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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 11 Abstracts search results
Document:
SP32-01
Date:
July 1, 1972
Author(s):
George Verbeck and L. E. Copeland
Publication:
Symposium Papers
Volume:
32
Abstract:
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.
DOI:
10.14359/6597
SP32-02
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.
10.14359/6598
SP32-03
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.
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
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