Wenbo Shi

The low yield of microbial calcium carbonate precipitation due to the strong pH environment has limited the development of biotechnology-based concrete crack repair techniques. In this study, Bacillus megaterium was selected to determine the optimal nutrient formulation through orthogonal tests. The growth and reproduction characteristics and urease activity of this strain were analysed by controlling different pH values, and the calcium carbonate precipitation yield under different pH conditions was investigated, and the lower precipitation yield under strong alkaline conditions was improved by using alkaline environment domestication with the addition of urea to the nutrient solution. It has been shown that higher pH results in lower growth and multiplication of Bacillus megaterium and weaker urease activity, and a strong alkaline environment can significantly suppress its growth and multiplication and urease activity. At pH 7, the growth and multiplication of Bacillus megaterium were the fastest, the urease activity was the strongest, and the precipitation yield was greater. The addition of urea to the nutrient solution to domesticate Bacillus megaterium in an alkaline environment can significantly increase the growth rate and precipitation yield, which can effectively solve the problem of insufficient calcium carbonate precipitation under alkaline conditions. Comparing the effectiveness of microbially induced calcium carbonate precipitation (MICP) in repairing concrete after damage before and after microbial domestication shows that the domesticated Bacillus megaterium is more effective in reducing the permeability characteristics of concrete and improving its strength.

Road surface monitoring is a significant issue in providing smooth road infrastructure for vehicles, and the key to road condition monitoring is to detect road potholes that affect driving comfort and transportation safety. This paper presents a simple, efficient, and accurate way to evaluate road service performance based on the acquisition of road vibration data by vibration sensors installed in vehicles. Inspired by the discrete fast Fourier transform, the vibration acceleration is processed, and the RMS value of vibration acceleration at 1/2 octave is calculated, after which the road vibration level is calculated. The vibration level is optimized according to the human body’s sensitivity to different frequencies of vibration, resulting in road service performance indicators that can reflect the human body’s real feelings. According to the road service performance index values on the road grading, combined with GPS data on the electronic map color block labeling, the results obtained for the road condition warning, road maintenance, driver route selection have an important significance.

In soft soil areas, such as the Nanjing, it is very important to quantitatively analyze the dynamic behaviors of soft soils during the metro train operation. A nonlinear coupling model of wheel‐track and a finite element calculation model of tunnel and soil were established based on the mechanical character of elastic supporting block ballastless track and the actual parameters of Nanjing soft soil. The time‐variant vertical acceleration of the rail, the sleepers, and the surface of the tunnel can be calculated by the models, and the frequency dependence acceleration was verified by the fast Fourier transform algorithm. A modified vibration power level for human sensitivity was used to quantify the vibration energy of each part of the system, and the impact of the parameters in the model was evaluated. The results can be applied to the metro design and construction, which also can be the guidance during the tunnel construction.

Dielectric constant is the basic material property for non-destructive testing based on ground penetrating radar (GPR). The real part and the imaginary part of dielectric constant of cement concrete materials at the different measuring frequency in different concrete mixture ages are measured, and the relationships between dielectric constant and the measuring frequency are obtained. The achievements will provide a technical support for the practical application of GPR.