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Data on setting time, strength, modulus of elasticity, drying shrinkage, and compressive creep of concrete containing a low-calcium fly ash under hot and humid (28 ñ 2 C, 75 ñ 15 percent, relative humidity) climate are reported. Tests were carried out for Grade 25 and 35 concretes. The cement replacements with fly ash were 0, 20, and 40 percent, by weight. Between 3 and 90 days under moist curing (28 ñ 1 C), fly ash concrete gives rise to strength increases of about 110 and 230 percent with the fly ash contents of 20 and 40 percent, respectively, compared to an increase of about 65 percent for the control concrete. The relationship between the modulus of elasticity and compressive strength was not influenced by the partial replacement of cement by fly ash. Both grades of concrete with 40 percent fly ash content and moist cured initially for 7 days showed about 35 percent more drying shrinkage after 90 days of drying than the corresponding shrinkage for the control concrete. However, the shrinkage was found to be about 7 percent lower than that for the control concrete when the initial moist curing period was increased from 7 to 28 days. For Grade 35 concrete, the creep coefficient of concrete with fly ash content of 40 percent was 11 percent lower than that of the control concrete. However, Grade 25 concrete showed a 4 percent higher creep coefficient for fly ash concrete with the same 40 percent fly ash content.

The chemical resistance of alkali-activated slag pastes and mortars in chloride solutions was studied. The four basic slag-alkali binding materials were prepared using granulated blast furnace slag, copper slag, and a mix of both these components. NaOH and Na?2CO?3 were used as activators. Some pastes and mortars containing 10 percent active silica additive were also made. The mortars were cured in standard conditions as well as subjected to low-pressure steam curing. The chemical resistance of alkali-activated slag mortars was compared with the chemical resistance of OPC mortars. The water-to-solid ratio was kept constant at 0.40. The samples cured in water were considered as reference samples. It has been found that the alkali-activated slag binders are chemical resistant in chloride solutions. These results were found not only from chemical resistance in chloride solutions and compressive and flexural strength tests, but also from the SEM observations of microstructure. The difference between the chemical resistance of slag and OPC mortars is probably the consequence of phase composition and porosity of the hydration products

Hydration of cements containing the supplementary cementing materials fly ash (FA) and silica fume (SF) is discussed and compared with the hydration of ordinary portland cement (OPC). Early stage heats of hydration, changes in the chemistry of the solution (both at early stages, and later pore solution compositions), microstructural development, and pore structure are compared. The hydration rates normally follow the order: SF > OPC > FA. The complex hydration processes may be controlled so that the use of these cements enables development of materials having superior strength and durability.

Gives results of an investigation on the chloride ion permeability of concretes incorporating supplementary cementing materials, using the Rapid Determination of Chloride Permeability Test (AASHTO T277-83). A total of 18 concrete mixtures were made. These included mixtures incorporating silica fume (8 percent replacement or addition to the cement by mass) or ground granulated blast-furnace slags (50 percent replacement by mass), or fly ash (25 percent replacement by mass). The w/c of the mixtures investigated ranged from 0.21 to 0.71. From each mixture, a number of 152 x 305 mm cylinders for compressive strength testing and 102 x 203 mm cylinders for determining the chloride permeability were made. Porosity measurements were also performed on some of the concrete specimens. The test results showed that the use of supplementary cementing materials significantly reduced the chloride ion permeability of concrete. Silica fume and blast furnace slags investigated seem to be particularly efficient for producing concrete almost impermeable to chloride ions.

Describes recently completed construction of a 175,000 mý (1.85 million ftý) 72-story office building. A unique feature of the structural system is the high-strength reinforced concrete-structural steel composite columns. Conventional aggregates and portland cement, with about 29 percent fly ash replacement, produced average 56 day compressive strengths of over 83 Mpa (12,000 psi), easily surpassing the design specified strength of 69 Mpa (10,000 psi). Most of the concrete was placed at a slump of 200 mm (8 in.), using a high-range water-reducing admixture. The structural design was based on 16 exterior columns, an arrangement that allowed excellent utilization of tenant space. Preconstruction research and development of the high-strength fly ash concrete mix designs proceeded simultaneously with the architectural and structural design. Results of these tests produced important data on modulus of elasticity, shrinkage, and creep that influenced the composite column design. Much of the concrete was placed under hot weather conditions typical of Texas, where summer ambient temperatures sometimes exceed 40 C (104 F). While fly ash was employed in all of the concrete mixes, this paper focuses on the high-strength aspects in which the use of fly ash was an essential ingredient.