Accelerated Study On Mortar Corrosion And Biofilm Transportation By Intensified Sewage

The durability problem of concrete is increasingly prominent in sewage environment.Because of the sewage on the corrosion of concrete with a long cycle,the more use of accelerated corrosion research methods.Through artificial compound intensified sewage of high concentration to accelerate the trials,but pay more attention to the deteriorating law of the concrete in the domestic.In addition,the concrete surface can form a biofilm,impact on the corrosion process in sewage environment.Therefore,this experiment by using different concentration,temperature of intensified sewage,sewage indexes and the dynamic change regularity of mortar specimen structure and performance is synchronous studied in the process of corrosion.By the Confocal Laser Scanning Microscope(CLSM)to observe the microscopic structure of the biofilm,using image analysis software analysis surface porosity of the biofilm.Finally,the dissolved oxygen mass transfer process was studied by using microelectrode.The results showed that sewage COD value is a cyclical fluctuation change within a certain range,with nutrients added on a regular basis and microbial metabolic activity,in the process of corrosion.In the early,pH and dissolved oxygen concentration are decreased significantly,but tend to be dynamic balance in the later,and the overall is on the decline.In the early,H2 S concentration increased significantly,but slow growth and tend to be stable in the late,as a whole is on the rise.With the increase of sewage concentration,sharp increase in the number of Bacteroidetes that lead to corrosion of concrete in sewage.Sewage temperature is 30?,sharp increase in the number of Bacteroidetes and Proteobacteria.Mortar surface spalling is serious,with the increase of sewage concentration by COD values from 300 to 9000 mg/l.The surface roughness increased from 77.17 ?m to 125.95 ?m,and calcium hydroxide content can be reduced from 12.62% to 5.34%,block pore rate increased from 37.35% to 55.61% in the block.SEM observation found that cement stone structure is loose,and produced a large number of holes and cracks in intensified sewage.There are a lot of ettringite crystal in the hole.And the calcium hydroxide crystal is few in number.Sewage temperature is 30?,mortar corrosion is the most intense.In this experiment,by using the least squares fitting from linear relationship of surface porosity and depth of biofilm,is a form of y = az + b.The slope of each equation is between 0.11 ~ 0.14.The interception of equation decreases with the increase of sewage concentration.Three different concentrations of intensified sewage,biological volume porosity are around 60%,that is decreased along with the increase of sewage concentration.The same concentration,the temperature is 30?,biofilm volume porosity is minimal.Other temperature conditions,the biological volume porosity were above 70%.This study found that the biofilm growth rapidly,and biofilm thickness can achieve stable in intensified sewage after 45 days.In original sewage,biofilm growth is slow.According to the diffusion-mass transfer model,calculated the diffusion coefficient of dissolved oxygen,that was influenced greatly by the structure of biofilm in low concentration sewage.However,the concentration of dissolved oxygen is dominant in the super high concentration sewage.By contrast,the quality loss of paste and mortar which surface has biofilm and has not biofilm.Determine the biofilm attached to the surface of the block,has a protective effect.And the concentration of intensified sewage is small,protective effect is more obvious.