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The underwater placement of small concrete volumes for repair operations necessitates that the fresh concrete be highly resistant to water erosion and segregation, as well as self-compacting and self-leveling. The hardened concrete must develop high wear resistance and excellent adhesion to underlying surfaces and reinforcing steel. Four potential repair concretes and one conventional tremie mixture were cast underwater in small and relatively shallow depressions using tremie pipes. Research findings indicate that an anti-washout admixture should be used to minimize the risks of water dilution and segregation and to enhance the spreadability and leveling of underwater-cast concrete. Proven concrete mixtures recommended in this research can produce relatively flat repair surfaces with in-place compressive strength in excess of 8000 psi (55.2 MPa) and relative density close to 100 percent of similar values for concrete cast and consolidated above water. Bond strength close to 400 psi (2.8 MPa) can develop between underwater-cast concrete and neighboring concrete repair surfaces.

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.

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.

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.

Reinforced concrete masonry structures can be effectively used in corrosive environments provided that the design is based upon a rational assessment of the exposure condition. An investigation of wall that had 6000 g of muriatic acid and 11,000 g of sodium hypochlorite stored along its exterior face indicated accelerated deterioration of the wall due to inadequate design and no protection afforded to the wall when the building's usage was changed from general warehouse to chemical storage. Poor construction practices also contributed to the distressed condition. The investigation utilized electrical, visual, and chemical means of assessing the structures's condition. The primary tool was a copper-copper sulfate (Cu-CuSO4) half cell conforming to ASTM C 876. The resulting equipotential contour map provided valuable information regarding the wall's corrosion potential. Visual observations of exposed, corroded reinforcing steel confirmed the half-cell readings. Chemical analysis of block, mortar, and grout samples extracted from the wall revealed high but inconsistent water-soluble chloride ion contents.