International Concrete Abstracts Portal

SP-126 In August 1991 the Canada Centre for Mineral and Energy Technology (CANMET) in association with the American Concrete Institute; the Institute for Research in Construction/ National Research Council, Ottawa; and the Eastern Ontario and Quebec Chapter of American Concrete Institute sponsored the 2nd CANMET/ACI International Conference on Durability of Concrete. More than 100 papers from 20 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute. Seventy were accepted for publication. The accepted papers are published in two volumes.

At the University of Salford, UK., a research team led by the author has developed a form of composite concrete construction in which fiber reinforced cement (FRC) units are employed as surface reinforcement. As part of an extensive program of investigation, full-sized rectangular and T-section beams, with and without FRC units as surface reinforcement, have been tested under fatigue in up to three million repetitions of loading. Companion beams having surface reinforcement have also been tested under short-term static loading. After a brief review of the concept of FRC composite concrete construction, the paper describes and details the test program. The behavior of the beams is examined regarding ultimate load, deflection, and cracking--the criteria of safety and serviceability. The performance under fatigue loading of beams with surface reinforcement is compared with that of companion beams without surface reinforcement but subjected to similar fatigue loading, and with surface reinforcement but tested under short-term static loading. It is concluded that the use of FRC as surface reinforcement is effective in controlling deflection and cracking well within the permissible limits without affecting ultimate load-carrying capacity for the beams subjected to fatigue loading.

Corrosion of steel reinforcement within concrete structural elements is a major problem in both research and practice. Laboratory studies have been conducted on fundamental mechanisms of corrosion within concrete in the presence of high chloride and others under conditions of reduced alkalinity. However, little has been published on the interactive effects of these two conditions and the ways in which corrosion rates of steel in concrete are thereby influenced. These two conditions occur concurrently under many practical environmental exposures. This paper presents data on methodology used to determine corrosion rates of steel in concrete. Information on corrosion activities in both carbonated and high-chloride environments is presented with reference to mechanisms involved in breakdown of steel passivation. Interactive effects of the two conditions are examined for a range of concrete types and grades. The data suggest that for normal reinforced concrete structural elements, the interactive effects of carbonation and chloride ion ingress lead to much more rapid corrosion than where the two phenomena occur independently. The interactive effects of carbonation and chloride ions as they influence concretes under service conditions are discussed. In particular, the reduction of carbonation rate in the presence of high-chloride ion concentrations is noted.

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.

Exposure tests of silica fume concrete with embedded steel bars were carried out in marine environments such as the Inland Sea of Japan, the Pacific Ocean, and the Sea of Japan, in the Kansai district. The effects of water-to-cementitious material ratio, silica fume content, chloride ion content in mixing water, and concrete cover on the chloride corrosion of reinforcing steel were studied by measuring half-cell potential, electric resistance, pH value, depth of carbonation, pore volume, and chloride ion content. When tap water was used as the mixing water and concrete cover was 10 mm, the longitudinal crack due to chloride corrosion was observed in silica fume concrete specimens in about 3 years. Chloride ion penetration into silica fume concrete was much lower in comparison with concrete without silica fume, however, chloride at the region 2 cm from the concrete surface was high enough for embedded steel to corrode. When concrete cover was 25 mm, no longitudinal crack was observed in silica fume concrete specimens until about 3 years. It is necessary to keep sufficient concrete cover, even in silica fume concrete. Chloride corrosion in concrete was accelerated by using silica fume when saline solution was used as the mixing water.