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Di Pino S, Perez Sirkin YA, Morzan UN, Sánchez VM, Hassanali A, Scherlis DA. Water Self-Dissociation is Insensitive to Nanoscale Environments. Angew Chem Int Ed Engl 2023; 62:e202306526. [PMID: 37379226 DOI: 10.1002/anie.202306526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 06/26/2023] [Accepted: 06/27/2023] [Indexed: 06/30/2023]
Abstract
Nanoconfinement effects on water dissociation and reactivity remain controversial, despite their importance to understand the aqueous chemistry at interfaces, pores, or aerosols. The pKw in confined environments has been assessed from experiments and simulations in a few specific cases, leading to dissimilar conclusions. Here, with the use of carefully designed ab initio simulations, we demonstrate that the energetics of bulk water dissociation is conserved intact to unexpectedly small length-scales, down to aggregates of only a dozen molecules or pores of widths below 2 nm. The reason is that most of the free-energy involved in water autoionization comes from breaking the O-H covalent bond, which has a comparable barrier in the bulk liquid, in a small droplet of nanometer size, or in a nanopore in the absence of strong interfacial interactions. Thus, dissociation free-energy profiles in nanoscopic aggregates or in 2D slabs of 1 nm width reproduce the behavior corresponding to the bulk liquid, regardless of whether the corresponding nanophase is delimited by a solid or a gas interface. The present work provides a definite and fundamental description of the mechanism and thermodynamics of water dissociation at different scales with broader implications on reactivity and self-ionization at the air-liquid interface.
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Affiliation(s)
- Solana Di Pino
- Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
- Condensed Matter and Statistical Physics, International Centre for Theoretical Physics, I-34151, Trieste, Italy
| | - Yamila A Perez Sirkin
- Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
| | - Uriel N Morzan
- Condensed Matter and Statistical Physics, International Centre for Theoretical Physics, I-34151, Trieste, Italy
| | - Verónica M Sánchez
- Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
| | - Ali Hassanali
- Condensed Matter and Statistical Physics, International Centre for Theoretical Physics, I-34151, Trieste, Italy
| | - Damian A Scherlis
- Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
- Condensed Matter and Statistical Physics, International Centre for Theoretical Physics, I-34151, Trieste, Italy
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2
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Hong F, Wang M, Dong B, Diao X, Zhang X, Pang K, Zhang Y, Hou D. Molecular Insight into the Pozzolanic Reaction of Metakaolin and Calcium Hydroxide. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:3601-3609. [PMID: 36848440 DOI: 10.1021/acs.langmuir.2c03115] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The reaction mechanism of the pozzolanic reaction of metakaolin (MK) from the atomic point of view has not yet been explored. To explain the process and mechanism of the pozzolanic reaction from the atomic point of view, molecular insight into the pozzolanic reaction of MK and calcium hydroxide (CH) was analyzed through the reaction molecular dynamics (MD) simulation. The results show that the pozzolanic reaction of MK and CH can be essentially regarded as the CH decomposition and penetration into MK. Also, the structure evolution after the pozzolanic reaction shows that the water molecules cannot penetrate the MK structure till the participation of Ca2+ and OH- ions of CH. The Ca2+ and OH- ions have strong interaction with MK and drill into the MK structure, followed by the destruction of a part of the MK structure and water penetration. The final structure of CH removed by MK can be regarded as the precursor of the CASH gel structure.
