International Concrete Abstracts Portal

Cements consisting of 60 percent ground granulated blast furnace slag and 40 percent fly ash activated by 7 percent sodium hydroxide have been investigated. Various slags were used, including some laboratory-made synthetic slags. The influence of additives like superplasticizers and defoaming agents has been examined. The most favorable composition with respect to strength development has been subjected to a durability testing program. A negative aspect appeared to be the carbonation resistance, which is low in comparison with portland cement. Carbonation leads to a decrease in strength. Other properties were favorable.

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.

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.

An extensive research program was performed on the rate of carbonation of concrete produced with ordinary portland cement, portland blast furnace slag cement, and portland fly ash cement, both with replacement of cement by fly ash and without. After various periods of wet curing, concrete samples were exposed to various exposure conditions. The wet curing ranged from 1 to 90 days, the exposure concerns outdoor sheltered from rain and at 20 C, 65 percent relative humidity in the laboratory. For the various exposure conditions, a relation has been found with respect to the carbonation rate as a function of the compressive strength at 7 days or at 28 days per type of cement and for all types of cement when the lime content is involved. Results of measurements over a period up to 2 years are presented.

The resistance to deicer scaling of lean concretes containing fly ash was evaluated using ASTM C 672-84. Concretes were prepared at cement contents of 250, 305, and 335 kg/m3. Six fly ashes were chosen for evaluation at cement replacement levels of 25 and 50 percent by mass in each of the mixtures. Specimens representative of residential flatwork were prepared and cured for 1 and 7 days under moist conditions, then air-dried until initiation of testing at 35 days of age. Results indicate that all mixtures containing fly ash exhibit more rapid and severe scaling than those mixtures prepared with cement alone at the same total cementitious material content. Scaling was found to increase with a decrease in the total cementitious content of the mixture and an increase in the amount of cement replaced. Data on compressive strength, and characteristics of air-void systems in these concretes are also presented.