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International Concrete Abstracts Portal

Showing 1-5 of 25 Abstracts search results

Document: 

SP122-12

Date: 

June 1, 1990

Author(s):

Joseph F. Lamond and M. K. Lee

Publication:

Symposium Papers

Volume:

122

Abstract:

The ultimate test of concrete durability to natural weathering is how it performs in the environment in which it is to serve. Laboratory testing yields valuable indications of service life and durability. However, the potential disrupting influences in nature are so numerous and variable that actual field exposures are highly desirable to assess the durability of concrete exposed to natural weathering The U.S. Army Corps of Engineers, through the Waterways Experiment Station, Structures Laboratory, maintains a natural weathering exposure station. It is located on Treat Island in Cobscook Bay near Eastport, Maine. This station has been in use since 1936 and is an ideal location for exposure tests, providing twice-daily tide reversals and severe winters. The average tidal range is about 18 ft (5.4 m) with a maximum of 28 ft (8.5 m) and a minimum of 13 ft (4 m). In the winter, the combined effect of air and water temperatures creates a condition at meantide where specimens are repeatedly thawed and frozen. There have been 23 completed investigations and many of these have been previously reported. There are currently 40 active investigations. Four of these investigations are briefly discussed in this paper.

DOI:

10.14359/3739


Document: 

SP122-07

Date: 

June 1, 1990

Author(s):

R. Pleau, M. Pigion, R. M. Faure, and T. Sedran

Publication:

Symposium Papers

Volume:

122

Abstract:

Samples from nine air-entrained concrete mixes made with and without a superplasticizer were examined under a scanning electron microscope to determine the size distribution of the voids in the 0.5 to 50 æm range. Concurrently, samples of the same mixes were examined under a binocular microscope to determine the size distribution of the voids in the 10 to 1000 æm range. The voids observed under the electron microscope were separated into two categories: air voids (spherical in shape or nearly so) and large capillary pores (irregularly shaped). The results show that, in mixes, the amount of capillary pores with diameters ranging from 0.5 to 50 æm is relatively important (the number of these voids generally represents approximately half the total number of entrained air voids). The role of these pores in the frost resistance of concrete is believed to be strongly dependent on their degree of saturation at the time of freezing. The number of air voids smaller than 10 æm in diameter, however, was found to represent less than 10 percent of the total number of entrained air voids. These small air voids are thus expected to have little influence on frost durability. The results also indicate that the distribution of the ir-void diameters is influenced by the nature of the air-entraining agent but not by the use of a superplasticizer. The distribution of air-void diameters was found to be approximately the same for all mixes, irrespective of the value of the spacing factor.

DOI:

10.14359/2478


Document: 

SP122-18

Date: 

June 1, 1990

Author(s):

S. Gebler, P. Nussbaum, W. Dziedzic, J. Glikin, A. Litvin, W. Bilenki, Jr., and J. Stefanik

Publication:

Symposium Papers

Volume:

122

Abstract:

Two concrete natural draft cooling towers exhibited honeycombing and freeze-thaw damage. This paper presents results of inspections and laboratory and field tests used to develop cooling tower rehabilitation repair strategies. Different repair materials were evaluated and tested in the laboratory. The repair strategy selected involved measures to dry out the marginally air-entrained saturated tower shell concrete to minimize future freeze-thaw damage and then replace concrete exhibiting honeycombing and condensate leakage with dry-mix shotcrete (gunite). The interior concrete shell was then coated with an impermeable membrane. Six materials for coating the interior shell concrete and two types of shotcrete processes were evaluated.

DOI:

10.14359/2540


Document: 

SP122-11

Date: 

June 1, 1990

Author(s):

N. M. Vanderhorst and D. J. Janssen

Publication:

Symposium Papers

Volume:

122

Abstract:

Some properly proportioned portland cement-concrete mixtures occasionally show distress when exposed to freezing and thawing, while some mixtures that do not contain entrained air may appear to perform adequately despite exposure to freezing and thawing. Obviously, there is a difference in the severity of freezing-and-thawing environments. The factors affecting the severity of freezing-and-thawing environments include the temperature and moisture conditions and salt exposure. These factors are examined, along with materials properties that relate to these factors. Comparisons are made between laboratory and field moisture and thermal conditions, and the damage mechanisms most appropriate for each set of conditions are discussed. Conclusions are drawn concerning the definition of a truly severe freezing-and-thawing environment in the field, and a qualitative relationship between the severity of freezing-and-thawing environments and cooling rates is proposed.

DOI:

10.14359/2497


Document: 

SP122-17

Date: 

June 1, 1990

Author(s):

Charles F. Kulpa and Cassandra J. Baker

Publication:

Symposium Papers

Volume:

122

Abstract:

When anaerobic conditions occur in a sewer pipe in the presence of sulfate, sulfur-reducing bacteria will produce hydrogen sulfide. As hydrogen sulfide is released, various populations of sulfur-oxidizing bacteria (thiobacilli), will proliferate. The proliferation of these organisms results in a decrease in pH due to the production of sulfuric acid. Different thiobacilli will be present depending on the pH of the environment. Samples from regions of deteriorated and nondeteriorated concrete pipe were taken to determine the presence of microorganisms that could cause microbially induced concrete deterioration. The results presented show that the degree of concrete deterioration can be correlated with the number and type of thiobacilli present. Extensive deterioration was observed at the crown of reinforced and asbestos concrete pipe, where the most acidophilic group of thiobacilli were present in elevated numbers. Areas of lesser deterioration were somewhat acidic, with a combination of different sulfur-oxidizing thiobacilli present. Areas that did not appear to be deteriorated were populated with the least acidophilic group of sulfur-oxidizing thiobacilli. The presence of microbially induced deterioration of concrete and the stage of deterioration can be determined by utilizing selective media to culture the various groups of sulfur-oxidizing bacteria associated with concrete decay.

DOI:

10.14359/2534


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