Coal gangue (CG) is a residual product from coal mining and washing processes. The reutilization of CG to produce geopolymers is a low-carbon disposal strategy for this material. In this study, the calcined CG (CG_700°C) was used as aluminosilicate precursors, and the effects of alkali activators (i.e., Na₂SiO₃/NaOH, NaOH concentration, and liquid–solid) on the mechanical characteristics and microstructure of CG_700°C-based geopolymers were investigated. The findings indicated that the specimens with a liquid–solid ratio of 0.50 (G_2.0-10-0.50) exhibited a compact microstructure and attained a compressive strength of 24.75 MPa. Moreover, increasing the Na₂SiO₃/NaOH mass ratio has shortened the setting times and facilitated geopolymer gel formation, resulting in a denser microstructure and improved compressive strength. The higher NaOH concentrations of alkali activators facilitated the dissolution of CG_700°C particles, and the geopolymerization process was more dependent on the condensation of SiO₄ and AlO₄ ions, which promoted the formation of geopolymer networks. Conversely, an increase in the liquid–solid ratio from 0.50 to 0.65 had a negative impact on compressive strength enhancement, impeding the polycondensation rate. Examination through scanning electron microscopy and mercury intrusion porosimetry revealed that employing a lower Na₂SiO₃/NaOH mass ratio (G_1.2-10-0.55), smaller NaOH concentrations (G_2.0-8-0.55), and a higher liquid–solid ratio (G_2.0-10-0.65) led to the presence of larger pores, resulting in decreased 28 days compressive strength values (15.87 MPa, 13.25 MPa, and 14.92 MPa, respectively), and a less compact structure. The results suggest that the performance of CG_700°C-based geopolymers is significantly influenced by alkali activators.

By reutilizing industrial byproducts, inorganic cementitious alkali-activated materials (AAMs) contribute to reduced energy consumption and carbon dioxide (CO₂) emissions. In this study, coal gangue (CG) blended with ground granulated blast furnace slag (GGBFS) was used to prepare AAMs. The research focused on analyzing the effects of the GGBFS content and alkali activator (i.e., Na₂O mass ratio and alkali modulus [SiO₂/Na₂O]) on the mechanical properties and microstructures of the AAMs. Through a series of spectroscopic and microscopic tests, the results showed that the GGBFS content had a significant influence on AAM compressive strength and paste fluidity; the optimal replacement of CG by GGBFS was 40–50%, and the optimal Na₂O mass ratio and alkali modulus were 7% and 1.3, respectively. AAMs with a 50% GGBFS content exhibited a compact microstructure with a 28 d compressive strength of 54.59 MPa. Increasing the Na₂O mass ratio from 6% to 8% promoted the hardening process and facilitated the formation of AAM gels; however, a 9% Na₂O mass ratio inhibited the condensation of SiO₄ and AlO₄ ions, which decreased the compressive strength. Increasing the alkali modulus facilitated geopolymerization, which increased the compressive strength. Microscopic analysis showed that pore size and volume increased due to lower Na₂O concentrations or alkali modulus. The results provide an experimental and theoretical basis for the large-scale utilization of AAMs in construction.

The reuse of coal gangue (CG) and ground-granulated blast furnace slag (GGBFS) to synthesize geopolymers presents a sustainable strategy for industrial waste recycling. This study investigates the influences of various GGBFS/CG mixtures on the mechanical behavior and microstructure of the synthesized geopolymers. Results show that the geopolymer matrix is composed of calcium aluminosilicate (C-(A)-S-H) and sodium aluminosilicate (N-A-S-H) hydrates, which is essential for enhancing the compressive strength of the specimens. With 100% GGBFS, the geopolymer matrix sets in 17 min, reaching a compressive strength of 107.55 MPa after 28 days. As the CG content increases, both compressive strength and compactness decrease gradually, while the setting time prolongs. When the GGBFS/CG mass ratio is 1:1, the specimens’ setting time increases by 64.7% (from 17 to 28 min). The corresponding compressive strengths at 3 days, 7 days, and 28 days are recorded to be 46.73 MPa, 53.25 MPa, and 54.59 MPa, respectively. Specimens with 100% CG exhibit a prolonged setting time (122 min), but the compressive strength is just 21.80 MPa. Microscopic analysis reveals that specimens with 50% CG have smaller average pore diameters (22.84 nm) and a compact microstructure. These findings indicate that the GGBFS content significantly influences geopolymer performance, highlighting the effective utilization of GGBFS/CG wastes.

