaps will provide important insights for future development of high-Ni WS towards the end-goal of integrating it in concrete structures. c 2022 Japan Concrete Institute.
Effects of Particle Size Distribution on the Performance of Calcium Carbonate Concrete
Bui N.K.; Kurihara R.; Kotaka W.; Hyodo H.; Takano M.; Kanematsu M.; Noguchi T.; Maruyama I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.691-702, 2022, .
(https://doi.org/10.3151/jact.20.691)
Abstract
The study investigates the effects of the particle size distribution (PSD) of aggregates on the properties of calcium carbonate concrete (CCC). Fifteen different types of aggregate PSDs were designed to select the appropriate PSD for CCC, based on the experimental data. Notably, the compressive strength of the CCC depends on the aggregate PSD, fineness modulus of the aggregates, packing ratio, and the amount of solution moving throughout the specimen. After one-day CCC processing, its compressive strength reached 7.2 MPa with an appropriate PSD. In addition, the X-ray diffraction and scanning electron microscopy analysis revealed that aragonite was the dominant contributor to the development of CCC strength. The amount of aragonite was influenced by the amount of solution passing through the specimen and the PSD of the aggregate blend. c 2022 Japan Concrete Institute. All rights reserved.
Influence of Transverse Sectional Pre-crack on Shear Failure Behavior of RC Slender Beams Based on Experimental Loading Test
Fu L.; Zhang L.; Yin Q.; Nakamura H.; Wang D.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.732-746, 2022, .
(https://doi.org/10.3151/jact.20.732)
Abstract
For the RC members under cyclic loading, flexural cracks commonly propagate in two opposite transverse directions at the zone under high bending moment and possibly form the cracks penetrating through the entire cross sections (precrack), which is considered as a crucial factor for flexure-shear failure of member. This paper clarified the influence of imitation pre-crack on the shear failure behavior of RC slender beams by three point bending test. Shear span depth ratio (a/d=3.14, 4.69) and location and thickness of pre-crack were set as main variables. As the important findings, it was revealed that the influence of pre-crack on the shear strength of RC slender beams is relatively small because it does not affect the formation of the critical diagonal crack and the mode of diagonal tension failure. It was also noted that the precrack at 2d (the section of pre-crack is 512 mm, which is twice of the effective depth d, far away from the loading plate center) leads to a reduction of shear strength with increasing pre-crack width, and the maximum reduction is 21.4%. Based on the detailed analysis of crack propagation, it was clarified that pre-crack may result in two patterns of critical diagonal crack, and in the condition that the pre-crack plane vertically intersects with the lateral splitting part of diagonal crack, the lateral splitting part becomes more severe and thereby reduces the shear strength and deformation ability. c 2022 Japan Concrete Institute.
Performance of Superplasticizers in Alkaline Environment of Self Compacting Geopolymer Mortar
Ghafoor M.T.; Fujiyama C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.676-690, 2022, .
(https://doi.org/10.3151/jact.20.676)
Abstract
Self-compacting geopolymer concrete (SCGC) is a revolutionary concept in the construction industry. This study fills the research gap by determining the impact of six different types of commercially available superplasticizers on the flow properties, dry density and compressive strength of SCGM. It was investigated that the relationship between relative flow area (Gm) and relative flow speed (Rm) of SCGM depends on the type of superplasticizer. The test results exhibited that a polyaryl ether-based superplasticizer performed better in increasing the flow deformability and flow speed of SCGM in comparison to melamine-based and naphthalene-based superplasticizers. The excessive increase in air content of SCGM paste with the addition of some superplasticizers had a negative impact on the flow properties. The increase in sodium oxide to silica molar ratio (Na2O/SiO2) and sodium oxide to water molar ratio (Na2O/H2O) both had a negative impact on the flow properties of SCGM. It was determined that beyond a trigger value of Na2O/SiO2 of 0.171, the impact of the superplasticizer in separating the flowing particles of SCGM became insignificant, resulting in the flash setting. Moreover, the addition of each type of superplasticizer had a negative impact on the dry density and compressive strength of SCGM. c 2022 Japan Concrete Institute.
Hardened Mechanical Properties of Self Compacting Geopolymer Mortar
Ghafoor M.T.; Fujiyama C.; Maekawa K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.287-299, 2022, .
