Physicochemical characteristics of fired clay-limestone mixes

The effect of calcination temperature on Belbeis clay and Sammlout limestone as well as hydration characteristics of calcined products were investigated. Three mixes 50/50, 60/40, 70/30 wt.\% clay-limestone were calcined at 700, 800, 900, and 1,000 degrees C for 2 h, then hydrated for up to 90 days. The degree of calcination was investigated from the free lime content and the ignition loss for each mixture. Also, the mineralogical composition of the fired mixes was investigated with the aid of X-ray diffractometry. The results revealed that the free lime of each mix increased up to 800 degrees C then decreased gradually up to 1,000 degrees C. Mix 60/40 clay-limestone fired at 800 degrees C shows the presence of Ca(OH)(2) with quartz. As the firing temperature increased gehlenite appeared and increased up to 1,000 degrees C with the disappearance of lime. Mix 50/50 gave the highest hydration kinetics as measured from determination of free lime and combined water contents. As the limestone decreased, the rate of hydration decreased. The suitable firing temperature of the clay-limestone mixes was 800 degrees C for 2 h. (C) 2000 Elsevier Science Ltd. All rights reserved.