The Experts below are selected from a list of 918 Experts worldwide ranked by ideXlab platform
Haitao Zhao - One of the best experts on this subject based on the ideXlab platform.
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mechanical properties and volumetric deformation of early age concrete containing cao mgo blended Expansive Agent and temperature rising inhibitor
Construction and Building Materials, 2021Co-Authors: Haitao Zhao, Yujiang Wang, Xiaodong Chen, Yu Xiang, Jie Huang, Penggang WangAbstract:Abstract The early-age cracking occurred frequently because of the large autogenous shrinkage and the substantial and rapid temperature drop in high-strength and high-performance concrete structure, which seriously prejudices the durability and even the safety of the structure. This paper aimed at utilizing the combination of CaO-MgO blended Expansive Agent (CMEA) and Temperature rising inhibitor (TRI) to compensate for the concrete contraction. The results showed that the addition of TRI and/or CMEA weakened the strength and dynamic elastic modulus (DEM) as well as increasing the curing temperature. The CMEA addition could improve the relative humidity (RH) in specimens with or without TRI. When TRI content increased, the RH of specimens with TRI only decreased apparently but the RH decline in specimens containing CMEA and TRI was negligible. The CMEA could compensate for the concrete shrinkage not merely at the early stage but the later stage. The combination of CMEA and TRI increased the expansion peak and reduced autogenous shrinkage compared to single CMEA addition. With the increasing TRI content, the autogenous shrinkage of concrete increased visibly but the autogenous shrinkage of specimens containing TRI and CMEA decreased first and then increased. Additionally, the autogenous shrinkage and shrinkage rate of specimens with TRI and CMEA decreased markedly with curing temperature due to CMEA better expansion effect at high curing temperature.
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microstructure evolution of cement mortar containing mgo cao blended Expansive Agent and temperature rising inhibitor under multiple curing temperatures
Construction and Building Materials, 2021Co-Authors: Haitao Zhao, Xiaodong Chen, Chunyu Qiao, Panxiu Wang, Hongwei SongAbstract:Abstract Autogenous shrinkage (AS) and thermal shrinkage often lead to cracking in high performance concrete (HPC) under restraint conditions. MgO-CaO blended Expansive Agent (MC) and temperature rising inhibitor (TRI) has been adopted to reduce the AS and thermal shrinkage of HPC. The macroscopic properties of HPC strongly depend on the pore structure. Therefore, this paper studied the effects of MC and TRI on the pore structure evolution of HPC under multiple curing temperatures using low-field nuclear magnetic resonance spectroscopy (LF-NMR). Experimental results showed that the most probable pore diameter (MPPD) and porosity of mortar increased as the MC content increased due to the crystallization pressure by the hydration of MC. But MPPD and porosity decreased as the TRI content increased owing to a better filling effect of hydration products. Meanwhile, the mortar with the combined use of MC and TRI exhibited notably smaller MPPD and porosity than the plain mortar. In addition, as the curing temperature increased, the porosity of mortar containing both TRI and MC first decreased and then increased, while MPPD increased continuously. MPPD and porosity of mortar with both MC and TRI addition cured at 20 °C and 40 °C continued to decrease with age. However, MPPD and porosity dramatically increased with age at 60 °C as a result of the over-accelerated hydration of MgO.
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mechanical properties and autogenous deformation behavior of early age concrete containing pre wetted ceramsite and cao based Expansive Agent
Construction and Building Materials, 2021Co-Authors: Haitao Zhao, Hui Liu, Yi Wan, Rita Maria Ghantous, Ying Liu, Junfeng GuanAbstract:Abstract Autogenous shrinkage (AS) of high-strength and high-performance concrete (HSHPC) is large, which easily leads to early-age cracks and then severely deteriorates the concrete durability. CaO-based Expansive Agent (CEA) is extensively applied to mitigate the AS of HSHPC, but CEA could not fully achieve its expansion efficacy in HSHPC because of its low water to binder ratio and water amount, causing that CEA hydrates incompletely and the concrete contracts sharply and substantially after the initial expansion. Pre-wetted ceramsite (PWC), as an internal curing Agent, could decrease effectively the AS of HSHPC. Based on the mechanism of AS reduction of CEA and PWC, the combination use of CEA and PWC could reach a synergistic effect on AS in HSHPC. However, there still lacks a synthetic study on the effects of the compound use of PWC and CEA on the mechanical properties and autogenous deformation of concrete. Thus, this study carried out the experiments on mechanical behaviors and autogenous deformation of concrete with PWC or/and CEA addition. The test results claimed that the PWC addition enhanced the compressive and splitting tensile strength while the opposite results were obtained by CEA addition. In addition, both PWC and CEA addition weakened the dynamic elastic modulus of concrete. Meanwhile, the PWC and CEA incorporation had a significant improving effect on the internal relative humidity in concrete. The AS of concrete was greatly mitigated by PWC addition. The IC water of PWC could improve the expansion efficacy of CEA as well as greatly decrease the contraction at the later stage. A remarkable synergistic mechanism on AS mitigation was observed with the combined use of PWC and CEA, which is significantly beneficial to control the AS-induced cracking.
