Experimental Research on the Structure and the In-situ Test Method for the Permeability of Cover Concrete
|Keywords||Protective layer of concrete Boundary effects Permeability Site detection method PERMIT ion migration test|
Refers to the outermost protective layer of concrete reinforced concrete between the outer surface of the layer of concrete, which is part of the reinforced concrete structure. Compared with concrete materials, the concrete structure and permeability of the protective layer is unique. The protective layer of concrete is an important line of defense for the reinforced concrete structures to resist external erosion on the durability of reinforced concrete structures is of great significance. This paper studies the structure and permeability of concrete protective layer, and a protective layer of concrete permeability field detection methods. The research results obtained are as follows: (1) using digital image analysis techniques, in millimeters, analysis of coarse aggregate volume content distribution in the one-dimensional direction of the vertical concrete protective layer surface layer characteristics. Boundary effects on concrete in the vertical direction of the molding surface gradually increase the volume content from the outside to the inside of coarse aggregate, exceed the boundary effect layer, the aggregate distribution tends to be uniform. The thickness of the boundary effect layer is in fact about 5mm. Maximum particle size of the coarse aggregate thickness boundary effects are not obvious. For well-graded coarse aggregate, to control the thickness of boundary effects is the smallest particle size of the coarse aggregate. The self-designed test method conducted a preliminary study reinforced jamming effect. Under the conditions to meet specification requirements, the reinforcement on adoption of the coarse aggregate has a blocking effect. This was reflected slightly less for the protection of the coarse aggregate content in the layer of concrete, slurry slightly more; jamming effect on the aggregate size distribution within the protective layer has little effect. (2) by comparative tests PERMIT ion migration test and NEL test proved that the experimental results are in good correlation of the two methods. PERMIT ion migration test method equipment is simple, easy to operate, test time, correctly reflect the protective layer of concrete or the structure of the surface layer of concrete resistance to chloride ion permeability. (3) combined with laboratory experiments Qingdao Bay Bridge Project field measurement, improvement PERMIT analysis of the test results and data processing methods, the chloride ion diffusion coefficient calculated using the the loop maximum current value, simplify the PERMIT ion migration test methods. PERMIT ion migration test methods can be used for the evaluation of infiltrating formwork improve impermeability of concrete protective layer effect. PERMIT ion migration test given chloride ion diffusion coefficient can be qualitative evaluation of concrete resistance to chloride ion penetration for concrete works on-site quality control.