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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 11 Abstracts search results
Document:
SP32-03
Date:
July 1, 1972
Author(s):
Sergey A. Mironov, Liarisa A. Malinina and Svetlana Cheryachukina
Publication:
Symposium Papers
Volume:
32
Abstract:
The disruptive expansion of concrete which is experienced with either early or rapid application of heat in the autoclave is caused almost entirely by the expansion of the air and water vapor enclosed within the concrete. Deformations in concretre speciments caused by this gaseous expansion during autoclaivng have ben measured. It has been found that if external steamair environment presure is applied properly, these deformations can be prevented. Te method used is to seal the autoclave immediately after introduction specimens, and not vent the air during steaming. The result is that the pressure buildup inside the specimen is actually offset by the couter-pressure of the environment. Higher strenghs were obtained on 10-cm cubes cured in this manner thatn those cured in the usal way. An additional benefit of the method is aht mositure is "locked into" the specimen. Apparently the lack of air migration toward the exteriro helps retain moisture, as indicated by the lower moisture loss meaused when curing with steam-and-using a pressure of 1 atmosphere of air show that pressure reduces moisture loss and increases strength.
DOI:
10.14359/6599
SP32-04
Thomas B. Redmond, Jr.
The report data are from three investigations on autoclave curing of block-type concrete mixes. Variables were presteaming time, heating time, heating rate, and time at maximum temperature and pressure of laboratory and plant-manufactured specimens of three aggregate types. The principal finding was the high strength and low drying shrinkage generally obtained with two hours of curing at 365 F. A one-hour cure at 400 F produced optimum strength in the test series investigating higher temperatures. With the industry trend to faster rail charging systems, data indi-cate the feasibility of four curing cycles per autoclave per day. However, author recommends that time at maximum temperature should not be shorter than five hours unless long-term individual plant tests have consistently demonstrated good results.
10.14359/6600
SP32-05
W. V. Friedlaender and F. V. Camarda
The influences of superheated steam on the strengths of autoclave cured cement mortar specimens and asbestos-cement compositions were examined. The test results show that superheated steam, apparently because it acts as a desiccant, generally causes reduced strengths that can be related to functions of the cured weight after autoclaving as well as a factor involvinggthe length and degrees of superheat. If super-heated steam is present during the early stages of the curing cycle it causes greater adverse strength effects.
10.14359/6601
SP32-06
Julie C. Yang
Curing of asbestos-cement products by high-pressure autoclave, including saturated steam and superheated steam conditions is dis-cussed and compared. The binder produced under the various conditions were characterized by x-ray diffraction, DTA, microscopic point-count estimation of composition, pore spectra, uncombined Ca(OH)2 analysis, density, and strength determinations. The desired high-strength binder was essenti-ally tobermorite and some CSHn gel. Al-substituted tobermorite and CSHII) may be present in small amounts, but C2SH, Al2O3, Fe2O3, and S03-bearing hydrous phases were not detected. Superheated steam conditions should be avoided at all time, and saturated steam autoclaving can be carried out usually at pressures around 100-l 10 psig (7.0 - 7.7 kgf/cm2) for times of about 16 hr Curing in saturated steam, utilizing a water spray technique, is recommended because it permits the desired binders to be formed over a broad pressure range and also reduces significantly the autoclaving time. An optimum autoclaving cycle is recommended that uses stepwise curing at two pressure levels in the presence of water spray: 5.5 hr at 115 psig (8.1 kgf/cm2 followed by a 3.0 hr at about 130 psig (9.1 kgf/cm2).
10.14359/6602
SP32-07
A. V. Satalkin, P. G. Komokhov, and I. P. Kromin
Autoclaved concretes using lime-silica binders can be made with strengths of 500-600 kgf/cm2 (7000-8500 psi) or more. Higher strengths are obtained with crushed stone than with sand and gravel aggregate, but concretes without coarse aggregate are more commonly made in the USSR. Although state standard specifications for autoclaved aproducts require that the limes used contain not more than 1 percent MgO, such pure limes are not available throughout the USSR. Concretes have been made in the laboratory using limes with MgO contents as high as 25 percent. Strengths of such concretes are lower, but with additives such as MgC12, CaC12, and NH4Cl these low strength levels can be improved considerably. Concretes made with magnesian limes have withstood more than 200 cycles of freezing and thawing. Reinforcing steel sometimes requires a protective coating to prevent cor-rosion.
10.14359/6603
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