Physico-Chemical Studies on Recycling of Some Industrial Wastes in the Manufacture of Building Materials

Abstract

This work focuses on characterization and measuring the activity of some of the industrial waste by-products. The selected waste by-products are; dealuminated kaolin (DK), silica fume (SF), air-cooled slag (AS} and water-cooled slag (WS). The feasibility of recycling these wastes in building materials and their hydration mechanism were a1so investigated. Although DK has a lower reactive silica content (less than 75 %) than SF (96

%), calorimetric studies and chemical activity in suspension proved that its reactivity is much higher,, especially at early age of hydration. Both AS and WS slags studied are hydraulically active at room temperature and WS has higher activity than AS. The hydration products of slag-lime mixes in suspension depend on the lime contents. In high lime mixes, calcium silicate hydrates and various hydrogamete series compositions formed. Calcium silicate hydrate, calcium aluminum silicate hydrate (CaAI2 Si7018.1.7H20) and calcium aluminum oxide hydroxide hydrate (Ca2AI(OH),.3H20) are formed in low lime slag mixes.

The hydration of the DK-Iime mixes indicate that tobemorite can be formed at I 00° C in the presence of aluminum and sulfate ions, provided the CIS ratio does not decrease below certain limits. Low Ca!Si ratio promotes the formation of poorly crystalline CSH and prevents the tobem1orite formation under hydrothermal processing at 180°C and up to 24 hours. Air-cooled slag-lime mixes attained a considerable strengths at room temperature. Thus, air-cooled slags of suitable compositions still can be exploited as hydraulic materials. Increasing the hydration temperature to I 00°C increases only the early age lime-slag reaction and compressive strengths (up to I day). However, reaction at I 00°C has little effect on the long-term hydration reaction rates of