In this study, a finite element (FE) analysis is conducted to investigate the effects of corrosio... more 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.
In November 2011, the Japanese government resolved to build "Revival Roads" in the Tohoku region ... more In November 2011, the Japanese government resolved to build "Revival Roads" in the Tohoku region to accelerate the recovery from the Great East Japan Earthquake of March 2011. Because the Tohoku region experiences such cold and snowy weather in winter, complex degradation from a combination of frost damage, chloride attack from de-icing agents, alkali-silica reaction, cracking and fatigue is anticipated. Thus, to enhance the durability performance of road structures, particularly reinforced concrete (RC) bridge decks, multiple countermeasures are proposed: a low water-to-cement ratio in the mix, mineral admixtures such as ground granulated blast furnace slag and/or fly ash to mitigate the risks of chloride attack and alkali-silica reaction, anticorrosion rebar and 6% entrained air for frost damage. It should be noted here that such high durability specifications may conversely increase the risk of early age cracking caused by temperature and shrinkage due to the large amounts of cement and the use of mineral admixtures. Against this background, this paper presents a numerical simulation of early age deformation and cracking of RC bridge decks with full 3D multiscale and multi-chemo-physical integrated analysis. First, a multiscale constitutive model of solidifying cementitious materials is briefly introduced based on systematic knowledge coupling microscopic thermodynamic phenomena and microscopic structural mechanics. With the aim to assess the early age thermal and shrinkage-induced cracks on real bridge deck, the study began with extensive model validations by applying the multiscale and multi-physical integrated analysis system to small specimens and mock-up RC bridge deck specimens. Then, through the application of the current computational system, factors that affect the generation and propagation of early age thermal and shrinkage-induced cracks are identified via experimental validation and full-scale numerical simulation on real RC slab decks.
Although applications of low water-to-cement ratio mixtures to practical structures have been inc... more Although applications of low water-to-cement ratio mixtures to practical structures have been increasing to enhance seismic resistance and long-term durability in recent years, it was experimentally observed that such a mixture causes peculiar hydration under long-term normal or high temperature curing. On the other hand, excessive hydration was revealed in the analysis using the original model, compared with the experiment in such an environment, because un-hydrated cement particles and existing condensed water reacted more significantly in the model. This study aims to enhance the integrated multiscale thermodynamic analysis, which is able to predict structural behavior in various conditions in a unified approach, by incorporating recent technical evolutions for its reverification and extending the original model to resolve the above peculiar concerns. Hence, the extensive modeling of continuous hydration considering spatial condensed water in fine micro-pore structures was propos...
The authors propose a so -called life-span simulator that can predict concrete structural behavio... more The authors propose a so -called life-span simulator that can predict concrete structural behaviors under arbitrary external forces and environmental conditions. In order to realize this kind of technology, two computational systems have been developed; one is a thermo -hygro system that covers microscopic phenomena in C-S-H gel and capillary pores, and the other is a structural analysis system, which deal with macroscopic stress and deformational field. In this paper, the unification of mechanics and thermo-dynamics of materials and structures has been made with the ion transport of chloride, CO 2 and O2 dissolution. This proposed integrated system can be used for the simultaneous overall evaluation of structural and material performances without distinguishing between structure and durability.
This research focuses on some efforts in laboratory scale to create artificial barriers by inject... more This research focuses on some efforts in laboratory scale to create artificial barriers by injecting alkalis to the heap of fly ash. The alkaline solution was combined from 2 to 12 Molar of sodium hydroxide and sodium silicate to have some variation of alkalis. Some barriers made from injecting alkalis with different concentration from 4M to 8M of sodium hydroxide show an optimum result. Internal shrinkage experiment which was conducted to examine the performance of geopolymer pastes indicated a rapid solidification less than one day. Boron concentration from specimens submerged in water determined by ICP Test was contributed by the barrier instead of the fly ash pile.
