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International Concrete Abstracts Portal

Showing 1-5 of 53 Abstracts search results

Document: 

SP172-51

Date: 

December 1, 1999

Author(s):

Mohammad-Reza Esfahani and B. V. Rangan

Publication:

Symposium Papers

Volume:

172

Abstract:

The paper presents studies on local bond and bond strength of splices. The study was conducted in two stages. In the first stage, an analytical equation was developed to calculate the bond strength of splices in normal strength concrete. The mean value of test/calculated bond strength for the proposed equation is 1.007 with a standard deviation of 0.08 1. The second stage of the study comprised the study on local bond and the bond strength of splices in the case of high performance concrete (HPC)/high strength concrete (HSC). The study on local bond involved tests on forty five short length specimens. Using these test results, a relationship for bond strength normalised with respect to the tensile strength of concrete is obtained. The study of bond in splices involved tests on twenty two beams made of HPC/HSC. In each beam, the tensile steel was spliced in the constant moment zone. Using the relationship for local bond in HPC/HSC, the analytical model developed for normal strength concrete is modified. Good correlation between calculated and test strengths of splices in the case of HPC/HSC is found.

DOI:

10.14359/6173


Document: 

SP172-09

Date: 

December 1, 1999

Author(s):

P. H. Emmons, A. M. Vaysburd and J. E. MacDonald

Publication:

Symposium Papers

Volume:

172

Abstract:

The purpose of this paper is to clarify the critical factors and properties that affect the long-term performance of repaired concrete structures. The discussion focuses on the need to consider a repair to an existing concrete structure as a three-phase composite system: the existing substrate, the repair material, and the transition zone (interface) between them. One of the principal factors that assures the durability of a concrete repair is its resistance to cracking. Because cracks make concrete vulnerable to a variety of physical and chemical attacks, factors that can contribute to cracking are identified. Restrained contraction of repair materials, the restraint being provided through bond to the existing concrete substrate, is a major factor leading to cracking and delamination of the repair phase. Those material properties that influence dimensional compatibility and their relative importance to durable repairs are reviewed. Critical issues that will affect future improvements in long-term performance of repairs are discussed.

DOI:

10.14359/6131


Document: 

SP172-36

Date: 

December 1, 1999

Author(s):

S. K. Kaushik and S. P. Singh

Publication:

Symposium Papers

Volume:

172

Abstract:

Ferrocement composite columns are used for prefabrication, repair/retrofitting and for insitu construction. Encasement of column end zone can be used to produce hinges for seismic retrofitting of columns. The presence of mesh reinforcement in encased columns exerts a confining pressure on the core concrete and consequently enhances its strength and ductility. This fact has been corroborated by various investigations conducted across the globe. The purpose of this work broadly includes verification of the analytical formulations available in the literature and a study of those parameters which have not been covered before. The primary emphasis is on ascertaining the impact of core reinforcement on the overall behaviour of ferrocement encased columns. For this, cylindrical specimens with varying quantities of mesh and longitudinal reinforcement were cast and tested in axial compression. Further, in one set of the specimens, lateral reinforcement was provided in combination with mesh layers. The dissertation by the second author makes an indepth study of the compressive ductility and failure modes of ferrocement composite columns. Finally, an endeavour has been made to correlate the analytical and experimental results so as to have a wholesome view of the behaviour of the ferrocement composite columns.

DOI:

10.14359/6158


Document: 

SP172-27

Date: 

December 1, 1999

Author(s):

Sidney Mindess, Perry Adebar and Julien Henley

Publication:

Symposium Papers

Volume:

172

Abstract:

An experimental study aimed at investigating the influence of hooked steel fibers on improving the structural performance of high strength concrete (HSC) members is described. Six columns were tested to investigate the ability of fibers to prevent premature cover spalling in HSC columns. While the final appearance of the columns was influenced by the presence of fibers, the axial capacity was unaffected. Eight elements constructed with concretes ranging in strength from 25 to 95 Mpa were tested under shear dominated loading. The addition of fibers changed the failure mode from brittle shear to a more ductile flexure/shear mode (diagonal cracking after significant flexural ductility). Eleven large size (600 mm deep) beam elements were also tested. Due to the addition of fibers, shear strength increases as high as 117 % were observed in these members.

DOI:

10.14359/6149


Document: 

SP172-42

Date: 

December 1, 1999

Author(s):

Graeme K. Moir and Steven Kelham

Publication:

Symposium Papers

Volume:

172

Abstract:

The short term performance aspects of portland limestone cements (setting, concrete slump, strength development and heat of hydration) are compared with those of portland slag, fly ash and pozzolanic cements. The early activity of the portland limestone cements, as indicated by initial setting time, early strength and early heat release, is generally higher than that of the other cement types. Ultimate strengths are, however, lower provided moist curing conditions are maintained. The longer term performance characteristics of, concrete carbonation rate, freeze-thaw resistance, sulfate resistance and chloride penetration are also compared. Generally the performance of cements containing up to 25% limestone was satisfactory and within the range of performance of the portland cements from 4 different sources. Portland limestone cements with similar late strengths and superior early strengths to normal portland cements can be produced if active mineralised clinker is used as the basis of the cement. The environmental impact of cement manufacture is reduced with this type of cement. The effective utilisation of portland limestone cements is dependent upon having appropriate cement and concrete standards in place. The European countries have largely achieved this and are in a good position to gain the economic and environmental advantages of portland limestone cement manufacture and use.

DOI:

10.14359/6164


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