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A discussion of the paper “pozzolanic activity of byproduct silica-fume from ferro-silicon production” by S. Chatterji, N. Thaulow, and P. Christensen
CEMENT and CONCRETE RESEARCH. Vol. 13, p. 585, 1983. 0008-8846/83 $3.00 + 00. Pergamon Press, Ltd.
Printed in the USA.
A DISCUSSION OF THE PAPER "POZZOLANIC ACTIVITY OF BYPRODUCT SILICA-FUME FROM FERRO-SILICON PRODUCTION" by S. CHATTERJI, N. THAULOW, AND P. CHRISTENSEN* Alan D. Buck and J. Pete Burkes Department of the Army Waterways Experiment Station P.O. Box 631, Vicksburg, MS 39180 The authors quote us ( I ) as saying the fume we examined was an e f f e c t i v e pozzolan; they then suggest on the basis of t h e i r x - r a y d i f f r a c t i o n r e s u l t s that the presence or absence of calcium hydroxide in t h e i r mixtures showed the fumes they examined to have low pozzolanic a c t i v i t y . We consider the strength indicated by tests of portland cement-pozzolan or of lime-pozzolan mixtures (by ASTM C 311 and C 618) as an appropriate basis for evaluation of the a c t i v i t y of a pozzolan. Our statement ( I ) t h a t ours was an e f f e c t i v e pozzolan was based on such strength tests plus the chemical r e a c t i v i t y with calcium hydroxide we described ( I ) plus expansion reduction tests (ASTM C 441, s u l f a t e r e s i s t a n c e ) . The Pozzolanic A c t i v i t y Index requirements in Table 2 of ASTM C 618 are t h a t the strength of t e s t mixture to control mixture with cement be a minimum of 75 percent at 28 days and that the t e s t mixture have a minimum strength of 800 psi at 7 days with lime. Our fume was 145 percent of the control mixture with cement at 28 days. While i t was not possible to make the s p e c i f i e d t e s t with lime because the fineness of the fume prevented t h i s t e s t as described, we did obtain a 7-day strength of 1870 psi using 200 g of fume, 100 g of lime, 375 ml of water, and a flow of 88. I t was not the purpose of our paper to r e p o r t on the pozzolanic a c t i v i t y of s i l i c a fume; we took t h a t as established. We sought to evaluate the e f f e c t i v e ness of the s i l i c a fume in doing things other pozzolans can do and found i t did them b e t t e r , i . e . , less fume was needed f o r a given e f f e c t than was needed of other pozzolans. We consider the work reported by the authors as i n t e r e s t i n g but not a wholly s a t i s f a c t o r y basis for judging pozzolanic a c t i v i t y , e s p e c i a l l y so since our own work ( I ) showed t h a t such factors as mixture proportions and water contents w i l l a f f e c t presence and amount of calcium hydroxide t h a t may be detected by X-ray diffraction. Perhaps the authors can provide some strength data of the sort referenced in ASTM C 618 to support t h e i r conclusion t h a t t h e i r s i l i c a fumes had low pozzolanic a c t i v i t y . ( I ) A.D. Buck, and Jo Pete Burkes, "Characterization and R e a c t i v i t y of S i l i c a Fume," Proceedings of the Third I n t e r n a t i o n a l Conference on Cement Microscopy, Houston, 1981, pp. 279-285. *CCR 12, 781-784 (19~'2). -
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585
Printed in the USA.
A DISCUSSION OF THE PAPER "POZZOLANIC ACTIVITY OF BYPRODUCT SILICA-FUME FROM FERRO-SILICON PRODUCTION" by S. CHATTERJI, N. THAULOW, AND P. CHRISTENSEN* Alan D. Buck and J. Pete Burkes Department of the Army Waterways Experiment Station P.O. Box 631, Vicksburg, MS 39180 The authors quote us ( I ) as saying the fume we examined was an e f f e c t i v e pozzolan; they then suggest on the basis of t h e i r x - r a y d i f f r a c t i o n r e s u l t s that the presence or absence of calcium hydroxide in t h e i r mixtures showed the fumes they examined to have low pozzolanic a c t i v i t y . We consider the strength indicated by tests of portland cement-pozzolan or of lime-pozzolan mixtures (by ASTM C 311 and C 618) as an appropriate basis for evaluation of the a c t i v i t y of a pozzolan. Our statement ( I ) t h a t ours was an e f f e c t i v e pozzolan was based on such strength tests plus the chemical r e a c t i v i t y with calcium hydroxide we described ( I ) plus expansion reduction tests (ASTM C 441, s u l f a t e r e s i s t a n c e ) . The Pozzolanic A c t i v i t y Index requirements in Table 2 of ASTM C 618 are t h a t the strength of t e s t mixture to control mixture with cement be a minimum of 75 percent at 28 days and that the t e s t mixture have a minimum strength of 800 psi at 7 days with lime. Our fume was 145 percent of the control mixture with cement at 28 days. While i t was not possible to make the s p e c i f i e d t e s t with lime because the fineness of the fume prevented t h i s t e s t as described, we did obtain a 7-day strength of 1870 psi using 200 g of fume, 100 g of lime, 375 ml of water, and a flow of 88. I t was not the purpose of our paper to r e p o r t on the pozzolanic a c t i v i t y of s i l i c a fume; we took t h a t as established. We sought to evaluate the e f f e c t i v e ness of the s i l i c a fume in doing things other pozzolans can do and found i t did them b e t t e r , i . e . , less fume was needed f o r a given e f f e c t than was needed of other pozzolans. We consider the work reported by the authors as i n t e r e s t i n g but not a wholly s a t i s f a c t o r y basis for judging pozzolanic a c t i v i t y , e s p e c i a l l y so since our own work ( I ) showed t h a t such factors as mixture proportions and water contents w i l l a f f e c t presence and amount of calcium hydroxide t h a t may be detected by X-ray diffraction. Perhaps the authors can provide some strength data of the sort referenced in ASTM C 618 to support t h e i r conclusion t h a t t h e i r s i l i c a fumes had low pozzolanic a c t i v i t y . ( I ) A.D. Buck, and Jo Pete Burkes, "Characterization and R e a c t i v i t y of S i l i c a Fume," Proceedings of the Third I n t e r n a t i o n a l Conference on Cement Microscopy, Houston, 1981, pp. 279-285. *CCR 12, 781-784 (19~'2). -
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585