Steel fibers are widely used in cementitious composite materials to enhance their mechanical properties, such as tensile strength and toughness. However, the effectiveness of these fibers largely depends on their surface characteristics and bonding with the cement matrix. This study investigated the effects of various treatment processes on the microhardness and mechanical strength of steel fibers in cementitious composite materials. These methods include acetone and acid washing, silane coupling agent treatment, and nanosilica coating. Fibers washed with acetone exhibited a cleaner surface, primarily due to the removal of impurities. Acid treatment resulted in a notably roughened surface, which significantly enhanced mechanical interlocking with the surrounding matrix. Silane treatment led to an uneven surface with distinct vertical textures, potentially improving adhesion properties. Meanwhile, fibers treated with nanosilica displayed a coating of nanoparticles adhering to the surface, which may further influence the fiber–matrix interaction. The results of the mechanical properties tests indicated that nanosilica coating was the most effective in improving both the flexural and compressive strengths, especially in the early strengths in the cement matrix.

The efficient treatment and resource utilization of shield tunnel spoil (STS) are important for sustainable underground construction in China. To improve the early mechanical performance and microstructural compactness of stabilized STS, this study investigated the solidification effect of a novel early-strength cementitious agent (ESCA) and compared it with ordinary Portland cement (P.O 42.5). Macroscopic mechanical tests, including unconfined compressive strength (UCS), stress–strain behavior, mass, and P-wave velocity measurements, were combined with scanning electron microscopy (SEM) and computed tomography (CT) analyses to reveal the mechanical response and microstructural mechanisms of stabilized STS. The results indicate that, compared with P.O 42.5, ESCA exhibits superior fluidity at lower water-to-solid (w/s) ratios, significantly shorter setting times, and higher compressive strength at all curing ages. The solidification efficiency of ESCA for STS is notably superior to that of P.O 42.5, with the peak strength, elastic modulus, mass, and P-wave velocity of ESCA-solidified specimens being higher than those of P.O 42.5-solidified specimens across the five dosages. Furthermore, ESCA material bonds more tightly with STS particles, resulting in lower porosity and a denser microstructure under the same stabilizer dosage. Overall, the combination of macroscopic mechanical properties and microstructural characterization demonstrates that ESCA material exhibits significant advantages in the efficient solidification and resource utilization of shield tunnel spoil.

An asphalt pavement model was established using ABAQUS finite element simulation software. Based on the dynamic modulus of low-temperature modified asphalt mixtures, mechanical response analyses were performed on pavement models with different surface course materials. The influence patterns of low-temperature modified asphalt mixture surface courses on the tensile strain at the bottom of the asphalt layer, surface vertical displacement, and tensile stress at the bottom of the base course were investigated. The optimal combination was determined to be an upper surface course of AC-13 USP-SBS asphalt mixture and a lower surface course of AC-20 SBS asphalt mixture.