The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Yukio Hama - One of the best experts on this subject based on the ideXlab platform.
-
distribution map of Frost resistance for cement based materials based on pore structure change
Materials, 2020Co-Authors: Takumi Noguchi, Nguyen Xuan Quy, Jihoon Kim, Yukio HamaAbstract:This paper presents a prediction method and mathematical model based on experimental results for the change in pore structure of cement-based materials due to environmental conditions. It focuses on Frost Damage risk to cement-based materials such as mortar. Mortar specimens are prepared using water, ordinary Portland cement, and sand and the pore structure is evaluated using mercury intrusion porosimetry. New formulas are proposed to describe the relationship between the pore structure change and the modified maturity and to predict the durability factor. A quantitative prediction model is established from a modified maturity function considering the influences of environmental factors like temperature and relative humidity. With this model, the Frost resistance of cement-based materials can be predicted based on weather data. Using the prediction model and climate data, a new distribution map of Frost Damage risk is created. It is found that summer weather significantly affects Frost resistance, owing to the change in pore structure of cement-based mortar. The model provides a valuable tool for predicting Frost Damage risk based on weather data and is significant for further research.
-
method for determining early age Frost Damage of concrete by using air permeability index and influence of early age Frost Damage on concrete durability
Construction and Building Materials, 2017Co-Authors: Hyeonggil Choi, Wenyan Zhang, Yukio HamaAbstract:Abstract In this study, a method for determining the early-age Frost Damage focused on the advantages of the Torrent air-permeability test, in which structures are measured nondestructively in their original locations was proposed, and the influence of early-age freezing on the durability of concrete is examined. In the experiment, series I for examining the influence of the freezing depth and series II for examining the influence of the beginning of the freezing age were carried out using by mortar specimen. And based on the results of the mortar test, a concrete experiment was performed to propose a method for determining the early-age Frost Damage and its influence on the durability. As a result, it is confirmed that the early-age Frost Damage to concrete could be determined by measuring the Torrent air permeability according to the freezing depth and beginning of the freezing age. In addition, by integrating the mortar and concrete test results, a criterion was proposed to determine the early-age Frost Damage by measuring the Torrent air permeability at 3 d. Furthermore, it indicate that even specimens with a compressive strength equal to or exceeding 5 N/mm2 are subject to durability deterioration when Damaged by early-age Frost. The proposed Torrent air-permeability method also can be used to identify such changes in the integrity of concrete.
Janghwa Lee - One of the best experts on this subject based on the ideXlab platform.
-
an experimental investigation on minimum compressive strength of early age concrete to prevent Frost Damage for nuclear power plant structures in cold climates
Nuclear Engineering and Technology, 2013Co-Authors: Kyungtaek Koh, Chunjin Park, Gumsung Ryu, Jungjun Park, Dogyeum Kim, Janghwa LeeAbstract:Concrete undergoing early Frost Damage in cold weather will experience significant loss of not only strength, but also of permeability and durability. Accordingly, concrete codes like ACI-306R prescribe a minimum compressive strength and duration of curing to prevent Frost Damage at an early age and secure the quality of concrete. Such minimum compressive strength and duration of curing are mostly defined based on the strength development of concrete. However, concrete subjected to Frost Damage at early age may not show a consistent relationship between its strength and durability. Especially, since durability of concrete is of utmost importance in nuclear power plant structures, this relationship should be imperatively clarified. Therefore, this study verifies the feasibility of the minimum compressive strength specified in the codes like ACI-306R by evaluating the strength development and the durability preventing the Frost Damage of early age concrete for nuclear power plant. The results indicate that the value of 5 MPa specified by the concrete standards like ACI-306R as the minimum compressive strength to prevent the early Frost Damage is reasonable in terms of the strength development, but seems to be inappropriate in the viewpoint of the resistance to chloride ion penetration and freeze-thaw. Consequently, it is recommended to propose a minimum compressive strength preventing early Frost Damage in terms of not only the strength development, but also in terms of the durability to secure the quality of concrete for nuclear power plants in cold climates.
-
effect of curing method on the strength development and freezing thawing durability of the concrete incorporating high volume blast furnace slag subjected to initial Frost Damage
Advanced Materials Research, 2012Co-Authors: Kyungtaek Koh, Gumsung Ryu, Janghwa LeeAbstract:In the case of construction with high volume blast-furnace slag(BFS) concrete during winter season, the setting and hardening are drastically delayed, so it has a high risk of initial Frost. Assuming that the concrete incorporating a high volume of BFS is affected by freezing at the early age during the winter conditions, then this study is to investigate the effect of curing method on the strength development and the resistance to freezing-thawing action. As a result, the concrete performing water curing at 5°C after subjected to initial Frost Damage improve the long-term strength and the freezing-thawing durability. The concrete implementing water curing at 30°C enhance the long-term strength and the resistance to freezing-thawing action as well as the early strength. However, the concrete with sealed curing at 30°C exhibits the improvement in the early strength, but not in the long-term strength and the freezing-thawing durability.
