International Concrete Abstracts Portal

The phenomenon of steel corrosion and concrete crack patterns under different water-to-cement ratios and cover depths of concrete was investigated. The steel corrosion of single reinforced concrete beam with different admixtures under repeated loading was also studied. It is possible to predict the crack patterns and mechanical behavior of concrete when steel corrosion is induced. The addition of inhibitors reduced the corrosion rate. If concrete undergoes repeated loadings, the resulting cracks will allow harmful elements in tidal zones to penetrate into the concrete. This will accelerate the corrosion rate, especially at high loading conditions.

Steel barges are often used by British Columbia's forest industry to carry wood chips. Generally, these chips have been offloaded at pulp mills by overhead gantry cranes using grab buckets. In time, this has severely damaged and dented the decks. The industry has recently realized considerable savings by changing the method of offloading so that the chips are placed on conveyors by front-end loaders. In 1989, a barge operator decided to upgrade his existing barge fleet to utilize the new method. This meant that new, smoother decks had to be constructed. The project was tendered with two alternatives: one using a new steel deck and the other a concrete topping. During the tender period, an alternate type of concrete deck was proposed that proved to be substantially cheaper. The method consisted of welding steel studs to the existing deck, placing reinforcement, and pouring a high-strength (55 Mpa) steel fiber reinforced concrete. This is expected to provide improved durability and abrasion resistance.

The concrete bridge structural members, called "skew members" (SM), which are positioned from 1.5 m above the sea level to about 20 m down in the sea, and are among the most important elements in bridge construction, were investigated for maintenance purposes after 11 years of service. The underwater arch foundation concrete was also tested. The compressive strength, determined as the average value of 10 concrete cores drilled out from each of two skew members--SM-St. Marko and SM-Mainland--was 62.3 Mpa and 57.4 MPa, respectively. Chlorides had penetrated through the high-alkaline composite by over 20 mm in the splash zone concrete and by over 45 mm in the fully submerged concrete, where {Cl-}-penetration was probably enhanced by hydrostatic pressure. The lack of corrosion of the steel in the concrete, even in the presence of high chloride concentration, could be explained by the absence of oxygen. The gas permeability coefficients Kg determined on the concrete core slices varied in the inner concrete layers of SM-St. Marko from 5.58 to 20.10 x 10-13 cmý and from 0.55 to 2.84 x 10-13 cmý in the concrete at SM-Mainland.

The results of investigation into the erosion-abrasion resistance according to CRD-C 63-80 test method and abrasion resistance according to Bohme test method of steel fiber reinforced concrete specimens are discussed in the paper. Nine mix proportions were used. The water-cement ratios (w/c) were varied from 0.30 to 0.65. The volumetric percentage of hooked steel fibers were varied from 0.25 to 2.0 volume percent at the w/c of 0.30 and at the others the quantity of fibers was constant. In addition, mixes without fibers were made at each w/c. The results show that adding steel fibers to the concrete improves the resistances as measured by both test methods. The erosion-abrasion resistance is improved by an increase of compressive strength and an increase in fiber content. It can be correlated to improvements of abrasion resistance from the Bohme test method but only at constant w/c and different content of fibers.

As part of an extensive investigation of the durability of roller-compacted concrete pavements, 28 different concrete loads were cast during the summer of 1988. Four types of cement, two different sands (one natural and one manufactured) and two water-cement ratios (0.27 and 0.35) were used to prepare these mixtures, An air-entraining agent was added to half of them. One-third of the test section was moist cured for 7 days, a white curing compound was sprayed on another third and the remaining portion received no special treatment. Samples representative of all mixtures and all curing conditions were taken from the pavement after 28 days. The air-void characteristics of all concretes were determined in accordance with ASTM C 457 and the salt scaling resistance of selected combinations (of the type of mixture and the type of curing) was evaluated using ASTM C 672 on both rolled and sawn surfaces. Results indicate that it is extremely difficult to entrain air in this type of concrete even if fairly large dosages of air-entraining agent are used and mixing time is increased. Despite the lack of spherical air bubbles, good scaling resistances were obtained with the silica fume and the fly ash concretes prepared with the natural sand and cured with a membrane.