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:The effects of cement and sand replacement by two classes of fly ash (C and F) on the strength and durability characteristics of concrete made using three grades of cement are discussed. The compressive strength. permeability, and sulfate resistance of a large number of samples made from three grades of ordinary concrete - common to hydraulic structures - were studied. Effects of’ cement and sand replacement ( 10%. 15%, and 20%) by the two types of fly ash were compared with the results from control specimens. They show the dependence of durability characteristics - permeability and sulfate resistance - on the class and fineness of fly ash. the grade of concrete, the amount and type of replacement. and. to a lesser degree, on the grade of cement.

In recent years, there has been a growing interest in the development of thin walled fiber reinforced cement composites for structural applications. In these composites, the discrete fibers used may be made of metallic, mineral, polymeric or naturally occurring materials. Each type of fibers is unique in geometrical shape, size, surface characteristics, strength, stiffness and ductility. As a result, different fibers offer different extent of improvement to the matrix mechanical properties. However, the most sought-after property in a cement-based composite is the strain-hardening response that is associated with multiple cracking. In order to achieve this property, different types of fibers may be suitably combined to exploit their unique properties. In addition, partial replacement of cement by fly ash which has much finer particles than ordinary cement, is likely to modify the properties of the composite by reducing the matrix fracture toughness and enhancing the interfacial bond strength between the fiber and the matrix, thus promoting a strain-hardening response of the composite material. It would also support the recent emphasis on environmental awareness by reducing the cement content in the composite. The present investigation is therefore undertaken with the main objective of developing a strain-hardening composite using hybrid fibers and high volume fly ash.

This investigation was conducted to establish database for manufacturing of concrete masonry products incorporating high volumes of ASTM Class F fly ash. A total of 15 mixture proportions for bricks, blocks, and paving stones, including reference mixture for each type of masonry product, was proportioned. The fly ash content was varied from 20 to 50% for brick and block mixtures, and from 15 to 30% for paving stone mixtures All masonry products were tested for compressive strength, density, absorption, freezing and thawing resistance, drying shrinkage, and abrasion resistance. Test results indicated that bricks and blocks with up to 30% fly ash are suitable for use in both cold and warm climates. Other brick and block mixtures containing up to 50% fly ash were appropriate for building interior walls in cold regions and both interior and exterior walls in warm regions. None of the paving stone mixtures, including the control mixture, strictly conformed to all ASTM requirements. However, all the paving stone mixtures with and without fly ash are suitable for normal construction applications.

The purpose of this research was to study the penetrating characteristics of chloride ions into fly ash concrete and the corrosion of steel reinforcement in concrete, where some parts of fine and coarse aggregates were replaced by fly ash . Several tests such as compressive strength test, chloride penetration test and corrosion diagnosis of steel reinforcement in concrete were performed. Through these tests, the physical properties and durability of fly ash concrete against aggressive environments have been studied.

Superior durability of fly ash concretes have been very well established by many research works throughout the world. However, the decision to use the fly ash concrete or not and also the fly ash content in the concrete is based on the cost of the concrete in most of the cases, if not all. Thus a methodology has been developed to estimate the optimum fly ash content for the lowest cost and maximum durability of the concrete. Concrete of different fly ash content were prepared and their costs were calculated. Durability properties of some of the concrete were determined by experimental measurement of their relative service life. The type of environment was also considered. Optimum fly ash content was determined based on cost, durability of the concrete, and the type of environment. The price structure of concrete-making materials in Australia was used as an example in the calculation of optimum fly ash content for the lowest price. It is expected that the price structure found in other countries would be different and accordingly the optimum fly ash content will be also different. However the methodology has been presented and this methodology can be used to calculate the optimum fly ash content for any price structure. This methodology provides scientific way of estimating the fly ash content which would give the lowest cost for an environment.