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Recently, a major North American City replaced a large collector sewer which was deteriorated due to corrosion of the reinforcement. This replacement was well in advance of the life cycle estimate of the pipe. The deterioration was caused predominately by the presence of chloride ion in the soils. As a part of this reconstruction, it was decided to design the concrete to resist the intrusion of chloride ion. Several proprietary admixtures were considered, as well as the use of silica fume, to produce this pipe. The contract was awarded to a conventional dry process pipe plant. Some modification of the mixture proportions was required. An interground silica fume cement was used to reduce the handling difficulties associated with silica fume. A preconstruction trial batch was evaluated for physical properties, including rapid chloride permeability and chloride ion diffusivity. The cost effectiveness of the modified cement and the relatively simple adjustments to the casting process resulted in a very minimal increase in the total construction cost. Design calculations and quality control methods are discussed.

Bamboo fiber-reinforced polymer-modified pastes using the bamboo fibers treated with humic acid solutions with different humic acid concentrations and a styrene-butadiene rubber latex are prepared with various fiber contents and polymer-cement ratios, and tested for flexural behavior and compressive strength. The flexural deformation, flexural strength, flexural toughness and compressive strength of the humic acid-treated bamboo fiber-reinforced polymer-modified pastes are discussed. The results show that the humic acid treatments of the bamboo fibers cause marked improvements in the flexur al behavior after a maximum load, flexural strength- and toughness of the bamboo fiber-reinforced polymer-modified pastes. Flexural

Severe deterioration caused by corroding reinforcing steel in concrete structures is a major concern in the maintenance of safe and reliable infrastructure. The corrosion behavior of steel fibers and steel bars under two different aggressive conditions of modified ferroxyl gel reagent and wet-dry salt spray are described. In general, the results in the aggressive gel environment indicate that when steel fibers and steel bars were contacting each other, the initiation of corrosion in the steel fibers became considerable. When the steel fibers were electrically connected to the steel bars, the steel fibers tend to become the anode while the steel bars tend to become the cathode. The corrosion initiation, its propagation and the growth of the corrosion zones occurred in the steel fibers. The steel bars, set in the cathode zone, were protected by the surrounding steel fibers which formed a corrosion protective shield. This galvanic protection behavior by steel fibers was clearly observed in ferroxyl transparent gel. To generalize the galvanic protection behavior of steel fibers in the gel environment, the behavior of reinforced concrete specimens under an accelerated aggressive environment with both a no-fiber and fibrous concrete matrix were investigated. For this purpose, galvanized steel fibers were used. Corrosion phenomenon in the galvanized steel fibers contacting steel bars showed a sacrificial role of fibers in protecting the steel bars. No corrosion of the embedded steel bars occurred in the steel fiber-reinforced concrete matrix, while corroded steel bars occurred in the no-fiber reinforced concrete beam, thus confirming the merit of galvanized steel fibrous matrix as a protection shield to inhibit corrosion of reinforced concrete members.

General concepts governing the interaction of fibers with paste, mortar and concrete matrices are presented for the freshly mixed and hardened states in the context of the need to reconcile these often conflicting interactions to produce useful composites. Problems and limitations arising from the addition of fibers are discussed in terms of fiber amount, material type, form (monofilament, multifilament, bundled, etc.), geometry and compatibility with the manufacturing process fi-om mixing to final consolidation in the freshly mixed state. Fiber-matrix compatibility considerations are also identified for the hardened state with respect to their importance for short-term and particularly sustained long-term property enhancement. Long-term performance is highlighted for circumstances where chemical incompatibility of fibers and matrix may lead to gradual deterioration in initially very satisfactory early-age properties.

This paper presents a critical evaluation of the use of fly ash and ground granulated blast-furnace slag in concrete. In order to develop a rational concrete mixture incorporating these siliceous materials, their inherent characteristics are assessed, including their limitations and weaknesses. Based on the mixture proportioning methodology advocated, it is shown that fly ash and slag concretes, having the same three-day cube strength as concrete without them, can be produced. Engineering implications of using these materials such as increased bleeding and times of setting, reduced heat of hydration, low-early strength, and slow rate of gain of strength are addressed, and the need and role of a minimum period of moist curing to mobilize the chemically-bound qualities of these materials are fully emphasized. It is shown that both high-early strength and high-strength concrete can be achieved with fly ash and slag. Even with all their limitations, the durability properties of concretes with fly ash and slag are superior to those of concrete made with portland cement alone. It is shown further that extremely fine siliceous materials are only of limited use in concrete, but that a moderate increase in fineness, about thrice that of portland cement, can not only preserve and fully use the benefits of fineness on a variety of engineering properties such as bleeding, time of setting and heat evolution, but also lead to excellent chemical resistance and durability with high strength at early and later ages. It is shown that a slag fineness of about 1200 m2/kg can produce concretes of high strength and exceptional durability.