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Affiliation(s)
- Fen Hong
- Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China
| | - Muhan Wang
- Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China
| | - Biqin Dong
- College of Civil and Transportation Engineering, Shenzhen University, Shenzhen 518060, China
| | - Xiaoxiang Diao
- Tianjin Housing Group Construction Engineering General Contraction Co., Ltd., Tianjin 300000, China
| | | | - Kai Pang
- China Construction Port Group Co., Ltd., Qingdao 266033, China
| | - Yongmin Zhang
- China Construction Port Group Co., Ltd., Qingdao 266033, China
| | - Dongshuai Hou
- Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China
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3
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Yadav A, Krishnan NMA. Role of steric repulsions on the precipitation kinetics and the structure of calcium-silicate-hydrate gels. SOFT MATTER 2021; 17:8902-8914. [PMID: 34545899 DOI: 10.1039/d1sm00838b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The microstructure and properties of calcium-silicate-hydrate (C-S-H) gels are largely controlled by the physicochemical environment during their precipitation. However, the role of the steric repulsive environment induced by the pore solution chemistry on the kinetics, structure, and properties of C-S-H gels remains unclear. Here, we develop two potential formalisms, namely sinusoidal and polynomial, to simulate the role of steric repulsions in C-S-H. The results show excellent agreement with experimental observations of precipitation kinetics and elastic properties. We demonstrate that the repulsive interactions result in delayed precipitation and percolation, and an open and branched microstructure. Interestingly, the elastic properties (which are equilibrium properties) are also significantly affected by these second-neighbor interactions. Overall, the present study demonstrates that the kinetics, structure, and equilibrium properties of colloidal gels are controlled by the steric repulsions induced by the chemical environment.
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Affiliation(s)
- Ashish Yadav
- Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India.
| | - N M Anoop Krishnan
- Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India.
- Department of Materials Science and Engineering, Indian Institute of Technology Delhi, New Delhi, India
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Kai MF, Zhang LW, Liew KM. Atomistic insights into structure evolution and mechanical property of calcium silicate hydrates influenced by nuclear waste caesium. JOURNAL OF HAZARDOUS MATERIALS 2021; 411:125033. [PMID: 33454570 DOI: 10.1016/j.jhazmat.2020.125033] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 12/24/2020] [Accepted: 12/29/2020] [Indexed: 06/12/2023]
Abstract
The fundamental mechanisms underlying the influence of nuclear wastes on concrete properties remain poorly understood, especially at the molecular level. Herein, caesium ions (Cs+) are introduced into calcium silicate hydrates (CSH) to investigate its effect using molecular dynamics simulation. Structurally, a swelling phenomenon is observed, attributed to the CSH interlayer expansion as Cs+ occupies larger space than Ca2+. The diffusion of interlayer water, Ca2+ and Cs+, following an order of water > Cs+ > Ca2+, is accelerated with increasing Cs+ content, owing to three mechanisms: expanded interlayer space, weakened interfacial interaction, and loss of chemical bond stability. Mechanically, the Young's modulus and strength of CSH are degraded by Cs+ due to two mechanisms: (1) the load transfer ability of interlayer water and Ca2+ is weakened; (2) the load transfer provided by Cs+ is very weak. Additionally, a "hydrolytic weakening" mechanism is proposed to explain the mechanical degradation with increasing water content. This study also provides guidance for studying the influence of other wastes (like heavy metal ions) in concrete.
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Affiliation(s)
- M F Kai
- Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong, China
| | - L W Zhang
- Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
| | - K M Liew
- Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong, China.
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5
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Elucidating the constitutive relationship of calcium-silicate-hydrate gel using high throughput reactive molecular simulations and machine learning. Sci Rep 2020; 10:21336. [PMID: 33288786 PMCID: PMC7721899 DOI: 10.1038/s41598-020-78368-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 11/24/2020] [Indexed: 12/05/2022] Open
Abstract
Prediction of material behavior using machine learning (ML) requires consistent, accurate, and, representative large data for training. However, such consistent and reliable experimental datasets are not always available for materials. To address this challenge, we synergistically integrate ML with high-throughput reactive molecular dynamics (MD) simulations to elucidate the constitutive relationship of calcium–silicate–hydrate (C–S–H) gel—the primary binding phase in concrete formed via the hydration of ordinary portland cement. Specifically, a highly consistent dataset on the nine elastic constants of more than 300 compositions of C–S–H gel is developed using high-throughput reactive simulations. From a comparative analysis of various ML algorithms including neural networks (NN) and Gaussian process (GP), we observe that NN provides excellent predictions. To interpret the predicted results from NN, we employ SHapley Additive exPlanations (SHAP), which reveals that the influence of silicate network on all the elastic constants of C–S–H is significantly higher than that of water and CaO content. Additionally, the water content is found to have a more prominent influence on the shear components than the normal components along the direction of the interlayer spaces within C–S–H. This result suggests that the in-plane elastic response is controlled by water molecules whereas the transverse response is mainly governed by the silicate network. Overall, by seamlessly integrating MD simulations with ML, this paper can be used as a starting point toward accelerated optimization of C–S–H nanostructures to design efficient cementitious binders with targeted properties.
