JOURNAL OF ADVANCED CONCRETE TECHNOLOGY(2021 - 2022)
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, MAR.
(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 alka -line 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 theoreti-cally.
Punching Shear Capacity of Prestressed Concrete Slabs Made of Lightweight Concrete Mixed with Short Fibers
Kitano, Y; Ito, H; Suzuki, S
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.1227-1244, 2021, DEC.
(https://doi.org/10.3151/jact.19.1227)
Abstract
The purpose of this study is to examine means of creating light and very strong prestressed concrete slabs made of lightweight aggregate concrete mixed with short fibers. The experiments reported in this paper demonstrated that the ratio of short fibers in the mix must be kept to 0.5 vol% or less, in order to obtain the same strength as that demonstrated by lightweight aggregate concrete designed to a standard strength of 50 N/mm2. In addition, the results of load testing various slabs confirmed that lightweight PC slabs mixed with 0.5 vol% of short PVA fibers had the same punching shear capacity as PC slabs made from normal weight concrete. The results led to the conclusion that the increase in the shear capacity of lightweight PC slabs mixed with short fibers was caused by the suppression of the progress of cracks in the RC direction and an accompanying tide arch formation in the PC direction. This paper is the English translation of the authors' previous work [Kitano, Y., Ito, H. and Suzuki, S., (2020). Study on lightweight and high strength prestressed concrete slab by using lightweight concrete mixed with short fibers. Journal of Japan Society of Civil Engineers, Ser. E2 (Materials and Concrete Structures), 76(3), 239-254. (in Japanese)].
A New Concept of Calcium Carbonate Concrete using Demolished Concrete and CO2
Maruyama, I; Kotaka, W; Kien, BN; Kurihara, R; Kanematsu, M; Hyodo, H; Hirao, H; Kitagaki, R; Tamura, M; Tsujino, M; Fujimoto, S; Noguchi, T
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.1052-1060, 2021, OCT.
(https://doi.org/10.3151/jact.19.1052)
Abstract
Countermeasures against carbon dioxide emissions are a concern in the construction field as well as in society. To solve this problem, a concept for new calcium carbonate concrete is proposed, and this concept is validated experimentally. In the proposed concept, calcium carbonate comprising Ca originating from demolished concrete or other Ca-containing industrial wastes and HCO3- from CO2 gas collected from the air or emitted by industrial plants acts as a binder for aggregates, which can be natural rocks or crushed demolished concrete. This short paper describes the details of the process of making calcium carbonate concrete and discusses future perspectives.
Modelling Concrete Degradation by Coupled Non-linear Processes
Oda, C; Kawama, D; Shimizu, H; Benbow, SJ; Hirano, F; Takayama, Y; Takase, H; Mihara, M; Honda, A
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.1075-1087, 2021, OCT.
(https://doi.org/10.3151/jact.19.1075)
Abstract
Concrete in a transuranic (TRU) waste repository is considered a suitable material to ensure safety, provide structural integrity and retard radionuclide migration after the waste containers fail. Modelling of concrete degradation often focuses solely on solid-water chemical reactions and related changes in porosity, however, cracking and damage from steel corrosion will likely exert significant control over the mass-transport properties of concrete. In the current study, coupling between chemical, mass-transport and mechanical, so-called non-linear processes that control concrete degradation and crack development were investigated by coupled numerical models. Application of such coupled numerical models allows identification of the dominant non-linear processes that will control long-term concrete degradation and crack development in a TRU waste repository.
General Overview of the Research Project Investigating the Radionuclide Solution Behavior in Mock Mortar Matrix Modeled after Conditions at the Fukushima-Daiichi Nuclear Power Station
Igarashi, G; Haga, K; Yamada, K; Aihara, H; Shibata, A; Koma, Y; Maruyama, I
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.950-976, 2021, SEP.
