The design of cementitious composites with advanced thermal properties

Abstract

The phyllosilicate mineral pyrophyllite can be utilized in cementitious composites design to replace quartz powder and boost workability, early strengths, and refractoriness. Employed as a mineral additive or microfiller, pyrophyllite is stable at high temperatures owing to its thermal conversion into mullite. In this study, mortar samples were prepared using andalusite as aggregate, high-alumina cement as a binder, and pyrophyllite as an additive (15%, 25%, and 35%). Compressive and flexural strengths, both at normal and elevated temperatures (samples were thermally treated at 1000°C) were tested on the samples, along with the refractoriness. The effects of pyrophyllite addition on the mineral composition, microstructure, and bonding and sintering mechanisms were studied using instrumental analytical techniques. Pyrophyllite acted as additional pozzolana during cement hydration as it formed microreinforcement in the shape of crystalline folia within the microstructure, which improved the compressive strengths of mortars. The differential thermal analysis highlighted that pyrophyllite did not negatively interfere with the cement hydration route; moreover, this mineral additive behaved as pozzolana. The investigation demonstrated that pyrophyllite additions of up to 25% can be used in cementitious composites without affecting their performance.