Synthesis of structural binder for red brick production based on red mud and fly ash activated using Ca(OH)2 and Na2CO3

•Red mud and cementless CNF binder were explored as precursor for brick production.•Up to ∼81% of red mud and fly ash inclusion, 7-day strengths were ∼17-34 MPa.•The use of NaOH increased flowability and early strength in this binder system.•NaOH greatly improved the degree of reaction, resulting in more C-S-H formation.

This paper explored the effectiveness of red mud and a mixture powder of Ca(OH)2 (C), Na2CO3 (N), and fly ash (F) (denoted CNF powder) as precursor materials to produce an environment-friendly high strength brick product. Overall, despite the inclusion of up to ∼81% of red mud and fly ash, 7-day strengths were developed ∼17-34 MPa; this was high enough to be used as a structural binder for brick production. In particular, the use of NaOH was very effective in increasing flowability, and, more importantly, early strength in the red mud-CNF blended system, despite the red mud inclusion, because NaOH greatly improved the degree of reaction of the system, resulting in more calcium silicate hydrates (C-S-H) formation as well as significant pore size refinement at early days of curing. Trial bricks were also prepared to examine possible toxicity due to the inclusion of red mud and fly ash using the toxicity characteristic leaching procedure (TCLP) test and the TCLP concentrations were very low.