(https://doi.org/10.3151/jact.20.287)
Abstract
The self-compacting geopolymer mortar (SCGM) is a new revolutionary concept in the construction industry. This study presents a summary of different influencing parameters that effect the compressive strength of SCGM. The test results showed that the water to geopolymer solid ratio (W/GPS), sodium hydroxide (NaOH) concentration, curing temperature, and curing rest period were the important parameters that had a significant impact compressive strength of SCGM. The increase in fly ash to sand ratio from 0.5 to 0.67 had a negative impact on the compressive strength of SCGM. The increase in curing temperature from 50C to 80C resulted in a continuous increase in the compressive strength of SCGM, however, its effect was much more significant at higher NaOH concentrations. Moreover, a continuous increase in the rest period before heat curing also had a negative impact on the compressive strength of SCGM. The increase in mixer speed resulted in an increase in compressive strength due to proper mixing of high viscosity SCGM paste. The 28 days compressive strength of more than 20 MPa with good flowability can be achieved for SCGM mix with W/GPS less than 0.349, NaOH molarity of 16 M, and cured at 50C to 80C without any rest period. c 2022 Japan Concrete Institute.
Multiscale Numerical Simulations of Static Shear and Long-Term Behavior of RC Members Considering Corrosion of Reinforcing Bars
Han S.-J.; Ishida T.; Tsuchiya S.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.492-506, 2022, .
(https://doi.org/10.3151/jact.20.492)
Abstract
In this study, a finite element (FE) analysis is conducted to investigate the effects of corrosion in tensile reinforcement on the shear performance of reinforced concrete (RC) members. In this regard, a multiscale chemo-hygral computational system is adopted, and its rationality is verified by comparing the FE analysis results with the shear test results of corroded RC beams. Based on the verified FE model, a parametric analysis is performed to examine the static shear and long-term behaviors of RC members according to the corrosion damage. The analysis results show that when the tensile reinforcement is simply straight anchored in the member, the ratio of reduction in shear strength due to corrosion decreases with the shear span-to-depth ratio. Meanwhile, when the tensile reinforcement is fully anchored, the shear strength of the corroded member increases owing to the formation of arch action despite the occurrence of splitting cracks caused by corrosion, and this tendency is more prominent as the shear span-to-depth ratio decreases. In terms of the long-term behavior of corroded RC members, it is shown that as corrosion progresses gradually over time, failure occurs with a rapid increase in deflection, including at low sustained load levels. c 2022 Japan Concrete Institute. All rights reserved.
Evaluation of Applicability of FRTP to Rebar in Concrete
Hokura A.; Miyazato S.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.188-199, 2022, .
(https://doi.org/10.3151/jact.20.188)
Abstract
Though the thermosetting FRP (FRTS) is commonly used, its cost is very high and has not been widely used in actual structures. On the other hand, thermoplastic FRP (FRTP) can be mass-produced and the cost can be reduced. However few studies have focused on the use of composites with concrete. This study clarifies the applicability of FRTP made of carbon fiber or glass fiber to reinforcing bars in concrete. In the case of the FRTP rod alone, the tensile strength and elastic modulus before and after exposure to water at room temperature and before and after immersion in a highly alkaline aqueous solution were evaluated. In the case of FRTP rods and concrete complexes, the variations in the pull-out test were evaluated. Based on these results, we summarize the applicability of FRTP rods to concrete reinforcements. Finally, the bending strength of concrete beams with embedded FRTP rods was evaluated experimentally and theoretically. Copyright c 2022 Japan Concrete Institute.
Biomineralization Analysis and Hydration Acceleration Effect in Self-healing Concrete using Bacillus subtilis natto
Huynh N.N.T.; Imamoto K.-I.; Kiyohara C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.609-623, 2022, .
(https://doi.org/10.3151/jact.20.609)
Abstract
Since concrete with bacteria incorporated in the matrix shows promising results in initial studies, more research has focused on using bacteria for the strength and durability enhancement of concrete. Bacterial concentrations varying from different positions on the crack surface were recorded and evaluated in conjunction with the amount of self-healing product formed. The change in bacteria concentration with the survival time in concrete was investigated and lasted for two years. The degree of mineralization of calcium carbonate from the microbial activity is also closely related to the level of survival and reduction of bacterial concentrations in concrete compared to the initial amount. These processes were tracked and analyzed through phase composition analysis and microstructure analysis. The role of nucleation sites of bacteria for accelerating mineral deposition was also investigated. The change in the content of hydrated cementitious minerals can be seen in groups of samples with different bacteria regarding cracking age (7-90 days). The increase in C-S-H content in the bacterial samples at early cracking age was significant compared with the control group. The effect on healed crack parameters through microscopic observation contributed to supporting and demonstrating the hypothesis of the combination of the formation of the calcium carbonate crystals around the bacterial cell as crystallization nuclei and the promotion of hydration for C-S-H formation. c 2022 Japan Concrete Institute.
