Capillary Absorption Dynamics for Cementitious Material Considering Water Evaporation and Tortuosity of Capillary Pores

This paper presents the theoretical analysis of capillary absorption dynamics for cemementitious material. Fractal theory is applied to analyse tortuosity of capillary pores in cementitious material and a definition of tortuosity is given. The dynamic equation of capillary absorption considering water evaporation and tortuosity of capillary pores is derived. Based on the dynamic model, the capillary coefficient and sorptivity of concrete are explained theoretically. In absorption test, water evaporation is one of the main reasons caused variations from linearity between water absorption height and the square root of time, or between water amount absorbed and the square root of time. In cementitious material, the evaporation rate is very small compare to capillary flow velocity at the initial time of absorption test. For simplification of testing procedure, there is no meaning to modify absorption test.

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About definition of the local entropy rate of production in experiment of pulse electric heating

Izmeritel`naya Tekhnika ◽

10.32446/0368-1025it.2020-3-29-34 ◽

2020 ◽

pp. 29-34

Author(s):

Alexandr V. Kostanovskiy ◽

Margarita E. Kostanovskaya

Keyword(s):

Thermal Diffusivity ◽

Electric Heating ◽

Thermal Capacity ◽

Entropy Rate ◽

Initial Time ◽

Local Entropy ◽

Linear Mode ◽

Electric Capacity ◽

Definition Of ◽

Pulse Electric

Work is devoted to studying of a linear mode thermodynamic – a mode which is actively investigated now. One of the main concepts of a linear mode – local entropy rate of production. The purpose of given article consists in expansion of a circle of problems for which it is possible to calculate a local entropy rate of production, namely its definition, using the experimental “time-temperature” curves of heating/cooling. “Time-temperature” curves heating or cooling are widely used in non-stationary thermophysical experiments at studying properties of substances and materials: phase transitions of the first and second sort, a thermal capacity, thermal diffusivity. The quantitative substantiation of the formula for calculation of the local entropy rate of production in which it is used thermogram (change of temperature from time) which is received by a method of pulse electric heating is resulted. Initial time dependences of electric capacity and temperature are measured on the sample of niobium in a microsecond range simultaneously. Conformity of two dependences of the local entropy rate of production from time is shown: one is calculated under the known formula in which the brought electric capacity is used; another is calculated, using the thermogram.

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Lyapunov Functions and Lipschitz Stability for Riemann–Liouville Non-Instantaneous Impulsive Fractional Differential Equations

Symmetry ◽

10.3390/sym13040730 ◽

2021 ◽

Vol 13 (4) ◽

pp. 730

Author(s):

Ravi Agarwal ◽

Snezhana Hristova ◽

Donal O’Regan

Keyword(s):

Differential Equations ◽

Fractional Differential Equations ◽

Lyapunov Functions ◽

Sufficient Conditions ◽

Initial Time ◽

Lipschitz Stability ◽

Comparison Results ◽

Liouville Fractional Derivative ◽

Fractional Differential ◽

Definition Of

In this paper a system of nonlinear Riemann–Liouville fractional differential equations with non-instantaneous impulses is studied. We consider a Riemann–Liouville fractional derivative with a changeable lower limit at each stop point of the action of the impulses. In this case the solution has a singularity at the initial time and any stop time point of the impulses. This leads to an appropriate definition of both the initial condition and the non-instantaneous impulsive conditions. A generalization of the classical Lipschitz stability is defined and studied for the given system. Two types of derivatives of the applied Lyapunov functions among the Riemann–Liouville fractional differential equations with non-instantaneous impulses are applied. Several sufficient conditions for the defined stability are obtained. Some comparison results are obtained. Several examples illustrate the theoretical results.

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SYNTHESIS OF POLYVINYL ALCOHOL-CHITOSAN HYDROGEL AND STUDY OF ITS SWELLING AND ANTIBACTERIAL PROPERTIES

SQUALEN Bulletin of Marine and Fisheries Postharvest and Biotechnology ◽

10.15578/squalen.v7i1.10 ◽

2013 ◽

Vol 7 (1) ◽

pp. 1 ◽

Cited By ~ 3

Author(s):

Thamrin Wikanta ◽

Mr Erizal ◽

Mr Tjahyono ◽

Mr Sugiyono

Keyword(s):

Polyvinyl Alcohol ◽

Irradiation Dose ◽

Gamma Ray ◽

Antibacterial Properties ◽

Positive Control ◽

Negative Control ◽

Initial Time ◽

Water Evaporation ◽

Combination Technique ◽

Pva Hydrogel

The aim of this research was to synthesize a hydrogel for wound dressing by mixing of polyvinyl alcohol (PVA) and chitosan (CTS) and processed by combination technique of freezing-thawing and irradiation by gamma ray, and to study of its properties. PVA aqueous solution 10% (w/v) was mixed with 2% (w/v) chitosan (CTS) solution and homogenized. The PVA-CTS mixture was processed by freezing-thawing up to 3 cycles, and then irradiated by gamma rays at the doseranged of 20-50 kGy (dose rate was 10 kGy/hour). Result showed that PVA-CTS hydrogel with the gel fraction of 83%, 87%, 90%, and 83% were obtained at the irradiation dose of 20 kGy, 30 kGy, 40 kGy, and 50 kGy, respectively. Increasing of irradiation dose caused increasing of water absorption of hydrogel, i.e. 1.700 %, 1.715 %, 1.913 %, and 2.036 %, respectively, and the hydrogel reached the equilibrium in 25 hours. The hydrogel showed very slow water evaporation rate (~ 2%) at the initial time (1 hour) and then increased very fast (up ~50 %) at 24 h, i.e. 43%, 39.13%, 44%, and 53%, respectively. The elongation at break of hydrogels were obtained 245%, 322%, 322%, and 205% with the maximum value were obtained at irradiation dose ranged of 30-40 kGy. The presence of chitosan in the PVA hydrogel made it having higher antibacterial properties with the inhibitionzone value of 8 mm at irradiation dose of 30-40 kGy compared to PVA hydrogel as a negative control (6 mm) and to chloramphenicol as a positive control (8 mm).

