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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: 

SP163-09

Date: 

August 1, 1996

Author(s):

James R. Mackechnie and Mark G. Alexander

Publication:

Symposium Papers

Volume:

163

Abstract:

The marine environment provides a severe durability test for reinforced concrete structures with premature deterioration often being associated with steel corrosion. The rate of chloride ingress from the sea through the concrete cover is of primary importance since the depassivation of steel and subsequent corrosion are largely controlled by the chloride concentration at the reinforcement. Accurate service-life predictions are made by defining the material, assessing the severity of exposure, and monitoring the durability performance in that environment. Concrete, therefore, needs to be characterized in terms of early age properties that control the diffusion of chlorides through the cover concrete. These characterized values may then be related to long-term characteristics which determine durability for different environmental conditions. Early age tests should only be used as indicators of potential durability once suitable relationships have been established with the durability performance of concrete under marine conditions. Results from a research program are presented, in which concrete specimens were initially characterized at 28 days before being exposed to four marine environments in South Africa. The concrete was tested using a newly developed chloride conductivity test which determined the chloride resistance of concrete using an accelerated technique. Chloride contents were measured after 24 months of exposure and the diffusion coefficients were related to the initial characterization values. Results indicated that the severity of exposure has a major influence on the relative rate of chloride ingress into the concrete. The chloride conductivity test was found to be a useful indicator of chloride resistance, but the results are specific to the type of concrete being tested. Comparisons of potential durability of concretes based solely on the results of rapid chloride tests at early ages may be misleading and should be used with caution.

DOI:

10.14359/1359


Document: 

SP163-21

Date: 

August 1, 1996

Author(s):

Irina L. Kondratova, Theodore W. Bremner, and Sakir Erdogdu

Publication:

Symposium Papers

Volume:

163

Abstract:

Presents results of a study on the effect of several types of coatings and surface treatmets on the corrosion activity on specimens containing U-shaped epoxy-coated reinforcing bars cast in concrete slabs. These reinforced concrete slabs were subjected to severe exposure conditions and evaluated after four years. To obtain results in a short time period, a high water-cement ratio of 0.6 and concrete cover of only 20 mm were used. Four different types of epoxy coatings were investigated, with some bars being coated before bending and some coated after bending. The reinforcing steel had been surface treated by the supplier in seven different ways before coating, with some of the bars receiving a primer coating before application of the epoxy coating. Also, the surfaces of some bars were contaminated with salt prior to coating. Some reinforcing steel bars were intentionally damaged with the damaged area being seven 6 mm x 6 mm square spots evenly distributed over the surface of each bar. The exposure conditions were a laboratory test chamber simulating a marine environment and a natural marine environment site at Treat Island, Maine. Assessment of corrosion activity was carried out using linear polarization resistance and open circuit potential techniques. A visual survey was done as well. The results indicated that undamaged epoxy-coated reinforcing steel bars performed very well, with no corrosion occurring after four years of severe exposure conditions with low strength concrete (w/c=0.6) and only 20 mm of cover. The test results indicate that, after four years of exposure, most of the various surface treatments or types of coating were equally effective in terms of long-term corrosion protection of the reinforcing steel. However, the exception was a salt contaminated surface, in which a corrosion rate of up to 50 percent of that for uncoated reinforcing steel was observed.

DOI:

10.14359/1370


Document: 

SP163-06

Date: 

August 1, 1996

Author(s):

Theodore W. Bremner, Thomas A Holm, and Dudley R. Morgan

Publication:

Symposium Papers

Volume:

163

Abstract:

Concrete has been used for ship construction for over 100 years; many of these ships are in locations where they can be readily examined. The condition of some of these ships is discussed in this paper and the results of tests on the ships reported. Instances of improper design, detailing, and construction have been identified. Most of the ships inspected were built under wartime conditions, with limited time for design and construction. Nevertheless, they performed well and, although many are now used for purposes which the designers had not anticipated, they continue to serve a useful purpose. The results of inspection and testing of various ships are given, including compressive strength, depth of carbonation, and chloride content. Recommendations are made for improvements in design, detailing, and construction that, combined with enhanced concrete material properties, should assure that concrete ships built in the future will perform even better than those in the past.

DOI:

10.14359/1356


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