been prepared

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NATIONAL BUREAU OF STANDARDS REPORT

8152

DETERMINATION OF MOISTURE IN REFRACTORY CONCRETES

by

K. D. Nekrasov, A. E. Fedorov, and V. I. Yastrubinskiy

Research Institute for Reinforced Concrete

of the Academy of Structures and Architecture of USSR

translated from

Ogneupory

v. 28, n. 6, 1963, p. 276-278

by

D. Watstein, NBS

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards include the development and maintenance of the national standards of measurement and the provision of means and methods for making measure - ments consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention

and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications, including assistance to industry, business and con- sumers in the development and acceptance of commercial standards and simplified trade practice

recommendations. The work includes basic and applied research, development, engineering, instru- mentation, testing, evaluation, calibration services, and various consultation and information services. Research projects are also performed for other government agencies when the work relates

to and supplements the basic program of the Bureau or when the Bureau’s unique competence is required. The scope of activities is suggested by the listing of divisionsand sections on the inside

of the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or in the journals of professional and scientific societies. The Bureau itself publishes

three periodicals available from the Government Printing Office: The Journal of Research, published in four separate sections, presents complete scientific and technical papers; the Technical

News Bulletin presents summary and preliminary reports on work in progress; and Central Radio

Propagation Laboratory Ionospheric Predictions provides data for determining the best frequencies

to use for radio communications throughout the world. There are also seven series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications, Technical Notes, Commercial Standards, and Simplified Practice Recommendations.

A complete listing of the Bureau’s publications can be found in National Bureau of Standards

Circular 460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240, July 1957 to June 1960 (includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of Documents, Government

Printing Office, Washington, D.C., 20402.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1002 - 12-10120

NBS REPORT

8152

DETERMINATION OF MOISTURE IN REFRACTORY CONCRETES

by

K. D. Nekrasov, A. E. Fedorov, and V. I. Yastrubinskiy

Research Institute for Reinforced Concrete

of the Academy of Structures and Architecture of USSR

translated from

Ogneupory

v. 28, n. 6 , 1963, p. 276-278

by

D. Watstein, NBS

NATIONAL BUREAU OF S'

for use within the Government, and review. For this reason, tl whole or in part, is not authc Bureau of Standards, Washing

the Report has been specifically

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015 .

iss accounting documents intended

; subjected to additional evaluation

i listing of this Report, either in

le Office of the Director, National

{ the Government agency for which

copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

DETERMINATION OF MOISTURE IN REFRACTORY CONCRETES*

by

K. D. Nekrasov, A. E. Fedorov, and V. I. Yastrubinskiy

Up to the present time there has been no development of

an optimum method of drying and preheating of newly constructed

furnaces and other installations constructed of refractory concrete. The control and adjustment of the heating procedure have

been delayed because of the absence of apparatus for continuous

determination of moisture content at various sections throughout

the thickness of the concrete at elevated temperatures.

In the laboratory for refractory concretes of the Scientific

Research Institute for Reinforced Concrete of the Academy of Structures and Architecture of USSR, an apparatus was developed for

the continuous determination of moisture in refractory concrete

during the drying process by measuring the electrical conductivity

of sensors embedded in concrete.

The apparatus is intended for studying the kinetics of

removal of moisture from concrete, establishing the optimum regime

of drying, and also the control and adjustment under industrial

conditions of the regime of drying and heating of thermal installations built of refractory concrete.

The method of determination of moisture of materials by the

change of electrical conductivity is fairly widely used. However,

the existing methods and available devices cannot be used for

measuring the moisture at various sections of refractory concretes

through their thickness during ,the drying process.

* Translated from the Russian Opredelenie vlazhnosti zharostoikikh

betonov . K. D. Fedorov and V. I. Iastrubinskii . Ogneupory.

T. 28, 'no. 6, 1983? P» 276-278, by D. Watstein.
2

-

The method proposed by the authors permits the measurement

of moisture in concrete by means of electrical gages. The small

dimensions of the gages permit us to measure the moisture even

in thin-wall constructions without affecting their strength. The

apparatus can measure the moisture of concrete at a temperature

up to 200°C. The precision of measurement of the moisture is

+ 0 . 3%.

The device consists of a gage embedded in concrete, a megohmeter of type M-101 and connecting leads. The sensor consists

of a prism of refractory concrete with dimensions of 20 x 20 x 70 mm

with steel foil electrodes, with an area of 10 x 50 mm and a

thickness of 0 . 5

- 0.

mm attached to two opposing longitudinal

edges (Figure 1).

The composition of the mortar for preparation of the sensor

is as follows: 8 parts by weight of a water glass with a density

of 1.38 grams per cc, 1 part by weight of sodium fluorosilicate,

8 parts by weight of finely ground grog, and 25 parts by weight

of anO-2.5 mm fraction of grog. This composition of the mortar

aids rapid development of moisture equilibrium by the sensor and

the concrete.

In the preparation of sensor prisms, 70 x 70 x 210 mm blocks

are cast. After they harden in air over a period of 3 days at

18 ± 3°C the required prisms are cut from the larger blocks and

are fired at 700°C for one hour.

After cooling^ electrodes are mounted using a cement of

the following composition: 10 parts by weight of water glass

with a density of I .38 grams per cc, 0.8 parts by weight of sodium

fluorosilicate and 15 parts by weight of finely ground grog. The

materials used in the preparation of the refractory mortar and

cement must meet the requirements of the applicable specificaticns.

