Reaction mechanism and compressive strength of geopolymer based on the synergistic excitation of red mud and rice husk ash

The main purpose of this study is to take advantage of the synergetic effect of two solid wastes (red mud (RM) and rice husk ash (RHA)) and also solve the problem that RM alone has low activity and poor geopolymerization. Thus, geopolymer was made using RM as the main raw material, RHA as the siliceous activated agent, and NaOH-water glass mixed alkali activator. The effect of RHA on the compressive strength of geopolymer based on RM was studied. Combined with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and other test methods, the reaction mechanism of the synergistic activation of geopolymer was revealed. The results indicate that the mechanical properties of RM-based geopolymer are significantly enhanced by RHA addition. With 30% RHA, its compressive strength reaches 15.8 MPa in 60 days, representing a 327% increase over pure RM geopolymer (3.7 MPa). The synergistic system produces a product dominated by N-A-S-H gel with a minor amount of C-(N)-A-S-H gel, forming a three-dimensional polyaluminosilicate network that becomes denser with prolonged curing. These findings demonstrate that RM–RHA geopolymer has promising potential for practical applications such as road base materials, non-load-bearing wall panels, and industrial flooring, offering a sustainable solution for the large-scale utilization of these two solid wastes.