Improvement in Long-term Strength and Flow of Mortar Containing Reed Ash and Powder
Hyodo M.; Shibahara S.; Ogata H.; Atarashi D.; Kawasaki Y.; Okamoto T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.267-276, 2022, .
(https://doi.org/10.3151/jact.20.267)
Abstract
The use of plants as resources has been investigated to improve the quality of closed water areas. In this study, the strength properties of mortar containing reed ash are examined to utilize the inorganic components of reeds; furthermore, the improvement in flowability due to the addition of reed powder to mortar is investigated to utilize the organic components of reeds. The results confirm that mortar containing reed ash improves the strength in the long term, and that mortar containing reed powder improves flowability. However, it is observed that reed ash decreases the flowability of mortar, and that reed powder inhibits strength development. To address these issues, mortar is mixed with both reed powder and reed ash. The resulting mixture exhibits improved flowability when mortar is mixed with phenols, which results in long-term strength via pozzolanic reaction. c 2022 Japan Concrete Institute.
Theory of Ionic Diffusion in Water-saturated Porous Solid with Surface Charge
Ichikawa T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.430-443, 2022, .
(https://doi.org/10.3151/jact.20.430)
Abstract
The theory of ionic diffusion in water-saturated porous solids with surface electric charges has been constructed by using the general theory of diffusion, Gaussfs law, and the condition of electrical neutrality. The theory derives the diffusion rate of ions not from the gradient of the ionic concentration but from the gradient of the chemical potential of ions. The chemical potential is obtained by rigorously solving the Poisson-Boltzmann equation that is derived by connecting the general theory of diffusion and the condition of electrical neutrality with Gaussfs law. Application of the theory to the ionic diffusion from an outer solution into a pore solution surrounded by two parallel charged plates indicates that the maximum concentration of ions penetrable into the pore solution is lower than that of the outer solution, though the penetration rate is not much affected by the surface charge. A simple approximation method of calculating the diffusion rate without solving the Poisson-Boltzmann equation is presented. Copyright c 2022 Japan Concrete Institute.
Numerical Simulation of Dimensional Stability of Precast Segments Exposed to Solar Radiation during Yard Storage
Igarashi G.; Ichimiya M.; Ohya F.; Ishida T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.200-211, 2022, .
(https://doi.org/10.3151/jact.20.200)
Abstract
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. Copyright c 2022 Japan Concrete Institute
Flexural Analysis Combined with Freeze-thaw Depth for Reinforced Concrete Beams and Columns
Kanazawa T.; Nakamura T.; Sakaguchi J.; Kawaguchi K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.18-29, 2022, .
(https://doi.org/10.3151/jact.20.18)
Abstract
This study presents a kinematic model for flexural analysis of RC beams and columns subjected to freeze-thaw action based on upper bound theorem. The developed model enables analytical derivation of the contribution of damaged concrete when actual deterioration profile is idealized as an assemblage of undamaged and damaged zones based on freeze-thaw depth obtained from concrete core specimens. The accuracy of the analysis is verified by comparing its predictions with available 21 RC columns and beams failing in flexure after freeze-thaw exposure. The predicted results show good agreement with the test results within error of 6% on average. Thereafter, the developed analysis predicts the ultimate moment capacity of a RC beam, which was taken from an existing bridge slab replaced because of the combined effect of frost damage and fatigue. Results demonstrate that the present analysis could support a rational decision-making regarding the need for repair or rehabilitation. This paper is the English translation from the authors' previous work. Copyright c 2022 Japan Concrete Institute
Properties of Concrete Subjected to Severe Accident Conditions at Fukushima Daiichi Nuclear Power Plant
Kontani O.; Ishikawa S.; Nishioka T.; Masaki H.; Tanaka N.; Goto Y.; Ishioka S.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.152-1570, 2022, .
