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Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
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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 18 Abstracts search results
October 1, 2004
Concrete is international, but made locally; has infinite variability, but can be made very uniform; and can be made to last as long as you want it to. Therefore, what is needed to more fully realize its potential as a construction material is to understand what we want it to do, learn how to make it so it will do so, use available methods to restrict undesired variability, consider the ethical and environmental aspects of its use, and help the people who are making it to do it better.
Concrete will be immune to the effects of freezing and thawing if (1) it is not in an environment where freezing and thawing take place so as to cause freezable water in the concrete to freeze, (2) when freezing takes place there are no pores in the concrete large enough to hold freezable water (i.e., no capillary cavities), (3) during freezing of freezable water, the pores containing freezable water are never more than 91 percent filled, i.e., not critically saturated, (4) during freezing of freezable water the pores containing freezable water are more than 91 percent full, the paste has an air-void system with an air bubble located not more than 0.2 mm (0.008 in.) from anywhere (L = 0.2 mm), sound aggregate, and moderate maturity. Sound aggregate is aggregate that does not contain significant amounts of accessible capillary pore space that is likely to be critically saturated when freezing occurs. The way to establish that such is the case, is to subject properly air-entrained, properly mature concrete, made with the aggregate in question, to an appropriate laboratory freezing-and-thawing test such as ASTM C 666 Procedure A. Moderate maturity means that the originally mixing water-filled space has been reduced by cement hydration so that the remaining capillary porosity that can hold freezable water is a small enough fractional volume of the paste so that the expansion of the water on freezing can be accommodated by the air-void system. Such maturity was shown by Klieger in 1956 to have been attained when the compressive strength reaches about 4,000 psi.
This lecture is about concrete - specifically, hydraulic-cement concrete. If one starts with the dry powder that is hydraulic cement - usually the particular class of hydraulic cement known as portland cement - and adds water, what results, depending on the amount of water added, is cement paste or grout. Grout can be poured like gravy. If fine aggregate is added, the result is mortar or sanded grout. If both fine aggregate and coarse aggregate are added, the result is concrete. As the Supreme Court of Pennsylvania once wrote in a decision dealing with cement-manufacturing plants, "cement is to concrete as flour is to fruitcake." My first point is, to get proper concrete, get the terminology right. There is no such thing as a cement mixer. And sand is not a synonym for fine aggregate; sand is a class of fine aggregate produced by nature rather than by rock crushers and grinding mills.
Excessive expansion of concrete due to alkali-silica reaction will not occur if any one of the following circumstances exists: (1) the aggregate is insufficiently reactive; (2) the pH of the pore fluid is not too high; (3) the amount of reaction product formed is not sufficiently large or not sufficiently expansive so that its expansion can cause damage; or (4) there is not enough available water to cause the reaction to progress so as to develop the expansive product and to be available for imbibition by the product so as to cause it to swell and disrupt the concrete. Put the other way around, excessive expansion can occur only if there is enough potentially expansive alkali-silica reaction product and water so that, as the product takes up the water and swells, the concrete expands excessively. Hence, what is needed to avoid excessive expansion is to be able to predict the probable reactivity of the available aggregates, the probable mechanisms by which the pH of the pore fluid might get well above 13, and, when justified, select and implement appropriate precautions against the undesirable consequences of these eventualities. Published by Elsevier Science Ltd. All rights reserved.
No one could question the appropriateness of "Research on Concrete" as a topic for a Stanton Walker Lecture on the Materials Sciences. Research, according to Webster’s Dictionary, is "critical and exhaustive investigation or experimentation having as its aim the discovery of new facts and their correct interpretation; the revision of accepted conclusions, theories, or laws, in the light of newly discovered facts; or the practical applications of such new or revised conclusions." Dr. Bates noted, in the first of these lectures in 1963,1 that it had recently been said that "concrete is not a material, it is a process." However, in 1967, when the American Concrete Institute finally got around to publishing an official definition of concrete,2 hat definition read: "A composite material which consists essentially of a binding medium within which are embedded particles or fragments of aggregate; in portland cement concrete, the binder is a mixture of portland cement and water."
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