| Concrete structures located in different depths own vary head pressure of corrosion solution outside the concrete, and the pressure is increased as the depth increases, so this kind of one-side corrosion of underground structures accompanies by head pressure. Simultaneously, the underground structures are subjected to continuous loads from overlaying soil and groundwater, concrete has been in a state of stress, so we need to consider the effects of head pressure and concrete stress at the same time.The experimental research of one-side corrosion was conducted in this paper on concrete of underground structures, which mainly considering the head pressure and the pressure level inside the concrete. The major factors took into account are: water-cement ratio of concrete(0.4, 0.5, 0.6); head pressure of corrosion solution(0MPa, 0.1MPa, 0,2MPa, 0.3MPa); pressure level inside concrete(Stress ratio: 0, 0.3). Base on the experimental results, the degradation law of corrosion performance of concrete corroded by sulfate was analyzed, and the appropriate mathematical model of corrosion layer thickness and corrosion time development was established. To be able to achieve pressure corrosion solution and load concrete specimens at the same time under the condition of one-side corrosion, we first design the appropriate device, produce and complete the patent application. The authorization notice of utility model patents of this test device has received and the invention patent of test method has also been accepted.During the experiment of one-side corrosion with non-head pressure, the corrosion time was extended from 270 days to 500 days based on our previous experiments, and superficial forms and ultrasonic velocity of concrete located in the adsorption zone, the adsorption zone above, the soak zone were measured. Results show the corrosion degree of concrete in different areas increase to varying degrees as corrosion time continuing: corrosion rate of concrete in the adsorption zone is the fast while the other two areas are slower. Mechanism analysis shows that larger humidity gradient and significant adsorption evaporation effect are the main reasons for accelerated corrosion in the adsorption zone. Finally, calculate the corrosion layer thickness according to degradation of ultrasonic velocity, and establish the mathematical model of head pressure of concrete in each area with time development under no head pressure.The one-side corrosion test under head pressure was conducted with experimental device designed by ourselves, lasting 270 days, during which ultrasonic propagation time was measured regularly, and the degree of corrosion damage and corrosion layer thickness were calculated in different corrosion time, then ultrasonic velocity, the damage degree, and the variation law of damage layer thickness with time were obtained. We simple the concrete in different depths at 270 days, and do fluorescence spectroscopic analysis, from which we get the variation law of element S with depth under vary pressure. The results showed that corrosion degree increased as head pressure increasing compared to non-head pressure. Mechanism analysis showed that with the increase in head pressure, the speed and depth of SO42- got into the concrete were accelerated, making a acceleration effect on sulfate corrosion of concrete. And finally, the corrosion rate model associated with head pressure was established based on the corrosion layer thickness.At last, one-side corrosion test with compressive stress level 0.3 of concrete was conducted, which also played an inhibitory effect on concrete corroded by sulfate under the condition of head pressure compared with non-head pressure. The mechanism is that the compressive stress level of 0.3 plays a role in compaction to the concrete pores, limiting the penetration speed of SO42-.The contents of S element were proved correspondingly through fluorescence spectroscopic analysis, and finally obtained a suppression coefficient of compressive stress level of 0.3. |
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