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effects of pre soaked zeolite and cao based Expansive Agent on mechanical properties and autogenous deformation of early age concrete
Construction and Building Materials, 2020Co-Authors: Haitao Zhao, Qian Tian, Gaoyang Sun, Jianhua Jiang, Weihong Xuan, Yuzhi Chen, Jiaping LiuAbstract:Abstract High-performance concrete (HPC) is prone to cracking at an early age due to the large autogenous shrinkage (AS), which severely weakens the durability of the concrete structure. CaO-based Expansive Agent (CEA) is widely utilized to compensate for the AS of HPC, but CEA cannot achieve its potential expansion in HPC due to a low water to binder ratio, resulting in an incomplete hydration, and a sharp and substantial retraction after initial expansion. Pre-soaked zeolite can be introduced as internal curing (IC) Agent to reduce the AS of HPC owing to the IC water released from zeolite. According to the AS-reduction mechanism of CEA and zeolite, a synergistic mechanism can be achieved by the combination use of CEA and zeolite in HPC. However, a comprehensive understanding of the effects of the combination use of zeolite and CEA on the mechanical properties and autogenous deformation of concrete is still lacking. Therefore, the influence of zeolite and CEA addition on mechanical properties and autogenous deformation were investigated experimentally. The investigation results showed that the zeolite addition weakened the mechanical properties of concrete while the CEA addition had the opposite effect. The internal relative humidity in concrete was significantly improved with zeolite and CEA incorporation. The IC water released from zeolite could not only enhance the expansion efficiency at an early age but also greatly reduce the retraction at the later age. The results exhibited an obvious synergistic mechanism with the combination use of zeolite and CEA on AS mitigation, which is of great benefit in AS-induced cracking control.
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temperature sensitivity of mgo Expansive Agent and its application in temperature crack mitigation in shiplock mass concrete
Construction and Building Materials, 2018Co-Authors: Qian Tian, Haitao Zhao, Jiaping LiuAbstract:Abstract The compensation of thermal shrinkage with the delayed expansion of MgO Expansive Agent has been used not only in mass concrete, but also in some underground sidewall in subway stations in China. This study investigated the expansion behaviors and crack resistance of three kinds of MgO with different reactivity values (90 s, 150 s and 250 s) in concrete based on a comprehensive test system including the length test using the differential strain gauge, a dual-ring test and the environment simulation test chamber. The results showed that the expansion behavior of MgO Expansive Agent was closely related to its reactivity value and the temperature history of concrete. MgO with lower reactivity value (90 s, 150 s) showed larger expansion in concrete than MgO with higher reactivity value (250 s) under the temperature history of low temperature rise and high cooling rate, while MgO with higher reactivity value showed larger expansion at temperature fall stage and better crack resistance under the temperature history of high temperature rise, low cooling rate and long cooling period. The results indicate that the reactivity value of MgO Expansive Agent should be properly selected according to the characteristics of temperature histories of different concrete structures to give full play of its shrinkage compensating efficiency.
Qian Tian - One of the best experts on this subject based on the ideXlab platform.
