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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.

The purpose of this research was to study the ability of Class C fly ash for high-volume concretes when its sulfate content reaches the limit in its specifications. The laboratory test items were compressive strength, length change in concrete cylinders 70 x 780 mm, and quantitative analysis of all materials. Calcium hydroxide content in concretes was also measured with a new method by selective extraction. This is suggested to determine the decreasing content of the calcium oxide in concretes, as responsible for he pozzolanic behavior or its carbonation degree. One type of Class C fly ash with different ages and three classes of cements with different C3A content were tested. The influence of curing conditions in tap water immersion, the different potential contents of ettringite, and calcium hydroxide were taken into account. The following results were obtained. The content of SO3 in fly ash very near the 5 percent specification limit used in high-volume concretes with substitutions of 60 percent of cement gave no undue expansions for given conditions. No significant length changes in concrete were observed in any of the tests. The strength development shows good values, especially when the concrete was cured in tap water.

Adequate curing is essential for all concrete, whether it contains fly ash or not, if the potential properties of concrete are to be fully realized. However, since the long-term benefits associated with the pozzolanic reaction have become more evident in well-cured concrete, it has been generally considered that concrete containing fly ash has a greater susceptibility to poor curing than plain concrete. Tests were carried out at the Department of Civil Engineering of the K. U. Leuven on a series of mortar mixes with a range of fly ash-cement ratios to study the effect of curing on the strength development of mortar. Mortar specimens were subjected to a range of moist-curing periods prior to air-storage. Compressive strength was determined at various ages. The results confirm the importance of curing, with reductions in curing period resulting in lower strength. The strength of the mortar containing fly ash appears to be more sensitive to poor curing than the plain mortar.

The use of high-volume fly ash as a supplementary cementing material in controlling alkali-aggregate reactivity is an attractive solution. Fly ashes are often used in reducing the expansions due to alkali-aggregate reaction in concrete. However, in the past, only smaller quantities of fly ash, less than 30 percent by weight of cement, have been used. This paper presents the results of a study to determine the influence of very high quantities of fly ash in reducing the expansion due to alkali-aggregate reactions. Ten samples of sands collected from various locations in South Dakota were tested for alkali-aggregate reactivity using both standard ASTM C 227 and accelerated test methods. Five of the sands that caused greater expansions than permitted were tested with high fly ash contents, using the accelerated test method. Cements satisfying ASTM Type I and a low-calcium fly ash (ASTM Class F) were used for the entire investigation. The water/fly ash + cement ratio was 0.44 and the fly ash/fly ash + cement ratios expressed as percentages were 40, 50, 60, and 70. Control mortar specimens containing the same Type I cement and alkali content were used for comparison. An accelerated test method proposed by the Canadian Standards Association was used for the detection of potentially deleterious expansion of mortar bars. The test results had shown that high fly ash replacement levels were very effective in reducing the expansion due to alkali-aggregate reaction. The expansions of the mortar bars made with the highly reactive sands and high volumes of fly ash were negligible as measured in the accelerated test method.

A considerable amount of natural zeolite has been used as an admixture for portland cement in the People's Republic of China. Paper first deals with a comprehensive characterization of inorganic admixtures such as natural zeolites with different mineralogical compositions, a fly ash, a fine blast furnace slag, and a silica fume. Binders, such as ordinary portland cement and a quick lime for the substitution of portland cement, were also subjected to the characterization. Next, bending and compressive strength and drying shrinkage of the test mortars were measured under the constant flow value. Standard test mortars were prepared by making use of the ordinary portland cement and quick lime-substituted portland cement, and blended cement mortars were also tested with the inorganic admixtures previously mentioned. As a result, natural zeolite was proven to be of sufficient applicability as an admixture for cement.