Red mud additive effect on fluidity, strength features and microstructure of viable geo-polymer grouting materials

Abstract

Being an alkaline solid waste, Bayer red mud (RM) is made during alumina extraction, whereas fly ash (FA) is a byproduct made during aluminum creation. RM-FA based geopolymer grouting materials were prepared for the first time by composite excitation of NaOH and NaSiO3. To enable RM's large-scale use, effect of RM content ranging from 50 % to 90 % on fluidity and strength features of grouting materials was investigated. UCS of samples with diverse RM content and ages was predicted to verify the synergistic effect of RM and FA. Some practices such as SEM and NMR were employed to analyze geopolymerization products and their pore structures. Lab findings direct that slurry's flow was enhanced by low equilibrium moisture content of RM and its slow geopolymerization reactivity during hardening. As a shear thinning slurry, its mini-slump is above 170 mm. FA can fast react to form geopolymer gel to run initial strength for hardened slurry while late-age UCS could be improved by continuous Si/Al dissolution in RM. 28-day UCS increased to 12.29 MPa as the RM content in hardened slurry reaching to 60 %, and actual strengths are higher than forecast ones. The plenty of geopolymerization products rises inter-gel and fine capillary pores' ratios while reducing total pore volume, which contributes to the development of slurry strength. However, as the RM content in the hardened slurry continues to rise, excess Na2O crystals form, leading to a transition of pores into larger vessel pores and a rise in total pore volume. Ultimately, the current study delivers valuable insights into designing viable grouting materials with low carbon emissions and high solid waste recycling rates.