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Fly ash concretes with and without superplasticizers, hardened under normal conditions of temperature and by heat treatment. The influence of superplasticizers on the harde fly ash concretes was studied at ages (24-72 hours) days. ning process of and 28-730 Some technico-economic advantages resulting from the use of FA and superplasticizer admixtures in concrete are discussed in terms of design, production and standards development.

In recent years there has been a renewed interest in the utilization of oil shales as a source for energy production and this was accompanied by research and development aimed at finding ways to utilize the ash by-product as a building material. The present paper discusses the various types of oil shale ash and their possible applications, and reviews recent studies carried out in Israel to utilize the cementitious characteristics of oil shale ash. The composition and properties of the oil shale ash can vary widely, ranging from high SiO2 materials which are only pozzolanic in nature, to higher CaO oil shale ash which can be hydraulic and can serve as a cementitious matrix without any need for an activator. Therefore, each type of oil shale ash must be evaluated separately. The experience and knowhow gained in the application of one kind of oil shale ash may not be relevant to others. This is considerably different than with other residues, such as fly ash, which do not exhibit this extent of variable properties.

The use of fly ash as a mineral admixture for lean concrete (road base concrete) has aroused a rather limited interest until now. However this comparative study shows that there are so-me advantages in using low calcium fly ash in lean concretes. The compactibility of lean concrete is improved : the maximum level of compaction (Modified Proctor test) is achieved at about 5 % fly ash addition, whereas it is equal at 0 % and 10 % addition . The CBR-indexes of the mixes are similar at Proctor maximum, but the higher the fly ash content, the more sensitive the index is to an increase in moisture content. At an early stage, fly ash is not very effective in strength development : it is essentially the portland cement content (2 to 5 %) that governs the rate of strength evolution. On the other hand, at longer periods (more than six months), fly ash contributes very largely to strength : a factor of 1.5 between the weakest mix and the reference lean concrete without fly ash. Accordingly a reduction of the cement content in practice can be taken into consideration. Water stability which is obtained rapidly, is not much affec-ted by the presence of the admixture. On the other hand, resistance to repeated freezing and thawing cycles is delayed because of the slower strength gain for mixes containing more fly ash and less cement. The results on the whole show that the optimum low-calcium fly ash content in lean concrete for road base lies around 5 % by mass with the possibility of reducing the cement content appreciably.

Dust collected from the hot exhaust gases emanating from the rotary kiln is known as cement kiln dust and presently it is considered as a solid waste material to be disposed of without polluting the environment. The composition of this dust is similar to that of cement kiln raw feed and often contains high concentration of alkalies. It contains partly calcined material and therefore it has some hydraulic and cementitious properties. This paper presents the results of a comparative study of the properties of concretes made with cement blended with kiln dust versus the properties of corresponding concretes made with plain Portland Cement. The blended cement was produced by blending 5% cement kiln dust with 95% by weight of regular Type I Portland Cement. Cement properties, mortar properties, fresh concrete properties, and hardened concrete properties like compressive strength, splitting tensile strength, flexural strength, impact strength, static modulus of elasticity, shrinkage, creep and creep recovery were studied using ASTM Test procedures. The result of the study showed that the addition of cement kiln dust slightly retards the setting time of cement and the fresh concrete properties of blended cement concrete mixes were almost the same as those of plain cement concrete mixes. B1ended cements did not adversely affect most of the hardened concrete properties.

The stilling basin of Kinzua Dam on the Allegheny River in western Pennsylvania has experienced severe abrasion-erosion damage since the structure was put into operation in 1967. The basin was repaired in 1973-74 using a steel fiber-reinforced concrete overlay. Deterioration continued to the extent that repairs were again necessary in 1983. A laboratory program was undertaken to evaluate the abrasion-erosion resistance of several concrete mixtures proposed for the 1983 repairs. This program showed that high-strength concrete made with silica fume and limestone aggregates available near the project site would provide suitable abrasion-erosion resistance at a reasonable price. The Corps of Engineers, owner of the structure, required potential suppliers of silica fume to conduct full-sized placements to demonstrate that this concrete could be made and placed outside the laboratory. Based upon these demonstrations and the laboratory program, the repair concrete was specified with a compressive strength of 86 MPa (12,500 psi) at 28 days as a means of obtaining the required abrasion-erosion resistance. Approximately 1500 m* (2000 yd3) of 250-mm (9 3/4-in.) slump concrete were placed using silica fume delivered as a slurry that included water-reducing admixtures. The average 28-day compressive strength was over 90 MPa (13,000 psi). Diver inspection of the concrete after one year in service, including a period with a very large volume of debris in the stilling basin, has indicated that the silica-fume concrete is performing as intended.