The faces of the prism on which the electrodes are mounted

must be parallel. Deviations must not exceed 0 ± 0.3 mm. Before

mounting, the steel foil is carefully cleaned and is heated.

The electrodes must be mounted opposite each other and the thickness of the cement must not exceed 0.2 mm.
- 3

-

After aging for one day, the sensors are heated for 2b

hours at 200°C in order to raise the reistance of the cement

to moisture. Then the electrodes are soldered to leads with

a cross section of 0.5 mm2 having vinyl chloride insulation.

In order to measure the moisture and the temperature

during the drying process as a function of thickness of the

concrete^ several sensors are embedded along with thermocouples.

The sensors are attached to megohmeters and the thermocouples

to potentiometers through a switching device.

The electrical resistance of the sensors in the concrete

is inversely related to the moisture in the concrete. The

device must receive preliminary calibration using a definite

type of refractory concrete. The calibration must be carried

out at 15° - 20°C and at the drying temperatures.

In order to determine the relationship between the moisture of the concrete and the electrical resistance of the

sensors at normal temperature we prepared, from the refractory

concrete, 10 specimens with dimensions of 50 x 50 x 100 mm;

the sensors were embedded in the specimens. After hardening,

the specimens were stored in the laboratory at 15° to 20°C

,

and were weighed daily and at the same time the electrical

resistance of the sensors was measured. The curve 1 shown in

Figure 2, is based on these data.

After the weight of the specimens and the electrical

resistance of the sensors became stable, they were dried in

an oven for 2b hours at 200°C and were weighed after cooling.

The moisture content of the specimens, W, was determined

by the formula

w = h ipa. . ioo,

P2

where Pn is the weight of the specimens in grams, and P

2 is

the weight of the specimens dried at 200°C grams.
The calibration of the specimens at drying temperatures

was carried out in the following manner: the specimens, with

embedded sensors, after hardening were dried to various moisture contents with one percent moisture increment and were

placed in special metallic containers with hermetic seals

(Figure 3)«

The hermetic containers are necessary for maintaining constant moisture of the system during the heating. The space

between the walls of the container and the specimen was filled

with an epoxy resin with a hardener, and the leads were brought

outside between 2 rubber inserts.

After 2b hours following placement of the specimens in

the containers, the electrical resistance at 15° - 20°C was

measured and then the containers were placed in a drying oven

where they were maintained at 50°C for a day; after which the

electrical resistance was measured in the heated condition.

The calibration was carried out by means of two parallel specimens for each percentage of moisture content.

From the data obtained we have constructed the curve

showing the relationship between moisture of the concrete and

the electrical resistance of the sensors (see Figure 2, curve 2).

The order of construction of the curve for 50°C is as

follows: from curve 1 we find the resistance of the specimen

at a definite moisture content at 15°C. From this point we

draw a horizontal line and upon it mark the resistance of the

very same specimen at 50°C.

Similar points are found for all 10 specimens of different

moisture content. Through the points thus obtained we derive

curve 2. Analogous curves are constructed for 100° and 150°C

(see Figure 2, curves 3 and ^).

Conclusions

A portable device for measuring moisture content of

concrete at temperatures up to 200°C was developed. The precision of measurements was ± .03 of 1%» The device was verified for basic types of refractory concrete and the results

were satisfactory.

USCOMM-NBS-DC
Fig. 1. Schematic drawing

of sensor for measurement

of moisture in concrete.

Fig. 2. Relationship between

electrical resistance of

sensors and moisture in

refractory concrete of

Portland cement and grog

at various temperatures:

1-15°C, 2-50°C, 3-100°C,

4-l50°C.

Resistance ohms

Fig. 3* Hermetically

sealed container for

calibration of sensors

at various temperatures:

1-specimen, 2-container,

3-metal lid, 4-rubber

seal, 5-clamping nuts

1 Cv

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fe. 3- : " •fSj&f -

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ft t?

. . ..1. ini'nilujUuLniiiw*'- «4-S -l*»

THE NATIONAL BUREAU OF STANDARDS

The' scope of activities, of the National Bureau of Standards at its major laboratories in Washington, D.C.,and

Boulder, Colorado, is suggested in the following listing of the divisions and sections (engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

WASHINGTON, D. G.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. High Voltage. Absolute Electrical Measurements.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Volume.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Appli ed Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics.. Engineering Mechanics. Rheology. Combustion

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.

Metallurgy. Engineering Metallurgy. Metal Reactions. Metal Physics. Electrolysis and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Ele- mentary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOLLDEK, COLO.

CRYOGENIC ENGINEERING LABORATORY

Cryogenic Processes. Cryogenic Properties of Solids. Cryogenic Technical Services. Properties of Cryogenic

Fluids. CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research. Troposphere and Space Telecommunications. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Spectrum Utilization Research. Radio-Meteorology. Lower Atmosphere

Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre- quency Utilization. Modulation Research. Antenna Research. Radiodetermination.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Standards Physics. Frequency and Time Disseminations. Radio and Microwave Materials. Atomic Fre- quency and Time-Interval Standards. Radio Plasma. Microwave Physics.

Radio Standards Engineering. High Frequency Electrical Standards. High Frequency Cal ibration Services. High

Frequency Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency

Calibration Services.

Joint Institute for Laboratory Astrophysics- NBS Group (Univ. of Colo.). USCOMM-NBS-DC
/ ?I