Abstract
Recently, there has been a great effort to incorporate industrial waste into cement-based materials to reach a more sustainable cement industry. In this regard, the Bayer process of obtaining alumina from bauxite generates huge amounts of waste called red mud. Few research articles have pointed out the possibility that red mud has pozzolanic activity. In view of that, the objective of this research is to analyse the short-term effects in the pore structure, mechanical performance and durability of mortars which incorporate up to 20% of red mud as a clinker replacement. As a reference, ordinary Portland cement and fly ash Portland cement mortars were also studied. The microstructure was characterised through mercury intrusion porosimetry and non-destructive impedance spectroscopy, which has not previously been used for studying the pore network evolution of red mud cement-based materials. The possible pozzolanic activity of red mud has been checked using differential scanning calorimetry. The non-steady state chloride migration coefficient and the mechanical properties were studied too. According to the results obtained, the addition of red mud entailed a greater microstructure refinement of the mortar, did not worsen the resistance against chloride ingress and reduced the compressive strength compared to control binders.
Highlights
Nowadays, recycling and reusing waste is an important challenge for achieving a more sustainable environment
The rise of the R1 with age and its higher values noted for the red mud mortars would agree with the mercury intrusion porosimetry results, especially with their important pore refinement noted, which has been explained in relation to the development of pozzolanic reactions of this addition [22,27]
The addition of red mud produced a higher microstructure refinement of the mortars compared to those made with cements type I and type II (Portland cement with fly ash), as shown by the higher number of pores with smaller diameters noted for red mud binders
Summary
Nowadays, recycling and reusing waste is an important challenge for achieving a more sustainable environment. Between the different wastes produced by industrial processes, it is important to highlight red mud, which is a residue generated by the digestion of bauxite minerals with caustic soda during the production of alumina through the Bayer process. For every tonne of alumina extracted, approximately 1.6 tons of red mud are produced and it is estimated that more than 66 million tons of this waste are generated annually worldwide [1,2]. This high amount constitutes a serious environmental problem, especially in areas where this industry is implanted. Red mud is generally presented as sludge with a concentration of solids
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