Effect Of Sulfur-Oxidizing Bacteria On Durability Of Marine Concrete

With the exploration and development of ocean engineering,concrete materials have been widely used in ocean engineering construction.Marine environment is very easy to cause corrosion of concrete structure,among which the common sulfur oxidizing bacteria in the ocean can adhere to the surface of concrete structure to induce corrosion.In view of the status quo that the effect of sulfur-oxidizing bacteria on concrete and the law of its influence on deterioration are not clear and there are few relevant studies,this paper explores the effect of sulfur-oxidizing bacteria and its biofilm on concrete macro performance and micro structure.In order to provide theoretical basis for the prevention and control of microbial corrosion of concrete in Marine environment.This paper mainly does two aspects of work.The first is the exploration of the evolution characteristics and adhesion force of the biofilm formed by the adhesion of sulfur-oxidizing bacteria on the surface of concrete.The adhesion process of sulfuroxidizing bacteria on the surface of concrete and the characteristics of the biofilm are studied.At the same time,based on the water scour test,the removal rate of sulfuroxidizing bacteria biofilm on the surface of concrete at each age is explored by changing the shear force of the water flow.Secondly,the influence of sulfur-oxidizing bacteria on the durability of concrete was explored.Firstly,a quantitative analysis was carried out on the changes of microbial metabolism acid production and sulfate ion concentration,and the deterioration degree of concrete was characterized from the surface p H loss,neutralization depth,frost resistance and chloride ion penetration resistance.X-ray diffraction(XRD),scanning electron microscopy(SEM)and electrochemical impedance spectroscopy(EIS)were used to study the changes of mineral composition and pore in corroded concrete in order to clarify the effects of microorganisms and their biofilms on the durability of concrete in Marine environment.Through the above research analysis,the main research conclusions and innovative achievements of this paper include the following three aspects:(1)The sticky substance attached to the gas-liquid-solid interface of concrete is a biofilm.When the concrete was soaked for 30 days,the sulfur-oxidizing bacteria attached to the gas-liquid-solid interface formed a biofilm with a thickness of 100 μm.At 120 days,the biofilm reached the maturity stage with a thickness of 2200 μm and began to fall off.The thickness of the biofilm decreased to 600 μm at 150 days and then increased until it reached the maximum thickness of 2900 μm at 240 days.(2)Large shear forces can effectively remove the biofilm attached to the concrete surface.When the shear force is less than 18.1135 k Pa,the removal effect of biofilm is poor.The biofilm at the mature aging stage will enter the shedding stage,and its adhesion is less than that at the rapid growth stage.This stage is the best time to remove the biofilm.(3)The samples of the bacteria-free test group were seriously deteriorated,with sulfate crystals on the surface and a few holes and losses near the edge.The roughness was more obvious than that of the samples of the sterile control group,while the samples of the sterile control group were slightly weathered and damaged.According to the changes of p H loss,neutralization depth and frost resistance,it was confirmed that the durability of samples in sterile control group was better than that in bacteriacontaining test group.The p H of bacteria-containing test group decreased from 11.4 to9.65,which was almost 1.75 times that of sterile control group.The neutralization depth of the bacteria-containing test group was 12.4 mm after 240 days,which was about 2.3times that of the sterile control group.After 100 freeze-thaw cycles,the samples of sterile control group showed better freeze-resistance.Sulfur oxidizing bacteria adhere to the surface of concrete,and then form a biofilm with complex network structure.Its internal structure is dense,which can slow the penetration of chloride ions into concrete.XRD,SEM and electrochemical impedance(EIS)analysis show that the infiltration of biological sulfuric acid leads to C-S-H gel dissolution,alkali loss and sulfate mineral crystallization expansion of concrete,and increases the porosity,accelerating the deterioration of concrete.