Jinchao Yue

Improving the flame-retardant performance of asphalt is particularly important for tunnel pavements, where confined environments can intensify fire hazards and smoke accumulation. This study prepared different modified asphalt binders to investigate their flame-retardant performance and rheological properties. The limiting oxygen index and smoke density rating were first used to evaluate the flame-retardant and smoke-suppression performance. Frequency sweep tests were then conducted to analyze the rheological behavior, aging characteristics, and low-temperature cracking resistance of the binders. Finally, microscopic tests were performed to reveal the thermal decomposition behavior and modification mechanism. Results showed that the incorporation of FR02 increased the limiting oxygen index of the warm-mix modified binders by more than 47%. Among the investigated binders, 13% fast-melting warm-mix flame-retardant composite modifier (SBS-WZ) exhibited the highest limiting oxygen index of 30.95% and the lowest smoke density rating of 57.73, indicating the best experimentally measured flame-retardant and smoke-suppression performance. At a reduced frequency of approximately 10⁻² rad/s, the unaged 13%SBS-WZ binder exhibited a complex modulus of approximately 2.0 × 10⁵ Pa, nearly one order of magnitude higher than those of the conventional 4%SBS- and 4%fast-melting SBS modifier (SBS-T), while its phase angle was approximately 6–10° lower. At −24 °C, the creep stiffness and creep rate of the unaged 13%SBS-WZ binder were approximately 654 MPa and 0.246, respectively. After Pressure Aging Vessel (PAV) ageing, these values changed to approximately 720 MPa and 0.237. Moreover, the onset decomposition temperature of 13%SBS-WZ was 392.1 °C, which was 17.2 °C higher than that of 4%SBS-T. Together with its higher residual mass, this result suggests enhanced thermal stability and residue-forming potential, which may partly explain the measured improvements in flame-retardant and smoke-suppression performance. However, the increased complex modulus and reduced creep rate indicate a concurrent loss of low-temperature flexibility. The findings can provide theoretical guidance and technical support for the application of this material in tunnel asphalt pavements.

This study used silicate cement as the base material and nano-silica, fly ash, and bentonite as the composite modification components. Through laboratory tests, the engineering characteristics and impermeability and drying shrinkage properties of the modified slurry were systematically investigated. The results showed that the verification test mix proportion of the slurry was a water–binder ratio of 0.7, a nano-silica content of 2%, a fly ash content of 40%, and a bentonite content of 6%. This ratio of the slurry had the best comprehensive performance. Compared with pure cement slurry, the water loss rate decreased by 61.90%; the 3d, 7d, and 28d compressive strengths increased by 30.60%, 36.08%, and 20.08% respectively; the fluidity decreased by 6.38%; and the initial setting time decreased by 9.77%. The anti-seepage pressure of the verification test mix proportion slurry group reached 1.05 MPa, which was 43.84% higher than the pure cement reference group and was superior to each single addition group. Combined incorporation of nano-silica, fly ash, and bentonite remarkably improved the impermeability. The 56d drying shrinkage rate was 1257 × 10⁻⁶, which was 19.16% lower than that of the reference group. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests, the microstructure was analyzed, and the hydration mechanism was discussed. The composite modification did not change the type of hydration products but significantly improved the microstructure. Nano-silica reacted with the hydration product Ca(OH)₂ in the early stage of hydration, accelerating the hydration process and promoting the interwoven coating of the hydration product on the calcium aluminosilicate crystals, thereby improving the compactness of the matrix. Fly ash participated in the pozzolanic reaction in the later stage of hydration, adhering to the secondary hydration products on the surface and gradually consuming them, further filling the pores and optimizing the interface structure. Combined with bentonite, nano-silica and fly ash jointly densified the matrix, refining the microstructure of modified samples and forming a continuous integrated hydration product network inside the grout.

Aiming at the challenges of lining cracking and water seepage in water conveyance tunnels under high internal water pressure, joint waterproofing is the key to improving the structural anti-seepage performance. This paper investigates the mechanical and anti-seepage properties of joint sealing materials, as well as the stress-deformation characteristics of the anti-seepage structure. Uniaxial tensile tests, bond tensile tests, and interfacial shear tests were conducted on three types of sealants—polysulfide, polyurethane, and polyurea—to systematically obtain the fundamental mechanical parameters. The results show that polyurea has the highest ductility, polysulfide exhibits the highest tensile strength (1.27 MPa), and polyurethane presents balanced performance. The interfacial shear strength between polysulfide and concrete reaches 0.5 MPa, demonstrating outstanding bonding performance. Based on the cohesive zone model, a numerical model of the joint sealing system was established to analyze the evolution of stress and deformation under two working conditions: inner-side water seepage and double-sided (inner and outer) water seepage. The results indicate that water pressure induces stress peaks at the contact interface between the sealing material and the segment. The stress peak under internal water pressure alone is significantly higher than that under combined internal and external water pressures. Comprehensive comparison shows that polysulfide sealant offers better stability in resisting internal water pressure and controlling deformation. The selection of sealant type in engineering should consider the stress characteristics, deformation requirements, and construction conditions of different structural locations.