(https://doi.org/10.3151/jact.19.950)
Abstract
Decommissioning of the Fukushima Daiichi Nuclear Power Station (F1NPS) in a proper manner requires assessment of the contamination levels and mechanisms for contamination in the concrete structures. Between January 2018 and March 2020, Japan's Ministry of Education Ministry of Education, Culture, Sports, Science and Technology (MEXT) conducted a project called The Analysis of Radionuclide Contamination Mechanisms of Concrete and the Estimation of Contamination Distribution at the Fukushima Daiichi Nuclear Power Station. In this review, we outline the results of this study. The experimental results from the first project indicate that concrete carbonation, Ca leaching, and drying conditions affected the adsorption behaviors of Cs and Sr and therefore, their penetration depths. Additionally, the studies showed that a-nuclides precipitated on the surface of the samples because concrete causes a high pH. A reaction transport model was developed to assess further the adsorption characteristics of Cs and Sr in carbonated cement paste and on concrete aggregates. The model used real concrete characteristics from the materials used at F1NPS and historical boundary conditions at the site, including radionuclide concentrations and penetration profiles within the turbine pit wall. Capillary water suction resulting from dried concrete was evaluated by considering structural changes in cement hydrates using X-ray CR and H-1-NMR relaxometry.
Influence of Degree of Deterioration and Electrolyte Solution on Repair Effect of Realkalization for Reinforced Concrete
Ueda, T; Takahashi, H; Nanasawa, A; Nakayama, K; Tsukagoshi, M
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.988-998, 2021, SEP.
(https://doi.org/10.3151/jact.19.988)
Abstract
Electrochemical realkalization has been applied to many concrete structures deteriorated by carbonation of concrete. As the repair effect of this method, it has been reported that the pH value of the carbonated concrete recovered by the electrolysis reaction at the steel in concrete and the electro-osmosis of the electrolyte solution in the anode system set on the concrete surface. However, the protection effect of the realkalization against the steel corrosion in concrete has not been clarified enough. Therefore, this study investigated the steel corrosion behavior in concrete after the application of realkalization in the cases of different degree of deterioration and different kind of electrolyte solution by measuring content profiles of several sort of ions and electrochemical indicators for evaluating steel corrosion. As a result, the electrochemical removal of Cl- ions from carbonated concrete and the electrochemical penetration of K+ ions from the electrolyte solution into carbonated concrete were both promoted compared with the case of non-carbonated specimen. Moreover, the protection ratio calculated by the corroded area ratio of steel bars in the electrochemically treated specimens and non-treated specimens subjected to the cyclic drying and wetting storage for 400 days after the period of realkalization achieved around 80% regardless of the difference of the deterioration condition before applying realkalization. This paper is an extended and enhanced version of an earlier work under different title [Takahashi, H., Ueda, T., Nanasawa, A., Nakayama, K. and Tsukagoshi, M., (2020). Repair effect of realkalization for reinforced concrete with different degree of deterioration. In: Proceedings of the 6th International Conference on Concrete Materials - Performance, Innovations, and Structural Implications (ConMat'20), Fukuoka, Japan 27-29 August 2020. Tokyo: Japan Concrete Institute, 1065-1075].
Theoretical Evaluation Equation for Capacities of Beam Action in Shear Resistance Mechanisms of RC Beams Reflecting Dowel Action of Main Reinforcements
Yamada, Y.
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.1025-1039, 2021, SEP.
(https://doi.org/10.3151/jact.19.1025)
Abstract
This study proposes a theoretical evaluation equation for the capacities of beam action in reinforced concrete (RC) beams. The equation reflects the dowel action of the main reinforcements for the development of rational evaluation methods for the shear capacity. To verify its accuracy, a static loading experiment and finite element (FE) analyses were conducted for the beams with 2.1 to 9.4% of the main reinforcement ratio. The fundamental equation that reflects the dowel action of the main reinforcement was developed using the equilibrium condition of the free body in beam action. The decrease in crack width by the main reinforcement, which was required to calculate dowel force, was derived by the assumption of perfect bonding between concrete and rebars. The governing equations were formulated to derive the experimental values of the contributing forces of arch action and beam action in RC beams with cross sections of multilayered rebars. The calculated values indicated that changes in load-carrying mechanisms could be explained from the equation. The accuracies of the proposed equation and evaluation equations of shear strengths based on design codes were compared against the capacities of beam action based on the analytical results. As a result, for the values based on the proposed equation, the coefficient of variation was 7.7% and the highest accuracy was observed in all the cases examined. It was confirmed that the proposed equation accurately reflected the dowel action of the main reinforcements and guaranteed rationality owing to its theoretical background.
