Asphalt concrete has been widely used in road engineering as a surface material. Meanwhile, ultrasonic testing technology has also been developed rapidly. Aiming to evaluate the feasibility of the ultrasonic wave method, the present work reports a laboratory investigation on damage detection of asphalt concrete using piezo-ultrasonic wave technology. The gradation of AC-13 was selected and prepared based on the Marshall’s design. The ultrasonic wave velocities of samples were tested with different environmental conditions firstly. After that, the samples were destroyed into two types, one was drilled and the other was grooved. And the ultrasonic wave velocities of pretreated samples were tested again. Furthermore, the relationship between velocity and damaged process was evaluated based on three point bending test. The test results indicated that piezoelectric ultrasonic wave is a promising technology for damage detection of asphalt concrete with considerable benefits. The ultrasonic velocity decreases with the voidage increases. In a saturated water environment, the measured velocity of ultrasonic wave increased. In a dry environment (50 °C), the velocity the ultrasonic waves increased too. After two freeze-thaw cycles, the voidage increased and the ultrasonic velocity decreased gradually. After factitious damage, the wave must travel through or most likely around the damage, the ultrasonic velocity decreased. During the process of three point bending test, the ultrasonic velocity increased firstly and then decreased slowly until it entered into a steady phase. At last the velocity of ultrasonic wave decreased rapidly. In addition, the errors of the results under different test conditions need to be further studied.

Isomorphism is a common phenomenon in clay minerals, which is one of the main reasons for the change of mineral chemical composition and physical and chemical properties. In this study, four kinds of palygorskite with different degrees of isomorphic replacement of octahedral cations were selected. The microstructure and surface-interface properties of different Mg2+/Al3+ palygorskite were analyzed by X-ray diffraction, infrared spectroscopy, N2 adsorption-desorption method, X-ray fluorescence spectroscopy and other characterization methods, and the effects of isomorphic replacement on microstructure such as Mg content and surface-interface properties such as hydroxyl concentration and acid content were discussed. Taking Cu2+ as the target pollutant, the adsorption capacity of different palygorskite to Cu2+ was measured and discussed. Combining the surface hydroxyl concentration and acid amount of palygorskite, as well as the concentration, time and temperature of the reaction system, the rule of adsorption of the four palygorskite for Cu2+ was Mg-rich palygorskite (a-ATP) > palygorskite with equal Mg and Al (c-ATP) > Al-rich palygorskite (d-ATP) > palygorskite with the most Mg (b-ATP), demonstrating that when Mg was partially replaced by Al, palygorskite contained appropriate hydroxyl concentration and acid amount, resulting in the best adsorption effect for Cu2+ (29.2 mg/g). It is of great significance for resource utilization of palygorskite to reveal the regularity of heavy metal adsorption by isomorphic replacement of palygorskite.

Mechanical properties are critical in engineering applications involving cementitious materials. While dehydrated cement paste-based materials are considered environmentally friendly, they suffer from poor mechanical properties, limiting their engineering applications. Therefore, enhancing the mechanical properties of these materials is crucial to overcoming their limitations in engineering and supporting the development of sustainable building engineering. Based on the pozzolanic reaction mechanism and alkali activation theory, a composite cementitious material was created by combining dehydrated cement paste with slag. Na₂SiO₃ and NaAlO₂ were used as alkali activators. The study investigated the effects of the ratio of dehydrated cement paste to slag, alkali activator dosage, water-binder ratio, and calcination temperature on the material’s mechanical properties through an orthogonal test. The optimized ratio, determined through the orthogonal test and mathematical model, resulted in a compressive strength of 37.33 MPa (7d) and 46.89 MPa (28d), surpassing the compressive strength of the original Portland cement paste. Hydration products of the composite cementitious material primarily comprised C-(A)-S-H, C-A-H, and CaCO₃, with no observed presence of AFt, AFm, and Ca(OH)₂. Notably, the hydration products of the composite material exhibited clear distinctions from those of Portland cement.