The high embodied energy and Carbon emissions of traditional binders have led to a search for alternative cements. This paper explores the composition and reactivity of a red mud (RM) generated in vast quantities in Saudi Arabia, with a view to replace non-sustainable binders in construction.
RM waste is produced when refining bauxite for the production of aluminium. Previous authors estimate that 70-120 million tons of RM are generated annually, and stored on land or in the ocean near alumina refineries. In Ma’aden, current production is around 6,000 tonnes per day (over 2 million tonnes per year) which leads to long term disposal problems and land decommissioning costs. To date, due to its high alkalinity, only small quantities RM (3 wt.%) have been incorporated into Portland cement. However, the quantities need to raise to at least 5-10% for a worthy disposal option, and a viable option has not yet been found.
This paper studies the physical properties, composition and reactivity of the Saudi RM, and concludes on its possible application as a binder. The silica content and alkalinity are considered, as well as the specific surface area and composition which determine reactivity. According to the results, the RM presents abundant surface available to reaction, superior to commercial Portland cement and to other pozzolanic and supplementary cements such as FA and GGBS. The results also evidenced that gibbsite- Al (OH)3 , hematite -Fe₂O3 and cancrinite – Na₆Ca₂[(CO₃)₂|Al₆Si₆O₂₄]• 2H₂O are the main components of the RM, and that some Boehmite- ϒ- AlO(OH) is also present, inherited form the parent bauxite. The high alkalinity and temperature of the Bayer process have transformed the original kaolinite into cancrinite. The phase transformation of the RM resulting from the pyroprocessing at several temperatures are determined with X-Ray Diffraction analyses. The paper explores the evolution of the crystalline phases and their reactivity based on the setting and strength development.
Dr. Sara Pavia is a Professor in the Dept. of Civil Engineering, University of Dublin Trinity College. Her work focusses on sustainable materials and construction including thermal insulation, alkali-activated cements and pozzolanic binders, earth construction, building limes, bio-aggregate concretes and waste activation. She also works on historic buildings in both industry and academia.
She has published seven books and 150 papers and she often works in industry, for Government bodies and in several European groups such as RILEM and CEN.