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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 1-10 of 11 Abstracts search results
July 1, 1972
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.
Y. M. Butt, V. V. Timashev, and V. S. Bakshutov
The phase compositions and crystal forms of calcium silicate hydrates and calcium aluminate hydrates formed during autoclaving are dependent on temperature, pressure, stoichiometric relationships, and the concentration of Ca2+, Na+, K+, and li+ ions in solution. Most crystals and crystal aggregations are of a characteristic type. Some crystal intergrowth occurs, mainly interpenetration and agglomeration. Illustrations are shown.
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.
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).
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.
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.
Sergey A. Mironov, Liarisa A. Malinina
and Svetlana Cheryachukina
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.
James C. Bailey and Ernest C. Clay
Automation in the block industry is at a primitive stage compared to some other industries. Within the block manufacturing process, the greatest advancement of automation has developed in proportioning and mixing. Those plants constructed in recent years that have been the most automated have all utilized single-stage autoclaving in some form. The efficiency of autoclave production depends on using a maximum portion of each 24 hr for curing, and a minimum I for loading and unloading the autoclave. Thus, efficient and b rapid movement of block from one end of the flow diagram to the other is important. It may be accomplished either by using transfer cars in a shuttle system or by using trains that operate over curved tracks and switches. Disadvantages of these systems suggest the desirability of a completely circular system if technical difficulties could be surmounted.
George Verbeck and L. E. Copeland
The effect of temperature on the physical and chemical properties of hydrating cement is considered from the effect temperature has on both rate of hydration and on the composition of the hydration product. The increased rate of hydration produced by elevated temperature is discussed in terms of its apparent effect on the uniformity of distribution of the hydration product within the paste matrix and the significance of degree of uniformity of distribution on strength. The general chemical and physical nature of the hydration products formed below 212 F (1OOC) is essentially unaffected by curing temperature. In high pressure steam curing above 212 F the properties of the product can be considerably altered depening upon the temperature and the composition of the cement. The various phases produced for different temperatures and compositions are described in terms of the inherent nature of the basic calcium silicates. The strength of high pressure steam cured paste is shown to depend upon the phase composition of the product primarily through the influence fo the phase composition on its relative ability to reduce the capillary porosity of the paste.
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