Long term stability of concrete made from red sand in a marine environment

Abstract

The desire of the minerals industry to be more sustainable has led towards the increasing development of by-products. One such industry is the production of Alumina. The Alumina industry in Australia is the major producer of alumina in the western world with over 25 million tonnes of Bauxite Residue per annum. Alcoa World Alumina (Alcoa) has three refineries in Western Australia producing approximately 20,000 tonnes of Mud and a similar level of Red Sand each day. These as yet unutilised potential resources are being stockpiled, occupying a significant footprint. It is widely recognised within industry that there would be economic, environment and social benefits if a sustainable use for these materials were found. One such potential by-product is the production of coarse bauxite residue (Red Sand), neutralised and washed low in salt. The main purpose of this research was to establish a potential market for this material, through scientific evaluation of Red Sand as a replacement of natural fine aggregate (Natural Yellow Sand) in concrete mixes. For this research, the mixed stream of Bauxite Residue (fine and coarse) obtained in the Bayer process was neutralized by a process of carbonation then washed using cyclones and counter current wash towers to a value added byproduct. The coarse particles (Washed and Carbonated Sand-WCS) of the stream were separated by Wet High Intensity Magnetic Separation technique (WHIMS) so that different segments such as High Iron Sand (HIS) and Low Iron Sand (LIS) were formed. Physical, chemical and mineralogical properties of these materials have been tested and compared with that of natural sand. Several mixes of concrete were then designed using Red Sand as a fine aggregate in order to verify their effects on strength and durability indicators of concrete.The comparative analysis between normal mix proportions and the mix proportions utilizing Red Sand was also achieved. In addition, the impact of marine environment on concrete mix design and properties of manufactured concrete were evaluated with a series of standard laboratory tests. The findings were promising in terms of both mechanical properties and durability and suggested that Red Sand, in particular Low Iron Sand is likely to be effective in place of fine aggregates and can be used within marine grade concrete with no major differences when compared to normal concrete. From the results obtained, it can be deduced that this material can be used in a wide range of concrete applications in Civil Engineering and Construction.