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There is an increasing tendency worldwide toward using cements blended with fly ash, silica fume, blast furnace slag, and natural pozzolans. Incorporation of these materials in concrete makes it dense and impermeable. While the effect of chloride and sulfate ions on the durability of blended cements is well documented, meager data are available on the synergistic effect of high concentrations of these salts on the durability performance of these cements. Since the structural components, especially foundations in the coastal areas in some parts of the world, are subjected to high concentrations of these salts, it is imperative to investigate the performance of blended cements in such environments. In this investigation, mortar and concrete specimens made with Type I cement blended with fly ash, silica fume, and blast furnace slag were exposed to a highly concentrated chloride-sulfate (2.1 percent SO4-- and 15 percent Cl- solution for a period of 540 days. The performance of these cements in resisting reinforcement corrosion was evaluated by monitoring half-cell potentials and measuring corrosion rates at periodic intervals. Deterioration due to sulfate ions was evaluated by visual survey, and measuring loss in compressive strength. Results indicate that surface deterioration and loss in strength was greater in blast furnace slag and silica-fume cement specimens compared to fly ash and plain cement specimens. Severe surface scaling and considerable reduction in strength (55 to 75 percent) was observed in the former cements. Moderate surface deterioration and loss in strength of about 25 percent was observed in fly ash and Type I cements. Corrosion of steel in silica fume and blast furnace slag was, however, much lower than in fly ash blended and Type I cements.

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.