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effects of pre soaked zeolite and cao based Expansive Agent on mechanical properties and autogenous deformation of early age concrete
Construction and Building Materials, 2020Co-Authors: Haitao Zhao, Qian Tian, Gaoyang Sun, Jianhua Jiang, Weihong Xuan, Yuzhi Chen, Jiaping LiuAbstract:Abstract High-performance concrete (HPC) is prone to cracking at an early age due to the large autogenous shrinkage (AS), which severely weakens the durability of the concrete structure. CaO-based Expansive Agent (CEA) is widely utilized to compensate for the AS of HPC, but CEA cannot achieve its potential expansion in HPC due to a low water to binder ratio, resulting in an incomplete hydration, and a sharp and substantial retraction after initial expansion. Pre-soaked zeolite can be introduced as internal curing (IC) Agent to reduce the AS of HPC owing to the IC water released from zeolite. According to the AS-reduction mechanism of CEA and zeolite, a synergistic mechanism can be achieved by the combination use of CEA and zeolite in HPC. However, a comprehensive understanding of the effects of the combination use of zeolite and CEA on the mechanical properties and autogenous deformation of concrete is still lacking. Therefore, the influence of zeolite and CEA addition on mechanical properties and autogenous deformation were investigated experimentally. The investigation results showed that the zeolite addition weakened the mechanical properties of concrete while the CEA addition had the opposite effect. The internal relative humidity in concrete was significantly improved with zeolite and CEA incorporation. The IC water released from zeolite could not only enhance the expansion efficiency at an early age but also greatly reduce the retraction at the later age. The results exhibited an obvious synergistic mechanism with the combination use of zeolite and CEA on AS mitigation, which is of great benefit in AS-induced cracking control.
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simplified chemo mechanical model of hydration expansion of calcium oxide type Expansive Agent in cement based materials
Magazine of Concrete Research, 2020Co-Authors: Jiaping Liu, Yujiang Wang, Qian TianAbstract:The restrained volume expansion of Expansive Agents during hydration is often used to offset strains caused by the shrinkage of cement-based materials (CBMs). The hydration and expansion process of...
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effect of cao and mgo based Expansive Agent on deformation and mechanical properties of concrete filled steel tubes
Construction and Building Materials, 2020Co-Authors: Yi Wang, Jiaping Liu, Yujiang Wang, Qian TianAbstract:Abstract The separation problem between core concrete and steel tube is one of the main bottlenecks restricting the construction of super large-span concrete-filled steel tubular arch bridges. One of the main measures to solve this problem is to prepare micro Expansive core concrete by using the shrinkage compensation property of Expansive Agent. This study investigated the deformation and mechanical properties of core concrete containing CaO-based and MgO-based Expansive Agent under both the constant temperature and the varying temperature. The results showed that concrete containing CaO-based and MgO-based Expansive Agents can produce remarkable expansion which increases with the increase of CaO-MgO ratios under the constant temperature of 20 °C, but decreases with the increase of CaO-MgO ratios under the varying temperature. Through the restraint from the steel tube can reduce the expansion value, proper selection of CaO-MgO ratio can still produce enough expansion in core concrete to compensate autogenous and thermal shrinkage, with the concrete still in expansion state when the temperature finally stabilizes. Thus it is beneficial to maintain the integrity between the core concrete and the steel tube. The results obtained will provide guidance for the application of this kind of Expansive Agent in concrete-filled steel tube structure.
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temperature sensitivity of mgo Expansive Agent and its application in temperature crack mitigation in shiplock mass concrete
Construction and Building Materials, 2018Co-Authors: Qian Tian, Haitao Zhao, Jiaping LiuAbstract:Abstract The compensation of thermal shrinkage with the delayed expansion of MgO Expansive Agent has been used not only in mass concrete, but also in some underground sidewall in subway stations in China. This study investigated the expansion behaviors and crack resistance of three kinds of MgO with different reactivity values (90 s, 150 s and 250 s) in concrete based on a comprehensive test system including the length test using the differential strain gauge, a dual-ring test and the environment simulation test chamber. The results showed that the expansion behavior of MgO Expansive Agent was closely related to its reactivity value and the temperature history of concrete. MgO with lower reactivity value (90 s, 150 s) showed larger expansion in concrete than MgO with higher reactivity value (250 s) under the temperature history of low temperature rise and high cooling rate, while MgO with higher reactivity value showed larger expansion at temperature fall stage and better crack resistance under the temperature history of high temperature rise, low cooling rate and long cooling period. The results indicate that the reactivity value of MgO Expansive Agent should be properly selected according to the characteristics of temperature histories of different concrete structures to give full play of its shrinkage compensating efficiency.
