12-09-2014, 12:05 PM
geopolimeric building matrials by synergetic uttilisation of idustrial waste
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INTRODUCTION
The concept of industrial ecology is based on integration of by-product and waste steams across industries leading to production of useful products with near zero flow of material to the environment. Building industry is one of the most dynamic sectors with enormous potential of industrial symbiosis and synergistic utilisation of industrial wastes. With increasing environment awareness, there is growing concern worldwide for updating production processes, as well as development of green building materials. The green material can be defined as products made from waste, recycled or by-products to conserve natural resources, circumvent toxic and other emissions, saves energy, and contribute towards a safe and healthy environment. Geopolymers, silico-aluminate materials formed through mimicking natural rock forming process, are fast emerging as new class of green building construction materials. In the process of geo-synthesis, silicon (Si) and aluminium (Al) atoms react to form molecules that are chemically and structurally comparable to those binding natural rock and allows for novel products synthesis that exhibit the most ideal properties of rock-forming elements, i.e., hardness, chemical stability and longevity. Fly ash, blast furnace slag and red mud are the three major industrial wastes in India. Presently over 100 million tonnes of fly ash, 12 million tonnes of blast furnace slag and nearly 4 million tonnes of red mud are generated. It is estimated that production of these wastes will double in foreseeable future due to rapid expansion coal based power generation, and increase in the production of iron & steel and aluminium through primary processing. These waste materials contain SiO2 and Al2O3 , along with Fe2O3 , CaO, MgO, MnO etc, and have immense potential as manmade raw materials for geopolymers.
GEOPOLYMERISATION OF WASTE
Most proposed mechanisms of geopolymerisation consist of dissolution of aluminosilicate phase, polymerisation and re-precipitation of gel phase, and transformation of the gel phase into geopolymer of varying crystallinity and structure. Depending upon experimental conditions, the different stages of geopolymer formation may overlap and even merge with each other. Isothermal conduction calorimetry was used to study the geopolymerisation of fly ash, mixture of (GBFS + fly ash), and the mixture containing (fly ash + GBFS + red mud). The calorimetry was carried out under following conditions:
. GEOPOLYMER CEMENT
Low reactivity of fly ash has often restricted the use of fly ash for geopolymer cements due to slow strength development. The reactivity of fly ash depends on its vitreous phase content, which participates in geopolymerisation reaction. The remaining constituents takes longer time for reaction due to poor reactivity and leads to slow setting and strength development in geopolymers. Various methods such as chemical activation, mechanical activation and size classification of fly ash has been suggested as a means to improve the reactivity. Recently observations were made for the use of mechanically activated fly ash leads to high compressive strength in geopolymers. Two different approaches were adopted to enhance reactivity of fly ash: (a) air classification to separate finer fractions, and (b) mechanical activation in attrition and vibratory mills. Small size cenosphere cools faster during their formation in coal combustion process and separation of finer fraction by air classification results in increase in the glass contents vis-à-vis raw fly ash. Mechanical activation results due to combined effect of particle breakage (surface area) and other bulk and surface physicochemical changes induced by the process of milling.
SELF GLAZED TILE
Conventionally ceramic tiles are produced by high temperature sintering/ vitrification of alumina-silicate and silicate minerals such as clay, quartz, feldspar, etc. The strength and other properties of tiles are developed due to formation of ceramic bonds. Development of stoneware tiles at 250-400°C by geopolymerisation of alumino-silicate minerals has been reported. The processing involved reaction between alumino-silicate mineral kaolinite and NaOH at 100°C-150°C resulting into the formation of hydro-sodalite
CONCLUSION
Due to their ability to polycondense Silicon and Aluminium into solid monolithic ceramic like structure during alkali activation, geopolymers have the potential of utilization of industrial wastes rich in silico-aluminates such as fly ash, GBFS, red mud, etc. Novel building materials such as high strength geopolymers cement can be developed by additional processing such as mechanical activation, and self-glazed tile and pavement tiles can be developed by synergistic use of industrial waste namely fly ash, GBFS and red mud. The developed geopolymer products qualify as new members in the spectrum of eco-friendly construction materials due to easy and simple processing, low energy requirement and no CO2 emission. The products have good commercialisation potential with significant returns