EFFECT OF POZZOLAN PROPERTIES ON THE PROPERTIES OF BUILDING COMPOSITES

Abstract

Pozzolans were used by ancient civilizations to enhance the properties of mortars and concrete and are now regaining popularity as sustainable, environmentally-friendly alternatives to cement. This paper studies the relationships amongst some properties of nine pozzolans and their impact on compressive strength and setting time of the resultant composites. Its objective is to assist in making informed choices in the selection of pozzolans for the production of mortars and concrete. Results indicate that each pozzolan has a specific water demand that increases with its specific surface area; and that a high water demand by the pozzolan slows down the setting of the paste but does not undermine the strength of the composite. It was also found that specific surface has a much greater influence on the water demand of the paste than particle size or lime:pozzolan ratio. The results exposed the adverse effect of a small water increase on setting time, and the lack of relationship between setting and reactivity. It was evidenced that the pozzolans accelerate the final set of lime by at least 40%, and that the specific surface area of the pozzolan and its amorphousness are the most important variables affecting reactivity and strength. Strength development and reactivity results allowed determining the most reactive pozzolans.