Pozzolanic Properties of Metakaolin Obtained from Paper Sludge

Abstract

This paper presents a research carried out to convert paper sludges from de-inking and water-treatment processing plants into a pozzolanic product usable in the cement and concrete industries. Paper sludges contain inorganic fillers like ground limestone, kaolinite, clay and organics. The process consists of heat treatment in the range of 600 to 700 degrees C in order to transform the kaolinite present in the sludge into metakaolinite, a very reactive pozzolan, without the formation of large amounts of free lime (due to decarbonation of the calcite also present in the sludge). In addition, the organic compounds in the sludge must be burned off and their presence reduces the use of fossil fuels to reach to temperature needed for processing. The results of both laboratory and field tests show the feasibility of the process. A reactive pozzolan is obtained when the amount of kaolinite present in the sludge is higher than 20% of the dry inorganic phase. This metakaolin is sometimes more reactive than that obtained by calcining pure kaolinic clays, and can be used to enhance the durability of concrete in severe environments.