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Concrete will be immune to the effects of freezing and thawing if: 1) it is not in an environment where freezing and thawing take place, i.e., where freezable water may be present in the concrete; 2) there are no pores in the concrete large enough to hold freezable water when freezing takes place (i.e., no capillary cavities); 3) during freezing of freezable water, the pores containing freezable water are never more than 91 percent filled, i.e., not critically saturated; 4) during freezing of freezable water, the pores containing freezable water are more than 91 percent full and the paste has an air-void system with an air bubble located not more than 0.2 mm (0.008 in.) from anywhere (L ó 0.2 mm), sound aggregate, and moderate maturity. Sound aggregate is aggregate that does not contain significant amounts of accessible capillary pore space that is likely to be critically saturated when freezing occurs. The way to establish that such is the case is to subject properly air-entrained, properly mature concrete, made with the aggregate in question, to an appropriate laboratory freeze-thaw test, such as ASTM C 666, Procedure A. Moderate maturity means that the original mixing water-filled space has been reduced by cement hydration so that the remaining capillary porosity that can hold freezable water is a small enough fractional volume of the paste so that the expansion of the water on freezing can be accommodated by the air-void system.

Chloride-induced corrosion is a problem common to steel reinforced concrete exposed to chloride ions. A severe case is the use of reinforced concrete in seawater. The high-chloride concentration in salt water, the geometry of concrete piles, and the moisture differential between concrete above and below the water line are all factors that complicate the problem. The corrosion resistance of steel reinforced concrete is a function of the concrete cover of the steel, concrete permeability, surface chloride concentration, and ambient temperature. In this paper, the authors present diffusion curves for chloride ingress into concrete piles. The diffusion coefficients are based on extensive laboratory and field studies. They also discuss the usefulness of this model, based on Fick's law of diffusion. By estimating the chloride ion concentration at the steel reinforcement after a given amount of time, the lifetime of the structure can be predicted. In addition to concrete quality, concrete admixtures affect the corrosion of steel in concrete. Two concrete admixtures are discussed--calcium nitrite and microsilica. As demonstrated in other publications, both of these additives delay the onset of corrosion. It has also been shown that calcium nitrite affects the rate of corrosion upon initiation. The appropriate dosage of each admixture can be determined using the chloride diffusion curves. Examples are described in the paper.

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.

During the 12 years since construction of the bridge, cracking and spalling have developed in the concrete superstructure, predominantly on the underside of the bridge deck in the area of expansion and construction joints. The evidence indicates the deterioration was initiated by leakage of expansion and construction joints, and that poor performance should be attributed to design and construction practices whose effectiveness falls short of the environmental demands. Moisture, deicing salts, and debris that spill through the joints had deteriorated concrete at an accelerated rate and penetrated to the reinforcing steel. The concrete breakdown caused by corrosion of reinforcing steel, as well as from freezing and thawing action, and the expansion resulting from alkali-aggregate reaction damaged the bearing areas of cantilever spans and adjacent parts of suspended slabs, and was a cause for concern for the bridge's structural integrity. The paper addresses the main factors involved in the initiation phase of the corrosion mechanism: carbonation, chloride diffusion, and water penetration into concrete. The selected materials and methods are discussed, as well as importance of compatibility of materials for durable repairs. The paper outlines a need to integrate knowledge and understanding of the mechanism of deterioration with concrete design, materials, and methods of repairs.