To address challenges posed by waste tires and greenhouse gas emissions associated with ordinary Portland cement, exploring eco-friendly construction materials is critical for sustainability. This study examines the workability and mechanical properties of straight steel fiber-reinforced rubberized geopolymer concrete (SFRRGC), where rubber powder is derived from recycled waste tires. The experimental variables included rubber powder (RP) content (0%, 6%, 12%, and 20% by volume of fine aggregate) and steel fiber (SF) content (0%, 0.5%, 1.0%, and 1.5% by volume). The results show that incorporating RP and SFs reduced the workability of SFRRGC but increased its peak strain. Specifically, RP addition decreased the elastic modulus, compressive strength, and toughness; increasing the SF content enhanced energy dissipation, while the effects of SF and RP contents on Poisson’s ratio were negligible. The specimens showed that a higher RP content would weaken the crack-bridging effect of SF. For example, specimens with 1.0% SF and 6% RP achieved 49.56 MPa compressive strength and 4.04 × 10⁻³ maximum peak strain; those with 0.5% SF and 20% RP had 118.40 J compressive toughness, which was 5.53% lower than that of the reference specimens (125.33 J). Furthermore, a constitutive model for SFRRGC was proposed, and its theoretical curves aligned well with the experimental results. This proposed model can reliably predict the stress–strain curves of geopolymer concrete with different SF and RP mixture proportions.

Square steel tube–high-strength spiral stirrup composite confined concrete (SHSCC) columns combine the advantages of external steel tube confinement and internal high-strength spiral reinforcement, offering considerable potential for improving the seismic performance of composite columns. However, systematic investigations of their cyclic compression–bending behaviour over a broad range of key design parameters remain limited, and the relative importance of these parameters has not been sufficiently clarified. In this study, a three-dimensional nonlinear finite element model was established in ABAQUS and validated against one experimental specimen in terms of hysteretic response, skeleton curves, ultimate lateral load and failure mode. The differences between the numerical and experimental peak lateral loads were 3.6% and 16.8% in the positive and negative loading directions, respectively, while the difference between the average absolute peak loads was approximately 7.5%. Based on the validated model, a comprehensive parametric study was conducted to investigate the influences of axial compression ratio, concrete strength, spiral spacing, spiral bar diameter and steel tube thickness on the cyclic behaviour of SHSCC columns. The results showed that increasing the steel tube thickness from 4 to 7 mm increased the ultimate lateral load, ductility coefficient and initial stiffness by 62.3%, 26.9% and 52.0%, respectively, indicating a pronounced beneficial effect of steel tube thickness within the investigated range. Increasing the axial compression ratio to 0.90 reduced the ultimate lateral load by 37.8% and the ductility coefficient by 31.8%, indicating a pronounced deterioration in cyclic performance at high axial compression levels. Increasing the concrete strength from C30 to C60 increased the ultimate lateral load and initial stiffness by 12.2% and 22.9%, respectively. In contrast, increasing the spiral spacing from 20 to 200 mm reduced the ultimate lateral load and ductility coefficient by 5.2% and 30.8%, respectively, whereas changing the spiral bar diameter from 8 to 12 mm produced only a 2.5% increase in ultimate lateral load. These results quantitatively clarify the relative effects of the principal design parameters on the cyclic response of SHSCC columns and provide numerical evidence for parameter selection and seismic performance optimization.