Abstract
Calcined clays have been used in pozzolanic portland cement manufacturing in Brazil for many years. However, their color imposes commercial limitation when cements show reddish or pinkish hues. This work presents two case studies consisting of reducing process calcination of two clays by reducing process in: electric static furnace to obtain maximum temperature (700–1000 °C) and burning time (5–20 min) conditions, as a function of color and pozzolanic reactivity, and; rotary kiln for both laboratorial and industrial scales. Chemical (XRF, TGA/DTA), mineralogical (XRD), physical-mechanical (compressive strength), pozzolanic reactivity (Chapelle´s method and Strength Activity Index) and color test (colorimeter spectrometer using CIE color system standard) were applied in clays and pozzolanic cements characterization. Results show satisfactory performance of grayish pozzolanic cements, and indicate an alternative process to obtain calcined clays according to cements specifications.
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