This study introduces five types of wax materials to replace traditional Sasobit warm mix agents (WMAs), aiming to reduce the aging performance of high-viscosity modified asphalt (HMA) under high temperatures and optimize wax-based WMAs for a better warm mix effect and more stable performance of HMA. In this study, styrene–butadiene–styrene (SBS) modifier was first used to prepare HMA, and then wax materials were added to prepare HMA. Thin-Film Oven Tests (TFOTs) and Pressure Aging Vessel (PAV) aging tests were conducted, followed by dynamic shear rheology (DSR) tests, to study the high-temperature rheological properties of each warm mix HMA. Fourier-transform infrared spectroscopy (FTIR) tests and fluorescence microscopy were used to observe the microstructures of the asphalt. The results show that all six wax materials exhibited good warm mix effects, among which refined Fischer–Tropsch Wax 1 (RFW1) outperforms conventional Sasobit WMA in terms of warm mix effect, high-temperature rheological properties, and anti-aging performance, indicating its potential to replace Sasobit in engineering applications.

To overcome the limitations of conventional high-viscosity high-elasticity modified asphalt, including high production costs, phase separation, and thermal degradation, this study introduces a novel fast melting Styrene-Butadiene-Styrene modifier (SBS-T) for asphalt modification. The primary novelty of SBS-T lies in its ability to mitigate phase separation and thermal degradation while simplifying the production process, thereby offering a more robust and cost-effective alternative. The viscoelastic properties of SBS-T-modified asphalt were characterized through frequency sweep tests under varying loading conditions, while its fatigue behavior was quantitatively assessed using the Simplified Viscoelastic Continuum Damage (S-VECD) model. The results indicate that the SBS-T-modified asphalt exhibits outstanding viscoelastic performance across a broad range of temperatures and loading frequencies, and can better adapt to the temperature and load changes in complex pavement environments. Among them, the influence of long-term aging on the linear viscoelastic characteristics of SBS-T-modified asphalt is greater than that of ultraviolet aging. The SBS-T-modified asphalt also shows better stiffness and resistance to shear deformation. The fatigue life of asphalt gradually decreases with the deepening of the aging degree, among which the impact of long-term aging on fatigue life is greater than that of ultraviolet aging. Under different aging conditions, SBS-T-modified asphalt has shown good fatigue performance and is suitable for practical engineering applications.

Increasing the frequency and duration of extreme heat events significantly compromises asphalt pavement performance, particularly in critical urban infrastructure such as heavily trafficked pavements, BRT lanes, and intersections subjected to slow-moving heavy traffic under extreme temperatures. This study systematically investigates rutting formation mechanisms through integrated theoretical and numerical approaches, addressing significant knowledge gaps regarding rutting evolution under coupled extreme-temperature (70 °C), heavy-load (100 kN–225 kN), and braking conditions (1 m/s²–7 m/s²). A three-dimensional thermo-mechanical finite element model integrating solar radiation heat transfer with the Bailey–Norton creep law was developed to quantify synergistic effects of axle loads, travel speeds, and braking accelerations. Results demonstrate that when the pavement surface temperature rises from 34 °C to 70 °C, the rutting depth is increased by 4.83 times. When the axle load is increased from 100 kN to 225 kN, the rutting of conventional asphalt pavements under 70 °C is increased by 56.4%. Rutting is exacerbated by braking acceleration; due to prolonged loading duration under low acceleration, the rutting depth is increased by 30–40% compared with that under emergency braking. These findings establish theoretical foundations for optimizing pavement design and material selection in slow-moving heavy-load environments, delivering significant engineering value for transportation infrastructure.

