1H nuclear magnetic resonance characterization of Portland cement: molecular diffusion of water studied by spin relaxation and relaxation time-weighted imaging

Wang, Pu Sen; Ferguson, Matt; Eng, George; Bentz, Dale P.; Ferraris, Chiara F.; Clifton, James R

doi:10.1023/a:1004331403418

Cited by 34 publications

(10 citation statements)

References 16 publications

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“…Considering that a rather unique tool to gain experimental information on water dynamics in the picosecond range (from 0.1 to a few hundred picoseconds) is incoherent inelastic neutron scattering (IINS), which takes advantage of the large incoherent scattering cross-section of hydrogen atoms with respect to the relatively small cross-sections of other constitutive atoms in cement paste, the dynamics of hydration water in tricalcium silicate and dicalcium silicate has been carefully studied by means of QENS; ,,,,,, however, not much has been reported using the technique in hardened cement pastes with different levels of hydration. Nonetheless, by means of proton NMR measurements − three states of mobility have been identified in hardened cement pastes: (i) protons confined in solid phases such as hydroxyl groups chemically bound into the C−S−H structure; (ii) semiliquid-like water that can hydrogen bond (less strongly) to the C−S−H at the pore surface, defined as “glassy-water” due to its similar behavior to supercooled bulk water; and (iii) and bulk-like pore water, the unbound molecules that are confined within the pores.…”

Section: Resultsmentioning

confidence: 99%

Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

2006

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Portland cement reacts with water to form an amorphous paste through a chemical reaction called hydration. In concrete the formation of pastes causes the mix to harden and gain strength to form a rock-like mass. Within this process lies the key to a remarkable peculiarity of concrete: it is plastic and soft when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, sidewalks and superhighways, houses, and dams. The character of the concrete is determined by the quality of the paste. Creep and shrinkage of concrete specimens occur during the loss and gain of water from cement paste. To better understand the role of water in mature concrete, a series of quasielastic neutron scattering (QENS) experiments were carried out on cement pastes with water/cement ratio varying between 0.32 and 0.6. The samples were cured for about 28 days in sealed containers so that the initial water content would not change. These experiments were carried out with an actual sample of Portland cement rather than with the components of cement studied by other workers. The QENS spectra differentiated between three different water interactions: water that was chemically bound into the cement paste, the physically bound or "glassy water" that interacted with the surface of the gel pores in the paste, and unbound water molecules that are confined within the larger capillary pores of cement paste. The dynamics of the "glassy" and "unboud" water in an extended time scale, from a hundred picoseconds to a few nanoseconds, could be clearly differentiated from the data. While the observed motions on the picosecond time scale are mainly stochastic reorientations of the water molecules, the dynamics observed on the nanosecond range can be attributed to long-range diffusion. Diffusive motion was characterized by diffusion constants in the range of (0.6-2) 10(-9) m(2)/s, with significant reduction compared to the rate of diffusion for bulk water. This reduction of the water diffusion is discussed in terms of the interaction of the water with the calcium silicate gel and the ions present in the pore water.

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Section: Resultsmentioning

confidence: 99%

Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

2006

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“…The motion of water in the pores relates directly to the cohesion of the C–S–H gel, determining the strength, creep, shrinkage, and chemical and physical properties of cementitous materials. The properties of the water confined in the gel pores or in the vicinity of the C–S–H surfaces have been studied by various experimental techniques. − By using 1 H nuclear magnetic resonance (NMR), ,, the water in C–S–H gels was distinguished into three types: chemically bound water that is incorporated into the structure and forms a strong chemical bond with the calcium silicate structure, physically bound water that is deeply adsorbed near the surface, and capillary water that is not bound and diffuses freely in the capillary pores. In addition, the quasi-elastic neutron scattering (QENS) technique characterizes the different water types by quantitatively using the diffusion coefficient.…”

