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Ultra-high performance concrete (UHPC) is a cementitious composite characterized by its ultra-high durability attributes and mechanical properties. It is primarily used in large-span and ultra-high-rise structures for control of deflections. However, its mechanical properties decrease significantly after exposure to fire or high temperatures, limiting its applicability. In this paper, the exceptional characteristics of glazed hollow beads (GHBs), including their lightweight, high strength, and thermal insulating properties, were utilized to develop a novel fire-resistant UHPC. UHPC specimens with varying GHB content were prepared, and the corresponding mass loss, thermal performance degradation, and compressive strength after exposure to high temperatures were evaluated. The test results demonstrate that adding GHBs can improve the fire resistance of UHPC. With 40 % (by volume) GHB addition, the resulting UHPC could retain 47 % of its original compressive strength even after exposed to 800°C. The effects of temperature on the UHPC microstructure were analyzed using scanning electron microscopy and X-ray computed tomography. It was found that the combination of polypropylene fibers and GHBs created a release channel for vapor pressure within the concrete, thereby enhancing its high-temperature resistance. This study proposes a practical solution to enhance the high-temperature resistance of UHPC.

Concrete materials, as the main component of airport pavement, provide essential attributes such as strength and toughness required by airport pavement. With the rapid development of air transportation, the compression and cracking resistance performances required by airport pavement are dramatically boosted with the ever-growing weight and the frequency of aircraft. In recent years, high-performance concrete materials with excellent properties have shown great potential in improving durability and extending the service life of pavement. This review presents a-state-of-the-art assessment guided by the pavement performance requirement, material design mechanism, application cases and future application guidance of advanced cementing materials in airport pavement improvement. Firstly, the functions of each structural layer of airport pavement and their effects on the surface layer are summarized. Then, the design mechanism and application cases of advanced concrete materials were summarized with the future application guidance to be given. Finally, the application scenarios, testing mechanism and testing effect of nondestructive testing methods for airport pavement performance evaluation are summarized. This review provides a comprehensive assessment of the development and applications of advanced concrete materials for airport pavement, paving avenue to achieve high performance and long service life of airport pavement.

The accurate prediction of urban road collapses is of paramount importance for public safety and infrastructure management. However, the complex and variable nature of road subsidence mechanisms, coupled with the inherent noise and non-stationarity in the data, poses significant challenges to the development of precise and real-time prediction models. To address these challenges, this paper develops an Adaptive Difference Least Squares Support Vector Regression (AD-LSSVR) model. The AD-LSSVR model employs a difference transformation to process the input and output data, effectively reducing noise and enhancing model stability. This transformation extracts trends and features from the data, leveraging the symmetrical characteristics inherent within it. Additionally, the model parameters were optimized using grid search and cross-validation techniques, which systematically explore the parameter space and evaluate model performance of multiple subsets of data, ensuring both precision and generalizability of the selected parameters. Moreover, a sliding window method was employed to address data sparsity and anomalies, ensuring the robustness and adaptability of the model. The experimental results demonstrate the superior adaptability and precision of the AD-LSSVR model in predicting road collapse timing, highlighting its effectiveness in handling the complex nonlinear data.

With the rapid development of multispectral detection, infrared and visible compatible camouflage becomes necessary. Metafilms with dielectric/metal/dielectric (D/M/D) structures can be highly transparent in visible band (380 ∼ 780 nm) and highly reflective in infrared atmospheric windows (3 ∼ 5 μ m, 8 ∼ 14 μ m). The metafilm can be deposited on the equipment surface, and the high visible transmittance can make the original camouflage coating continue to achieve visible camouflage, while the low infrared emissivity can inhibit the infrared signal to achieve infrared camouflage. Compatible camouflage is urgently needed by high-temperature targets such as exhaust pipes and engine cabins. Therefore, the thermal stability of multilayer structure is very important. In this study, a D/M/D-structured metafilm with improved thermal performance is proposed. Al-doped zinc oxide (AZO) is selected as the material of the dielectric layers due to good thermal stability, and high visible transmittance is realized through the mechanism of admittance matching. Ag is selected as the material of the metal layer to increase infrared reflectance. The metafilm with the structure of AZO/Ag/AZO is rigorously designed and fabricated. The results from Fourier transform infrared spectrometer and spectrophotometer show that the integrated visible transmittance and infrared emissivity at room temperature is higher than 0.87 and lower than 0.05, respectively. The camouflage performance of the metafilm is demonstrated on a flexible polyethylene terephthalate (PET) substrate. The camouflage performance of metafilm samples at 20 ∼ 140 °C is tested on a model cabin. The metafilm does not affect the original camouflage coating, so it can achieve visible camouflage. The radiation temperature of the metafilm is approximately 80 °C lower than that of the control surface, and the infrared signature is significantly attenuated. In order to further investigate the thermal stability and thermal fatigue resistance of the metafilm, metafilm deposited on quartz substrate is continuously heated and periodically heated at different temperatures. It is found that the sample can withstand continuous heating at 450 °C for 4 h or repeated heating for 20 cycles. SEM (scanning electron microscope) and EDS (energy dispersive spectrometer) scanning shows that if heated at higher temperature or for more cycles, the AZO layer becomes blocky, and the proportion of Ag and O changes significantly. This leads to the decrease of visible transmittance and the increase of infrared emissivity of samples.

Color change metafilm is promising for the color printing of displays and imaging. A metallic array on an elastic film can realize dynamic color change by mechanical extensions, such as uniaxial or biaxial stretching. In this study, an electromagnetic model of a flexible metafilm composed of a microscale Al cylindrical array on a polydimethylsiloxane elastic film was constructed to study the underlying optical mechanism of color change, especially brightness and saturation changes, of the flexible metafilm with structural parameters (diameter and height of the Al cylinders) and stretching methods (uniaxial or biaxial stretching). The 3D finite time domain difference method was used to simulate the propagation behavior of electromagnetic waves through metafilm. With increasing diameter, the lightness increases while the saturation decreases, which is due to the change of surface plasmon resonance from local surface plasmon resonance (LSPR) to propagation surface plasmon (PSP) and Wood Anomaly (WA) and finally to magnetic polariton excitation. With increasing height, lightness first decreases and then increases, while the change in saturation is opposite, which is due to the first increasing and then decreasing of the intensities of PSP and WA. By comparing the dynamic color changes of metafilm under uniaxial stretching and biaxial stretching, it is found that uniaxial stretching achieves lower lightness and saturation under small strain and higher lightness and saturation under large strain, which is caused by the enhanced WA and PSP on the Al-air interface at short wavelengths and the weakened LSPR on the Al-PDMS interface at long wavelengths. This discovery paves the way for practical applications of structural color display with high saturation and brightness.