The Influence of Storage Conditions on the Electric Conductivity of Concrete

Theoretical and experimental investigations of the influence of concrete moisture, its age, holding conditions after its thermal moisture treatment and other factors on the specific electric resistance of the concrete of a C32/40 grade used for reinforced concrete sleepers have been carried out. The obtained research data allowed us to specify holding modes and the duration of them and these enable the generation of objective information on the specific electric resistance of the concrete used for the sleepers during their operation.

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Toward Structural Health Monitoring of Civil Structures Based on Self-Sensing Concrete Nanocomposites: A Validation in a Reinforced-Concrete Beam

International Journal of Concrete Structures and Materials ◽

10.1186/s40069-020-00451-8 ◽

2021 ◽

Vol 15 (1) ◽

Author(s):

Diego L. Castañeda-Saldarriaga ◽

Joham Alvarez-Montoya ◽

Vladimir Martínez-Tejada ◽

Julián Sierra-Pérez

Keyword(s):

Reinforced Concrete ◽

Damage Detection ◽

Direct Current ◽

Health Monitoring ◽

Electrical Resistance ◽

Concrete Beam ◽

Reinforced Concrete Beam ◽

Structural Member ◽

Rc Beam ◽

Electric Resistance

AbstractSelf-sensing concrete materials, also known as smart concretes, are emerging as a promising technological development for the construction industry, where novel materials with the capability of providing information about the structural integrity while operating as a structural material are required. Despite progress in the field, there are issues related to the integration of these composites in full-scale structural members that need to be addressed before broad practical implementations. This article reports the manufacturing and multipurpose experimental characterization of a cement-based matrix (CBM) composite with carbon nanotube (CNT) inclusions and its integration inside a representative structural member. Methodologies based on current–voltage (I–V) curves, direct current (DC), and biphasic direct current (BDC) were used to study and characterize the electric resistance of the CNT/CBM composite. Their self-sensing behavior was studied using a compression test, while electric resistance measures were taken. To evaluate the damage detection capability, a CNT/CBM parallelepiped was embedded into a reinforced-concrete beam (RC beam) and tested under three-point bending. Principal finding includes the validation of the material’s piezoresistivity behavior and its suitability to be used as strain sensor. Also, test results showed that manufactured composites exhibit an Ohmic response. The embedded CNT/CBM material exhibited a dominant linear proportionality between electrical resistance values, load magnitude, and strain changes into the RC beam. Finally, a change in the global stiffness (associated with a damage occurrence on the beam) was successfully self-sensed using the manufactured sensor by means of the variation in the electrical resistance. These results demonstrate the potential of CNT/CBM composites to be used in real-world structural health monitoring (SHM) applications for damage detection by identifying changes in stiffness of the monitored structural member.

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A Study on Thermal and Electrical Conductivities of Ethylene-Butene Copolymer Composites with Carbon Fibers

International Polymer Processing ◽

10.1515/ipp-2020-4003 ◽

2021 ◽

Vol 36 (4) ◽

pp. 417-422

Author(s):

Y. Hamid ◽

P. Svoboda

Keyword(s):

Mechanical Properties ◽

Thermal Conductivity ◽

Carbon Fiber ◽

Electric Conductivity ◽

Carbon Fibers ◽

Mechanical Strain ◽

Electric Resistance ◽

Resistance Change ◽

Electrical Conductivities ◽

Fiber Sample

Abstract Ethylene-butene copolymer (EBC)/carbon-fiber (CF) composites can be utilized as an electromechanical material due to their ability to change electric resistance with mechanical strain. The electro-mechanical properties and thermal conductivity of ethylene butene copolymer (EBC) composites with carbon fibers were studied. Carbon fibers were introduced to EBC with various concentrations (5 to 25 wt%). The results showed that carbon fibers’ addition to EBC improves the electric conductivity up to 10 times. Increasing the load up to 2.9 MPa will raise the electric resistance change by 4 500% for a 25% fiber sample. It is also noted that the EBC/CF composites’ electric resistance underwent a dramatic increase in raising the strain. For example, the resistance change was around 13 times higher at 15% strain compared to 5% strain. The thermal conductivity tests showed that the addition of carbon fibers increases the thermal conductivity by 40%, from 0.19 to 0.27 Wm–1K–1.

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3. Note on the Rate of Decrease of Electric Conductivity with Increase of Temperature

Proceedings of the Royal Society of Edinburgh ◽

10.1017/s0370164600028996 ◽

1875 ◽

Vol 8 ◽

pp. 33-34

Author(s):

D. H. Marshall

Keyword(s):

Electric Conductivity ◽

Boiling Point ◽

Pure Metal ◽

Absolute Temperature ◽

Electric Resistance ◽

Rate Of Increase

These experiments were undertaken in order to determine how closely the hypothesis “that the electric resistance in a pure metal is directly as its absolute temperature” holds for various metals at two easily ascertained temperatures,—that of the air in the room, and the boiling point of water. The apparatus used was a Wheatstone's bridge; one coil of wire kept in a vessel of water at the temperature of the air in the room being put against another, which could be heated up to 100° C. The experiments showed that the rate of increase of resistance with temperature was different for hard and soft specimens of the same metal, being always less in the hard.

