Factors Influencing the Mechanical Properties and Reaction Kinetics of Wasted Ultrabasic Tuff Used as a Binder

Abstract Ultrabasic tuff powder, a solid waste generated from manufactured sand and aggregate production without calcination treatment, contains less than 45% SiO 2 stabilized in aluminosilicate. Due to its high crystallinity, few studies have explored its viability as a raw material for binder preparation. Using an orthogonal experimental design, this study revealed the impacts of three key factors on the mechanical properties of ultrabasic tuff-based binder (UTB): the mass ratio of silica to alumina (S/A), the mass ratio of sodium oxide (Na 2 O) to binders (N/B), and curing temperature ( T ). To elucidate the reaction kinetics, an array of analytical techniques, including Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS), were employed. The results indicate that an increase in S/A and T enhanced the dissolution degree of precursors, along with improved compressive strengths. Conversely, an increase in N/B led to a minimal reduction in the dissolution degree, with compressive strengths initially rising and then declining. The optimal combination of three factors was S/A = 5, N/B = 0.10, and T  = 80°C, resulting in a maximum compressive strength exceeding 80.0 MPa. The ratio of dissolved silicon (Si) to aluminum (Al) was approximately 50:1, signifying a composition profoundly different from traditional alkali-activated binders. Additionally, the proportions of dissolved silica (SiO 2 ) and alumina (Al 2 O 3 ) were determined to be 46.38% and 4.48% of the total, respectively, suggesting that UTB comprised both reactive and unreactive components. The reactive portion, consisting of quartz, calcite, chlorite, and silica fume, forms an amorphous (N, C)-A-S-H gel, connecting with the unreactive part.