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In the third year of a research project on roller-compacted concrete pavements, a test section was cast during the summer of 1989, using 13 different mixtures. Five types of binder (ASTM Types I, I + slag, I + fly ash, a blended silica fume cement, and a blended silica fume cement + fly ash) were used to prepare these mixtures. To verify whether a proper air bubble network could be obtained, two different air-entraining admixtures were utilized. Approximately half of the mixtures were air-entrained. Half of the test section was moist-cured for 14 days and a white curing compound was sprayed on the remaining portion. 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 all 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. In accordance with previous results, good scaling resistances were obtained with the silica fume concretes cured with a membrane.

Expansion of mortar bars with and without selected pozzolans exposed to saturated calcium hydroxide and sodium chloride solutions at 50 C has been measured up to 20 weeks of exposure. The mixes contained a Danish low-alkali sulfate-resistant cement or a French high-alkali cement, and inert quartz sand added 2 and 6 percent of synthetic cristobalite and varying amounts of pozzolans. Additions were 5, 15, and 25 percent fly ash; 3, 5, and 7 percent silica fume; 5 percent silica fume plus 15 percent fly ash; and 35 percent slag. Both fly ash and silica fume were found to prevent deleterious alkali-silica reactions. The amount of pozzolan necessary to prevent expansion increased with the amount of reactive aggregate and varied with the type of pozzolan. Additions of 5 percent fly ash or 3 percent silica fume were enough to suppress deleterious reactions in the mixes with 2 percent synthetic cristobalite during the period of testing. Twenty-five percent fly ash or 5 percent silica fume plus 15 percent fly ash were found to prevent deleterious reactions in the mixes with 6 percent synthetic cristobalite until 15 weeks of exposure.

The behavior of mortars containing fly ashes and slag in seawater has been studied under two different exposure conditions. Examined first was whether the achievement of strengths at 28 days, either similar to or higher than those of reference mortars, would lead to mortars with a durability as high as in the case of reference mortars or even higher, due to the addition of superplasticizers and the substitution of fly ashes or slag for some cement quantities. Secondly, a cement portion issued from a reference mortar was replaced by corresponding fly ash and slag quantities, the E/C ratio and the workability being kept constant, and variations of the duration of humid curing were imposed to observe their influence on the behavior in seawater. Results obtained show that: a) the criterion of strength at 28 days does not allow a guarantee of the durability in seawater; b) the direct substitution, in the mortar, of fly ashes or slag, for a certain amount of cement (known in the French regulations as nonresistant to seawater) does not improve the long-term behavior; and c) the humid curing during 7 days is, by far, the best.

The effectiveness of one ground granulated blast furnace slag, two condensed silica fumes (high-silica/low-alkali, low-silica/high alkali), and three pulverized fly ashes (low-alkali/low-calcium, low-alkali/moderate calcium, high-alkali/high-calcium) have been evaluated in the presence of two very alkali-silica reactive aggregates from Canada, a siliceous limestone and a rhyolitic tuff. Mortar bars and concrete specimens were made with various admixture contents and different cements (high- and low-alkali), and tested for expansion with the accelerated mortar bar method (ASTM C 9-P214) and the concrete prism method (CAN/CSA-A23.2-14A). The mineral admixtures were also submitted to the pyrex mortar bar method (ASTM C 441). Based on the results, the ASTM C 441 test is not recommended for assessing the effectiveness of mineral admixtures in suppressing expansion due to alkali-aggregate reaction, unless account is taken of a number of modifications concerning mix design (admixture content, water/cement ratio, alkali content, etc.) and performance criteria. Pyrex does not behave like a natural aggregate. The results from ASTM C 9-P214, using a limit of 0.1 percent expansion at 14 days, are in agreement with those from the concrete prism method, which is the most recommended test procedure. However, when testing concrete, the alkali content of the mix must always be increased to 1.25 percent of the mass of cement (Na?2O equivalent), otherwise the test is not accelerated sufficiently and low expansion will be observed in the presence of reactive aggregates, even with no mineral admixtures. The long-term effectiveness of mineral admixtures against alkali-aggregate reactions (AAR), in particular silica fume, is presently questioned by a number of workers. Therefore, it is firmly recommended that conservative limits be used when conducting laboratory tests on concrete specimens, and that the tests be extended to at least two years. The mineral admixture under study should be used in amounts such that expansion never exceeds 0.04 percent in the long term (two years or more). A more conservative, and more recommended, performance criterion is to obtain expansion in the long term that is similar to that of a control made with a low-alkali cement and containing no mineral admixture

A study was made of the effects of Saskatchewan lignite fly ash on the resistance of concrete to freezing and thawing. Concrete was made with either ASTM Types I or V cement and different percentages of fly ash with an air content of 4 to 6 percent. Performance of the concrete was evaluated by measuring the changes in its dynamic modulus and its mass. A scanning electron microscope was also used to examine the changes in the microstructure of the cement paste due to exposure to freezing and thawing. Results show that the use of high percentages of fly ash in concrete (35 and 50 percent) reduced its resistance to freezing and thawing even though it contained about 6 percent air and was cured in water for 80 days. However, concrete containing 20 percent fly ash gave satisfactory performance, provided its air content and strength were comparable to control concrete that contained no fly ash. Results from the SEM examination show that the decrease in resistance of fly ash concrete to freezing and thawing may be due to the slow migration of portlandite and ettringite crystals from the dense C-S-H zones to the air voids. Concrete with fly ash was less susceptible to the migration of portlandite, but its air voids contained more fibrous hydrates, which may have led to an increase in the past porosity.