Using Fly Ash for the Production of Light Weight Composites

Abstract

Among the materials (metals, ceramics, glasses) which are applicable as reinforcement for composite synthesis, fly ash can be an extremely attractive material because of its low price, low density and of the interesting physical and mechanical properties. Additionally, as a waste by-product obtained in very large amounts during the combustion of coal by thermal power plants (e.g. about 80 millions tons annually in the USA), fly ash presents ecological problems associated with its storage and disposal. So far, only 25% of fly ash is used in constructions and other applications. Therefore the development of suitable scientific, technical and economic solutions of fly ash utilization is very pressing and important [1, 2]. Fly ash forms at 920–1200°C and oxides such as SiO₂, Al₂O₃, Fe₂O₃ and CaO are its major chemical constituents. Microscopically, fly ash powder represents a heterogeneous mixture of two types of solid (precipitator) or partially solid hollow (cenosphere) spherical particles, which are otherwise quite expensive to produce. Depending on the type and chemical composition of the particles due to different coal sources, the particle size ranges from 1 to 150 μm for precipitator fly ash and from 10 to 250 μm for cenosphere, while the densities range from 1.6 to 2.6 g/cm³ and from 0.4 to 0.6 g/cm³. This very unique and inexpensive resource (Figure 1) with wide ranges of size and density may be successfully selected to a fraction [3] that may be suitable in different lightweight structural applications.