Section: Introductionmentioning

confidence: 99%

Reactive Molecular Simulation on Water Confined in the Nanopores of the Calcium Silicate Hydrate Gel: Structure, Reactivity, and Mechanical Properties

et al. 2015

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Calcium silicate hydrate (C−S−H) is a mesoporous amorphous material with water confined in the gel pores, which provides the medium for investigating the structure, dynamics, and mechanical properties of the ultraconfined interlayer water molecules. In this study, C−S−H gels with different compositions expressed in terms of the Ca/Si ratio are characterized in the light of molecular dynamics. It is found that with increasing Ca/Si ratio, the molecular structure of the silicate skeleton progressively transforms from an ordered to an amorphous structure. The calcium silicate skeleton, representative of the substrate, significantly influences the adsorption capability, reactivity, H-bond network, and mobility of the interlayer water molecules. The structures were tested for mechanical properties by simulated uniaxial tension, and the mechanical tests associated with structural analysis reveal that the stiffness and cohesive force of C−S−H gel is weakened by both breakage of silicate chains and penetration of water molecules. In addition, the reactive force field is coupled with both the mechanical response and chemical response during the large tensile deformation process. On the one hand, the silicate chains, acting in a skeletal role in the layered structure, depolymerize to enhance the loading resistance. On the other hand, water molecules, attacking the Si−O and Ca−O bonds, dissociate into hydroxyls, which are detrimental to the cohesive force development.

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“…The properties of the water confined in gel pores or in the vicinity of C-S-H surfaces have been studied by various experimental techniques. By using 1 H nuclear magnetic resonance (NMR), [1][2][3] the water in C-S-H gels was distinguished into three types: chemically bound water that is incorporated into the structure and forms a strong chemical bond with the calcium silicate structure, physically bound water that is deeply adsorbed near the surface and capillary water that is not bound and diffuses freely into the capillary pores. Furthermore, the quasi-elastic neutron scattering (QENS) technique 4 characterizes the different water types by quantitatively using the diffusion coefficient.…”

Section: Introductionmentioning

confidence: 99%

Water transport in the nano-pore of the calcium silicate phase: reactivity, structure and dynamics

Hou

Zhao

et al. 2015

Phys. Chem. Chem. Phys.

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Reactive force field molecular dynamics was utilized to simulate the reactivity, structure and dynamics of water molecules confined in calcium-silicate-hydrate (C-S-H) nano-pores of 4.5 nm width. Due to the highly reactive C-S-H surface, hydrolytic reactions occur in the solid-liquid interfacial zone, and partially surface adsorbed water molecules transforming into the Si-OH and Ca-OH groups are strongly embedded in the C-S-H structure. Due to the electronic charge difference, the silicate and calcium hydroxyl groups have binomial distributions of the dipolar moment and water orientation. While Ca-OH contributes to the Ow-downward orientation, the ONB atoms in the silicate chains prefer to accept H-bonds from the surface water molecules. Furthermore, the defective silicate chains and solvated Caw atoms near the surface contribute to the glassy nature of the surface water molecules, with large packing density, pronounced orientation preference, and distorted organization. The stable H-bonds connected with the Ca-OH and Si-OH groups also restrict the mobility of the surface water molecules. The significant reduction of the diffusion coefficient matches well with the experimental results obtained by NMR, QENS and PCFR techniques. Upon increasing the distance from the channel, the structural and dynamic behavior of the water molecules varies and gradually translates into bulk water properties at distances of 10-15 Å from the liquid-solid interface.

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1H nuclear magnetic resonance characterization of Portland cement: molecular diffusion of water studied by spin relaxation and relaxation time-weighted imaging

Cited by 34 publications

References 16 publications

Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

Reactive Molecular Simulation on Water Confined in the Nanopores of the Calcium Silicate Hydrate Gel: Structure, Reactivity, and Mechanical Properties

Water transport in the nano-pore of the calcium silicate phase: reactivity, structure and dynamics

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