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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 11 Abstracts search results
July 1, 1972
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).
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.
Clayton M. Crosier.
In connection with extensive laboratory investigations of auto-claved, foamed cellular concretes data have been secured on the effects of variations in the curing on the compressive strength and elasticity. The concretes were made of portland cement. Type I or III, with one of several Kansas pozzolanic materials, or with a fly ash used for comparison. In each of 53 laboratory batches, one curing factor was varied between the 2 or 3 sets of cylinders. This inves tigation covered the effects of each of the four curing variables (in order of extent of coverage): maximum autoclaving pressure, moist storage prior to autoclaving, duration of the maximum pressure, and rate of heating and cooling. The effects of each variable are found to be dependent on the properties of the pozzolan, especially fineness. For the proportions of volcanic ash used and the curing conditions studied, Type III cement was more effective than Type I, but for one fly ash the reverse was true. The analyses are discussed and tentative conclusions are summarized.
C. James Gulde
of the materials used in autoclaved block and beick manufacutre contribute to the color, but piin ents contribute the most. Mineral pigments and some others are satisfactory, but all are not effective, and some contain undesirable contaminants. For many colors it is possible to duplicate, in masonry units, any combination of hue, value, and chroma. Versatility in color production and reproduction requires a simple color laboratory and the es-tablishment of a library of color specimens made with the masonry ingredients used by the plant. One patented procedure is based on the introduction of a fluidized color mix onto one face of the machine mold box immediately before each filling of the mold box.
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.
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