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efficacy of internal curing combined with Expansive Agent in mitigating shrinkage deformation of concrete under variable temperature condition
Construction and Building Materials, 2017Co-Authors: Ming Li, Qian Tian, Yujiang Wang, Wen XuAbstract:Abstract The benefits of internal curing (IC) have been confirmed by extensive laboratory studies under constant room temperature. In practical engineering, sidewall concrete undergoes a variable temperature evolution, which involves significant physical, chemical, and thermal changes during the hydration process at the early age and a high cracking risk at the temperature drop stage. Expansive Agent (EA) has always been used to mitigate early-age cracking, but it has limited efficacy in the temperature drop stage and low mechanical properties. This study examines the efficacy of IC through pre-soaked lightweight aggregate (SLWA) and the combined use of SLWA and EA in mitigating shrinkage deformation under constant and variable temperature conditions. Results indicate that SLWA shows a higher efficacy than EA in mitigating shrinkage deformation during the temperature drop stage and can provide continuous expansion at the later stage. The combined use of SLWA and EA exhibits high efficacy in mitigating shrinkage deformation under constant and variable temperature conditions and can limit the reduction of mechanical properties caused by a single EA.
Khandaker M A Hossain - One of the best experts on this subject based on the ideXlab platform.
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Internally cured high performance concrete with magnesium based Expansive Agent using coal bottom ash particles as water reservoirs
Construction and Building Materials, 2020Co-Authors: Roberto Rodríguez-Álvaro, Belén González-fonteboa, Sindy Seara-paz, Khandaker M A HossainAbstract:Abstract Shrinkage is one of the main concerns related to high performance concrete (HPC) durability. Its high density paste, consequence of a low water to binder ratio, can be unprofitable if cracks appear due to excessive tension when volume changes are restrained. Therefore, volume stability is a priority. In this work, three different strategies have been studied with that purpose: integration of fly ash as a low reactive supplementary cementitious material, internal curing via coal bottom ash particles as water reservoirs and the use of an Expansive Agent based on magnesium oxide (MEA). Many research works address the three shrinkage reduction strategies individually. However, studies regarding their simultaneous use are not prevalent so this work proposes its combined application. Results indicate that internal curing and MEA have a synergistic effect in HPC. Internal curing enhances MEA expansion due to the lack of water in this kind of concrete, contributing to autogenous shrinkage compensation. When concrete is affected by air-drying conditions, the use of MEA, internal curing, or both together make shrinkage to increase. MEA effectively expands in wet cured HPC although internal curing is not effective in this condition due to the absence of self-desiccation and limited porous aggregate water desorption. Taking into account the effects of each shrinkage reduction strategy and curing condition, it has been concluded that the use of fly ash as supplementary cementitious material, internal curing and MEA is recommended together with prevention of water evaporation from HPC surface.
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permeation and transport properties of self healed cementitious composite produced with mgo Expansive Agent
Journal of Materials in Civil Engineering, 2018Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:AbstractThis study evaluated the self-healing capability of engineered cementitious composite (ECC) produced with 5% MgO Expansive Agent (MEA) compared with standard ECC counterparts. The efficienc...
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the influence of mgo type Expansive Agent incorporated in self healing system of engineered cementitious composites
Construction and Building Materials, 2017Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract Engineered Cementitious Composites (ECCs) are found to be better replacements for traditional concretes due to their higher damage tolerance under loading, as well as the ability to induce multiple-cracking with a smaller width and potential crack healing capability. This paper presents the development and performance of an effective self-healing concrete system made of ECC and MgO-type Expansive Agent (MEA) (made of lightly burnt MgO powder). New measures were implemented in examining the performance of ECC-MgO self-healing system based on accelerated autoclave test to simulate the experimental results relevant to the field conditions. Test results suggested the best calcination system to be 900 °C with 2 h of holding time using 45 µm particle size based on higher hydration activity of MEA in a powder state. Low calcium Class-F fly ash was found to be the best supplementary cementing materials (SCMs) to produce ECC-MgO system based on lower expansion effect of MgO. The high volume of fly ash (HVFA) was used to achieve very low expansion within the crack walls just to heal hairline micro-cracks in ECC-MgO self-healing system without jeopardizing the durability. Similar behavior was shown by the MgO in powder state in terms of loss of CO2 content and remaining hydration activity as well as after utilizing it in the ECC-MgO system in water and autoclave linear expansion tests coupled with scanning electron microscope (SEM) and thermogravimetric analyses (TGA). The higher flexural strength recovery of pre-cracked ECC-MgO prismatic specimens cured under accelerated autoclaved conditions compared to their pre-cracked ECC (without MgO) counterparts confirmed the self-healing capability and potential of the proposed ECC-MgO system.