-
evaluation on the compressive strength of concrete incorporating high volume blast furnace slag subjected to initial Frost Damage
Applied Mechanics and Materials, 2011Co-Authors: Kyungtaek Koh, Chunjin Park, Gumsung Ryu, Ki Hong Ahn, Janghwa LeeAbstract:Construction works that uses concrete incorporating a high volume of blast-furnace slag (BFS) during the winter season increases the risk of being subjected to initial Frost Damage as it noticeably delays setting and hardening. Assuming that the concrete incorporating a high volume of BFS was affected by freezing at an early age during the winter conditions, this study is to investigate the effect of strength degradation by early freezing and curing methods on compressive strength. As a result, freezing at early age highly degraded the compressive strength regardless of the types of concrete. After influenced by initial Frost Damage, water curing at 5°C improved the long-term strength and water curing at 30°C enhanced the long-term strength as well as the early strength.
Xiaojian Gao - One of the best experts on this subject based on the ideXlab platform.
-
hydration mechanism and early Frost resistance of calcium sulfoaluminate cement concrete
Construction and Building Materials, 2020Co-Authors: Xiaojian Gao, Kejin Wang, Vivian W Y TamAbstract:Abstract This study investigated the hydration mechanism and mechanical properties of ordinary Portland cement (OPC) blended with calcium sulfoaluminate (CSA) cement. Heat evolution, hydration products, pore size distribution, and microstructure were investigated for OPC-CSA blends concrete with different contents of CSA cement. Macroscopic properties, such as internal temperature, dynamic elastic modulus, and compressive strength, are also studied through concrete subjected to early Frost conditions. The results show that the OPC-CSA blended cement displayed a higher early strength and exhibited enhanced resistance to the early Frost Damage compared to OPC. The OPC-CSA blended cement also exhibits a higher hydration rate and a larger amount of heat of hydration than that in the OPC at the early stage. The increased heat of hydration can effectively prolong the hydration duration at sub-zero temperatures. However, incorporating CSA delayed the hydration of C3S at the late stage, thus affecting the development of compressive strength and dynamic elastic modulus. On the other hand, the hardened blended cement exhibited an higher porosity, which was corresponding to the increasing proportion of macropores (diameter over 1000 nm). If concrete directly is suffered from early Frost after casting, blended cement with 20% of CSA can effectively reduce strength loss from Frost Damage by 100% at −5 °C, and that from Frost Damage by 80% at −15 °C respectively. Furthermore, when the calcium nitrite is incorporated as the antifreeze admixture with OPC-CSA blended concrete, the early stage Frost resistance of concrete infrastructures can be significantly improved.
-
potential application of portland cement calcium sulfoaluminate cement blends to avoid early age Frost Damage
Construction and Building Materials, 2018Co-Authors: Ling Qin, Xiaojian Gao, Ailian ZhangAbstract:Abstract This paper aims to investigate mechanical strength and hydration behavior of Portland cement (PC) and calcium sulfoaluminate (CSA) cement mixtures when exposed to different temperatures from −5 °C to 20 °C. Setting time and compressive strength were evaluated for mixtures with different PC-CSA ratios. The exothermic hydration heat flow, hydration products, pore size distribution and microstructure for typical samples were determined by using isothermal calorimetry measurement, TG/DTG, XRD, MIP and SEM facilities. The results indicate that the setting time of PC-CSA blends decreases with the higher dosage of CSA cement. Compressive strength of cement mortar is increased by the higher incorporation of CSA cement (5–10%) at early ages, but it is decreased by CSA cement at late ages. This negative effect on late age strength is alleviated by the lower curing temperature. The compressive strength degradation of Portland cement induced by early age exposure to −5 °C is improved by the addition of 5–10% CSA cement. Moreover, the negative effect can be avoided by the incorporation of 20% CSA cement due to the achievement of critical strength after 6 h pre-curing. The hydration of CSA cement during the first several hours is accelerated by the existence of PC and this is favorable for improve the resistance to early age Frost. The pore structure and porosity of cement paste under room temperature is aggravated when the incorporation of CSA is higher than 5% due to the fast formation of massive AFt crystals. But the pore structure and microstructure is improved after exposure to early age Frost due to the higher resistance to Frost Damage. Therefore, the incorporation of suitable content CSA provides a potential method for avoiding early age Frost Damage for cement concretes under minus temperatures.