(https://doi.org/10.3151/jact.20.152)
Abstract
The Fukushima Daiichi Nuclear Power Plant lost its core cooling function due to the massive tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake, which caused core meltdown, resulting in high temperature inside the containment vessel and exposing the RPV pedestal, a reinforced concrete structure, to an abnormally high temperature environment. In order to cool the molten core, water was poured into the containment vessel, and the concrete structure was gradually cooled in the process. Since it will take at least 40 years from the earthquake to remove the fuel from the core, the long-term integrity of the RPV pedestal is a major concern for the decommissioning of Fukushima Daiichi. In this study, the effects of high temperature exposure and subsequent wetting conditions on concrete properties were experimentally investigated. As a result, it was confirmed that the strength of concrete decreased by heating at high temperature, but recovered under subsequent wetting conditions. Copyright c 2022 Japan Concrete Institute
Effects of Severe Accident Conditions on Integrity of RPV Pedestal of Fukushima Daiichi Nuclear Power Plant
Kontani O.; Okayasu T.; Kawasumi K.; Ishikawa S.; Masaki H.; Tanaka N.; Goto Y.; Ishioka S.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.444-483, 2022, .
(https://doi.org/10.3151/jact.20.444)
Abstract
The Fukushima Daiichi Nuclear Power Plant lost its core cooling function due to the massive tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake, which caused core meltdown, resulting in high temperature inside the containment vessel and exposing the RPV pedestal, a reinforced concrete structure, to an unusually high temperature environment. After the earthquake, water was poured into the containment vessel to cool the molten core, and the concrete structure was gradually cooled in the process. Since it will take at least 40 years to remove the fuel from the core, the integrity of the RPV pedestal is a major concern for the decommissioning of the Fukushima Daiichi Nuclear Power Plant. In order to assess the long-term integrity of the RPV pedestal, a horizontal loading test was conducted using a 1/6 scaled model of the RPV pedestal of Unit 1 considering the effect of the high temperature heating and subsequent wet conditions. And then, the static stress analysis of the RPV pedestal was performed considering the degradation phenomena revealed by the experiments. As a result, it was confirmed that the RPV pedestal of Unit 1 would be structurally sound for 40 years against the current design basis earthquake even if the material degradation due to severe accident and aging was considered. Copyright c 2022 Japan Concrete Institute.
Experimental Study on Prestressing Force of Corroded Prestressed Concrete Steel Strands
Li J.; Miki T.; Yang Q.; Mao M.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.550-563, 2022, .
(https://doi.org/10.3151/jact.20.550)
Abstract
This study presents the effect of corrosion of prestressed concrete (PC) strands on the prestressing force and the reduction mechanism of the uniaxial force. A total of 14 strands was tested by combining a rigid frame testing machine with an electrified accelerated corrosion device. The specimens were divided into two groups having prestressing levels of 70% and 50% of tensile strength of PC strands. The expected degree of corrosion of the specimens, which was defined by the mass loss, was calculated from controlled electric current and time. A rigid frame testing machine was used to sustain the tensile force of the PC strands, and the prestressing force and deformation of the strand were continuously measured during the corrosion test. The test results indicate that the prestressing force decreases with the increase of corrosion. After the corrosion tests, tensile loading tests were carried out on the specimens that did not rupture during the corrosion test. It was found that corrosion led to the deterioration of the tensile properties of the PC strands, and the ultimate tensile capacity of the corroded PC strand was related to the fracture condition. Copyright c 2022 Japan Concrete Institute.
Effect of Multi-directional Restraint Induced by Reinforced Steel Bars on ASR Expansion and Bond Performance
Li P.; Tan N.; An X.; Maekawa K.; Ren M.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.342-358, 2022, .
(https://doi.org/10.3151/jact.20.342)
Abstract
In this study, we aim to investigate the interaction between alkali-silica reaction (ASR) expansion and multi-directional reinforced steel bars, and to clarify the weakening mechanism of bond performance under the influence of this interaction. First, a series of pullout specimens considering the influence of the steel bar diameter and stirrup number were prepared and then to different degrees of the accelerated ASR test to quantify the multi-directional restraint effect of the reinforced bars. After the accelerated ASR test, pullout tests were conducted to quantify the effect of ASR on the bond performance of the reinforced concrete. The test results show that uniform reinforcement results in a uniform expansion of concrete and a relatively small volumetric expansion rate. Moreover, the specimens without stirrups showed an increase in bond performance when the volumetric expansion rate was lower than 0.2%; however, the bond performance of some specimens with stirrups increased when the volumetric expansion rate was lower than 0.3% because the attenuation of bond performance was delayed by the stirrups. Finally, by comparing the analysis results and the experimental results, a chemo-mechanical analysis method coupled with an ASR expansion model and a poro-mechanical model was verified. This method can accurately predict ASR expansion, stress-strain state, and the bond damage caused by ASR. c 2022 Japan Concrete Institute.
