Yao Xu

The development of polymeric materials for the repair and reinforcement of damaged sites in water has many practical applications, especially in ocean engineering. However, it is difficult to construct an anticorrosion coating in water. In addition, curing kinetics, which are the key to enhance the performance of coatings, seem to hardly be observed and regulated in an underwater condition. Herein, a novel underwater in situ repairing coating was prepared. Meanwhile, electrochemical impedance spectroscopy (EIS) was applied to observe its curing behavior underwater. Adhesion tests showed that the coatings cured underwater had good adhesion to different substrate surfaces and the ideal ratio of curing agent to epoxy resin was 0.6. Long-term anticorrosive tests demonstrated that the coatings had an excellent anti-corrosion performance. The viscosity changes in different curing stages were well reflected by frequency response characteristics from Bode and Nyquist curves by EIS. Two equivalent electrical circuits were selected to simulate the impedance date at the initial and final curing stage. A formula was put forward to evaluate the curing degree during the curing process. Finally, the effects of temperature and the ingredient ratio on the reaction rate and curing degree were also investigated here. This underwater in situ repairing coating may find applications in many offshore engineering structures in marine environments, and the EIS technique has attractive development and application prospects when observing the curing information of thermosetting resin systems under special circumstances.

Conventional statistical models provide inaccurate predictions of concrete crack openings because they do not consider the nonlinear temperature response and the residual characteristics of concrete. To address this problem, this study introduces a nonlinear temperature factor and develops an improved statistical model of crack openings. The chaotic characteristics of residual time series of the improved statistical model are analyzed based on chaos theory and phase-space reconstruction theory. These theories are integrated with back-propagation (BP) artificial neural networks and genetic algorithms (GAs) to establish a GA-BP neural network model for predicting residuals. Finally, a hybrid model is developed for predicting the concrete crack opening behavior. The predictions of the conventional statistical model, the statistical model considering nonlinear temperature component, and the hybrid model are compared using the case study on the crack openings of a regulating sluice. The results show that the proposed hybrid model in this study for predicting concrete crack openings is significantly more accurate than the conventional statistical model and the statistical model considering nonlinear temperature component.

In this research, we studied a roller‐compacted concrete (RCC) arch dam which was reinforced during the construction period to investigate the properties of mechanical parameters of the dam concrete after long‐term operation. Firstly, multiple methods involving core drilling, computerized tomography (CT), spectral analysis of the surface wave (SASW) of elastic waves, and an on‐site inspection were adopted to detect the quality of the dam concrete, which was followed by a forward‐analysis of the measured displacement of the arch dam and the water pressure component of the measured displacement was separated through regression analysis of statistical model of radial horizontal displacement. Subsequently, an optimization inversion of the elastic modulus of the dam body and dam foundation was conducted using a hybrid optimization method. The results showed that the compressive strength of the concrete in the body of the reinforced arch dam was over 30 MPa and the inversion results for the elastic modulus of the dam body were in the range of 30.1 ~ 33.3 GPa. According to the research results of multi‐source inspected and monitoring data during the operation period, the results suggest that the performance of the concrete of the dam body is in accordance with design requirements and the reinforced arch dam is properly operated.

Selecting four types of sand with different ranges of particle diameter, the strength tests of sand solidification with microbial cement are carried out in this paper. With experimental conditions in this paper, most of the strengths of solidified sand with microbial cement are in the range of 1.2∼2.7MPa. Particle gradation is an important factor that affects the solidification of microbial cement. And the perfusion method is more suitable for the sand with appropriate porosity and good connectivity which is easy to be perfused, but not for clay and sludge. The stirring molding method is more suitable for clay and sludge which have much content of fine powder. The strength of solidified sand is related to the direction of perfusion; and the strength of its upper part is higher than that of the lower part. Compared with other solidification materials, the solidified sand with microbial cement has no obvious advantages, due to its low strength, many limitations as well as complex construction technology; dnd its application field needs further study and exploration.

The current methods for evaluating the contact condition between concrete and lining were the ground penetrating radar (GPR) and the coring method. The penetration of radar electromagnetic waves was greatly affected by steel reinforcement and water, which often made the detection results of GPR unsatisfactory. A spectral analysis of the surface wave (SASW) method was used to evaluate the concrete-bedrock interface condition for hydraulic tunnel linings in this paper, since the impact elastic wave is less affected by steel bars and water content. An SASW implementation program based on fast Fourier transformation (FFT) was developed to analyze data from numerical simulations and field tests. Various models were studied to investigate the feasibility of using numerical analysis. For the first time, the study was employed to find out the influences of different receiver spacings and impact duration on the efficiency of detecting the existence of a weak layer underneath the concrete using the SASW method. On this basis, in-situ tests were carried out to verify the applicability in the field and results were verified by coring. In the research, the following results were found: (1) The finite element analysis results of different uniform or layered models showed that the SASW method could accurately identify the interface contact condition between the concrete lining and bedrock, especially the existence of voids; (2) when the receiver spacing was 1.0–1.5 times the thickness of the target object to be inspected, the quality of the collected signal data was the best; (3) under a certain reasonable range, the impact duration had an insignificant effect on the phase spectra and dispersion curves of a concrete-weak layer model; (4) in-situ SASW inspection could accurately tell whether the voids exist at the concrete-bedrock interface; and (5) the data processing program of the SASW method based on the MATLAB platform was accurate, convenient, and worth promoting.

Large leakage occurred in several concrete-face rockfill dams (CFRDs) around the world recently, resulting in economic losses and safety problems. To rehabilitate these dams, it is necessary to identify leakage locations on the concrete face slabs and understand the severity of leakage at each location. This technical note presents a method for localizing and quantifying leakage through CFRDs. Analysis models are developed to estimate the leakage rate from horizontal and vertical leakage sources. The relationship between water level and leakage is described for these two leakage sources. Based on a monitored water level-leakage relation, the elevations of leakage are determined, and the leakage rate at each elevation is estimated using these models. A case study on the Buxi CFRD is presented to illustrate the method. The calculated water level-leakage relation is in good agreement with the measured one before rehabilitation, and the leakage has decreased over 80% after rehabilitation.