Effects of vermiculite on in-situ thermal behaviour, microstructure, physical and mechanical properties of fired clay bricks

Vermiculite is a hydrous clay mineral that occasionally occurs in raw materials for brickmaking. The presence of vermiculite affects the drying and firing processes of brick production; thus, the functions of this clay mineral should be clarified. In this study, vermiculite from 0 wt% to 30 wt% have been added to clay mixtures for brick button firing. Through effective integration of in-situ XRD, thermogravimetric and dilatometric analyses, the realtime thermal behaviours have been interpreted, and the microstructure, physical and compressive characteristics of brick buttons have been investigated. The incorporation of vermiculite has changed the temperatures of kaolinite dehydroxylation and rutile formation. Enstatite, cordierite and amorphous contents increased in fired brick buttons, while mullite, quartz and cristobalite decreased. Vermiculite retained a partial sheet-like morphology at 1150 degrees C firing. From 25 to 1150 degrees C, five weight loss steps have been defined with six shrinkage/expansion processes observed. Cracks appeared on brick button surfaces when 30 wt% of vermiculite was added. The colour of fired brick buttons changed from "light camel" to "black olive". Drying shrinkage, firing shrinkage and bulk density increased with an increased proportion of vermiculite. The maximum compressive strength reached 150.94 MPa (a rise of 21.6% towards the control sample) when 5 wt% of vermiculite was added.