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State-of-the-Art Review on Experimental Investigations of Textile-Reinforced Concrete Exposed to High Temperatures

Journal of Composites Science ◽

10.3390/jcs5110290 ◽

2021 ◽

Vol 5 (11) ◽

pp. 290

Author(s):

Panagiotis Kapsalis ◽

Tine Tysmans ◽

Danny Van Hemelrijck ◽

Thanasis Triantafillou

Keyword(s):

Reinforced Concrete ◽

High Temperatures ◽

Mechanical Response ◽

Mechanical Performance ◽

State Of The Art ◽

Experimental Investigations ◽

Textile Reinforced Concrete ◽

Structural Applications ◽

Promising Solution ◽

Good Heat Resistance

Textile-reinforced concrete (TRC) is a promising composite material with enormous potential in structural applications because it offers the possibility to construct slender, lightweight, and robust elements. However, despite the good heat resistance of the inorganic matrices and the well-established knowledge on the high-temperature performance of the commonly used fibrous reinforcements, their application in TRC elements with very small thicknesses makes their effectiveness against thermal loads questionable. This paper presents a state-of-the-art review on the thermomechanical behavior of TRC, focusing on its mechanical performance both during and after exposure to high temperatures. The available knowledge from experimental investigations where TRC has been tested in thermomechanical conditions as a standalone material is compiled, and the results are compared. This comparative study identifies the key parameters that determine the mechanical response of TRC to increased temperatures, being the surface treatment of the textiles and the combination of thermal and mechanical loads. It is concluded that the uncoated carbon fibers are the most promising solution for a fire-safe TRC application. However, the knowledge gaps are still large, mainly due to the inconsistency of the testing methods and the stochastic behavior of phenomena related to heat treatment (such as spalling).

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Clinopyroxene Solid Solutions in the CaMgSi2O6 – Ca0,5AlSi2O6 Cross-Section at High P-T Parameters

The Bulletin of Irkutsk State University Series Earth Sciences ◽

10.26516/2073-3402.2020.34.37 ◽

2020 ◽

Vol 34 ◽

pp. 37-54

Author(s):

S. V. Banushkina ◽

◽

A. I. Turkin ◽

A. I. Chepurov ◽

◽

...

Keyword(s):

Cross Section ◽

Solid Solutions ◽

Atmospheric Pressure ◽

High Pressures ◽

Experimental Investigations ◽

Electric Resistance ◽

Resistance Furnace ◽

Mineral Association ◽

Electric Resistance Furnace ◽

Piston Cylinder

Clinopyroxenes (Cpx) are one of the main rock-forming minerals, but stoichiometry of their compositions was called into question. In particular, an idea of hypothetical calcium molecule Eskola (CaEs, Ca0,5AlSi2O6) existence was expressed. This minal has structure vacancy and silica excess. Numerous experimental investigations in CMAS-system (CaO-MgO-Al2O3-SiO2) have showed that the question of non-stoichiometric Cpx existence remains open. This paper presents the results of an experimental study of the diopside Di (CaMgSi2O6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6) cross-section in the CMAS-system. The experiments were carried out in the following pressure and temperature range: P=10-4 – 3,0 GPa; T=966 – 15250C. Experiments at atmospheric pressure (10-4 GPa) were performed on a vertical shaft electric resistance furnace; high-pressure ones were performed on a "piston-cylinder" type apparatus. Samples obtained were analyzed using electron microprobe (EMP), scanning electron microscope (SEM) and Raman spectrometer. Depending on the P-T conditions, the samples contain the following phases: anorthite An, garnet Grt, diopside Di, clinopyroxene Cpx, quartz Qtz (tridymite Tr – for experiments at atmospheric pressure), and glass L. The data array on the composition of clinopyroxenes crystallized in this cross-section with diopside in various associations is generalized and supplemented. Clinopyroxenes were found to form quaternary solid solutions of diopside Di (CaMgSi2O6) – enstatite En (Mg2Si2O6) – calcium molecule Tschermak CaTs (CaAl2SiO6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6). The CaTs and CaEs minals contents are positively correlated with the amount of aluminum in clinopyroxene, and this relationship is particularly pronounced for CaTs. It is confirmed that clinopyroxenes in this cross-section can contain an excess of silica at both atmospheric and high pressures. Apparently, the cation vacancy that exists in pyroxene structure can participate in ordering processes. As a result the pyroxenes of another structure (not diopside – C2/c-symmetry) can be crystallized from total compositions in the Di-CaEs cross-section. Additional research is needed to support this hypothesis. Besides, at present investigation it was not possible to establish an unambiguous relationship between the Cpx composition and P-T-parameters, since it is also associated with both the mixture initial composition and the mineral association. Further experiments are required to justify any geothermobarometric dependence.

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