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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 63 Abstracts search results
June 1, 1995
N. Otsuki, S. Nagataki, and M. Hisada
It is necessary for concrete engineers to get more information on the ion movement through and in concrete for the development of new technologies, such as cathodic protection, desalination, and re-alkalization for reinforced concrete members. In concrete members with these treatments, various ions should be moved through and in concrete members. The movement of ions could influence concrete properties and steel reinforcing bars. Ground granulated blast furnace slag, fly ash, and silica fume have been recognized as high quality mineral admixtures for concrete. Since structures built with these materials might eventually be subjected to electro-migration processes, a set of experiments to assess the effects of these pozzolans were devised. In this study, considering the conditions mentioned above, the movement of several kinds of ions through hardened mortar with mineral admixtures was investigated. As ions, Na +, K +, and Cl - were selected because the ions were closely related to alkali-aggregate reaction or chloride attack. As mineral admixtures, ground granulated blast furnace slag, fly ash, and silica fume were used. Also, the influences of water-to-binder ratio on the movement of ions were investigated. Electrochemical cells were used for the experimental work; the current was applied to a cell in the range between 0.1 A/m 2 and 10.0 A/m 2. Analyzing the data from the experimental work, the following conclusions were obtained. 1. The electromigration of ions through mortar are reduced with the addition of admixtures. 2. The electromigration of ions increases with the water-to-binder ratio. 3. The electromigration of ions is closely related to the pore size distribution of mortar and paste.
A. Xu and S. L. Sarkar
As focus increasingly shifts to protecting the environment through recycling of industrial byproducts and wastes, as well as conserving energy and resources, corresponding restructuring of conventional production technology and practices has become imperative. Because of these considerations, mixtures of kiln dust and fly ash were hydrothermally treated and calcined to produce a new type of beta-C 2S rich cement. Fly ash, which is the most abundantly generated industrial byproduct, is still largely disposed of as waste; kiln dust is the waste product of the cement industry, vast quantities of which are discarded due to its high alkali content. The former is composed of alumino-silicate glass, while the latter has a composition similar to that of partially calcined cement raw meal. This study demonstrates that it is possible to produce C 2S cement of dequate 28-day strength by suitably proportioning fly ash and kiln dust. The results of variations in factors such as the CaO:SiO 2 ratio and two different precalcination treatments are presented. Prehydration-dehydration (sintering at 950 C) processes were specially applied for the production of this cement, in contrast to the direct calcination method in the presence of a mineralizer. The cement was constituted of beta-C 2S and calcium aluminates. The formation of these minerals in relation to the clinkering sequence is discussed. The cement is sufficiently hydraulic, and its strength development largely depended on the CaO:SiO 2 ratio of the raw mix and the precalcination process.
B. Fournier, W. S. Langley, and V. M. Malhotra
Three reactive aggregates from New Brunswick, Canada, a greywacke, a gneiss, and a meta-volcanic rock were evaluated for their potential alkali reactivity (AAR) in concrete mixtures incorporating 420 kg/m 3 of cementitious materials. The concrete mixtures consisted of the control made with CSA Type 10 low- and high-alkali cements and mixtures incorporating ASTM Class F fly ash at 20, 30, and 56 percent replacement levels of the high-alkali cement. The susceptibility of the concretes to AAR was evaluated by casting test prisms and subjecting these to various accelerated curing conditions in the laboratory. For comparison purposes, mortar bars were also made and tested according to the ASTM C 1260-94 Accelerated Mortar Bar Test procedure. The AAR concrete prism tests performed in this study have shown that none of the test prisms cast from concrete mixtures incorporating 20, 30, and 56 percent fly ash showed significant expansion after two years of testing at 38 C and relative humidity >95 percent. These results were in good accordance with those obtained in the accelerated mortar bar test. Some alkaline immersion tests results would indicate, however, that concrete incorporating 20 percent fly ash might not offer adequate protection against potential deleterious expansions with highly reactive aggregates.
M. I. Sanchez De Rojas and M. Frias
Exothermal reactions take place during cement hydration and heat the cement mass. This temperature increase, from the initial moment of setting until the hardening of the cement, causes shrinkage which contributes to the cracks that can be seen in some constructions that are made of large masses of concrete or cement rich mixtures. The use of pozzolans reduces the heat given off by the cements during hydration. However, the reactions of the pozzolanic materials with the lime also produce heat; the decrease should not be proportional to the level of clinker substitution in the mixed cements. The first hours show that most of the additions, which present higher activity at early stages, increase the hydration heat of the mixed cements in relation to the control cement. The effect of different silica fumes on the hydration heat with respect to a control cement and other pozzolanic materials was studied and is presented in this paper.
H. A. W. Cornelissen, R. E. Hellewaard and J. L. J. Vissers
In the present research project, fly ash was mechanically processed to 1 to 5 micron particle size. Mortars and concretes were made from these processed fly ashes. In this paper, the results of the micronized fly ash are compared to the results gained with air classified fly ash, silica fume, and blends. It was found that using ground fly ashes, very fluid mixtures can be produced with excellent strength and durability properties. Because of the growing interest in ultra-fine supplementary cementing materials (SCM's) for high-performance concrete, there is a need to find ways to micronize fly ashes in an economical way.
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