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International Concrete Abstracts Portal

Showing 1-5 of 46 Abstracts search results

Document: 

SP186-27

Date: 

May 1, 1999

Author(s):

A. E. P. Guimaraes, J. S. Giongo, and T. Takeya

Publication:

Symposium Papers

Volume:

186

Abstract:

High-performance concrete (HPC) has been studied extensively at many research centres, because of its increasing use in reinforced concrete buildings. Since HPC is a brittle material, studies have been done to increase its ductility. Increases in longitudinal and /or transverse steel ratios can improve the ductility of HPC elements. The addition of fibres also increases the deformability and thus the ductility. Hence, the transverse steel ratio can be reduced by using fibres. This paper presents a study of axially loaded columns made with high-performance concrete containing steel fibres. The average compressive strength of the concrete was 80 Mpa. The volumetric ratios of fibres were: .25%; .50% and 1.00%, and the stirrup ratios were .55% and .82%. The longitudinal steel ratio was the same for all columns tests, the W/C was .37, 10% silica fume was added and it was also necessary to use about 3% superplasticizer to improve workability. A comparison was made between the results for columns in high-strength concrete with and without fibres. It was observed that only the cross-sectional core effectively contributed to the load capacity of the columns.

DOI:

10.14359/5572


Document: 

SP186-18

Date: 

May 1, 1999

Author(s):

C. K. Ong, T. W. Bremner, T. A. Holm, and S. R. Boyd

Publication:

Symposium Papers

Volume:

186

Abstract:

Results of an experimental investigation on the performance of cracked fiber reinforced concrete in a simulated marine environment are presented. A total of 111 prismatic specimens (150 by 150 by 510 mm) comprising both lightweight and normal weight concretes were used in this investigation. Cracked specimens with crack sizes of "hairline", .25 mm, 1.0mm, and uncracked specimens were exposed in either simulated seawater for up to a period of 7 years or 5300 alternate wetting and drying cycles. It was found, for both lightweight and normal weight concrete, that the strength development of uncracked specimens is not hampered by alternate wetting and development of uncracked specimens is not hampered by alternate wetting and drying. At the end of 7 years exposure, compressive strength gain of 90% was observed over the seven day moist cured strength for both types of concrete. Corresponding uncracked prismatic specimens showed approximately 25% flexural strength gain; however their post-cracking strength decreased under a prolonged period of alternate wetting and drying. Precracked specimens with cracks of up to .25 mm showed improvement in load carrying capacity up to 1440 wetting and drying cycles. However specimens with cracks of 1.0 mm showed a reduction in load carrying capacity.

DOI:

10.14359/5563


Document: 

SP186-08

Date: 

May 1, 1999

Author(s):

W. Langley

Publication:

Symposium Papers

Volume:

186

Abstract:

A 12.9 km bridge was recently constructed across the Northumberland Strait in Eastern Canada, connecting Prince Edward Island (Canada's smallest province and major tourist area) with the mainland. The bridge is a precast, post-tensioned segmental box grinder structure. The bridge is believed to be the longest highway structure over seasonally frozen water. Durability concerns which had to be addressed in the design and construction of the bridge included abrasion of ice on the piers in late winter and early spring, corrosion of reinforcement in a marine environment, alkali-aggregate reactivity, sulphate attack, freezing and thawing resistance of concrete in a saturated condition, salt scaling and control of thermal cracking. The design life of the bridge was 100 years, a first of this magnitude in Canada. The paper discusses some of the unique features of the bridge and the selection of concrete mixture proportions to meet the durability requirements of bridge components.

DOI:

10.14359/5553


Document: 

SP186-31

Date: 

May 1, 1999

Author(s):

W. Radomski

Publication:

Symposium Papers

Volume:

186

Abstract:

The needs concerning improvement in durability of existing and new bridges in Poland are briefly presented. The requirements to ensure a high durability of new bridge structures constructed on a new network of motorways are especially emphasized. Material possibilities to product high-performance concrete in Poland are presented. Application of high-performance concrete to construct bridge structures with the use of modern erection methods (e.g. incremental launching, cast-in-place canilever balance) is analyzed and exemplified in the light of technical and economical aspects. Especial attention is given to the development of the researches on high-performance concrete in Poland. Some chosen problems are presented in particular, namely: testing an technological problems, hydration and thermal effects and their influence on material properties, bond strength, strength test of structural members subjected to different type of loading. Design problems concerning structural applications of high-performance concrete are also listed requirements in existing design standards or codes is emphasized and a consequence of it for engineering practice is discussed. Concluding remarks summarizing research of high-performance concrete in Poland and its up-to-date and future potential structural applications are formulated.

DOI:

10.14359/5576


Document: 

SP186-01

Date: 

May 1, 1999

Author(s):

M. Collepardi

Publication:

Symposium Papers

Volume:

186

Abstract:

The present paper provides an example of the application of the holistic model to the study of one of the most complex phenomenon in the science of concrete durability, namely the deterioration caused by delayed ettringite formation (DEF) in a sulfate-free environment. By adopting the holistic approach, a new model to explain this damage is proposed. The model is based on three essential elements: late-sulfate release, microcracking, and exposure to water. Late-sulfate release from a cement with high-sulfate content (especially that with high content of clinker sulfate in less available form) can cause the delayed deposition of ettringite in pre-existing microcracks after sulfate ions diffuse through the pore solution in concrete, either intermittently, or continuously exposed to environmental water. Microcracking may be promoted by alkali-silica reaction, steam curing at high temperatures, localized high stress in prestressed concrete structures or other causes. Theoretically, the DEF-included damage occurrence can be reduced or prevented by controlling at least one of the above three parameters. In practice, the best way of reducing the DEF-induced damage risk is either to avoid cements with high clinker sulfate that are responsible for the late-sulfate release, or to adopt lower and more homogenous stress distribution derived from the prestressing process in precast elements, such as concrete ties.

DOI:

10.14359/5546


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