Hexagonal ice in hardened cement

Schulson, E. M.; Swainson, I. P.; Holden, T. M.; Korhonen, Charles J.

doi:10.1016/s0008-8846(99)00229-x

Cited by 22 publications

(11 citation statements)

References 10 publications

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“…To our knowledge, this clear, repeatable (in the same closed system over 6 months), equilibrium PT hysteresis between growth and dissociation has not previously been reported for clathrate hydrates in porous media. Similar (although not so consistently repeatable) equilibrium hysteretic behaviour has been described for ice -water transitions in hardened cement pastes (Schulson et al 2000;Swainson & Schulson 2001), however it is generally not reported in most literature studies of solidliquid transitions in mesoporous materials.…”

Section: Resultssupporting

confidence: 56%

Gas hydrate growth and dissociation in narrow pore networks: capillary inhibition and hysteresis phenomena

Anderson

Tohidi

Webber

2009

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Marine sediments hosting gas hydrates are commonly fine-grained (silts, muds, clays) with very narrow mean pore diameters ($0.1 mm). This has led to speculation that capillary phenomena could play an important role in controlling hydrate distribution in the seafloor, and may be in part responsible for discrepancies between observed and predicted (from bulk phase equilibria) hydrate stability zone (HSZ) thicknesses. Numerous recent laboratory studies have confirmed a close relationship between hydrate inhibition and pore size, stability being reduced in narrow pores; however, to date the focus has been hydrate dissociation conditions in porous media, with capillary controls on the equally important process of hydrate growth being largely neglected. Here, we present experimental methane hydrate growth and dissociation conditions for synthetic mesoporous silicas over a range of pressure-temperature (PT) conditions (273-293 K, to 20 MPa) and pore size distributions. Results demonstrate that hydrate formation and decomposition in narrow pore networks is characterized by a distinct hysteresis: solid growth occurs at significantly lower temperatures (or higher pressures) than dissociation. Hysteresis takes the form of repeatable, irreversible closed primary growth and dissociation PT loops, within which various characteristic secondary 'scanning' curve pathways may be followed. Similar behaviour has recently been observed for ice-water systems in porous media, and is characteristic of liquid-vapour transitions in mesoporous materials. The causes of such hysteresis are still not fully understood; our results suggest pore blocking during hydrate growth as a primary cause.

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Section: Resultssupporting

confidence: 56%

Gas hydrate growth and dissociation in narrow pore networks: capillary inhibition and hysteresis phenomena

Anderson

Tohidi

Webber

2009

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“…A value k = 1 is expected for spherical pores i.e. freezing and thawing occur at the same temperature whereas a value of k = 0.5 occurs when ice melts in cylindrical pores [13,34]. The shape factor will also be affected by the connectivity of the pores and generally falls in the range 0 \ k B 1 [9].…”

Section: Pc Concretesmentioning

confidence: 99%

“…Based on the assumption that the ice-water interface adopts a spherical shape during freezing, the following expression for cement pastes has been presented to estimate the pore-neck radius, r pn (in nm, see Fig. 4 adapted from [39]), from the measured undercooling in freezing, DT f [9,13,14],…”

Section: Pc Concretesmentioning

confidence: 99%

“…Equations (6) and (7) also assume that an unfrozen layer of water of thickness 0.8 nm lines the pore walls [9,13].…”

Section: Pc Concretesmentioning

confidence: 99%

“…Other techniques include thermoporometry (TPM) and cryoporometry [9][10][11][12]; both these methods exploit the dependence of freezing temperature on pore size, whereas cryoporometry detects the phase transition using nuclear magnetic resonance imaging, TPM is undertaken using differential scanning calorimetry and measuring heat flux due to ice penetration in cement pores. Neutron diffraction [13,14], ultrasonic and dielectric techniques [3] have also been developed to study ice formation in cement paste. With many investigative techniques, specimens tend to be confined be relatively small samples of cement-pastes although low-temperature calorimetry has been applied to study ice formation in high-strength concrete [7].…”

Section: Introductionmentioning

confidence: 99%

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Conductivity/activation energy relationships for cement-based materials undergoing cyclic thermal excursions

et al. 2014

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The electrical conductivity of a range of concrete mixes, with and without supplementary cementitious materials (SCM), is studied through multiple cycles of heating and cooling over the extended temperature range -30/?70°C. When presented in an Arrhenius format, the experimental results display hysteresis effects at the lowtemperature end of the thermal cycle and, in those concretes containing supplementary cementitious materials at higher water/binder ratios, hysteresis effects were evident over the entire temperature range becoming more discernible with increasing number of thermal cycles. The depression in both the freezing and thawing point could be clearly identified and was used to estimate pore-neck and pore-cavity radii. A simplified approach is presented to evaluate the volumetric ratio of frozen pore water in terms of conductivity measurements. The results also show that the conductivity and activation energy of the concrete specimens were related to the water/binder ratio, type of SCM, physical state of the pore water and the thermal cycling regime.

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