Accelerated Simulation Study On The Corrosion Of Non-full Flow Concrete Sewers

At present,urban underground sewage pipelines in China are aging,coupled with increased sewage discharge and imperfect sewage treatment technology,resulting in the destruction of underground sewage pipelines in most cities in China.Corrosion of concrete sewage pipeline is a long process,especially the internal environment of gravity pipeline is complex.In order to further study the corrosion degradation mechanism of concrete inside non-full-flow sewage pipeline,this paper comprehensively considers the interior of real sewage pipeline through self-designed accelerated corrosion simulation device.Under the environmental conditions,the hydrogen sulfide concentration and the sewage concentration in the gas phase and the liquid phase were accelerated.The appearance,surface pH and mass loss of the concrete specimens in the gas phase and water level were studied under different conditions of temperature,humidity and hydrogen sulfide concentration.Corrosion depth,microscopic morphology,mineral composition,compositional elements,etc.were analyzed for the corrosion induction period and development period of concrete specimens.In addition,the corrosion development process of concrete was also explored.The results show that with the increase of hydrogen sulfide concentration and temperature and humidity,the corrosion of the gas-phase and water partially-submerged specimens is more serious.For the gas-phase specimens,the hydrogen sulfide concentration has the most significant effect on the corrosion of the test piece,the humidity is second,and the temperature is the smallest;for the partially-submerged specimens,the hydrogen sulfide concentration has the most significant influence on the corrosion of the test piece,the temperature is second,and the humidity is the smallest.In the gas-phase environment,the specimens showed obvious mass loss around 90 d under the condition of 500 ppm.At this time,the surface pH of the specimens also dropped to about 7,indicating that the specimens entered the rapid development stage of corrosion after that;For the partially-submerged specimens,the surface pH of the test piece decreased to 7 when the apparent quality appeared under the same conditions,but it only took about 60 d,which may be caused by the difference in the corrosion effect of the gas phase chemical acid and the sewage bio-acid.In addition,in the corrosion development test,by analyzing the depth distribution map of the S element in specimens,it is known that there is a significant difference in the depth distribution of the S element from the corrosion layer along the inside of the test piece,that is,the corrosion layer with the most S element content,corrosion transition layer with fluctuating content and uncorroded layer with stable content.The area where the corrosion layer and the transition layer appear as the surface and the inside becomes larger,and the content of the S element is lowered.Through observation of the biofilm morphology of the test piece,it was found that the biofilm at the full bubble position was black,and there was white floc at the water level,and the thinner the biofilm was,the looser it was.From the calculation of the porosity of the biofilm,the thickness of the biofilm at the full bubble position,the water level position,and the gas phase position were 763 mm,567 mm,and 340 mm,respectively.The calculation of the S element pixel points in different parts shows that the S element content is the highest at the full bubble position,the S element content is the second in the water level area,and the gas phase position is the smallest.The pixel point value shows a law of decreasing along the gas phase direction.