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Lyngdoh GA, Kumar R, Krishnan NMA, Das S. Dynamics of confined water and its interplay with alkali cations in sodium aluminosilicate hydrate gel: insights from reactive force field molecular dynamics. Phys Chem Chem Phys 2020; 22:23707-23724. [PMID: 33057524 DOI: 10.1039/d0cp04646a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This paper presents the dynamics of confined water and its interplay with alkali cations in disordered sodium aluminosilicate hydrate (N-A-S-H) gel using reactive force field molecular dynamics. N-A-S-H gel is the primary binding phase in geopolymers formed via alkaline activation of fly ash. Despite attractive mechanical properties, geopolymers suffer from durability issues, particularly the alkali leaching problem which has motivated this study. Here, the dynamics of confined water and the mobility of alkali cations in N-A-S-H is evaluated by obtaining the evolution of mean squared displacements and Van Hove correlation function. To evaluate the influence of the composition of N-A-S-H on the water dynamics and diffusion of alkali cations, atomistic structures of N-A-S-H with Si/Al ratio ranging from 1 to 3 are constructed. It is observed that the diffusion of confined water and sodium is significantly influenced by the Si/Al ratio. The confined water molecules in N-A-S-H exhibit a multistage dynamic behavior where they can be classified as mobile and immobile water molecules. While the mobility of water molecules gets progressively restricted with an increase in Si/Al ratio, the diffusion coefficient of sodium also decreases as the Si/Al ratio increases. The diffusion coefficient of water molecules in the N-A-S-H structure exhibits a lower value than those of the calcium-silicate-hydrate (C-S-H) structure. This is mainly due to the random disordered structure of N-A-S-H as compared to the layered C-S-H structure. To further evaluate the influence of water content in N-A-S-H, atomistic structures of N-A-S-H with water contents ranging from 5-20% are constructed. Qn distribution of the structures indicates significant depolymerization of N-A-S-H structure with increasing water content. Increased conversion of Si-O-Na network to Si-O-H and Na-OH components with an increase in water content helps explain the alkali-leaching issue in fly ash-based geopolymers observed macroscopically. Overall, the results in this study can be used as a starting point towards multiscale simulation-based design and development of durable geopolymers.
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Affiliation(s)
- Gideon A Lyngdoh
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, USA.
| | - Rajesh Kumar
- Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
| | - N M Anoop Krishnan
- Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India. and Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India
| | - Sumanta Das
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, USA.
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Lyngdoh GA, Kumar R, Krishnan NMA, Das S. Realistic atomic structure of fly ash-based geopolymer gels: Insights from molecular dynamics simulations. J Chem Phys 2019. [DOI: 10.1063/1.5121519] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Affiliation(s)
- Gideon A. Lyngdoh
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, Rhode Island 02881, USA
| | - Rajesh Kumar
- Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - N. M. Anoop Krishnan
- Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
- Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Sumanta Das
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, Rhode Island 02881, USA
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Wei C, Zhao W, Shi X, Pei C, Wei P, Zhang J, Li H. Thick Two-Dimensional Water Film Confined between the Atomically Thin Mica Nanosheet and Hydrophilic Substrate. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:5130-5139. [PMID: 30907594 DOI: 10.1021/acs.langmuir.8b04232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The interesting properties of water molecules confined in a two-dimensional (2D) environment have aroused great attention. However, the study of 2D-confined water at the hydrophilic-hydrophilic interface is largely unexplored due to the lack of appropriate system. In this work, the behavior of water molecules confined between an atomically thin mica nanosheet and a hydrophilic SiO2/Si substrate was investigated using an atomic force microscope in detail at ambient conditions. The confined water molecules aggregated as droplets when the relative humidity (RH) of the environment was 11%. A large-area 2D water film with a uniform thickness of ∼2 nm was observed when the mica flake was incubated at 33% RH for 1 h before being mechanically exfoliated on a SiO2/Si substrate. Interestingly, the water film showed ordered edges with a predominant angle of 120°, which was the same with the lattice orientation of the mica nanosheet on top of it. The water film showed a fluidic behavior at the early stage and reached a stable state after 48 h under ambient conditions. The surface properties of the upper mica nanosheet and the underlying substrate played a crucial role in manipulating the behavior of confined water molecules. When the surface of the upper mica nanosheet was modified by Na+, Ni2+, and aminopropyltriethoxysilane (APS), only some small water droplets were observed instead of a water film. The surface of the underlying SiO2/Si substrate was functionalized by hydrophilic APS and hydrophobic octadecyltrimethoxysiliane (OTS). The small water droplets were imaged on a hydrophobic OTS-SiO2/Si substrate, while the water film with regular edges was maintained on a hydrophilic APS-SiO2/Si substrate. Our results might provide an alternative molecular view for investigating structures and properties of confined water molecules in 2D environments.
