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.

Pretensioned precast pavement slabs exhibit reduced compressive stress near their free ends owing to the finite transfer length of prestressing strands. This study investigated an 800 mm self-stressing concrete end segment using five mixtures containing 0%, 6%, 10%, 12%, and 18% expansive agent and a 3700 mm × 975 mm × 240 mm instrumented slab monitored during strand release and for 180 days thereafter. The E10 and E12 restrained specimens developed calculated self-stresses of 1.36 and 1.53 MPa, respectively, whereas the E18 specimen exhibited a visible longitudinal crack. At 28 days, the expansive mixtures attained compressive and flexural strengths of at least 59.2 and 7.7 MPa, respectively. In the slab, strand-induced compression was approximately 0.50 MPa at 125 mm from the end and 1.25 MPa in the interior, indicating a local deficit of 0.75 MPa. The mean end-segment strain 24 h before release was 221.23 με, corresponding to 1.86 MPa of calculated restraint stress. Total compression at 125 mm reached 2.24 MPa immediately after release and was estimated at 1.58 MPa on day 140 before thermal correction. A full-length compatibility model estimated the end-plate device contribution at 0.12 MPa after release and 0.07 MPa on day 140. The monitored release response indicates that restrained expansion restored compression in the slab end relative to the interior reference.

This study aims to develop a green composite cementitious material (GCCM) by partially replacing cement with multiple industrial solid wastes and to further enhance its toughness by incorporating basalt fibers (BF) for the effective disposal of shield tunnel spoil (STS). The deterioration behavior of STS synergistically improved by GCCM and BF was systematically investigated under drying–wetting (D-W) cycles using unconfined compressive strength (UCS) tests, mass loss and P-wave velocity measurements, as well as industrial computed tomography (CT) and scanning electron microscopy (SEM). The results show that BF significantly improves the early-age strength and deformation toughness of STS, with an optimal UCS increase of about 13% at 0.45% BF. Although the mechanical properties of the specimens deteriorated with an increasing number of D-W cycles, the “bridging effect” of BF effectively inhibited the propagation and coalescence of cracks. Quantitative CT analysis further revealed that the addition of 1.00% BF reduced the pore volume (V_k) and crack volume (V_l) by 54.3% and 63.2%, respectively, after eight D-W cycles. The damage mechanism is primarily attributed to the loss of cementitious materials caused by water migration and the swelling–shrinkage stress of clay minerals. The three-dimensional (3D) network structure formed by BF, through its pull-out energy dissipation mechanism, effectively maintained the macro- and microstructural integrity of the material. This study highlights the novelty of combining GCCM with BF to enhance the long-term durability of STS, providing a theoretical basis and technical support for its green disposal and engineering application in complex environments.