International Concrete Abstracts Portal

The use of industrial by-products such as fly ash, blast-furnace slag and ferro-silicon condensed silica fume for making concrete block stripped immediately after molding was investigated in order to save natural resources. Zero-slump concretes containing varying by-products were used. Each concrete block having the size of, 150 x150 x540mm,was manufactured by using an instant-stripping mold. After stripping, the blocks were cured in a steam chamber and a water tank of standard manner. Concrete qualitiessuch as compressive strength, dynamic modulus of elasticity, solidity ratio and surface texture were investigated at given ages. The results of these investigations reveal that there is no great difference between the quality of concretes containing small amounts of by-products and that of the plain concrete. The use of blast-furnace slag is more effective for 28- day strength development. The color of concrete using fly ash or slag is white, and the condensed silica fume substitution is advantageous for steam curing. These by-products may have a useful role in concrete block industry.

Granulated blast furnace slag and low-calcium fly ashes have long been used as portland cement additives or as mineral ad-mixtures in concrete. With the addition of high-calcium fly ash, rice husk ash, and condensed silica fume to the list of traditional mineral admixtures, a scientific approach for characterization and evaluation of all industrial byproducts which are suitable for use as admixtures in concete is needed. Since it is not the source of origin or the chemical composition of a mineral admixture but the mineralogical composition and particle characteristics which determine its contribution to concrete behavior, in this review the entire area is treated as a unified discipline. This approach seems to provide a better basis for explaining the similarities and differences in behavior between mineral admixtures originating from either the same or different sources. Mineralogical compositions, particle characteristics, current production rates, and utilization of major pozzolanic and industrial byproducts available in the United States and Canada are included. Mechanisms by which the use of these byproducts in portland cement concrete can improve engineering properties are discussed, and examples of data from field and laboratory investigations are given.

Concretes containing both portland cement and fly ash were evaluated to determine the effect of fly ash on air-void stability. Ten fly ashes were used, they have a wide range of chemical and physical properties as well as geographical origins. Air contents of plastic concretes were determined, and both air content and air-void parameters were measured in hardened con-cretes cast at four time intervals after initial mixing. These tests indicate that air contents of concretes containing Class C fly ash appear to be more stable than those in concretes containing Class F fly ash. The higher the organic matter content of a fly ash, the higher will be the air-entraining admixture requirement for concrete in which the admixture is used. In addition, the higher the air-entraining admixture requirement, the greater is the air loss on extended mixing. Even though the air volume is reduced the spacing factor, specific surface, and number of voids are little affected. A "Foam Index" was determined for each of the ten fly ash-Portland cement combinations. Air-entraining admixture requirements of actual concretes containing both portland cement and fly ash were compared to the "Foam Index" test results. These tests indicate that the "Foam Index" could be especially useful to concrete pro-ducers as a quality control test for checking the air-entraining admixture requirements for different sources or lots of fly ash.

The paper describes commercial use of concretes containing fly ash in Australia. comparison is made between fly ash and other concrete types, mainly on the basis of equal 28 day strength. Setting times, Bleeding, Workability, Air Entrainment, Rate of Strength Gain, Elastic Properties, Flexural and Indirect Tensile Strength, Heat of Hydration, Shrinkage Creep, Sulphate Resistance, Carbonation, Abrasion Resistance, Alkali Aggregate Reactivity are discussed. Field observations of concrete structures containing fly ash after prolonged environmental exposure are also included.

The paper describes investigations undertaken to develop a suitable fly ash blended Portland cement for concrete used in two large water dam projects in Yugoslavia, which have recently been completed. The fly ash selected for this purpose is produced at a power station using brown coal with combustion temperatures 1550-1600°C, as compared to other Yugoslavian power stations using lignite coal with combustion temperatures generally in the range of lOOO-12OO°C. It was shown that the combustion temperature is the single most important factor in controlling the quality of fly ash, with excellent physical and pozzolanic properties being produced at higher temperatures. A fly ash content (F) of 50% in Portland cement (C), i.e. F/(F+C) = 0.50, was selected for these projects, as it was shown to be the most suitable blend with regard to the heat of hydration, setting time, consistency and soundness properties. A concrete mix with 225 kg/m3 of this fly ash blended Portland cement and aggregate of maximum size 63 mm (24 in) was adopted and both the laboratory and site tests showed this mix to possess good properties in the fresh and hardened states. A comparison of these results was made with the comparable concrete prepared with commercially available Portland cement and slag cement, and the use of fly ash blended Portland cement was found to be advantageous.