Properties of calcined lias delta clay—technological effects, physical characteristics and reactivity in cement

Abstract

The investigation reveals chances for calcined clay comprising a mixture of different clay minerals as supplementary cementitious material. There is ample supply in southern Germany of the source material with its quartzous clay combined with a high content of mica and other clay minerals. Its content of kaolinite is less than 25% by mass. The calcinations were done following two different procedures. On laboratory scale the raw clay was dried initially, crushed to a maximum particle size of less than 4 mm and subsequently calcined in small quantities of 50 g in a muffle furnace. On an industrial scale the raw clay was crushed coarse to a maximum particle size of 100 mm and subsequently fed in campaigns of 180 tons each into a tripartite rotary kiln normally used for the production of expanded clay. The resulting calcined clay particles had a maximum size up to 40 mm. Characteristic chemo-mineralogical properties and physical parameters (e.g. mineral composition and amorphous content, lime-retention, ion solubility in alkaline medium and BET-surface) of the calcined clays were measured. The comparison of the clays calcined in the laboratory and those calcined on industrial scale revealed a broader optimum temperature range for the latter accompanied by a partially reduced pozzolanic reactivity when used in combination with cement.