Gongcheng Kexue Yu Jishu/Advanced Engineering Science

The experimental study investigates the takeoff characteristics of lower jet trajectory from the dovetail-shaped flip bucket under different inlet conditions. The experiment analyzes the influences of velocity and water depth on lower takeoff characteristics, especially the variation of takeoff angle of lower jet trajectory. The following items are addressed 1) relationship between takeoff angle of lower jet trajectory and inlet velocity as well as inlet water depth 2) characteristics of the takeoff angle as a function of changes of inlet Fr0 3) the empirical formulas for calculating takeoff angle of lower jet trajectory. The results indicate that the effects of inlet conditions are significant on lower takeoff characteristics. Additionally, with the established empirical formulas, the calculated values of horizontal distance of lower nappe profile are in good agreement with the experimental data.

Geopolymer is a novel binding material produced from the reaction of fly ash with an alkaline solution. In Geopolymer mortar, Portland cement is not utilized at all. In this research, the influence of various parameters on the short term engineering properties of fresh and hardened low-calcium fly ash-based geopolymer mortar were studied. Tests were carried out on 70.71 × 70.71 × 70.71 mm cube geopolymer mortar specimens. The test results revealed that as the concentration of alkaline activator increases, the compressive strength of geopolymer mortar also increases. Study showed that higher mixing temperature and higher curing temperature exhibited higher compressive strength in early stages and still develop with longer curing. When the samples were mixed at room temperature, the compressive strength was low at an early stage, but gradually increased and finally, had as high strength.The mass ratio of activator/fly ash of 0.416 produced the highest 28 days compressive strength for the specimen.

The ultra wide bandwidth nature of ground penetrating radar antenna has made a raw data acquired with the tool prone to unwanted noise and hence low signal to noise ratio. Quantitative interpretation of the data is desirable for radar image quality enhancement. This study used multiresolution analysis to process radar image at different levels of decomposition. Daubechie wavelets family was used to decompose the image into 4-different levels of details. Level 3 diagonal details and level 4 horizontal details provide a noise-free visualization of the subsurface discontinuities. This led to the detection of buried utility and unique identification of its spatial location. The depth of the buried utility was estimated based on the image scale. The work demonstrates the effectiveness of Daubechie wavelet transform analysis as yet another technique of utility survey data acquired with GPR.

Chloride erosion is the most important factor affecting the corrosion of steel bars in the marine environment, salt lakes and saline soil areas. Therefore, timely and accurate grasp of the distribution of chloride ions inside reinforced concrete structures is of great significance to the durability evaluation, protection and repair of reinforced concrete structures under severe environmental conditions. In this paper, a solid Mn/MnO2 reference electrode for concrete with compact structure and stable performance is prepared by physical powder compaction method. The results show that the loading pressure is an important parameter that affects the strength and density of the Mn/MnO2 electrode prepared by the tablet method. When preparing Mn/MnO2 electrodes, the loading pressure needs to be controlled, and the recommended loading pressure is 96 MPa. The electrode must be activated before use. The response time of the activated Mn/MnO2 electrode is less than 60 s, and the stability, reproducibility and anti-polarization performance are good. When the Mn/MnO2 electrode works in the temperature range of 5~65 °C, the electrode potential is linearly related to the temperature. When the Mn/MnO2 electrode works in the pH range of 8.36~13.00, the electrode potential remains constant. Therefore, if the Mn/MnO2 electrode prepared by this method is used as the reference electrode of the chloride ion sensor to be buried in concrete, the temperature inside the concrete must be tested and corrected at the same time. Keywords: reference electrode; powder compaction method; performance characterization; influencing factors.

The experiment focused on the absorption and drainage characteristics of recycled coarse aggregate. The recycled coarse aggregate bonded with strain gauges was embedded in C30 strength grade concrete, and the shrinkage strain of recycled coarse aggregate in concrete during drying shrinkage was measured directly. Based on the relationship between the strain and drainage rate of recycled coarse aggregate under different humidity conditions, the drainage characteristics of recycled coarse aggregate in concrete were calculated, and the relationship between the drainage rate of recycled coarse aggregate and the drainage rate of recycled coarse aggregate was established. The results showed that the trend line of strain and saturation curve of regenerated coarse aggregate was relatively close to that of natural coarse aggregate in the process of draining and drainage, and the strain variation caused by dry and wet of the two kinds of aggregate had a reversible trend. There was a linear relationship between the strain and the drainage rate of recycled coarse aggregate and natural aggregate. The shrinkage strain of coarse aggregate in concrete was smaller than that of specimen, and the shrinkage strains of recycled coarse aggregate and recycled concrete were larger than that of natural aggregate and concrete. The drainage rate of recycled concrete was higher than that of internal recycled coarse aggregate.