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The underwater placement of small concrete volumes for repair operations necessitates that the fresh concrete be highly resistant to water erosion and segregation, as well as self-compacting and self-leveling. The hardened concrete must develop high wear resistance and excellent adhesion to underlying surfaces and reinforcing steel. Four potential repair concretes and one conventional tremie mixture were cast underwater in small and relatively shallow depressions using tremie pipes. Research findings indicate that an anti-washout admixture should be used to minimize the risks of water dilution and segregation and to enhance the spreadability and leveling of underwater-cast concrete. Proven concrete mixtures recommended in this research can produce relatively flat repair surfaces with in-place compressive strength in excess of 8000 psi (55.2 MPa) and relative density close to 100 percent of similar values for concrete cast and consolidated above water. Bond strength close to 400 psi (2.8 MPa) can develop between underwater-cast concrete and neighboring concrete repair surfaces.

Some properly proportioned portland cement-concrete mixtures occasionally show distress when exposed to freezing and thawing, while some mixtures that do not contain entrained air may appear to perform adequately despite exposure to freezing and thawing. Obviously, there is a difference in the severity of freezing-and-thawing environments. The factors affecting the severity of freezing-and-thawing environments include the temperature and moisture conditions and salt exposure. These factors are examined, along with materials properties that relate to these factors. Comparisons are made between laboratory and field moisture and thermal conditions, and the damage mechanisms most appropriate for each set of conditions are discussed. Conclusions are drawn concerning the definition of a truly severe freezing-and-thawing environment in the field, and a qualitative relationship between the severity of freezing-and-thawing environments and cooling rates is proposed.

Twenty roller-compacted concrete loads were cast at St. Constant near Montreal during the fall of 1987. Three types of cement (Canadian Types 10, 30, and 10SF), four different aggregate gradings, and three water-cement ratios (0:27, 0:33, and 0:35) were used to prepare the various mixes. Most of these mixes contained an air-entraining admixture. Approximately one-third of each concrete surface was moist-cured for 7 days, another third was covered with a white curing compound, and the remaining portion was not cured at all. Samples representative of all mixes and all curing conditions were taken from the pavement after 28 days and then tested for freeze-thaw durability (ASTM C 666) and deicer salt scaling resistance (ASTM C 672). The characteristics of the air-void system of all concretes were determined in accordance with ASTM C 457. With no exception, all samples withstood, without any significant deterioration, 300 cycles of freezing and thawing in water. However, the loss of mass after 50 cycles in the presence of a deicer salt solution ranged between 2 and 18 kg/mý (i.e., higher than the usual 1 kg/mý limit in all cases), even if most of the spacing factor values were below 250 æm. The best results (a weight loss of approximately 2 kg/mý after 50 cycles) were obtained for a mix containing Type 10 cement and no air-entraining admixture. In addition, this mix was not cured at all. Overwoking of the concrete surface during compaction is considered to be one of the possible explanations for the discrepancy between the results of the C 666 and the C 672 tests. It is also possible that the relationship between spacing factor and freeze-thaw durability does not apply to such concretes with a high permeability, numerous irregularly shaped compaction air voids, and large porous zones in the paste. This series of tests is the first phase of a 3-year research project on roller-compacted concrete pavements at Laval University, in collaboration with Canada Cement Lafarge. In the second and third years of this project, various ways to improve the scaling resistance (mostly by micro structural changes) will be studied.

Paper reports the results of part of a program to determine the extent and severity of carbonation in buildings in Canada. About 350 core samples drilled from 28 buildings in Toronto were tested by two procedures to determine the depth of carbonation. Tests were made on cast-in-place balconies and vertical components and on precast cladding. A proportion of the total sample was found to be susceptible to carbonation damage within a reasonable service life.

An investigation was conducted to assess the structural integrity of a 17-year-old precast prestressed concrete conveyor bridge used to transport sodium chloride rock salt from a storage building to an outside stockpile area. The stockpile, depending on storage requirements, quite often buried most of the structure and/or subjected it to sodium chloride dust. The investigation revealed that the structure had performed remarkably well, considering the small concrete cover used to protect the reinforcing elements and the inadequate consideration of structural cracking induced by unanticipated loading from stockpiled salt. The concrete strength of the single tee members was estimated to be 7000 psi (48 MPa), with cover to the stirrups varying from virtually 0 to 1 1/2 in. (0 to 38 mm) and cover to the prestressing strands varying from 3/4 to 2 in. (19 to 51 mm). It was observed that aggressive prestressing strand corrosion causing pitting and some brittle wire failures occurred locally at flexural crack locations in single tee column members with little corrosion activity immediately adjacent to the cracks, even after 17 years of aggressive chloride exposure. This observation seems to conflict with the prevailing theory of the role of cracking on corrosion--that cracks perpendicular to steel reinforcement should result in limited early localized corrosion but, with time, chloride ions penetrate even uncracked concrete and initiate widespread corrosion.