Sulfate Resistance of Mortars Made from Cements Containing Fluidized-Bed Coal Combustion Wastes

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Title: Sulfate Resistance of Mortars Made from Cements Containing Fluidized-Bed Coal Combustion Wastes

Author(s): Z. Pytel

Publication: Special Publication

Volume: 242

Issue:

Appears on pages(s): 511-524

Keywords: aggressive environment; amount of C3A; blended portland cements; bottom ash; cement mortar; corrosive solution; delayed ettringite; durability to sulfate attack; linear dimension; mineral additives; sulfate exposure; sulfate resistance

Date: 4/1/2007

Abstract:
The purpose of the research program was to investigate how the addition of new-generation wastes produced in the coal-fired power plant, fluidized-bed type installations, impact mechanical properties and chemical durability of cements. Tests were made on cements derived from two portland cement clinkers containing widely different amounts of C3A. With addition of the fluidized-bed material from the brown and black coal combustion systems blended portland cements were made. The properties of these blended cements were compared with those of the reference portland cements. The composition of all cements was adjusted to achieve the maximum permissible amount of SO3 i. e. 3.5%. Three different curing procedures were used for mortar specimens: normal temperature and humidity conditions, low pressure steam curing, and autoclaving. Durability to sulfate attack was studied using two methods: one method involved monitoring of linear dimensions of 20 x 20 x 160 mm mortar prisms cured under different conditions and exposed to aqueous solutions of Na2SO4 and MgSO4, with 16±0.5 g/l concentration of SO42- anions. The other method involved investigation of changes of mechanical properties of 25x25x100 mm mortar prisms cured under different conditions and subjected to prolonged sulfate exposure. The strength of samples was measured after different times of exposure in sulfate. Five percent aqueous solutions of Na2SO4 and MgSO4 were used for sulfate immersion test. Compressive and flexural strength tests were measured after 90, 180, 365, and 730 days of exposure. SEM and EDS techniques were used for microstructure studies.