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International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

Document: 

SP144-08

Date: 

March 1, 1994

Author(s):

J. A. Bickley, R. T. Hemmings, R. D. Hooton, and J. Balinski

Publication:

Symposium Papers

Volume:

144

Abstract:

Discusses the severe deterioration of concrete that can result from an unusual form of sulfate attack, in which C-S-H and calcium hydroxide in the cement paste are converted to gypsum and thaumasite. This deleterious reaction only occurs at low temperatures in the presence of continuous moisture and where sources of sulfate and carbonate ions are available. Severe deterioration of this type occurred in concrete columns and slab-on-grade at facilities in the Canadian Arctic within 2 years of casting, to the point where some replacement was necessary. Evidence of continuing deterioration led to an extensive investigation of the structures when the concrete was 4 years old. Although it has been relatively well documented in Europe, a few cases of concrete deterioration due to thaumasite formation have been reported in North America. Currently, North American codes and standards do not include any guidance for the avoidance of this type of sulfate attack. Paper contains data that should be of interest to agencies responsible for the development of codes and standard specifications for concrete construction practices in cold areas.

DOI:

10.14359/4396


Document: 

SP144-07

Date: 

March 1, 1994

Author(s):

M. Pigeon

Publication:

Symposium Papers

Volume:

144

Abstract:

It is now commonly accepted that there are two basic frost durability problems: internal cracking due to freezing and thawing cycles, and surface scaling, generally due to freezing in the presence of deicer salts. Although there are still parts of the problem that are not well understood and warrant further investigation, particularly with respect to the differences between laboratory tests and field exposure, the way to make concrete resistant to freezing and thawing cycles is very well known. It is simply to insure that the hardened concrete has an adequate system of entrained air voids. Field experience as well as laboratory data have shown conclusively that internal cracking due to frost in properly air-entrained concrete is almost nonexistent. In the years to come, it will be necessary to increase our knowledge of some of the parameters that influence air entrainment, particularly in the new types of concrete that are being used, such as, for instance, high-strength concrete and roller compacted concrete. Simple methods to determine the characteristics of the air-void system in fresh concrete will also be required. Scaling due to freezing in the presence of deicer salts is a much more complex problem than internal cracking for many reasons, but probably mainly because it is related to the microstructure of the surface layer or "skin" of concrete. Laboratory as well as field data are often contradictory. But if scaling is a complex problem, this does not mean that it is a monumental one. It is only one aspect of the complex question of the durability of concrete structures.

DOI:

10.14359/4395


Document: 

SP144

Date: 

March 1, 1994

Author(s):

Editor: P. Kumar Mehta

Publication:

Symposium Papers

Volume:

144

Abstract:

SP-144 Eighteen review papers and twelve research papers are included in the Proceedings of the Mohan Malhotra Symposium on Concrete Technology: Past, Present, and Future. The purpose of the Symposium was to serve as a forum for discussion on the current state of the concrete industry and technology, and to identify important issues that need to be addressed in the future. The proceedings of the Mohan Malhotra Symposium, which excel for the variety and richness of information contained in the 30 papers, reflect the respect and admiration of the authors for the honoree. As a researcher, scholar, and technology-transfer crusader, Mohan has undoubtedly made unique contributions to the concrete technology. It would indeed be a fitting tribute to him if the deliberations of the Mohan Malhotra Symposium are able to make a significant impact in preparing the concrete industry for the 21st century.

DOI:

10.14359/14184


Document: 

SP144-24

Date: 

March 1, 1994

Author(s):

P. Richard and M. H. Cheyrezy

Publication:

Symposium Papers

Volume:

144

Abstract:

The use of ultra-high-strength concrete for the construction of some types of structural members can be considered if nonbrittle behavior is achieved. Paper introduces reactive powder concretes (RPC) that exhibit ultra-high strength and high ductility at the same time. Compared to conventional concretes, the ductility estimated in terms of fracture energy is increased by one to two orders of magnitude, while the compressive strength values are in the range of 200 to 800 MPa..

DOI:

10.14359/4536


Document: 

SP144-13

Date: 

March 1, 1994

Author(s):

V. Ramakrishnan, G. C. Hoff, and Y. U. Shankar

Publication:

Symposium Papers

Volume:

144

Abstract:

Presents the results of an experimental investigation conducted to determine the flexural fatigue strength of high-strength lightweight concrete under water. This concrete was produced using expanded shale aggregate and high-performance concrete admixtures such as silica fume and superplasticizer. Properties of fresh concrete and elastic and mechanical properties of hardened concretes are presented. The fresh concrete was tested for slump, air content, unit weight, and temperature. The hardened concrete was tested for moist-cured dry weight, compressive strength, modulus of elasticity, and flexural fatigue strength. The investigation indicates that a highly workable high-strength lightweight concrete can be produced successfully. The high-strength lightweight concrete had a higher endurance limit (10 to 16 percent) than normal weight concrete of equal compressive strength. In general, there was no reduction in the flexural fatigue strength for the lightweight concretes when tested under water. The static flexural strength determined from specimens that had successfully resisted 2 million cycles was always greater than that of specimens which had not undergone fatigue loading.

DOI:

10.14359/4401


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