In high geothermal tunnels (>28 °C), curing temperature critically affects early-age concrete mechanics and durability. Uniaxial compression tests under six curing conditions, combined with CT scanning and machine learning-based crack analysis, were used to evaluate the impacts of curing age, temperature, and fiber content. The test results indicate that concrete exhibits optimal development of mechanical properties under ambient temperature conditions. Specifically, the elastic modulus increased by 33.85% with age in the room-temperature group (RT), by 23.35% in the fiber group (F), and decreased by 26.75% in the varying-temperature group (VT). A Weibull statistical damage-based constitutive model aligned strongly with the experimental data (R² > 0.99). Fractal analysis of CT-derived cracks revealed clear fractal characteristics in the log(Nr)–log(r) curves, demonstrating internal damage mechanisms under different thermal histories.

Conventional fabrication processes for fiber-reinforced composites are complex and stepwise, limiting their application in blast protection engineering. In this study, KH550 surface-modified glass fiber powder (1.5 wt%) was incorporated into a polyurea matrix, and a homogeneous glass fiber-reinforced polyurea (GFRPU) composite was successfully synthesized via an optimized one-step spray process. The strain-rate-dependent mechanical behavior (0.01–100 s⁻¹), fracture mechanisms, molecular structure, and blast mitigation performance of GFRPU were systematically investigated through mechanical testing, SEM, FTIR, 75 g TNT contact explosion tests, and calibrated and partially verified finite element simulations. Results show that the surface-modified fibers form chemical crosslinks with the matrix, shortening the N–H hydrogen bond length from 3.023 Å to 2.983 Å and increasing the hydrogen bonding degree of the urea carbonyl region from 80.0% to 84.1%, thereby enhancing structural ordering and strength. At a strain rate of 100 s⁻¹, the tensile strength of GFRPU reaches 50.27 MPa, 26% higher than that of the polyurea matrix. Under contact explosion, a 4 mm back-face GFRPU coating reduced the center-point deflection of the steel plate by 31.6% and suppressed brittle cracking, with interfacial debonding and coating tensile failure as the dominant failure modes. Considering protective efficiency and structural safety, 4 mm is recommended as the optimal coating thickness.