Silicate bonded unsintered ceramics of Bayer process waste
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Sodium silicates are investigated to enhance the strengths of Bayer process muds and develop structural ceramics without sintering. With an impregnation of sodium silicate from 2% to 10% concentration in red mud, the fracture toughness is enhanced from 0.2 to 0.9 MPaVm. Compression strengths of 25.1 MPa (3628 psi) have been attained with red mud at 10% silicate concentration. Similar enhancements by a factor of 4 to 5 have been obtained for modulus of rupture and Brinell hardness number. It is shown that these properties do not deteriorate in acidic and neutral environment in water, implying stability to weathering conditions. SEM investigations reveal elongated crystal formation, possibly of aluminum and iron silicates in the aggregate. These crystals act like whiskers enhancing the strength. The process is applicable for development of low-cost construction components.
I. INTRODUCTION
Lateritic soils are defined by their unique property of hardening in the sun and rain and when exposed to the atmosphere.1 These soils are rich in aluminum and iron and cover most of the tropical countries. Jamaican bauxite, and the bauxite waste (red mud), which is a residue left after the extraction of alumina from the parent bauxite, are examples of laterites. This article deals with stabilization of red mud. In an earlier article,2 the development of sintered ceramics using red mud was reported. Unfortunately, sintering is an energy intensive process and sintered ceramics are expensive in many developing countries, where energy is scarce. In particular, the construction industry has been hard hit due to a lack of sintered bulk products such as bricks, and this can be seen in Jamaica, where the traditional brick industry has virtually become extinct due to the scarcity of energy. Often, in countries where sintered bulk construction components are in use, the environment is affected by the use of wood as a source of energy. This has resulted in widescale denuding of forests. It is, therefore, necessary to develop processes involving chemical stabilization, which can replace the traditional sintering techniques for the development of construction materials with local soils, and reduce the consumption of energy. The traditional stabilizing and bonding agent in the construction industry has been cement, in which calcium silicate hydrate plays a key role in the binding a)
Address correspondence to this author at Materials and Components Technology Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439. b) Current address: Jamaica Bureau of Standards, 6 Winchester Road, Kingston 10, Jamaica. 1094 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 5, May 1991 Downloaded: 13 Mar 2015
mechanism. An attempt was made to use cement to stabilize red mud and develop bricks in Jamaica.3 Unfortunately, the maximum compression strength of the bricks was only 4.83 MPa, and silica sand was a major component in the aggregate. The ASTM standard C62 for bricks requires a compression strength of 8.6 MPa (1250
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