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The possibility of Fe loaded on BP (Fe@BP) as an efficient gas sensor for the detection of toxic gases such as NO2, NO, and CO is studied by the first‐principles calculation, and it is proposed that Fe@BP is an excellent gas‐sensitive material. The adsorption behaviors of gases on Fe@BP were analyzed in terms of adsorption configurations and electronic properties. It is found that all gases adsorbed on Fe@BP exhibit significantly enhanced interactions, and the adsorption intensity is much larger than that of molecules adsorbed on the surface of pure BP. Fe@BP has high selectivity for toxic and ambient gas molecules. In addition, the adsorption strength of NO2 and NO molecules on Fe@BP increases after compression strain is applied (within −3%), while the adsorption strength of CO decreases gradually. After the tensile strain is applied, the adsorption intensity of NO2 and NO is decreased, but that of CO is increased gradually. It is speculated that the strain causes changes in the electronic structure, which affects the adsorption behavior. The adsorption of NO has a stronger strain sensitivity. For these reasons, Fe@BP with high adsorption strength and strain selection is the ideal gas‐sensitive material. [ABSTRACT FROM AUTHOR]

Carbonation depth is essential to determine the durability and predict the remaining service life of concrete structures. This study proposes a multi-frequency Rayleigh wave approximation method (MFRWA) to evaluate carbonation depth by exploiting the frequency-dependent penetration depths of ultrasonic Rayleigh waves. A series of numerical simulations are conducted to investigate the effective penetration depth of Rayleigh waves and the feasibility of the proposed MFRWA method on carbonation depth evaluation. Subsequently, the accelerated carbonation experiment is conducted to evaluate the carbonation depth using low-frequency and high-frequency Rayleigh waves, and the measured results from the Rayleigh wave method are compared with the ones from the phenolphthalein indicator and thermalgravimetric analysis (TGA) method. The results show that carbonation depth measured by Rayleigh wave method meets well with the one from TGA technique, demonstrating that the proposed method could provide a non-destructive and precise carbonation depth estimation. The proposed MFRWA method contributes a novel scheme for concrete carbonation evaluation and holds substantial potential in both laboratory and field applications. [ABSTRACT FROM AUTHOR]