Aiming at the problems of complex process flow, high energy consumption, and difficult emulsification in the preparation of traditional SBS-modified emulsified asphalt, a preparation method of fast-melting SBS (referred to as SBS-T) modified emulsified asphalt based on the integration of modification and emulsification is proposed. Based on surface free energy theory, the contact angles between three rapid-melting SBS-modified emulsified asphalts with different dosages and three probe liquids (deionized water, glycerol, and formamide) were measured using the sessile drop method. The adhesion performance of the asphalt–aggregate system was studied by means of micromechanical methods. The evaluation indicators such as the cohesion work of the emulsified asphalt, the adhesion work of asphalt–aggregate, the spalling work, and the energy ratio were analyzed. The results show that the SBS-T modifier can significantly improve the thermodynamic properties of emulsified asphalt. With increasing modifier content, the SBS-T-modified emulsified asphalt demonstrated enhanced cohesive work, improved asphalt–aggregate adhesive work, and increased energy ratio, while showing reduced stripping work. At equivalent dosage levels, the SBS-T-modified emulsified asphalt demonstrates a slight improvement in adhesion performance to aggregates compared to conventional SBS-modified emulsified asphalt. The SBS-T emulsified modified asphalt provides an effective technical solution for the preventive maintenance of asphalt pavements.

In shield tunneling, ensuring bonding performance at new-to-old concrete interfaces between segments and linings is crucial for composite lining stability. While extensive research exists on the mechanical bonding behavior of such interfaces, comparative studies on two prevalent treatment methods—scabbling and grooving—remain limited. This study systematically evaluates these techniques’ effects on interfacial bonding via direct shear tests, benchmarking against smooth-interface specimens. Complementary cohesive zone modeling simulations further analyze stress distribution and damage evolution during shear failure. The results demonstrate that scabbled specimens exhibit 10.5%~18.2% higher shear strength than grooved counterparts under increasing normal stress, with both treatments significantly enhancing load–transfer synergy through mechanical interlocking. Furthermore, the energy-based bilinear cohesive model accurately predicts full-interface behavior, providing practical guidance for interface treatment selection in tunneling engineering.

The road construction sector urgently requires environmentally friendly, low-carbon, and high-performance base materials. Traditional materials exhibit issues of high energy consumption and carbon emissions, making it difficult for them to align with sustainable development requirements. While slag- and fly ash-based geopolymers demonstrate promising application potential in civil engineering, research on their application in road-stabilized soils remains insufficient. To address the high energy consumption and carbon emissions associated with conventional road base materials and to fill this research gap, this study investigated the utilization of industrial solid wastes through slag-based geopolymer and fly ash as stabilizers, systematically evaluating the pavement performance of two distinct soil types. Unconfined compressive strength tests and freeze–thaw cycling tests were conducted to elucidate the effects of stabilizer dosage, fly ash co-stabilization, and compaction degree on mechanical properties. The results demonstrated that the compressive strength of both stabilized soils increased significantly with higher slag-based geopolymer content, achieving peak values of 5.2 MPa (soil sample 1) and 4.5 MPa (soil sample 2), representing a 30% improvement over cement-stabilized soils with identical mix proportions. Fly ash co-stabilization exhibited more pronounced reinforcement effects on soil sample 2. At a 98% compaction degree, soil sample 1 maintained a stable 50% strength enhancement, whereas soil sample 2 displayed a dose-dependent exponential strength increase. Freeze–thaw resistance tests revealed the superior performance of soil sample 1, showing a loss of compressive strength (BDR) of 78% with 8% geopolymer stabilization alone, which improved to 90% after fly ash co-stabilization. For soil sample 2, the BDR increased from 64% to 80% through composite stabilization. This study confirms that slag/fly ash-based geopolymer-stabilized soils not only meet the strength requirements for heavy-traffic subbases and light-traffic base courses, but also demonstrates its great potential as a low-carbon and environmentally friendly material to replace traditional road base materials.

Asphalt pavements are prone to various distresses under complex environmental influences during service, which significantly affects their fatigue life. This study conducted complex environmental simulation tests, including pressure aging, ultraviolet (UV) aging, and coupling effects with salt solutions at different concentrations. A dynamic shear rheometer (DSR) was employed to perform frequency sweep tests, linear amplitude sweep (LAS) tests, and fatigue–healing–fatigue tests. The fatigue self-healing properties of fast-melting SBS (SBS-T)-modified asphalt were evaluated based on the viscoelastic continuous damage theory. The results indicate that coupled aging effects significantly increase the viscoelastic characteristic parameters of SBS-T-modified asphalt, with more elastic components transforming into viscous components. Compared to other aging effects, the coupled pressure-UV-salt solution condition induces the most severe degradation in the fatigue durability of SBS-T-modified asphalt. Simultaneously, the self-healing capability of aged asphalt is also reduced. Specifically, with increasing strain, more complex aging conditions lead to the faster deterioration of asphalt fatigue life and lower self-healing capacity. While asphalt demonstrates measurable fatigue life restoration through self-healing, the synergistic coupling of salt solution exposure and multi-factor aging significantly compromises both the absolute fatigue resistance and the relative recovery efficiency.