Radiation-induced Alteration of Meta-chert
Maruyama I.; Kondo T.; Sawada S.; Halodova P.; Fedorikova A.; Ohkubo T.; Murakami K.; Igari T.; Rodriguez E.T.; Suzuki K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.760-776, 2022, .
(https://doi.org/10.3151/JACT.20.760)
Abstract
Concrete aggregate identified as gmeta-cherth was irradiated with gamma-rays and neutrons. To identify the volume expansion of the aggregate under neutron irradiation, the following analyses were performed for pristine and irradiated ¿-quartz and meta-chert: X-ray diffraction (XRD)/Rietveld analysis, dimension change, water pycnometry, He-pycnometry, light optical microscopy (LOM), and scanning electron microscopy (SEM). From the difference of volume expansion observed from dimension change and water/helium pycnometry, the crack opening inside the aggregate subjected to irradiation was elucidated, and this was confirmed by LOM and SEM analysis. The crack contribution to the expansion of the aggregate was significant for neutron fluence > 6.99 ~ 1019 n/cm2, for E ? 0.01 MeV. Based on the XRD analysis, changes in lattice parameters were identified and the cell volume expansion was compared with the data obtained by helium pycnometry. Based on the density change calculation and phase calculation data, the density of X-ray amorphous phase was consistent with that of expanded crystal ¿-quartz. Copyright c 2022 Japan Concrete Institute.
Measurement Method for Macrocell Corrosion in Concrete Specimen using a Segmented Steel Bar
Miyazato S.; Otsuki N.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.222-235, 2022, .
(https://doi.org/10.3151/jact.20.222)
Abstract
Regarding the spatial distribution of the corrosion process it is important to distinguish between macrocells and microcells, and to measure them quantitatively when experimentally clarifying the mechanism of corrosion of steel reinforcement embedded in concrete to decide an appropriate countermeasures. Therefore, this study is aimed to develop a method for measuring macrocell and microcell currents while dividing the rebar embedded in a concrete specimen into segments. The macrocell current is defined as the current flowing between rebar segments, whereas the microcell current flows within a single segment. First, it can be confirmed that the segment length does not influence the magnitude of the total corrosion current, which is the total of the macrocell anodic current and the microcell current. In addition, it can be confirmed that the magnitude of the macrocell current increases as the segment length decreases. From the experimental results obtained, the magnitude of the macrocell anodic current or the microcell current became constant when the length of individual segments was 15 mm or less. Also, the measured value of the macrocell current flowing between the neighboring segments could evaluate the macrocell current flowing between all elements. Additionally, the amount of steel loss derived from the corrosion current using electrical measurement methods became equal to the total corrosion weight loss. Copyright c 2022 Japan Concrete Institute
Image Analysis for Deformation Behaviors of RC Beams with Simulated Deteriorations under Moving Wheel Load
Nagai T.; Deng P.; Matsumoto T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.85-102, 2022, .
(https://doi.org/10.3151/jact.20.85)
Abstract
In Japan, RC bridges slabs constructed during the high economic growth period are suffering from severe deteriorate due to fatigue. In cold and snowy regions, in addition to fatigue, the deterioration is accelerated and aggravated simultaneously by freeze-thaw cycles and water penetration simultaneously. Hence, in this study, aiming at investigating the deterioration due to this combined action, three RC beams were artificially damaged on the top surface by introducing expansion agents to simulate the freeze-thaw cycle damages beforehand, and then subjected to moving wheel load under either dry or wet condition. In the experiment, a scaling-off and a disintegration were observed on the top surface due to the existence of water. Besides, to facilitate the elucidation of the mechanisms, image analysis was employed to obtain the displacement distributions and strain distributions on the side surfaces of the specimens during the test. The results of image analysis clearly manifested that the water-induced deteriorations lead to a localized compressive strain on the upper part of the beams as well as detrimentally affected the propagation of the shear and bending cracks under the moving wheel load. In summary, the mechanical reasons of the remarkably shortened fatigue life of artificially damaged RC bridge slabs due to combined fatigue loads and water penetration were uncovered in this study taking advantage of the strengths of image analysis, which also provides reference and inspiration for further related studies. c 2022 Japan Concrete Institute. All rights reserved.