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Affiliation(s)
- Cong Wei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Weihao Zhao
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Xiaotong Shi
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Chengjie Pei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Pei Wei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Jindong Zhang
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Hai Li
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
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Hajilar S, Shafei B. Structure, orientation, and dynamics of water-soluble ions adsorbed to basal surfaces of calcium monosulfoaluminate hydrates. Phys Chem Chem Phys 2018; 20:24681-24694. [PMID: 30187069 DOI: 10.1039/c8cp03872d] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transport of water molecules and chloride ions in nanopores of hydrated cement paste (HCP) is proven to adversely affect the long-term durability of reinforced concrete structures exposed to seawater or deicing salts. The resistance against chloride attack is primarily associated with the chloride binding capacity of the main HCP constituents. Experimental tests revealed that AFm phases of HCP play a central role in binding the chloride ions. However, many aspects of AFm-solution interactions were largely unknown, especially at their interfaces. This was the motivation of the current study, in which the atomistic processes underlying the transport of water-soluble ions are investigated in detail using the classical molecular dynamics (MD) method. To this end, an aqueous layer containing various concentrations of sodium chloride solution is sandwiched between two basal surfaces of calcium monosulfoaluminate hydrate, which is the most abundant phase of AFm. The adsorption mechanisms of water molecules and diffusing ions are then characterized for inner- and outer-sphere distance ranges from the basal surfaces of monosulfoaluminate. It is found that the self-diffusion coefficient of the chloride and sodium ions present in the outer-sphere range are 83% and 47% larger than those residing in the inner-sphere range. With increasing the distance from the solid surface, an increase in the self-diffusion coefficient is captured. This increase in mobility is larger for chloride ions than sodium ions. This can be understood based on the observation that the inner- and outer-sphere complex formation are the governing adsorption mechanisms for the chloride and sodium ions, respectively.
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Affiliation(s)
- Shahin Hajilar
- Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50011, USA.
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Hajilar S, Shafei B. Atomic-scale investigation of physical adsorption of water molecules and aggressive ions to ettringite's surfaces. J Colloid Interface Sci 2018; 513:104-116. [PMID: 29132102 DOI: 10.1016/j.jcis.2017.09.019] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Revised: 08/31/2017] [Accepted: 09/02/2017] [Indexed: 11/15/2022]
Abstract
The strength and durability of cementitious composite materials are adversely affected by the ingress of water molecules and aggressive ions into their intrinsic meso- and nano-pore spaces. Among various phases of hydrated cement paste (HCP), aluminum-rich phases play an important role in controlling the diffusivity of aqueous solutions, which can contain aggressive ions. To this date, however, there has been no systematic study to understand the adsorption mechanisms and chloride binding capacity of the aluminum-rich phases of HCP. This research gap has been the motivation of the current study to investigate the physical adsorption characteristics of ettringite as the main aluminum-rich phase of HCP and the primary hydrated product of calcium sulfoaluminate cement. Through a set of Molecular Dynamics simulations supported by macro-scale experimental tests, a fundamental insight into the molecular origins of the diffusion of water molecules, as well as sodium and chloride ions, in contact with ettringite is provided. As the primary objective of this study is to evaluate the transport properties at and near solution/solid interfaces, the molecular adsorption mechanisms are characterized for inner- and outer-sphere distances from the solid substrate. With an in-depth understanding of the structure and dynamics of water molecules and aggressive ions in contact with ettringite's surfaces, the outcome of this study provides reliable measures of physical adsorption, binding capacity, and self-diffusion coefficient, which can be further employed to introduce strategies to avoid the degradation of a wide variety of cementitious materials exposed to harsh environmental conditions.
