Properties of a High-Alkali Lignite Fly Ash in Concrete


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Title: Properties of a High-Alkali Lignite Fly Ash in Concrete

Author(s): R. Doug Hooton

Publication: Special Publication

Volume: 91


Appears on pages(s): 333-346

Keywords: alkali-aggregate reactions; alkali content; concretes; fly ash; freeze-thaw durability; lignite; strength; sulfate resistance.

Date: 2/1/1986

Recently, a high alkali high calcium fly ash, (6 t o 7.5 % Na20 equivalent) has started to be produced from Western Canadian lignite coal at Ontario Hydro’s Thunder Bay Generating Station. Because of its high alkali content, ASTM C 441 mortar bars containing Pyrex fine aggregate and 25 volume percent fly ash were tested initially. Even with its 2.9% available alkali content , the fly ash replacement reduced expansions at one year by approximately 50 percent relative to the high-alkali portland cement alone.Based on the C441 results and good pozzolanic properties, a program was undertaken to evaluate the performance of this lignite ash in air-entrained concrete. In this program, strength deve lopment, air-void parameters, resistance to freezing and thawing (ASTM C 666 Procedure A), permeability, and pore size parameters were evaluated. For up to 35 weight percent replacement with fly ash and with mixtures adjusted to constant slump, significantly lower water to cementing materials ratios were achieved, equal strengths were attained in only 6 days along with higher later-age strengths, freezing-and-thawing resistance was excel lent and permeabilities and porosities were reduced. In addition, while the sulfate resistance of many lignite ashes is poor , the performance of ASTM C 1012 mortar bars with 35 weight percent replacement for a 12.8% C 3 A portland cement was similar to that for moderate sulfate resisting portland cements (C3A L, 8 .0 %).