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Because of the shortage of aggregate, the reinforced concrete -containing sea sand and/or sea water can probably be used for marine structures. These marine structures may experience corrosion problems due to salt attack that can result in early deterioration. Therefore, such structures should be protected against corrosion damage induced by chloride ion to extend the service life. This study was focused on a basic counter-plan against concrete corrosion related to marine infrastructures, especially the evaluation of effects of various corrosion inhibitors with different cover thicknesses. Several electrochemical/corrosion test techniques, i.e. half -cell potential, linear & cyclic polarization behaviors & autopsy inspection, were included. Based on this long-term(7 years) study, it was concluded that a chloride ion accelerated reinforcement corrosion seriously, however, a increase of cover thickness and adoption of some inhibitors could provide positive effects against the chloride-induced corrosion. In addition, it was recognized that the electrochemical corrosion tests generally agreed with those of visual autopsy examinations in these long-term experiments.

One of ways to improve the durability of the reinforced concretete structures is sealing with various coating materials on the surface of the concrete that represses the penetration of moisture, chloride ions and carbon dioxide gases which may cause the reduction of durability. Up to now epoxy and urethane-based coating materials are widely used for coating. However, these amterials have the characteristics of poor crack bridging, large thermal expansion and vulnerable color by ultraviolet rays. Also their coating effect depends on application methods that it is dubious of maintaing long-term durability so the development of new alternative coating materials is in demand.Test were performed on an aluminum oxide-isocyanate-based material for coating in order to improve the weather resistance, adhexiveness to concrete surface, resistance of chloride penetration and carbonation by forming the aluminum oxide coating on the surface. Aluminum oxide-isocyanate-baced coating material is compared with other coating materials, and shows higher color retention against ultraviolet rays and resistance of chloride penetration and carbonation and protection of reinforcing steel against corrosion.

This study focused on the investigation of durability characteristics of very early strength concretes incorporating polypropylene fibers and application feasibility of these into the highway pavements. A series of laboratory tests were performed to assess the strength development and scaling resistance. The test of surface scaling resistance was performed according to ASTM C 672 exposed to frost in the presence of de-icing chemicals. The experimental variables included cement types, fiber contents and concrete mixtures. The compressive strength of very early strength concrete at 3 hours was measured as 22 MPa, which corresponded to the strength at 7 days or 28 days of ordinary portland cement concrete. This may enable the repaired concrete pavement to be opened to traffic 3 hours after concrete placement. There was little effect of polypropylene fiber reinforcement on compressive strength. The fiber reinforced concretes exhibited noticeably higher flexural strength than the reference concrete at all ages. The plain concrete slabs were given a visual rating of 3 or 4, and according to ASTM Standard C 672. This corresponds to moderate to severe scaling. The fibrous concrete performed better than the plain concrete slab which was given a visual rating of 0 or 1. This corresponds to no scaling or very light scaling. As the amount of fiber reinforcement increased the surface scaling resistance increased. The scaling resistance of very early strength concrete was comparable to that of ordinary concrete from the visual rating. Thus, the developed very early strength concrete may be satisfactory for use in repair works for pavements.

This paper presents results of an investigation into the tension stiffening effects of steel fiber reinforced concrete members in direct tension. Tension stiffening effects and losses of strain energy were analyzed from the load-defl .ection curves with the main experimental variables such as concrete strength, steel fiber content, and concrete cover depth. Tension stiffening effect of RC members increases linearly until first crack, decreases inversely with number of cracks, and then decrease rapidly when splitting cracks occur. The higher the content of steel fiber the higher tension the stiffening due to its bridging effect after cracking inside of member. Therefore, it is necessary to consider the tension stiffening effects with a nonlinear analysis. From the comparison between the results of experiment and existing models, it is found that the existing models could not incorporate the effects of concrete strength, cover depth and fiber reinforcement. Thus, it is required to develope a new model which could include these factors. This study proposes a new model which is defined by tension stiffening factor by considering concrete strength. and the ratio of cover depth with al and a2, respectively. The tension stiffening model for steel fiber reinforced concrete is, also, proposed as a shape of u-i-bilinear, considering concrete cover. depth. The analysis using the proposed model shows good agreement with that of experiment on direct tension and flexural members at all concrete strength levels.

This paper deals with the effect of different curing methods on the strength and durability of high performance concrete exposed to medium temperature. Strength was measured in terms of compressive strength while durability was indicated in terms of initial surface absorption of surface layer concrete or covercrete. High performance concretes were prepared with the water-binder ratio of 0.35. Cylindrical specimens were cast for the test of compressive strength and they were cured under three types of curing conditions such as standard (2O°C) and moderately elevated curing temperatures (35°C & 5O°C). Initially the three groups of specimens were cured for 3, 7 and 14 days respectively at 20°C. Later, the curing continued at 35°C and 50°C up to 9 1 days. The aim was to determine the most efficient curing method, period and temperature to get higher compressive strength. Test results indicated that the performance of water curing as well as wrapped curing was consistently better. Specimens at the age of 7 and 14 days of initial water curing provided good results. Silica fume (SF) concrete produced the highest compressive strength at the age of 91 days under these curing conditions. This finding suggests that high performance concrete should be cured by water and the minimum curing period ought to be at least 7 days. Test results also showed that higher compressive strength develops in the temperature range of 20°C to 35°C. Besides, cubical specimens were also prepared, cured and tested at the age of 28 days to determine the initial surface absorption. Test results revealed that water-cured specimens of silica fume concrete had the lowest initial surface absorption. Hence, the performance of concrete containing silica fume was consistently better with water curing.