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International Concrete Abstracts Portal

Showing 1-5 of 25 Abstracts search results

Document: 

SP163-20

Date: 

August 1, 1996

Author(s):

L. Z. Hales and D. E. Wilson

Publication:

Symposium Papers

Volume:

163

Abstract:

Many Corps of Engineers rubble-mound breakwaters and jetties have become permeable to sand transport and wave transmission, resulting in increased dredging costs, risks and delays to navigation, and damage to moored vessels by excessive wave activity. Some Corps coastal districts have applied grouting techniques for sealing these structures by using cementitious and chemical grouts for creating a vertical barrier through a series of vertical holes drilled along the centerline of the structure. To ascertain the effective useful life of such grouts, durability time-dependent tests were conducted by U. S. Army Engineer Waterways Experiment Station (WES) to determine how the materials would endure under near-actual field conditions. A cementitious mixture previously used at Buhne Point, California (Buhne Point Mixture), and a new mixture design (WES Mixture) developed by the WES Structures Laboratory (SL) were evaluated. Specimens were exposed at three weathering stations (including Treat Island, Maine) for the eight-year period 1987 to 1995. Nondestructive tests (ultrasonic pulse velocity and transverse flexural frequency) were conducted periodically during the eight-year evaluation period. Long-term durability exposure field tests revealed spalling of the Buhne Point Mixture due to freezing and thawing. However, nondestructive tests indicated the integrity of all specimens was maintained, as there appeared to be minimal changes in the properties of these cementitious grouts. Grout laced within the core of rock structures may not actually be exposed to the extreme conditions on the weathering platform at Treat Island. Either the WES Mixture or the Buhne Point Mixture may be used as grouting materials to rehabilitate existing Corps rubble-mound breakwaters and jetties by filling voids to prevent passage of excessive wave energy and sediment through such structures.

DOI:

10.14359/1369


Document: 

SP163-02

Date: 

August 1, 1996

Author(s):

George C. Hoff

Publication:

Symposium Papers

Volume:

163

Abstract:

The fire resistance of high-strength (greater than 60 MPa) concretes has been reported to be reduced when compared to normal strength concrete. This behavior has been attributed to the very dense concrete matrix usually associated with high-strength concrete. This dense matrix does not allow rapid transmission of water vapor within the concrete exposed to high temperatures, thus leading to disruptive vapor pressures. This problem is aggravated further when the fire is a hydrocarbon fire which reaches 880 C within three minutes. Offshore concrete platforms, which are typically built with high-strength concrete, are therefore at risk from hydrocarbon fires. This paper presents the results of two test programs involving hydrocarbon fires and high-strength concretes. Both lightweight aggregate concrete and modified normal density concrete (blends of normal density and lightweight aggregate coarse aggregates) were evaluated. Small beams of lightweight concrete, using different lightweight aggregate types, were evaluated for spalling resistance. Polypropylene fibers, used in some beams, were successful in greatly reducing spalling. Large wall sections of modified normal density concrete experienced significant spalling, but retained adequate concrete strength behind the reinforcing bars because of the low rates of heat transfer within the large sections.

DOI:

10.14359/1345


Document: 

SP163-03

Date: 

August 1, 1996

Author(s):

Daksh Baweja, Harold Roper, and Vute Sirvivatnanon

Publication:

Symposium Papers

Volume:

163

Abstract:

Presents some results from a major research project carried out on corrosion of steel reinforcement in concrete. The performance of a range of portland and blended cement concretes containing fly ash and blast furnace slag exposed to simulated marine conditions was evaluated over a period of six years. A large amount of data relating to corrosion of embedded steel in concrete was obtained in this project. Long-term half-cell potential data on reinforcement within concrete slabs and resistivity data on the same concrete specimens are considered in detail in this paper. Rates of corrosion of steel in concrete were also measured using potentiodynamic anodic polarization procedures. Trends observed in the data were different for the portland and blended cement concretes investigated. It was found that concrete resistivity may influence the measured half-cell potential of steel in concrete. This factor needs to be taken into account for half-cell potential data interpretations.

DOI:

10.14359/1346


Document: 

SP163-04

Date: 

August 1, 1996

Author(s):

MichalI Ceza and Peter J. M. Bartos

Publication:

Symposium Papers

Volume:

163

Abstract:

Admixtures for concrete to be placed underwater are now widely used. The use of such admixtures allows concrete to be placed underwater with much less risk than has been previously possible. However, such concrete has to satisfy several requirements when fresh (workability, washout resistance), as well as when hardened (strength, durability). Workability and washout resistance are particularly important for underwater placing. Several test methods and related equipment have been designed to evaluate the required properties of the fresh underwater mixtures, including devices to evaluate their washout resistance. One of the problems facing both producers and users of underwater (UW) concrete admixtures up to now has been an absence of a standardized and realistic test method for the assessment of performance of such products in practical concrete construction. This research project aims to develop efficient new tests for the practical evaluation of the washout resistance and nondispersability of fresh concrete mixtures placed underwater. The paper briefly reviews existing washout tests, assesses the potential of alternative tests, and introduces the new tests designed by Ceza. The principle of the new test, the apparatus required, and the test procedure are described. Results of tests on practical underwater mixtures are shown and effects of UW admixtures discussed. The apparatus simulates well the actual washout condition; its performance and design satisfy requirements of a viable test suited for standardization.

DOI:

10.14359/1347


Document: 

SP163

Date: 

August 1, 1996

Author(s):

Editor: V.M. Malhotra

Publication:

Symposium Papers

Volume:

163

Abstract:

SP-163 This specialized publication offers 24 papers presented at the Third CANMET/ACI International Conference held on August 4 -9, 1996 in New Brunswick, Canada on the subject of Performance of Concrete in Marine Environments.

DOI:

10.14359/14203


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