International Concrete Abstracts Portal

Presents the results of a study to evaluate the potential of modified fly ash for use as a construction material. Areas of utilization investigated were: structural fill for embankments and dykes; lining material for canals, waste disposal sites, etc.; replacement of cement in concrete; and cement-stabilized base and subbase course. This modified fly ash was evaluated mainly on the basis of its compressive strength at various ages. Availability of only a limited quantity of fly ash necessitated use of miniature specimens for strength test. Results indicate that modified fly ash with and without cement developed adequate compressive strength to be used as fill material in embankments and dykes. Compacted modified ash also exhibited very low permeability characteristics. Replacement of 35 percent cement by modified fly ash produced 20 percent more strength than portland cement mix at 28 days.

Paper is concerned with the research of the effective utilization of fly ash produced from power plants. Three classes of "classified fly ash" produced by classifying conventional fly ash by air separation with the maximum particle diameters of about 20, 10, and 5 æm have been investigated. Special attention has been given to concrete strength enhancement effect due to classified fly ash. Experimental studies have reported on the basic properties of fresh concrete and hardened concrete having low water-binder ratio and high strength, produced by mixing the classified fly ash having the maximum particle diameter of about 10 æm, alone or in combination with ground granulated blast furnace slag. It is shown that the classified fly ash is an effective material that contributes to the reduction of superplasticizer requirements that are generally used in high-strength concrete, improvement of workability by reduced viscosity, and improvement of strength development, whether the classified fly ash is used alone or in combination with ground granulated blast furnace slag.

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.