International Concrete Abstracts Portal

A natural amorphous silica with a purity of approximately 90% is mined from an extensive geothermal deposit near Rotorua, New Zealand. After refining and processing to remove impurities, the ‘Microsilica 600TM’ has properties which comply with Australian Standard AS 3582 Part 3 ‘Silica Fume’ as a supplementary cementitious material for use with portland cement. The performance characteristics of concrete incorporating the ‘Microsilica 600’ were evaluated at two cement levels of 320 and 400 kg/m 3 and two silica addition levels of 7 and 10%. Properties evaluated were compressive strength, tensile strength, concrete shrinkage, sulfate resistance, resistance against chemical attack, abrasion resistance, and chloride permeability. Performance improvement compared favorably with published data on concretes incorporating processed ‘conventional’ silica fume.

Rice husk ash (RHA) is a very reactive pozzolanic material. It has been succesfully used as a mineral admixture in concrete. Rice husks are readily and in large quantities available in Vietnam. Hence, it would be of economic interest to study the use of RHA for the production of high-strength and durable concretes based on indigenous raw materials. This con-cept should also encompass the aggregates, with coarse-grained crushed rock (granite) and very fine river sand as natural candidates. The particle size distribution of this sand violates the building code, however. Since blending with coarse (imported) sand would be too expensive, this study focused on gap-graded mixtures. For the binder an ASTM Type I portland cement was employed, being the only quality produced in the region in Vietnam. RHA with a significant carbon content was obtained after burning rice husks at temperatures below 75OOC. The ash was thereupon finely ground in conjunc-tion with a naphtalene-based superplasticizer. The application of the RHA in conjunction with this superplasticizer in the gap-graded concretes with very fine sand made it possible to produce high consistency and cohesive mixtures with a relatively low sand content. 28-days compressive strengths values of 70-90 MPa were obtained for mixtures with slumps of 140-225 mm and water to binder ratios of 0.40-0.33. For stiff mixtures, with water to binder ratios of 0.35-0.27, the 28-days compressive strength values were in the range of 60-100 MPa.

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.