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development and recovery of mechanical properties of self healing cementitious composites with mgo Expansive Agent
Construction and Building Materials, 2017Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract This paper presents the performance of engineered cementitious composites (ECCs) produced with MgO utilized as Expansive self-healing Agent to heal micro cracks. ECCs capability to keep small crack width of less than 60 µm even under ultimate loads can stimulate the autogenous crack healing and thus, improving the mechanical properties of structural elements. Different test schemes were adopted to quantify the long-term self-healing capability of proposed ECC-MgO system (made of 5% MgO Expansive Agent ‘MEA’ as fly ash replacement in ECC matrix) through studying the development and recovery of strength (compressive and flexural) and Ultrasonic Pulse Velocity (UPV) of pre-loaded multiple damaged (cracked) cubic and prismatic specimens subjected to long term water and natural curing conditions. Test results indicated that preloaded cracked ECC-MgO specimens had high tendency to recover original mechanical properties of virgin (un-cracked) specimens through healing of micro-cracks. This study confirmed the self-healing capability of proposed ECC-MgO system.
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self healing and expansion characteristics of cementitious composites with high volume fly ash and mgo type Expansive Agent
Construction and Building Materials, 2016Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract Discovering new cement based materials characterised with self-healing capability is essential for sustainable infrastructure with longer service life. Engineered cementitious composite (ECC) with high potential of micro-crack healing can enhance ductility and durability of concrete structures. MgO-type Expansive Agent (MEA) having low water demand and with the ability of densification of concrete microstructure was utilized in this research to develop ECC-MgO self-healing system. The effect of dosages of MEA and fly ash of different types as cement replacements was investigated based on lower expansion characteristics of ECC-MgO bar specimens through both water and autoclave linear expansion tests. The performance of ECC-MgO self-healing system was examined based on compressive strength recovery of pre-cracked cubic specimens and matrix micro-structural densification through Scanning Electron Microscope (SEM). Test results indicated that 5% lightly burnt MgO in combination with high volume of Class-F fly ash with 55% cement replacement should be used to design ECC-MgO self-healing system just to heal micro-cracks without affecting the durability. The higher compressive strength of 50% and 80% pre-cracked ECC-MgO cubic specimens cured under accelerated autoclaved conditions compared to ECC-control (without MEA) confirmed the self-healing capability and potential of the proposed ECC-MgO system.
Jiaping Liu - One of the best experts on this subject based on the ideXlab platform.
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effects of pre soaked zeolite and cao based Expansive Agent on mechanical properties and autogenous deformation of early age concrete
Construction and Building Materials, 2020Co-Authors: Haitao Zhao, Qian Tian, Gaoyang Sun, Jianhua Jiang, Weihong Xuan, Yuzhi Chen, Jiaping LiuAbstract:Abstract High-performance concrete (HPC) is prone to cracking at an early age due to the large autogenous shrinkage (AS), which severely weakens the durability of the concrete structure. CaO-based Expansive Agent (CEA) is widely utilized to compensate for the AS of HPC, but CEA cannot achieve its potential expansion in HPC due to a low water to binder ratio, resulting in an incomplete hydration, and a sharp and substantial retraction after initial expansion. Pre-soaked zeolite can be introduced as internal curing (IC) Agent to reduce the AS of HPC owing to the IC water released from zeolite. According to the AS-reduction mechanism of CEA and zeolite, a synergistic mechanism can be achieved by the combination use of CEA and zeolite in HPC. However, a comprehensive understanding of the effects of the combination use of zeolite and CEA on the mechanical properties and autogenous deformation of concrete is still lacking. Therefore, the influence of zeolite and CEA addition on mechanical properties and autogenous deformation were investigated experimentally. The investigation results showed that the zeolite addition weakened the mechanical properties of concrete while the CEA addition had the opposite effect. The internal relative humidity in concrete was significantly improved with zeolite and CEA incorporation. The IC water released from zeolite could not only enhance the expansion efficiency at an early age but also greatly reduce the retraction at the later age. The results exhibited an obvious synergistic mechanism with the combination use of zeolite and CEA on AS mitigation, which is of great benefit in AS-induced cracking control.
