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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.

The demand for high-performance concrete is steadily rising in the construction market. Whereas it may not be difficult to attain high compressive strength with these concretes, controlling the rheology in the fresh state can create problems. The composition and properties of several high-performance concretes in their fresh and hardened states, made with reground Type 50 (ASTM Type V) cement of Blaine fineness 650 mý/kg, and silica fume, slag, and fly ash at w/c 0.30 or lower are presented. All these high-performance concretes present long slump retention, combined with high elastic modulus, modulus of rupture, and splitting tensile strength. The actual compressive strength can be as high as 124 to 136 MPa at 1 year. These results are compared with a reference concrete made with the same cement at the same w/c, but without any mineral admixtures. The microstructural characteristics of these concretes at 1 year are described. The correation between the microstructure and the mechanical properties are discussed.

Discusses the relationship between the composition and the mechanical properties (compressive strength, modulus of elasticity, autogenous shrinkage) of high-strength concretes (HSC) in the range of 50 to 100 Mpa. The models proposed for each of these properties are based on an analysis of the hardened concrete as a composite material, making it possible to go from the properties of the concrete to those of its matrix. The properties of the matrix are related to the two main parameters of composition (water-cement and silica-cement ratios) by empirical models obtained by smoothing the experimental data. Eleven concretes were made using the same constituents; the parameters of composition were varied separately to determine their influence on the properties in question. These experimental data, together with other data taken from the literature, were used to evaluate the accuracy of the proposed models. It is finally shown that these models, which sum up the current knowledge of the material, can be useful in designing HSCs according to specifications.

The chloride-ion attack on low water-cement ratio pastes containing silica fume was studied by soaking small paste disks in four different pH-controlled sodium chloride solutions for periods of up to 12 months. The pastes were made using water-cementitious material ratios of 0.30 and 0.25. Three types of cementitious materials were used: an ASTM Type III cement (Canadian CSA Type 30), the same Type III cement with 6 percent silicafume, and a French CPA-HPR cement with 6 percent silica fume. The four solutions in which the paste disks were soaked were the following: 3 percent NaCl (by weight) at a pH of 13.0, 3 percent at 11.5, 0 percent at 13.0, and 0 percent at 11.5. The curing period was fixed at 28 days for all mixtures. Mercury intrusion porosimetry, x-ray diffraction, scanning electron microscopy, and electron microprobe measurements were the techniques used to study the various samples after removal from the solutions. The chloride-ion attack on these low water-cementitious material ratio pastes was always very small, even after 12 months of exposure to 3 percent NaCl solutions at pH values of 13.0 and 11.5. After several months of exposure at a pH of 13, only very small amounts of chloride ions ( 1 percent) were detected and only minor changes to the microstructure were noted. At a pH of 13.0, the penetration of chloride ions was not found to be a function of the paste characteristics [w/(c + sf), type of cement, silica fume content]. The major parameter controlling chloride-ion penetration in low water-cementitious material ratio pastes is the pH of the NaCl solutions. When the pH is 11.5, the penetration of chloride ions into the pastes is easier because of the leaching of calcium ions creating a very fine microporosity. For this relatively low pH, it was found that the use of lower water-cementitious material ratios and silica fume can reduce the amount of chloride ions that can penetrate the cement paste.