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The resistance to freezing-and-thawing and chloride diffusion of antiwashout underwater concrete was investigated to evaluate the applicability for tidal zone in cold districts or reinforced concrete structures in marine environments. Comparisons were made with ordinary portland cement concrete of similar mix design. Two types of cement (ordinary portland cement and portland blast furnace slag cement) were used. Two types of blast furnace slag (Blaine fineness 500 and 700 m²/kg) were used as a cement replacement (slag content 30 and 50 percent by weight). The results show that antiwashout underwater concrete without blast furnace slag shows poor resistance to freezing-and-thawing compared with normal concrete. But the freezing-and-thawing resistance can be improved with blast furnace slag. This is due to the fact that concrete containing blast furnace slag has dense pore structures. Pore volume in the range of 10 to 10 3 nm in radius decreases significantly with blast furnace slag. Similarly, chloride diffusion depth becomes smaller with blast furnace slag.

Report presents data on the effects of a mineral admixture such as fly ash, blast furnace slag, or silica fume on the pore structure and chloride permeability of concrete stored under various environmental conditions for a long time. Cubic concrete specimens with all surfaces coated with a polymer except for one surface were initially cured in water for 7 or 28 days, and then exposed to three environmental conditions for 1 year: in water at 20 C; in a room at 20 C, at 60 percent relative humidity; and outdoors. Cores from the specimens were investigated for the degree of hydration and the characteristics of pore structure of concretes both with and without mineral admixtures. The test involved ignition loss, mercury intrusion porosimetry, and scanning electron microscopy. The chloride permeability of exterior and interior portions of specimens was determined according to AASHTO T 277-831. The test results showed that, at the surface of concretes containing mineral admixtures, the hydration of portland cement and the pozzolanic reaction of mineral admixture were considerably depressed, and coarse pores were developed when the concrete specimens were exposed to dry environment for a long time; however, at 5 cm depth from the surface, there was little change in both the degree of hydration of cement and the pore structure. AASHTO T 277-831 data showed that both the surface layer and the interior concretes with mineral admixtures were much less permeable to chloride ions than the corresponding portland cement concrete specimens, irrespective of the curing and environmental conditions.

Reports research on the beneficial utilization of waste husk from rice production. The husk was burned in the furnace at two different temperatures, 400 and 500 C for « hr, and it was observed that all the silica obtained was amorphous at both burning temperatures. The mortars were prepared by substituting cement with husk at 10, 20, and 30 percent by weight. The ratio of (water + superplasticizer)/(cement + ash) was kept constant at 0.57 for all batches. The mortars were stored in sodium sulfate solution until the testing date after the initial 28 days normal curing in water. Compressive and flexural strength tests were carried out on the mortar specimens at 4, 8, and 12 week periods of storing in solution. It was observed that durability and strength of mortars were increased by using rice husk ash.

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.