Zhao Wang - One of the best experts on this subject based on the ideXlab platform.
-
experimental examination of electrical characteristics for portland cement mortar Frost Damage evaluation
Materials, 2020Co-Authors: Tamon Ueda, Fuyuan Gong, Yi Wang, Dawei Zhang, Zhao WangAbstract:Electrical measurements are promising for evaluation of Frost Damage of concrete, but the index is still controversial. In this paper, to propose an efficient index, various electrical characteristics were examined to correlate them with the mechanical property degradation of meso-scale mortar samples due to combined effects of sodium chloride and freeze–thaw cycles (FTCs). While the electrical responses of specimens were measured during FTCs, the mechanical properties were obtained from three-point bending tests after FTCs. Typical microstructural change after the Damage was also analyzed by using a water absorption test. The results showed that no clear degradation tendency was observed for electrical resistivity at the lowest temperature, the activation energy or the freezing/thawing point change with the FTCs. The reduction in electrical resistivity at reference temperature has a consistent tendency with that of elastic modulus and flexural strength, thus can be an efficient index for quantitative Frost Damage evaluation. The change due to salt-Frost Damage is mainly due to the increase of connectivity rather than porosity.
-
structural behaviors evaluation of rc beam under Frost Damage a methodology with meso macro material bond simulation and integrating into structural analysis
Engineering Structures, 2020Co-Authors: Zhao Wang, Dawei Zhang, Fuyuan Gong, Hiroshi Hayashida, Tamon UedaAbstract:Abstract The structural performance under freezing and thawing environment shows severe deterioration, which has drawn large attention recently. Usually the deterioration owing to Frost Damage could attribute to two parts: the degradation of concrete mechanical properties and the degradation of bond properties between concrete and rebars. In this paper, a systematic study was accomplished and a multi-scale structural evaluation methodology was proposed. The macroscale degradations of both concrete and bond properties were simulated and modeled using a mesoscale discrete analytical approach - Rigid Body Spring Method. The proposed constitutive relationships for Damaged concrete and bond properties were adopted in Finite Element Method to conduct structural analysis with considering the temperature history during the freezing-thawing process. Finally, experiment was conducted to verify the stated multi-scale methodology where satisfactory agreements were found between the experiment and FEM analysis.
-
mesoscale simulation of bond behaviors between concrete and reinforcement under the effect of Frost Damage with axisymmetric rigid body spring model
Construction and Building Materials, 2019Co-Authors: Zhao Wang, Dawei Zhang, Fuyuan Gong, Saeid Mehrpay, Tamon UedaAbstract:Abstract Frost Damage is a key deterioration factor for concrete structures in cold and wet areas which has been studied for several decades. For reinforced concrete (RC) structures, bond between reinforcement and concrete plays an important role and its degradation under freezing-thawing environment would affect the service life of the RC structures. This paper aims to develop a mesoscale simulation approach which could estimate and investigate the bond behaviors under the effect of Frost Damage. Based on the axisymmetric discrete element model - Rigid Body Spring Model, the micro-mesoscale mechanical strengthening/damaging effects by Frost action were implemented to non-air entrained concrete and the bond interface. One-way pulling-out test was simulated and the calculated bond strength was compared with experimental results where good agreement was found.
-
mesoscale simulation of concrete behavior with non uniform Frost Damage with verification by ct imaging
Construction and Building Materials, 2017Co-Authors: Zhao Wang, Dawei Zhang, Fuyuan Gong, Hiroshi Hayashida, Tamon UedaAbstract:Abstract The degradation of concrete materials under freezing and thawing cycles is an important issue for structures in cold and wet regions and concrete material degradation in real environment is to be predicted. This paper proposed a mesoscale simulation program to investigate the material deterioration considering the non-uniform environmental condition, which causes non-uniform distribution of humidity and temperature inside concrete. Theoretical coupled heat and moisture transfer model, internal pressure model and degradation constitutive model are applied in a discrete numerical method (Rigid Body Spring Model) to simulate the crack propagation as well as the strength degradation of concrete with non-uniform Frost Damage. In addition to simulation studies, experimental work is conducted to verify the reliability of the simulation program, where satisfactory agreement is found. With this program, further research related to prediction of structure performance is planned to be conducted.
