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The mechanical and structural properties of mortars containing silica fume were studied. Mortars containing 5 and 10 percent active silica additive were made. Mortars without silica fume (standard mortars) were also prepared. A first set of mortar specimens was cured entirely in water. A second set of mortars was cured in air. The third was immersed in water and then subjected to alternating cycles of storage in water and air. The results show a very close relation between the conditions of the mortars' curing and their mechanical properties. The flexural strengths of mortars containing silica fume, subjected to variable curing conditions, show periodic increases and reductions. SEM observations confirmed the relations found in the flexural strength tests.

Compressive strength of concrete with silica fume cured at high temperatures generated by heat of hydration during early age was studied. The curing temperatures simulated the site-curing conditions of structural members. Four types of aggregates and four types of admixtures were used, and a total of seven concrete samples were cured at four temperature conditions ranging from 20 to 75 C. Results indicated the following: 1) at higher curing temperatures, the 1-week strength was higher but the strength gain from 1 to 4 weeks tended to be low; 2) independent of curing temperature, the type of aggregate greatly influenced the strength, and the results were the same with all the admixtures; 3) high-temperature curing influenced concrete strength independently of the admixture and aggregate; 4) equivalent age at 20 C based on the Arrhenius equation gave a reasonable estimation of compressive strength gain.

This paper gives the results of an investigation on the performance of high-volume fly ash concrete made with ASTM Class F fly ashes from three different sources. Cementitious materials contents of 300, 370, and 430 kg/m3 were used. The percentage of fly ash used was 58 percent of the total cementitious materials content. All the concrete mixtures were air-entrained and superplasticized. A large number of concrete specimens were subjected to the determination of compressive and flexural strengths, Young's modulus of elasticity, creep strain, drying shrinkage, abrasion resistance, deicing salt-scaling resistance, and resistance to chloride-ion penetration. High-volume fly ash concrete with adequate early-age strengths and excellent later age strengths can be produced with cement and total cementitious materials as low as 125 and 300 kg/m3, respectively. The Young's modulus of elasticity, creep, and drying shrinkage of high-volume concrete are comparable to those of the plain portland cement concrete. The high-volume fly ash concrete shows excellent resistance to chloride-ion penetration and outperforms plain portland cement concrete. The total charge in coloumbs at 91 days, a measure of resistance to the chloride-ion penetration, ranges from 278 to 1078. The corresponding values for reference concrete range from 1003 to 2313. Further research is needed to explain the relatively poor performance of the high-volume fly ash concrete under deicing salt scaling and abrasion tests.

The Akashi Kaikyo Bridge, with a center span of 1990 m, will be the world's longest suspension bridge when it is completed in 1998. The two main tower foundations are being constructed in water. A total volume of about 500,000 m3 of antiwashout underwater concrete has been placed, and about 180,000 m3 of ordinary reinforced concrete is currently being placed. Since this antiwashout underwater concrete had to be placed over a wide area and placed about 10,000 m3 per pour, it was necessary to choose a low-heat, high-flowability concrete. The cement used for this antiwashout underwater concrete was a three-component type containing about 80 percent granulated blast furnace slag and fly ash. Report describes the physical properties and workability of the antiwashout underwater concrete and the results of construction.

Purpose of this study was to search for ecologically acceptable ways to stimulate the natural self-purification activities in water areas. For this purpose, attachment of marine organisms to the surface of no-fines concrete (NFC), which contains continuous voids that may be effective in promoting establishment of a biologically favorable environment, was examined. When this type of concrete is immersed in shallow seawater, not only its rough surface, but also its continuous interior voids, are fully exposed to water and rapidly neutralized. This will then lead to the attachment and growth of marine microbes and eventually to the formation of a layer of biotic membranes. Attachment of organisms seems to occur in a form of multilayered biotic membrane consisting of bacteria, various microbes, unicellular algae, small animals, large seal algae, and shellfish, etc. Results show that decomposition and ineralization of the marine organic matters and the growth of algae, attached animals, and bacteria are accelerated, thereby providing the water area with a better biological environment. Thus, this type of concrete may be useful in the establishment of a well-balanced biological environment and, although there is a limitation due to its thickness, in the construction of gathering places for fish. In addition, assimilation and fixation of carbon dioxide by attached algae and shellfish, respectively, may be also possible.