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RECYCLING OF FLY ASH IN CEMENT MANUFACTURING

J. Paceagiu

Abstract

This paper presents the results obtained by utilization of pulverized coal fly ash both as raw mix component for Portland cement clinker and as admixture to cement type CEM II/B-V, too. The fly ash was analyzed from point of view of chemical, mineralogical and of radioactivity content. Two samples of raw mixes were prepared, one with raw materials as a reference sample consisting from limestone, clay, sand and pyrite cinder, and another with 10.14\% fly ash instead of clay. Raw mixes were ground at a fineness expressed by a residue R009 of about 10\%. Grindability and burnability of raw mixes were evaluated as well as the heat theoretic consumption. Both raw mixes were sintered at 1450oC. The produced clinkers were analyzed by chemical, optical microscopy and X-ray diffraction analyses. They are characterized by high silica modulus (approx. 2.4), a lime saturation factor of 0.96 and alumina modulus of 1.45. From mineralogical composition point of view do not appear important modifications compared with a clinker having same modulus characteristics but which contains clay as silica/aluminous component in raw mix. The cements were obtained through grinding of laboratory clinkers with addition of gypsum, with and without addition of 30\% fly ash up to fineness about 3500 cm2/g. Physical and chemical characteristics of cements comply with requirements of SR EN 197-1. Besides this, the cements showed comparable mechanical strength values at 2, 7 and 28 days; the cement without fly ash additions attained the strength class 42.5N, while the cement with 30\% fly ash attained class 32.5R.

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