International Concrete Abstracts Portal

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.

The service conditions for concrete construction in the coastal areas of the Arabian Gulf are considered to be those of one of the most aggressive environments in the world. Deterioration of hardened cement paste due to salt attack is one of the leading reasons for poor performance of concrete structures in this region. Calcium, magnesium, sodium salts of sulfates, chlorides, and carbonates extensively contaminate the ground, groundwater, and the aggregates. In such an environment, structures built with concrete which can be rated as good in temperate climatic conditions can hardly last for a decade or two. Field and laboratory studies are in progress at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, to formulate preventive measures. As a part of this endeavor, the performance of in-service concrete structures is monitored. This paper details the investigations carried out to evaluate the performance of these concrete structures. Data developed in this investigation show that the aggressive service environment is the major cause for concrete deterioration, as such appropriate mix design techniques and construction practices are to be adopted for the production of a very dense and impermeable concrete.

"A collection of 24 papers form an international panel of experts on topics ranging from fundamental laboratory studies of concrete durability to case histories of concrete rehabilitation. The volume is arranged in three parts. Part 1: covers the more fundamental aspects and laboratory investigations. Topics include freeze-thaw resistance, durability of high strength concrete, corrosion of reinforcing steel, air voids in concrete, and effects of high range water-reducers. Part 2: covers field studies where concrete is exposed to natural conditions. Topics include carbonation of concrete, deicer scaling resistance of roller compacted concrete pavements, performance in marine environments, and microbiologically-induced deterioration. Part 3: covers case histories of the performance and rehabilitation of concrete structures in severe service environments. The types of structures include cooling tower shells, precast prestressed concrete conveyor bridge, heavy duty dock, elevated road way, and a masonry structure under corrosive exposure." Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP122