SP79 It's a virtual encyclopedia of what mineral by-products do to concrete--and why. 1196 pages of essential information in 62 clearly defined, easy reference chapters. Key subjects include: effects on durability, fiber reinforced concrete, fly ash, pozzolans, sulfate resistance and concrete workability. With the rapidly increasing usage of by-product additives in concrete, every designer and builder needs the answers which these volumes provide.

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.

Three natural pozzolans, a fly ash, and a sample of silica fume have been characterized by means of chemical analysis and nitrogen adsorption. lanic activity i.e. the The pozzo-lime consuming capacity of each of these pozzolans has been evaluated by making portland cement - pozzolan paste and determining free calcium I : hydroxide contents after different intervals of hydration. Mechanical strengths of the above portland cement -pozzolan mixtures have also been determined. The results indicate why previous workers in this area have obtained discordant results.

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.

In current practice in the U.S.A., the term "blended cements" is applied only if the addition to portland cement is blast-furnace slag or pozzolan. Blended cements are covered by ASTM specification C 595 and the most generally used types (IS and IP) are required to give a level of "performance" as good as Type cement. The user, if he pays the same price per unit mass pur-chased, pays a lower price per solid volume. A few people believe that a greater degree of sulfate resistance of concrete could be attained by the addition of "a suitable" pozzolan to Type V portland cement. Some pozzolans with high silica content can improve the sulfate resistance of an otherwise non-sulfate resistant portland cement, other pozzolans can make sulfate-resistance worse. Merits or demerits in the performance of cements may be quite unrelated to whether or not the cement is "blended." As ASTM specifications require that IS and IP cements meet the same 3-day strength limits as Type I portland cements, such blended cements are seldom competitive in mass concrete construction. Batching of pozzolan or slag at the ready-mixed concrete plant has the advantage that a wider range of admixture materials may be made available and the quantity of blending material can be varied at will. The disadvantages are that there is another ingredient to procure, test, store, and control and that it is possible to make a concrete with all slag or pozzolan and no portland cement. U.S.A. specifications for blended cements and for pozzolans still show serious deficiencies. For instance, the present classification of fly-ashes into Type F and C is misleading. Also, no basis exists for measuring for specification purposes the benefits of blended cement as compared with a straight portland cement with regard to sulfate resistance or reduction in tendency to concrete expansion due to alkali-silica reaction. The view is expressed that prices should be fixed according to performance requirements. If the customer wants more early strength or lower heat, the extra costs should be added on to the basic price. Producers of hydraulic cements in general and of blended cement in particular will have great opportunities in the future if they are aware that cement production is part of the chemical industry and concrete making is not simply putting mud in a hole. Quality control can save costs and permit the use of a variey of cements of a variety of levels of performance and prices. To make progress, efforts in research and development must be improved. Better methods of characterizing slags and pozzolans for better specifications must be developed.