Study on Mechanical Properties and Hydration Characteristics of Bauxite-GGBFS Alkali-Activated Materials, Based on Composite Alkali Activator and Response Surface Method

To address the limitations in determining the amount of activator and optimizing the mix proportion during the preparation of bauxite tailings (BX)-based alkali-activated materials (AAMs), as well as the insufficient research on the interactions of multiple factors, this study aims to synthesize and optimize composite cementitious materials with BX and granulated blast furnace slag (GGBFS) as precursors via response surface methodology and central composite design (RSM-CCD). The optimal alkali activator proportion and slag content for alkali-activated, bauxite tailing, powder slag cementitious materials were investigated. A series of tests, including XRD, FTIR, TG-DSC, and SEM-EDS, were used for analysis to further investigate the effects of the alkali activator dosage on the mechanical properties and the influence of the slag content on the hydration products and microstructure. The results show that the optimal composition of alkali-activated bauxite tailings-based cementitious material is 35% slag content, 4% alkali content, a water glass modulus of 1.3, and a water-solid ratio of 0.32. The relationship model between the activator parameters and compressive strength fits well, with model determination coefficients of 0.9803 for <i>f</i>_3c and 0.9789 for <i>f</i>_28c. The identified hydration products were mainly C-S-H and C-(N)-A-S-H gels in the form of SiQ₃ and SiQ₄ tetrahedra. The SEM-EDS results show that the incorporation of slag changes the silicon-aluminum ratio of the system, promoting an increase in the content of hydration products and increasing the complexity and density of the structure. GGBFS also has a micro-aggregate filling effect and a nucleation effect, which improve the distribution of hydration products. This study demonstrates the significant potential of BX in the preparation of cementitious materials, which contributes to the sustainable development of the construction industry.