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The service conditions for concrete construction in the coastal areas of the Arabian Gulf are considered to be those of one of the most aggressive environments in the world. Deterioration of hardened cement paste due to salt attack is one of the leading reasons for poor performance of concrete structures in this region. Calcium, magnesium, sodium salts of sulfates, chlorides, and carbonates extensively contaminate the ground, groundwater, and the aggregates. In such an environment, structures built with concrete which can be rated as good in temperate climatic conditions can hardly last for a decade or two. Field and laboratory studies are in progress at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, to formulate preventive measures. As a part of this endeavor, the performance of in-service concrete structures is monitored. This paper details the investigations carried out to evaluate the performance of these concrete structures. Data developed in this investigation show that the aggressive service environment is the major cause for concrete deterioration, as such appropriate mix design techniques and construction practices are to be adopted for the production of a very dense and impermeable concrete.

Concrete will be immune to the effects of freezing and thawing if: 1) it is not in an environment where freezing and thawing take place, i.e., where freezable water may be present in the concrete; 2) there are no pores in the concrete large enough to hold freezable water when freezing takes place (i.e., no capillary cavities); 3) during freezing of freezable water, the pores containing freezable water are never more than 91 percent filled, i.e., not critically saturated; 4) during freezing of freezable water, the pores containing freezable water are more than 91 percent full and the paste has an air-void system with an air bubble located not more than 0.2 mm (0.008 in.) from anywhere (L ó 0.2 mm), sound aggregate, and moderate maturity. Sound aggregate is aggregate that does not contain significant amounts of accessible capillary pore space that is likely to be critically saturated when freezing occurs. The way to establish that such is the case is to subject properly air-entrained, properly mature concrete, made with the aggregate in question, to an appropriate laboratory freeze-thaw test, such as ASTM C 666, Procedure A. Moderate maturity means that the original mixing water-filled space has been reduced by cement hydration so that the remaining capillary porosity that can hold freezable water is a small enough fractional volume of the paste so that the expansion of the water on freezing can be accommodated by the air-void system.

The commercial utilization of high-strength concrete with 60 to 120 Mpa compressive strength is a recent phenomenon; therefore, long-term field experience with regard to durability in corrosive environments is not available. In this paper, a critical review of the factors necessary to obtain high strength and high durability is presented. Typically, the concrete mixtures contain high cement content, low water content, and several admixtures, such as a superplasticizer, a pozzolan, and at times an air-entraining agent. When properly placed, consolidated, and cured, such mixtures should have low permeability and high durability to corrosive environments. However, there is some concern that microcracking in the aggregate-cement paste transition zone, possibly due to a variety of causes, may impair the impermeability and durability. The results of a recent investigation are discussed, which show that the aggregate type can play an important role in controlling the strength of the transition zone and, therefore, the degree of potential microcracking of concrete in service.

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.