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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.

Class F fly ash was used as the basic granulating material. Catalysts and binders were added to evaluate the behavior of granulated material. The accelerated curing method was also considered. Results indicate that granulation rate depends closely on the slant angles of the disc, the revolving rate, the methods of adding admixtures, and granulation time. Though aluminum powder reduced unit weight and raised the strength of fresh particles, it had a detrimental effect on other properties. Addition of hydrophilic seed reduced the granulation time and increased productivity. The results showed that at a constant relative humidity, the higher the temperature, the more rapid and higher the strength development. It is important to maintain constant temperatures or low strengths may result. Normal steam curing, autoclave curing, and microwave steam curing have beneficial effects on the strength of fly ash lightweight aggregates. The differences in curing results are due to differences in mix proportioning of aggregates and duration of curing.

High-lime fly ashes obtained from the combustion of lignites or subbituminous coals are common by-products of thermal power plants in many countries, including Turkey. Chemical analyses, mineralogical analyses, and the formation of hydration and pozzolanic reaction products at different ages of three Turkish high-lime fly ashes were carried out using X-ray diffraction (XRD) techniques. The relationships between the mineral phases in the fly ashes and the hydration and pozzolanic reaction products were investigated. Fly ash is formed at combustion temperatures of approximately 1000 C, at which the clay impurities decompose. These fly ashes contained highly reactive silica and alumina. The reaction of these oxides with the free lime and anhydrite present in two of the fly ashes led to the formation of C-S-H gel and ettringite starting with the beginning of hydration. The third fly ash, having anhydrite as the only major calcium-bearing compound, produced gypsum upon hydration. However, introduction of Ca(OH)2 into the system resulted in similar reaction products. At later ages, beside the previously mentioned products, C4ACH11 and C4AH13 were also observed in all three cases. Interpretation of the results indicated that although all three fly ashes were of high-lime type, two of them were hydraulic and autopozzolanic, whereas the third was pozzolanic only.