Hydration characteristics of calcined clay limestone

On calcining clay and limestone up to 1000 degreesC some physicochemical reactions occur leading to change of the nature of Clay minerals and giving pozzolanic and cementitious properties for burnt clay. The dehydration of clay gives the metakaolin as an amorphous mixture of Al2O3 and SiO2. The limestone is dissociated and calcium silicate as well as aluminosilicate such as gehlenite and anorthite are formed. The aim of this article is to investigate the hydration characteristics of fired clay limestone. Three mixes having the composition 50/50, 60/40 and 70/30 are calcined from 700 degreesC up to 1000 degreesC for 4 hours and suspended hydrated up to 90 days. The kinetics of hydration were measured from the free and combined water contents as well as the hydration products by XRD analysis. The results revealed that the free lime contents are sharply decreased up to 28 days and slightly decreased up to 90 days for the samples fired at 800 degreesC. Also, the combined water increases with firing temperature as well as limestone content. The XRD patterns of the fired 60/40 mix show that the gehlenite hydrate as well as CSH increases with firing temperature up to 900 degreesC. The CSH increases and the Ca(OH)(2) is completely consumed with curing time up to 90 days. Finally we can conclude that, mix II 60:40 clay/limestone fired at 800 degreesC for 4 hours gives reasonable hydration characteristics, which can be used as building material.