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simplified chemo mechanical model of hydration expansion of calcium oxide type Expansive Agent in cement based materials
Magazine of Concrete Research, 2020Co-Authors: Jiaping Liu, Yujiang Wang, Qian TianAbstract:The restrained volume expansion of Expansive Agents during hydration is often used to offset strains caused by the shrinkage of cement-based materials (CBMs). The hydration and expansion process of...
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effect of cao and mgo based Expansive Agent on deformation and mechanical properties of concrete filled steel tubes
Construction and Building Materials, 2020Co-Authors: Yi Wang, Jiaping Liu, Yujiang Wang, Qian TianAbstract:Abstract The separation problem between core concrete and steel tube is one of the main bottlenecks restricting the construction of super large-span concrete-filled steel tubular arch bridges. One of the main measures to solve this problem is to prepare micro Expansive core concrete by using the shrinkage compensation property of Expansive Agent. This study investigated the deformation and mechanical properties of core concrete containing CaO-based and MgO-based Expansive Agent under both the constant temperature and the varying temperature. The results showed that concrete containing CaO-based and MgO-based Expansive Agents can produce remarkable expansion which increases with the increase of CaO-MgO ratios under the constant temperature of 20 °C, but decreases with the increase of CaO-MgO ratios under the varying temperature. Through the restraint from the steel tube can reduce the expansion value, proper selection of CaO-MgO ratio can still produce enough expansion in core concrete to compensate autogenous and thermal shrinkage, with the concrete still in expansion state when the temperature finally stabilizes. Thus it is beneficial to maintain the integrity between the core concrete and the steel tube. The results obtained will provide guidance for the application of this kind of Expansive Agent in concrete-filled steel tube structure.
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effect of temperature rising inhibitor on expansion behavior of cement paste containing Expansive Agent
Construction and Building Materials, 2019Co-Authors: Hao Zhang, Wenbing Wang, Jiaping LiuAbstract:Abstract The present study aims to examine the mechanism influencing the expansion characteristics of Expansive cement paste in presence of different dosages of Temperature Rising Inhibitor (TRI). The expansion of cement pastes showed a higher expansion strain of the OPC-EA mixture with 0.2% and 0.4% TRI in comparison to the reference sample and a decreased shrinkage of cement pastes containing Expansive Agent (OPC-EA). Meanwhile, dynamic elastic modulus, hydration kinetics, mineral phase compositions and microstructure characterization of hydration products were also investigated by ultrasonic method, isothermal calorimetry, quantitative X-ray diffraction and scanning electron microscope, respectively. The delayed hydration process of Expansive Agent increases the amount of Expansive Agent available to react after the setting of cement pastes, resulting in the increased expansion strain of OPC-EA-0.2%TRI sample. The higher expansion strain of OPC-EA-0.4%TRI sample can be attributed to the lower stiffness of cement paste affected by TRI. The results showed that the addition of TRI is the main force in delaying the hydration process of ye’elimite in Expansive Agent by acting on the formation and morphology of ettringite. The delayed ye’elimite hydration process can be explained by inhibition of the precipitation or/and growth of ettringite.
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temperature sensitivity of mgo Expansive Agent and its application in temperature crack mitigation in shiplock mass concrete
Construction and Building Materials, 2018Co-Authors: Qian Tian, Haitao Zhao, Jiaping LiuAbstract:Abstract The compensation of thermal shrinkage with the delayed expansion of MgO Expansive Agent has been used not only in mass concrete, but also in some underground sidewall in subway stations in China. This study investigated the expansion behaviors and crack resistance of three kinds of MgO with different reactivity values (90 s, 150 s and 250 s) in concrete based on a comprehensive test system including the length test using the differential strain gauge, a dual-ring test and the environment simulation test chamber. The results showed that the expansion behavior of MgO Expansive Agent was closely related to its reactivity value and the temperature history of concrete. MgO with lower reactivity value (90 s, 150 s) showed larger expansion in concrete than MgO with higher reactivity value (250 s) under the temperature history of low temperature rise and high cooling rate, while MgO with higher reactivity value showed larger expansion at temperature fall stage and better crack resistance under the temperature history of high temperature rise, low cooling rate and long cooling period. The results indicate that the reactivity value of MgO Expansive Agent should be properly selected according to the characteristics of temperature histories of different concrete structures to give full play of its shrinkage compensating efficiency.
Mohamed Lachemi - One of the best experts on this subject based on the ideXlab platform.
