This paper delineates some of the interesting results obtained during the course of experiments that were conducted using a Differential Thermal Analysis (D.T.A.) apparatus on Calcined Clay puzzolana. The soils tested were of predominantly single mineral types- some Kaolins and bentonites. Single-mineral types were first chosen for studies, as it was felt that any systematic approach to the understanding of the properties of burnt-clay puzzolana should begin with such soils in preference to those of the mixed types, for, it is known in a general way that the mineralogical nature of a soil has close connection with puzzolanic activity.
The salient features of the conclusions that have emerged out of these studies are as follows:—
(1) Kaolinite soils exhibit high puzzolanic activity while pure kaolin exhibits highest activity.
(2) The temperature of calcination conducive to highest puzzolanic activity for these soils is located in the vicinity of the “end-point” of the endothermic reaction trough, as exemplified by the differential thermal curve of kaolin.
(3) The physical changes accompanying the structural breakdown of the kaolinite soils which lose their lattice mater irreversibly on calcination to about 700°C, seem to be responsible for the highest activity of these soils. Soil-clay minerals of montmorillonite types do not exhibit such high activity as their lattice water is not lost irretrievably.
(4) An interesting application of the differential thermal technique is that of a quality control device in the large scale manufacture of burnt-clay puzzolana.