Long-term Performance Assessment of Concrete Exposed to Acid Attack and External Sulfate Attack
Qiao, D; Matsushita, T; Maenaka, T; Shimamoto, R
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.796-810, 2021, JUL.
(https://doi.org/10.3151/jact.19.796)
Abstract
This study aims to assess the degradation of below-grade concrete of nuclear power plants (NPP) in Japan, considering possible acid and sulfate attacks. A survey on the underground environments of several NPPs and residential buildings across the country was conducted, and their associated concrete performance was evaluated where concrete samples from core drillings were available. Moreover, acid and sulfate exposure tests on mortar specimens lasting for up to four years were carried out in the laboratory to simulate actual field situations. The effects of exposure conditions, such as solution concentrations, temperature, and immersion conditions, were examined. The surveyed environments were classified into non-aggressive or slightly aggressive environments. The concrete core samples investigated showed insignificant degradation and satisfactory strength after 40 years of exposure. The laboratory test results showed that the accelerated tests using highly concentrated solutions could exacerbate the extent of decalcification and even alter the degradation mechanism for magnesium sulfates. Therefore, a close-to-reality concentration is preferred for reproducing field situations. The carbonation/neutralization depth was used as an indicator to estimate the degradation extent. The measured values in the laboratory using low-concentration solutions correlated well with the field results, suggesting that the below-grade concrete's degradation in the NPPs investigated may be less than 10 mm after 60 years of exposure.
Maintenance Scenario of Concrete Structures Damaged by Reinforcement Corrosion Based on Corrosion Propagation Mechanism of Steel and Moisture Behavior in Concrete
Takaya, S; Saito, R; Satoh, S; Yamamoto, T
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.614-629, 2021, JUN.
(https://doi.org/10.3151/jact.19.614)
Abstract
It can be said that corrosion of reinforcing steel is a serious problem for concrete structures. However, the corrosion mechanism of steel is still unclear, and it is difficult to prevent corrosion perfectly. In this study, in order to make clear the corrosion process in alkaline environment, the corrosion products formed in solutions of various OH - and Cl - concentrations were evaluated by Raman spectroscopy. In addition, the influence of dissolved oxygen on corrosion products was investigated. Furthermore, the corrosion mechanism of steel in concrete was investigated based on field study. These investigations made it clear that the behavior of moisture in concrete has large influence on corrosion propagation. Therefore, the influence of W/C, chloride ions and cracks on the behavior of moisture in concrete was also investigated. Based on the the results obtained, the authors propose a maintenance scenario for concrete structures damaged by corrosion of the reinforcement.
41 Year Long-Term Durability of High Volume Blast-Furnace Slag Cement Concrete
Hashimoto, M; Kurata, K; Ohtsuka, Y; Dan, Y
JOURNAL OF ADVANCED CONCRETE TECHNOLOGY, Japan Concrete Institute, Vol.19, pp.248-258, 2021, MAR.
(https://doi.org/10.3151/jact.19.248)
Abstract
In this study, we investigated the durability of high-volume ground granulated blast furnace slag (GGBS) blended cement concrete containing over 70% of GGBS for possible general structural applications. The concrete specimens used were exposed to natural outdoor conditions for 41 years on a building rooftop. The following is found. The exposed top surface of concrete with 88.5% GGBS 4000 replacement, the exposed top surface and the corners of sulfated slag cement showed peel failure of the paste, but the specimens of concrete with 68.5% GGBS 4000 and GGBS 2000 replacement were in sound condition. The compressive strength of all mix proportions did not decrease significantly over 41 years. The carbonation depth of concrete specimens containing 70% GGBS was about 7 to 9 mm, and about 15 mm for specimens containing 90% GGBS. Despite the high volume of GGBS content (70%) in the concrete specimens, traces of Ca(OH)(2), which is involved in the chemical reaction of GGBS, were found in parts that remained uncarbonated. Ca(OH)(2) increases the alkalinity of the specimen and is thus considered to have a rebar corrosion-inhibiting effect. This paper is the English translation from the authors' previous work [Hashimoto, M., et al., (2019). A study on the long-term durability of high-volume bast-furnace slag cement concrete for 41 years. Concrete Research and Technology, Vol.30, pp.77-84. (in Japanese)].