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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.

The U.S. Army Corps of Engineers has used fly ash as amaterial that partially replaces portland cement in concrete for twenty-five years. Initially research was performed on use offly on concrete properties for bleeding, permeability, heat rise, resistance to freezing and thawing, elasticity, and compressive and flexural strength development. Those properties affected by partial replacement of portland cement with fly ash were heat rise in mass concrete, resistance to freezing and thawing and strength development. The concrete materials properties of three massive concrete gravity dams are reported. Since construction, these dams have been periodically inspected. Although these structures have some minor cracking, spalling, and erosion, their performance has been similar to other concrete gravity dams constructed using concrete without fly ash. Cost savings per cubic yard of concrete has been the benefit derived from using fly ash as a partial cement replacement material in massive concrete structures. Fly ash is specified to conform to ASTM C618, Class C or Class F with modifications to this specification as needed based on location or type of structure. Fly ash may replace portland cement up to 35 percent by absolute volume in interior mass concrete and 25 percent by absolute volume in exterior mass concrete and in structural concrete. Fly ash concrete has performed satisfactorily on Corps of Engineers projects over the last twenty-five years.

Since before the first utilization of imported fly ash by Ontario Hydro as a pozzolan in mass concrete in 1950, research programs on many aspects of its influence on durability were undertaken. Majo. areas addressed have been: 1. thermal crack resistance in mass concrete; 2. reduction of alkali reactivity; 3. freezing and thawing resistance, and 4. sulphate resistance (preliminary). When the first fly ash was produced by Ontario Hydro from thermal plants used for peak load power, the problems with utilizing variable and often high carbon content fly ash were also studied. This problem was overcome by selective storage along with provisior for fineness and carbon content checks for each tanker of ash leaving the plant. Major findings of the research include: 1. Fly ash has and is being used successfully in lieu of both CSA Types 20 and 40 (ASTM Types II and IV) moderate and low-heat cements to control temperature rise and thermally induced cracking in mass concrete. 2. The replacement of 25 percent of normal portland cement with fly ash has been found to be effective in reducing alkali silicate expansions. 3. As long as adequate air contents are obtained, carbon content does not adversely affect the freezing and thawing resistance of concrete at least within the 12 percent CSA and ASTM limits. As long as carbon contents are established for each delivery of fly ash, dosages of air entraining agents can be modified easily.

Three types of cements and three types of fine aggregates, viz seashore sand, crushed stone and a blend of the two were utilized for this study. The water-to-cement ratio by weight ranged from 0.40 to 0.50. All mixes were made at a slump of 10-cm (4-in.) and air content of 4 percent. The blended cement concrete with fly ash showed the lowest shrinkage among the three cement concretes. The creep tests showed similar results. Good workability, high strength, low shrinkage and creep could be achieved using fly ash concretes.

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.