Studies on Lightweight High-Strength Shotcrete
With small deadweight, light-weight shotcrete can avoid the shotcrete lining from falling off, which benefits the bolt-shotcrete support of the roadway better under same bond strength. Light-weight shotcrete can be made by using clay ceramsite, polystyrene particles and fly-ash ceramsite to replace some gravel and sand. The experiments show that the characteristic of fly-ash ceramsite shotcrete is superior to that of clay shotcrete, while by replacing part of gravel and sand with polystyrene particles and fly-ash ceramsite, light-weight high strength shotcrete will have excellent combination properties.
Slag Micro Powder Affected to the Mine Shotcrete Performance
A study was conducted in the lab on the different added quantity of the slag micro powder affected to the compressive strength,tensile strength,bending strength,and anti chlorine ion permeability of the light shotcrete.The paper analyzed those influence causes and mechanism occurred.The study results showed that the compressive strengths of the light shotcrete with 30% slag micro powder added would be increased individually after 3 days and 7 days and the bending strength of the shotcrete would be reduced with the slag micro powder added quantity increased.The tensile strength of the shotcrete could be increased within 10% slag powder added and would be reduced over 20% slag powder added.With the slag powder added increased,the toughness index of the shotcrete would be reduced and the anti chlorine ion permeability would be steadily increased.The suitable added quantity of the slag powder would be ranging from 10% to 20%.
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.