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permeation and transport properties of self healed cementitious composite produced with mgo Expansive Agent
Journal of Materials in Civil Engineering, 2018Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:AbstractThis study evaluated the self-healing capability of engineered cementitious composite (ECC) produced with 5% MgO Expansive Agent (MEA) compared with standard ECC counterparts. The efficienc...
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the influence of mgo type Expansive Agent incorporated in self healing system of engineered cementitious composites
Construction and Building Materials, 2017Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract Engineered Cementitious Composites (ECCs) are found to be better replacements for traditional concretes due to their higher damage tolerance under loading, as well as the ability to induce multiple-cracking with a smaller width and potential crack healing capability. This paper presents the development and performance of an effective self-healing concrete system made of ECC and MgO-type Expansive Agent (MEA) (made of lightly burnt MgO powder). New measures were implemented in examining the performance of ECC-MgO self-healing system based on accelerated autoclave test to simulate the experimental results relevant to the field conditions. Test results suggested the best calcination system to be 900 °C with 2 h of holding time using 45 µm particle size based on higher hydration activity of MEA in a powder state. Low calcium Class-F fly ash was found to be the best supplementary cementing materials (SCMs) to produce ECC-MgO system based on lower expansion effect of MgO. The high volume of fly ash (HVFA) was used to achieve very low expansion within the crack walls just to heal hairline micro-cracks in ECC-MgO self-healing system without jeopardizing the durability. Similar behavior was shown by the MgO in powder state in terms of loss of CO2 content and remaining hydration activity as well as after utilizing it in the ECC-MgO system in water and autoclave linear expansion tests coupled with scanning electron microscope (SEM) and thermogravimetric analyses (TGA). The higher flexural strength recovery of pre-cracked ECC-MgO prismatic specimens cured under accelerated autoclaved conditions compared to their pre-cracked ECC (without MgO) counterparts confirmed the self-healing capability and potential of the proposed ECC-MgO system.
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development and recovery of mechanical properties of self healing cementitious composites with mgo Expansive Agent
Construction and Building Materials, 2017Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract This paper presents the performance of engineered cementitious composites (ECCs) produced with MgO utilized as Expansive self-healing Agent to heal micro cracks. ECCs capability to keep small crack width of less than 60 µm even under ultimate loads can stimulate the autogenous crack healing and thus, improving the mechanical properties of structural elements. Different test schemes were adopted to quantify the long-term self-healing capability of proposed ECC-MgO system (made of 5% MgO Expansive Agent ‘MEA’ as fly ash replacement in ECC matrix) through studying the development and recovery of strength (compressive and flexural) and Ultrasonic Pulse Velocity (UPV) of pre-loaded multiple damaged (cracked) cubic and prismatic specimens subjected to long term water and natural curing conditions. Test results indicated that preloaded cracked ECC-MgO specimens had high tendency to recover original mechanical properties of virgin (un-cracked) specimens through healing of micro-cracks. This study confirmed the self-healing capability of proposed ECC-MgO system.
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self healing and expansion characteristics of cementitious composites with high volume fly ash and mgo type Expansive Agent
Construction and Building Materials, 2016Co-Authors: Mohamed A A Sherir, Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract Discovering new cement based materials characterised with self-healing capability is essential for sustainable infrastructure with longer service life. Engineered cementitious composite (ECC) with high potential of micro-crack healing can enhance ductility and durability of concrete structures. MgO-type Expansive Agent (MEA) having low water demand and with the ability of densification of concrete microstructure was utilized in this research to develop ECC-MgO self-healing system. The effect of dosages of MEA and fly ash of different types as cement replacements was investigated based on lower expansion characteristics of ECC-MgO bar specimens through both water and autoclave linear expansion tests. The performance of ECC-MgO self-healing system was examined based on compressive strength recovery of pre-cracked cubic specimens and matrix micro-structural densification through Scanning Electron Microscope (SEM). Test results indicated that 5% lightly burnt MgO in combination with high volume of Class-F fly ash with 55% cement replacement should be used to design ECC-MgO self-healing system just to heal micro-cracks without affecting the durability. The higher compressive strength of 50% and 80% pre-cracked ECC-MgO cubic specimens cured under accelerated autoclaved conditions compared to ECC-control (without MEA) confirmed the self-healing capability and potential of the proposed ECC-MgO system.