Journal of Japan Society of Civil Engineers, Ser. E2 (Materials and Concrete Structures), 2012
Drying shrinkage, which has long been a subject of study, occurs when concrete is exposed to a lo... more Drying shrinkage, which has long been a subject of study, occurs when concrete is exposed to a low relative humidity (RH). Shrinkage is also an issue in concrete with a low water/cement (w/c) ratio, which is now being widely used. Although a low w/c results in high strength and low permeability, it has been found that autogenous shrinkage becomes non-negligible. Any shrinkage would induce tensile stress, which can cause cracking and undermine the long-term performance of a structure. To evaluate and predict the influence of shrinkage, empirical formulas have been suggested in previous studies. From another standpoint, shrinkage behavior is associated with microscale thermodynamic properties, such as hydration, pore-structure formation, and the behavior of water in micropores. These properties vary according to the raw materials, mix proportion, age, and ambient conditions of the concrete. Without
An investigation into the long-term excessive deflection of PC Viaducts by using 3D multi-scale i... more An investigation into the long-term excessive deflection of PC Viaducts by using 3D multi-scale integrated analysis
mechanics of structures. Our research group has been developing two numerical simulation tools. O... more mechanics of structures. Our research group has been developing two numerical simulation tools. One is a thermo-hygro system named DuCOM [1], which covers the microscale phenomena governed by thermodynamics. This computational system can evaluate an early age development of cementitious materials and deterioration processes of hydrated products under long-term environmental actions. In the following section, the overall scheme of this system and each material modeling will be introduced. The other one is a nonlinear path-dependent structural analytical system named COM3 [2, 3]. For arbitrary mechanical actions including temperature and shrinkage effects, the structural response as well as mechanical states of constituent elements can be predicted. The solidification model of hardening concrete composite has been also installed in this system for predicting timedependent behavior depending on temperature, moisture profile, and micropore structure of materials [4, 5].
This paper presents a novel methodology to appropriately account for boundary conditions in numer... more This paper presents a novel methodology to appropriately account for boundary conditions in numerical analyses of moisture fields in cementitious materials. The proposed methodology consists of using experimentally obtained moisture emissivity coefficients together with the vapour pressure difference between the environment and the exposed surface (based on the average surface humidity content). The performance of such methodology (implemented on DuCOM, a computational code suitable for calculation of moisture/temperature fields in cementitious materials) is evaluated by comparing the numerical predictions with the experimental results presented in the Part I companion paper. Influences of the many environmental conditions reported in Part I are investigated for validation of the proposed numerical methodology: temperature, relative humidity, wind speed and age of exposure of specimens. Furthermore, an additional numerical
In this study, a finite element (FE) analysis is conducted to investigate the effects of corrosio... more 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.
In November 2011, the Japanese government resolved to build "Revival Roads" in the Tohoku region ... more In November 2011, the Japanese government resolved to build "Revival Roads" in the Tohoku region to accelerate the recovery from the Great East Japan Earthquake of March 2011. Because the Tohoku region experiences such cold and snowy weather in winter, complex degradation from a combination of frost damage, chloride attack from de-icing agents, alkali-silica reaction, cracking and fatigue is anticipated. Thus, to enhance the durability performance of road structures, particularly reinforced concrete (RC) bridge decks, multiple countermeasures are proposed: a low water-to-cement ratio in the mix, mineral admixtures such as ground granulated blast furnace slag and/or fly ash to mitigate the risks of chloride attack and alkali-silica reaction, anticorrosion rebar and 6% entrained air for frost damage. It should be noted here that such high durability specifications may conversely increase the risk of early age cracking caused by temperature and shrinkage due to the large amounts of cement and the use of mineral admixtures. Against this background, this paper presents a numerical simulation of early age deformation and cracking of RC bridge decks with full 3D multiscale and multi-chemo-physical integrated analysis. First, a multiscale constitutive model of solidifying cementitious materials is briefly introduced based on systematic knowledge coupling microscopic thermodynamic phenomena and microscopic structural mechanics. With the aim to assess the early age thermal and shrinkage-induced cracks on real bridge deck, the study began with extensive model validations by applying the multiscale and multi-physical integrated analysis system to small specimens and mock-up RC bridge deck specimens. Then, through the application of the current computational system, factors that affect the generation and propagation of early age thermal and shrinkage-induced cracks are identified via experimental validation and full-scale numerical simulation on real RC slab decks.
Although applications of low water-to-cement ratio mixtures to practical structures have been inc... more Although applications of low water-to-cement ratio mixtures to practical structures have been increasing to enhance seismic resistance and long-term durability in recent years, it was experimentally observed that such a mixture causes peculiar hydration under long-term normal or high temperature curing. On the other hand, excessive hydration was revealed in the analysis using the original model, compared with the experiment in such an environment, because un-hydrated cement particles and existing condensed water reacted more significantly in the model. This study aims to enhance the integrated multiscale thermodynamic analysis, which is able to predict structural behavior in various conditions in a unified approach, by incorporating recent technical evolutions for its reverification and extending the original model to resolve the above peculiar concerns. Hence, the extensive modeling of continuous hydration considering spatial condensed water in fine micro-pore structures was propos...
