International Concrete Abstracts Portal

This research project was undertaken to determine the effect on the chloride permeability of concretes of increasing amounts of fly ash in low water-cementitious material ratio concrete as compared with comparable high-quality concretes containing combinations of portland cement, silica fume, and ground-granulated blast furnace slag. The test method utilized was the Rapid Determination of the Chloride Permeability of Concrete (AASHTO T-277). Fifteen superplasticized concrete mixtures were evaluated for compressive strength at ages of 28 and 56 days, and for chloride permeability at 56 days. The inclusion of fly ash, silica fume, and ground-granulated blast furnace slag all significantly reduced the chloride permeability of concrete as compared with concrete containing only portland cement. Increasing amounts of fly ash generally showed decreased permeability in the tests conducted.

Long-term exposure test results of reinforced concrete beams are reported. One hundred forty-nine pairs of beams with open cracks were exposed to sea air for 2 to 20 years. The main variables were thickness of concrete cover, type of cement, cement content (water/cement), and crack width. The type of cement has a great influence on the depth of chloride ion penetration. The thickness of concrete cover is the most important factor in the prevention of corrosion of the reinforcing steel. With a thin cover, the crack width has no influence on corrosion of reinforcing steel. Epoxy coating is effective in improving corrosion protection. Measurements of electrical potential on the surface of concrete give valuable information on corrosion activity of reinforcing steel.

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.

Studies of slag activation by alkalies have been carried out since 1973 at the Institute of Building and Refractory Materials, Academy of Mining and Metallurgy, in Cracow, Poland. Laboratory tests were followed by production of the activated slag on a large scale. It appeared that the new cementing material composed of the granulated blast furnace slag mixed with an alkaline activator showed high strength and corrosion resistance. The present work deals with the problem of reinforcing steel corrosion in the alkali-activated slag mortar exposed to the attack of concentrated chloride solution. The observations of reinforcement in ordinary portland cement (OPC) mortars, OPC plus silica fume (SF) mortar, or OPC plus limestone flour mortar were carried out simultaneously. The resistance of alkali-activated slag mortar to the attack of a solution of high Cl- concentration was proved previously. The effective, protective action of the alkali-activated slag mortar was confirmed by electrochemical measurements and weight loss determination after 365 days' exposure to a chloride solution. A similar effect was found in the case of silica fume or limestone flour addition to the OPC mortar, but the corrosion of the reinforcement was clearly visible, as shown by corrosion pits in the reference standard OPC mortar samples.