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A stress sensitivity model for the permeability of porous media based on bi-dispersed fractal theory

International Journal of Modern Physics C ◽

10.1142/s0129183118500195 ◽

2018 ◽

Vol 29 (02) ◽

pp. 1850019 ◽

Cited By ~ 9

Author(s):

X.-H. Tan ◽

C.-Y. Liu ◽

X.-P. Li ◽

H.-Q. Wang ◽

H. Deng

Keyword(s):

Porous Media ◽

Fractal Dimension ◽

Fractal Theory ◽

Stress Sensitivity ◽

Maximum Diameter ◽

Proposed Model ◽

Fractal Parameters ◽

Stress Changes ◽

Capillary Bundle ◽

Definition Of

A stress sensitivity model for the permeability of porous media based on bidispersed fractal theory is established, considering the change of the flow path, the fractal geometry approach and the mechanics of porous media. It is noted that the two fractal parameters of the porous media construction perform differently when the stress changes. The tortuosity fractal dimension of solid cluster [Formula: see text] become bigger with an increase of stress. However, the pore fractal dimension of solid cluster [Formula: see text] and capillary bundle [Formula: see text] remains the same with an increase of stress. The definition of normalized permeability is introduced for the analyzation of the impacts of stress sensitivity on permeability. The normalized permeability is related to solid cluster tortuosity dimension, pore fractal dimension, solid cluster maximum diameter, Young’s modulus and Poisson’s ratio. Every parameter has clear physical meaning without the use of empirical constants. Predictions of permeability of the model is accordant with the obtained experimental data. Thus, the proposed model can precisely depict the flow of fluid in porous media under stress.

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A quantitative measure of nonlinearity

Clinical Chemistry ◽

10.1093/clinchem/39.5.766 ◽

1993 ◽

Vol 39 (5) ◽

pp. 766-772 ◽

Cited By ~ 37

Author(s):

K Emancipator ◽

M H Kroll

Keyword(s):

Analytical Method ◽

Response Curve ◽

Polynomial Regression ◽

Quantitative Measure ◽

Square Root ◽

Straight Line ◽

The Mean ◽

The Difference ◽

Definition Of ◽

Fitting In

Abstract Quantitative measures of the nonlinearity of an analytical method are defined as follows: the "(dimensional) nonlinearity" of a method is the square root of the mean of the square of the deviation of the response curve from a straight line, where the straight line is chosen to minimize the nonlinearity. The "relative nonlinearity" is defined as the dimensional nonlinearity divided by the difference between the maximum and minimum assayed values. These definitions may be used to develop practical criteria for linearity that are still objective. Calculation of the nonlinearity requires a method of curve-fitting. In this article, we use polynomial regression to demonstrate calculations, but the definition of nonlinearity also accommodates alternative nonlinear regression procedures.

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Rammed earth hygric properties and evolution

MATEC Web of Conferences ◽

10.1051/matecconf/201928202100 ◽

2019 ◽

Vol 282 ◽

pp. 02100

Author(s):

Margaux L. Indekeu ◽

Chi Feng ◽

Hans Janssen ◽

Monika Woloszyn

Keyword(s):

Rammed Earth ◽

Capillary Absorption ◽

Absorption Test ◽

Hygric Properties

The hygric characterisation of authentic rammed earth materials is presented. Since these materials expand and liquefy upon contact with moisture, currently available methods are adapted to deal with this material evolution during the tests. In particular a thin permeable wick is introduced in the capillary absorption test. Moreover, confined and unconfined ways of testing are addressed. The results show that both the material origin and the material evolution can significantly impact the hygric properties.

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X-Ray computed tomography and traditional analysis of a capillary absorption test in cement pastes

Cement and Concrete Composites ◽

10.1016/j.cemconcomp.2020.103634 ◽

2020 ◽

Vol 113 ◽

pp. 103634

Author(s):

Carmen Andrade ◽

Luis Saucedo ◽

Nuria Rebolledo ◽

Sandra Cabeza ◽

Dietmar Meinel

Keyword(s):

Computed Tomography ◽

Capillary Absorption ◽

Absorption Test ◽

Cement Pastes ◽

X Ray ◽

X Ray Computed

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Experimental Study on Improving Concrete Sulfate Attack Resistance Ability with Silane Impregnation

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.2621 ◽

2013 ◽

Vol 405-408 ◽

pp. 2621-2624

Author(s):

Zhi De Huang

Keyword(s):

Sulfate Solution ◽

Hydration Product ◽

Sulfate Attack ◽

Cementitious Material ◽

Material System ◽

Absorption Test ◽

Test Results ◽

Binder Ratio ◽

Water Absorption Test ◽

Drying Test

Silane impregnation effects on concrete sulfate attack resistance ability are systemic researched, through forming different cementitious material system and different water cement ratio mortar specimens, treating with silane impregnation and then curing to 14d age naturally, and doing sulfate solution wetting-drying test. Results shows that silane impregnation effect is poor when fly ash amount is large or water gel is relatively low. Through XRD microscopic, the improving sulfate attack resistance ability mechanisms are analyzed from aspect of cementations material hydration product; water-binder ratio effect on silane impregnation is explained by water absorption test.

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