The authors propose a so -called life-span simulator that can predict concrete structural behavio... more The authors propose a so -called life-span simulator that can predict concrete structural behaviors under arbitrary external forces and environmental conditions. In order to realize this kind of technology, two computational systems have been developed; one is a thermo -hygro system that covers microscopic phenomena in C-S-H gel and capillary pores, and the other is a structural analysis system, which deal with macroscopic stress and deformational field. In this paper, the unification of mechanics and thermo-dynamics of materials and structures has been made with the ion transport of chloride, CO 2 and O2 dissolution. This proposed integrated system can be used for the simultaneous overall evaluation of structural and material performances without distinguishing between structure and durability.
This research focuses on some efforts in laboratory scale to create artificial barriers by inject... more This research focuses on some efforts in laboratory scale to create artificial barriers by injecting alkalis to the heap of fly ash. The alkaline solution was combined from 2 to 12 Molar of sodium hydroxide and sodium silicate to have some variation of alkalis. Some barriers made from injecting alkalis with different concentration from 4M to 8M of sodium hydroxide show an optimum result. Internal shrinkage experiment which was conducted to examine the performance of geopolymer pastes indicated a rapid solidification less than one day. Boron concentration from specimens submerged in water determined by ICP Test was contributed by the barrier instead of the fly ash pile.
Journal of Japan Society of Civil Engineers, Ser. E2 (Materials and Concrete Structures), 2012
Drying shrinkage, which has long been a subject of study, occurs when concrete is exposed to a lo... more Drying shrinkage, which has long been a subject of study, occurs when concrete is exposed to a low relative humidity (RH). Shrinkage is also an issue in concrete with a low water/cement (w/c) ratio, which is now being widely used. Although a low w/c results in high strength and low permeability, it has been found that autogenous shrinkage becomes non-negligible. Any shrinkage would induce tensile stress, which can cause cracking and undermine the long-term performance of a structure. To evaluate and predict the influence of shrinkage, empirical formulas have been suggested in previous studies. From another standpoint, shrinkage behavior is associated with microscale thermodynamic properties, such as hydration, pore-structure formation, and the behavior of water in micropores. These properties vary according to the raw materials, mix proportion, age, and ambient conditions of the concrete. Without
An investigation into the long-term excessive deflection of PC Viaducts by using 3D multi-scale i... more An investigation into the long-term excessive deflection of PC Viaducts by using 3D multi-scale integrated analysis
mechanics of structures. Our research group has been developing two numerical simulation tools. O... more mechanics of structures. Our research group has been developing two numerical simulation tools. One is a thermo-hygro system named DuCOM [1], which covers the microscale phenomena governed by thermodynamics. This computational system can evaluate an early age development of cementitious materials and deterioration processes of hydrated products under long-term environmental actions. In the following section, the overall scheme of this system and each material modeling will be introduced. The other one is a nonlinear path-dependent structural analytical system named COM3 [2, 3]. For arbitrary mechanical actions including temperature and shrinkage effects, the structural response as well as mechanical states of constituent elements can be predicted. The solidification model of hardening concrete composite has been also installed in this system for predicting timedependent behavior depending on temperature, moisture profile, and micropore structure of materials [4, 5].
This paper presents a novel methodology to appropriately account for boundary conditions in numer... more This paper presents a novel methodology to appropriately account for boundary conditions in numerical analyses of moisture fields in cementitious materials. The proposed methodology consists of using experimentally obtained moisture emissivity coefficients together with the vapour pressure difference between the environment and the exposed surface (based on the average surface humidity content). The performance of such methodology (implemented on DuCOM, a computational code suitable for calculation of moisture/temperature fields in cementitious materials) is evaluated by comparing the numerical predictions with the experimental results presented in the Part I companion paper. Influences of the many environmental conditions reported in Part I are investigated for validation of the proposed numerical methodology: temperature, relative humidity, wind speed and age of exposure of specimens. Furthermore, an additional numerical
Uploads
Papers by Tetsuya Ishida