Low-Level Radioactive Waste Disposal in Japan and Role of Cementitious Materials
Nakarai K.; Niwase K.; Miyamoto M.; Sasaki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, 2022, .
(https://doi.org/10.3151/jact.20.359)
Abstract
Radioactive waste disposal is a very important issue when constructing a sustainable society with nuclear energy. To construct disposal facilities, cementitious materials are used for various purposes, such as structural elements, storage cells, tunnel plugs and engineered barriers. This technical report describes the history and current status of the disposal of low-level radioactive waste (LLW) in Japan, particularly near surface disposal of relatively low-level LLW (L2-LLW) and intermediate depth disposal of relatively high-level LLW (L1-LLW) as two major types of LLW. The classification of radioactive wastes and disposal methods and concept of design and long-term dose assessment are outlined to demonstrate the importance of cementitious materials in nuclear waste management. c 2022 Japan Concrete Institute. All rights reserved.
Estimation of Corrosion Risk Using Concrete Electrical Resistivity Model
Suzuki M.; Ishida T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.389-403, 2022, .
(https://doi.org/10.3151/JACT.20.389)
Abstract
The purpose of this study is to develop a prediction method for the durability of reinforced concrete against salt attacks for any mix proportions and environmental conditions. To accomplish this, we investigate the effects of concrete composition and water content on resistivity and then model resistivity for any aggregate volume fractions using a modification of McCarter's resistivity model of concrete. We separately model the resistivity of cement paste, taking into account the effective amount of liquid water in the capillary and gel pores and the structure of C-S-H. This is incorporated into the proposed resistivity model. As a result, it is possible to predict the risk of corrosion due to salt attacks for a range of concrete compositions and environmental factors. In particular, it has become possible to model the corrosion resisting effect of using blast furnace slag as a mineral admixture. Further, it has become possible to determine the corrosion risk in consideration of the length of the drying periods between times of wetting. Copyright c 2022 Japan Concrete Institute.
In-Situ Deep-Sea Monitoring of Cement Mortar Specimen at a Depth of 3515 m and Changes in Mechanical Properties after Exposure to Deep Sea Condition
Takahashi K.; Kawabata Y.; Iwanami M.; Kobayashi M.; Kasaya T.; Yamanaka T.; Nomura S.; Makita H.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.254-266, 2022, .
(https://doi.org/10.3151/jact.20.254)
Abstract
The results of the first-ever in-situ monitoring of a large mortar specimen at a depth of 3515 m in the Nankai Trough are presented in this study targeted at creating a technology platform for in-situ monitoring and evaluation of cement-based materials at the seabed to realize deep-sea infrastructures. We successfully monitored in situ the development of strain and hydraulic pressure in the specimen. In addition, the short-term behavior of the specimen can be explained by hydraulic confinement and stress relaxation due to water infiltration. Some contraction strain remained in the specimen even after approximately an exposure to the deep sea condition for one year, causing microstructural damage. The pore entry volume was enhanced toward the center of the specimen, and a decrease in compressive strength and Youngfs modulus were observed in the specimen after exposure due to the microstructural damage. Further improvement of the in-situ measurements is required to ensure the waterproofing and pressure resistance of the strain and pressure gauges. Copyright c 2022 Japan Concrete Institute
Extended Multi-directional Crack Model Applied to the RC Precast Joint Interface with Shear Dowel
Zewdie E.; Soltani M.; Maekawa K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.20, pp.535-549, 2022, .
(https://doi.org/10.3151/JACT.20.535)
Abstract
The extended multi-directional non-orthogonal crack model was applied to the joint interface area between RC members connected by shear dowel and the experimental verification was conducted in use of the low cycle fatigue experiments. The splitting tension field induced by the dowel action around the reinforcing bar is successfully reproduced with the coupled joint crack model and the beam finite elements, and the splitting tension cracking under cyclic fatigue loading and the joint degradation were fairly captured computationally. The effect of spiral steel confinement on the shear dowel performance can be quantitatively evaluated by the generic full 3D nonlinear analysis. c 2022 Japan Concrete Institute. All rights reserved.