-
mesoscale simulation of fatigue behavior of concrete materials Damaged by freeze thaw cycles
Construction and Building Materials, 2017Co-Authors: Fuyuan Gong, Tamon Ueda, Yi Wang, Dawei Zhang, Zhao WangAbstract:Abstract Frost Damage is a common durability problem for concrete structures in cold and wet regions, and in many cases, the Frost Damage is coupled with fatigue loadings such as the traffic loads on bridge decks or pavements. In this paper, to investigate the basic fatigue behavior of concrete materials affected by Frost Damage, a mesoscale approach based on Rigid Body Spring Method (RBSM) has been developed, of which the concrete material can be divided into three parts: mortar, coarse aggregate and interfacial transition zone (ITZ) between them. First, the cyclic constitutive laws are developed at normal and shear directions for mortar and ITZ, and verified with the existing experimental data in compression and tension fatigue. Then, several levels of Frost Damage are introduced by different numbers of freeze-thaw cycles (FTCs), and finally, the static tests and fatigue tests are conducted using the Frost Damaged concrete. The simulation results on the static strength and fatigue life show a good agreement with experimental data, and found that as the Frost Damage level (irreversible plastic deformation) increases, not only the static strength, but also the fatigue life at each stress level will decrease. The S-N curves of Frost Damaged concrete still follow a linear relationship but with bigger slopes, and the Frost Damaged concrete will become more ductile under fatigue loadings.
Kyungtaek Koh - One of the best experts on this subject based on the ideXlab platform.
-
an experimental investigation on minimum compressive strength of early age concrete to prevent Frost Damage for nuclear power plant structures in cold climates
Nuclear Engineering and Technology, 2013Co-Authors: Kyungtaek Koh, Chunjin Park, Gumsung Ryu, Jungjun Park, Dogyeum Kim, Janghwa LeeAbstract:Concrete undergoing early Frost Damage in cold weather will experience significant loss of not only strength, but also of permeability and durability. Accordingly, concrete codes like ACI-306R prescribe a minimum compressive strength and duration of curing to prevent Frost Damage at an early age and secure the quality of concrete. Such minimum compressive strength and duration of curing are mostly defined based on the strength development of concrete. However, concrete subjected to Frost Damage at early age may not show a consistent relationship between its strength and durability. Especially, since durability of concrete is of utmost importance in nuclear power plant structures, this relationship should be imperatively clarified. Therefore, this study verifies the feasibility of the minimum compressive strength specified in the codes like ACI-306R by evaluating the strength development and the durability preventing the Frost Damage of early age concrete for nuclear power plant. The results indicate that the value of 5 MPa specified by the concrete standards like ACI-306R as the minimum compressive strength to prevent the early Frost Damage is reasonable in terms of the strength development, but seems to be inappropriate in the viewpoint of the resistance to chloride ion penetration and freeze-thaw. Consequently, it is recommended to propose a minimum compressive strength preventing early Frost Damage in terms of not only the strength development, but also in terms of the durability to secure the quality of concrete for nuclear power plants in cold climates.
-
effect of curing method on the strength development and freezing thawing durability of the concrete incorporating high volume blast furnace slag subjected to initial Frost Damage
Advanced Materials Research, 2012Co-Authors: Kyungtaek Koh, Gumsung Ryu, Janghwa LeeAbstract:In the case of construction with high volume blast-furnace slag(BFS) concrete during winter season, the setting and hardening are drastically delayed, so it has a high risk of initial Frost. Assuming that the concrete incorporating a high volume of BFS is affected by freezing at the early age during the winter conditions, then this study is to investigate the effect of curing method on the strength development and the resistance to freezing-thawing action. As a result, the concrete performing water curing at 5°C after subjected to initial Frost Damage improve the long-term strength and the freezing-thawing durability. The concrete implementing water curing at 30°C enhance the long-term strength and the resistance to freezing-thawing action as well as the early strength. However, the concrete with sealed curing at 30°C exhibits the improvement in the early strength, but not in the long-term strength and the freezing-thawing durability.
-
evaluation on the compressive strength of concrete incorporating high volume blast furnace slag subjected to initial Frost Damage
Applied Mechanics and Materials, 2011Co-Authors: Kyungtaek Koh, Chunjin Park, Gumsung Ryu, Ki Hong Ahn, Janghwa LeeAbstract:Construction works that uses concrete incorporating a high volume of blast-furnace slag (BFS) during the winter season increases the risk of being subjected to initial Frost Damage as it noticeably delays setting and hardening. Assuming that the concrete incorporating a high volume of BFS was affected by freezing at an early age during the winter conditions, this study is to investigate the effect of strength degradation by early freezing and curing methods on compressive strength. As a result, freezing at early age highly degraded the compressive strength regardless of the types of concrete. After influenced by initial Frost Damage, water curing at 5°C improved the long-term strength and water curing at 30°C enhanced the long-term strength as well as the early strength.
