Experimental Research On The Structure And The In-situ Test Method For The Permeability Of Cover Concrete

The cover concrete is defined as a layer of concrete between the most outside steel bar and the concrete surface. It is a part of the real reinforcement concrete structure. The structure and permeability of cover concrete aredifferent from the bulk concrete. Cover concrete is the most important defensive layer of reinforcement concrete structure to resist environmental deteriorations. The structure and permeability of cover concrete, as well as the in-situ test method for testing the permeability of cover concrete are researched. The main content and results are listed as follows:(1) Using digital image processing techonology, along the vertical direction of the concrete surface, the distribution characterics of coarse aggregate are studied millimeter by millimeter. The coarse aggregate volume amount increases from the surface to the inside caused by wall effect. Exceeding the wall effect layer, the distribution characteristics of coarse aggregate become uniform. In fact, the thickness of wall effect layer is about 5mm and the maximum diameter of coarse aggregate does not influence the thickness of wall effect layer obviously. When the grading design of coarse aggregate is reasonable, the thickness of wall effect layer is ones equaling almost to the minimum diameter of coarse aggregate. Using self designed method, the obstruction effect is studied elementarily. Although the neat distance of steel bars meets the request of code, the steel bars still obstruct some coarse aggregates. It behaves that there is more mortar and less aggregate in cover concrete. But the grading is not influenced by the obstruction effect.(2) Parallel experiments are carried out for PERMIT ion migration test and NEL test. The experimental results prove that there is a good correlation between them. The PERMIT ion migration test can be carried out quickly and effectively on site with minimum prior planning. It can reflect the permeability of cover concrete or surface concrete correctly.(3)Through the laboratory tests and in-situ test in the construction of Qingdao Bay, the analysis and calculation procedure of experimental data is modified and a new equation for calculating the chloride diffusivity using the peak current is given. It can simplified the test and reduce experimental error. The PERMIT ion migration test can be used to evaluate the improving effect of the resistance to the chloride ion penetration caused by CPF. The chloride diffusivity of the PERMIT ion migration test is capable to be used for evaluating the resistance to the chloride ion penetration of cover concrete and controlling the construction quality in-situ.