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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.

This paper gives the results of an investigation undertaken to determine the scaling resistance of concrete incorporating fly ash, and discusses factors affecting that resistance. A total of 21 air-entrained concrete mixtures were made. Water/(cement + fly ash) ratios of 0.35, 0.45, and 0.55 were used, and reference concrete (without fly ash) and concrete incorporating 20 and 30 percent fly ash as replacement by mass for cement were made. Two aggregate types were used in the investigation. The test results show that concrete incorporating up to 30 percent fly ash performed satisfactorily under the scaling test with minor exceptions. Extended moist-curing or drying periods did not affect significantly the performance of the reference and fly ash concretes in the scaling test, at least within the periods investigated. Membrane curing appears to improve somewhat the durability of concrete under the combined action freezing and thawing and deicing salts; this is especially true for fly ash concrete.

The use of high-strength concrete with compressive strengths between 60 and 100 MPa has been studied in Finland since the early 1980s. This study stated that the frost resistance and salt-frost resistance of non-air-entrained, high-strength concrete is generally high. The best results were achieved with rapid hardening portland cement with or without silica fume. Blended slag cement and slow-hardening portland cement did not show as good resistance, and especially after ageing their resistance was decreased. The microstructure of high-strength concrete is dense. According to the porosity and optical studies, the frost damage causes first the increase of size of pores with initial diameter more than 50 to 100 nm and secondly increase in size of pores with initial diameter more than 50 to 100 nm, and secondly an increase of pore volume but not average size in capillary range.

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.