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Affiliation(s)
- Shahin Hajilar
- Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50011-1066, United States.
| | - Behrouz Shafei
- Department of Civil, Construction and Environmental Engineering, Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011-1066, United States.
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Hsiao YH, La Plante EC, Krishnan NMA, Le Pape Y, Neithalath N, Bauchy M, Sant G. Effects of Irradiation on Albite’s Chemical Durability. J Phys Chem A 2017; 121:7835-7845. [DOI: 10.1021/acs.jpca.7b05098] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | | | | | - Yann Le Pape
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Narayanan Neithalath
- School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona 85287, United States
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Krishnan NMA, Wang B, Sant G, Phillips JC, Bauchy M. Revealing the Effect of Irradiation on Cement Hydrates: Evidence of a Topological Self-Organization. ACS APPLIED MATERIALS & INTERFACES 2017; 9:32377-32385. [PMID: 28870068 DOI: 10.1021/acsami.7b09405] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Despite the crucial role of concrete in the construction of nuclear power plants, the effects of radiation exposure (i.e., in the form of neutrons) on the calcium-silicate-hydrate (C-S-H, i.e., the glue of concrete) remain largely unknown. Using molecular dynamics simulations, we systematically investigate the effects of irradiation on the structure of C-S-H across a range of compositions. Expectedly, although C-S-H is more resistant to irradiation than typical crystalline silicates, such as quartz, we observe that radiation exposure affects C-S-H's structural order, silicate mean chain length, and the amount of molecular water that is present in the atomic network. By topological analysis, we show that these "structural effects" arise from a self-organization of the atomic network of C-S-H upon irradiation. This topological self-organization is driven by the (initial) presence of atomic eigenstress in the C-S-H network and is facilitated by the presence of water in the network. Overall, we show that C-S-H exhibits an optimal resistance to radiation damage when its atomic network is isostatic (at Ca/Si = 1.5). Such an improved understanding of the response of C-S-H to irradiation can pave the way to the design of durable concrete for radiation applications.
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Affiliation(s)
| | | | | | - James C Phillips
- Department of Physics and Astronomy, Rutgers, The State University of New Jersey , Piscataway, New Jersey 08854-8019, United States
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Dynamics of nano-confined water in Portland cement - comparison with synthetic C-S-H gel and other silicate materials. Sci Rep 2017; 7:8258. [PMID: 28811588 PMCID: PMC5557859 DOI: 10.1038/s41598-017-08645-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 07/12/2017] [Indexed: 11/30/2022] Open
Abstract
The dynamics of water confined in cement materials is still a matter of debate in spite of the fact that water has a major influence on properties such as durability and performance. In this study, we have investigated the dynamics of water confined in Portland cement (OPC) at different curing ages (3 weeks and 4 years after preparation) and at three water-to-cement ratios (w/c, 0.3, 0.4 and 0.5). Using broadband dielectric spectroscopy, we distinguish four different dynamics due to water molecules confined in the pores of different sizes of cements. Here we show how water dynamics is modified by the evolution in the microstructure (maturity) and the w/c ratio. The fastest dynamics (processes 1 and 2, representing very local water dynamics) are independent of water content and the degree of maturity whereas the slowest dynamics (processes 3 and 4) are dependent on the microstructure developed during curing. Additionally, we analyze the differences regarding the water dynamics when confined in synthetic C-S-H gel and in the C-S-H of Portland cement.
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