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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 31 Abstracts search results
March 1, 1994
J. M. Shilstone, Sr., and J. M. Shilston, Jr.
The authors have been involved in concrete technology in the field over the past half-century. While there have been many beneficial advances, there have also been subtle, but important, regressions. To gain full advantage of concrete's potential, the undesirable effects of those regressive aspects must be corrected through a series of paradigm shifts. Performance requirements are changing, accentuating the need for new and advanced technologies. Concrete qualities other than 28-day strength must be recognized when durability is considered. High strength does not assure high durability. However, the characteristics that improve durability will generally produce higher strength than that required for structural purposes for concrete exposed to an aggressive environment. When this occurs, strength based on durability must be a deciding strength factor. Standard concrete practices are not always in the best interest of quality and constructability. These conditions are traced and solutions are offered. The principal concern is that most engineers are no longer trained to provide broad concrete industry leadership, as in the past. A major technical void has developed between design and construction teams. Just as geotechnical engineers took over foundation design, concrete engineers must be trained to lead concrete design and construction into the 21st century.
R. N. Swamy
The mention of alkali-aggregate reactivity (AAR) often conjures up visions of an intolerable and unremediable cancerous disease to which all concrete is subjected. It generates a lack of precise and thorough understanding of the phenomenon and strikes fear in the minds of concrete technologists, engineers, and the public alike. The aim of this paper is to put the phenomenon of AAR in a proper perspective in relation to its mechanisms, effects, and influences. An attempt is made to unravel the mysteries of AAR and the myths and mythologies associated with it. Paper describes the behavior and method of operation of the phenomenon, and assesses its impact on the engineering properties of concrete and structural performance of load-bearing members. It is shown that it is possible to check, and indeed contain, the effects of the attack both in new construction and in existing structures.
K. W. Nasser and S. Biswas
A new model of the K-slump tester was developed that can be used to evaluate the slump of concrete in 40 sec. The new apparatus features an electronic digital readout giving the slump value to the nearest 1 percent. Experimental studies were performed in accordance with ASTM C 670 and C 802 using the new K-slump tester to determine its reliability and precision. The results indicate that the new apparatus is accurate and reliable in evaluating concrete slump.
B. C. Gerwick Jr..
Durability criteria for major bridges differ from those of most other structures in that, currently, major bridges are designed to serve for 100 to 125 years. Challenging this longevity are not only the normal physical and chemical attacks on the concrete itself and on the reinforcement, but also the intentional application of salts to highway bridge decks and, in the case of railroad and floating bridges, the accumulation of internal damage (fatigue) due to cyclic dynamic loading. Great progress has been made recently in identifying causes and finding preventive and mitigating measures aimed at specific phenomena. Advanced laboratory technology and equipment have been combined with field observations to describe the processes, prescribe tests for early diagnosis, and develop appropriate countermeasures. A number of tests of specific parameters have recently been developed and are now being implemented as mandatory criteria for concrete in major bridges designed for lives in excess of 100 years. Ever more refined linear elastic finite element analyses are being employed to reveal areas of probable cracking due to structural response. Rigid enforcement of specified quantitative criteria, focused on specific parameters, ignores the interactive complex processes involved. Excessive reliance on such criteria impedes rather than helps construction progress, and may on occasion be counterproductive to durability. What is required, instead, is a holistic systems approach that addresses not only individual processes and phenomena but their interaction.
P. J. M. Monteiro and P. R. L. Helene
There are many methods for determining the mixture proportions of concrete when compressive strength is the design criterion. However, there is not much information when other criteria, such as fracture energy, elastic modulus, or durability aspects, are specified. For these cases, a new mix design nomogram developed from well-established concrete relationships is reported. The application of this method is demonstrated by showing the influence of cement content, water-cement ratio, and aggregate-cement ratio on the compressive strength, modulus of elasticity, fracture energy, depth of carbonation, and permeability. The mixture design nomogram, apart from being a practitioner's tool, can also help the researcher select the most appropriate parameters for experimental studies.
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