JOURNAL OF ADVANCED CONCRETE TECHNOLOGY(2022 - 2022)
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, 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.
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, 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, 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.
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, 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, 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.
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, 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.
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, 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.