Study On The Three Stages Microbial Corrosion Resistance And Mechanism Of Alkali-activated Mortar In Sewage Environment

With the increase of the service period of urban sewage systems,corrosion and deterioration of sewage pipes have appeared all over the world,which has brought serious consequences and huge economic losses.Concrete corrosion caused by microorganisms is considered to be one of the main degradation mechanisms,so it is urgent to find more corrosion-resistant building materials to replace ordinary concrete.Alkali-activated materials(AAM)is a new green cementitious material which is made by reacting alkali activator with active aluminite solid waste as raw material.It has the potential to replace traditional cement for sewage pipes.However,its chemical composition and structure are complex,so the mechanism of microbial corrosion resistance remains to be further studied.In order to simulate the whole process of concrete corrosion in gravity sewage pipe,a three-stage accelerated corrosion simulation device was designed and processed by ourselves,and alkali-activated mortar of different kinds of silicon aluminum powder(fly ash and slag)was prepared.The corrosion process was compared with ordinary Portland cement mortar(OPC)and aluminate cement mortar(CAC)of the same strength grade.Observe the morphology of mortar specimens,measure the mass change,strength loss and corrosion depth of specimens.Analyze the microstructure of mortar and the macro and micro structure of biofilm,and study the performance and deterioration mechanism of alkali-activated materials of different systems in the simulation of microbial corrosion of sewage pipes in the corrosion induction and development stage.The interaction mechanism between different mortar and biofilm and its influence on the deterioration of mortar were investigated.The results show that: In the corrosion induction stage in sewage environment,the neutralization depth of alkali-activated fly ash mortar(AAF)is larger,and the surface p H of AAF is the first to reach the condition of microbial attachment,and it only takes2 months to enter the corrosion development stage.When the p H value of OPC reached9,it was 1.5 times that of AAF,indicating that the neutralization rate of AAF was faster in the induction stage.In the corrosion development stage in sewage environment,compared with alkali-activated slag mortar(AAS),OPC and CAC,the appearance of AAF is relatively complete,and the mass loss and compressive strength loss are less,which are 1.90% and 11.60%,respectively.The surface of OPC and AAS specimens was covered with a thick layer of gypsum,and some surface slurry of CAC mortar was peeled off.With the increase of corrosion time,OPC properties deteriorated seriously,with mass loss and strength loss up to 4.3% and 36.46%,respectively.However,OPC showed the best performance in neutralization depth performance,only reaching 5 mm after the whole corrosion process.AAF will leach more aluminum ions,thus reducing the microbial activity in the sewage.Therefore,the p H of the mortar surface drops slowly,there are fewer biofilms attached to the mortar surface,and the formation of a hard high-silicon skeleton keeps the surface intact.Although the content of aluminum ions leached from CAC mortar was lower than that of AAF specimen,the ratio of dead bacteria to live bacteria in the biofilm was the highest 1:1.2.The number of pores larger than 1000 nm increased in AAS and OPC specimens after microbial corrosion,indicating that bacteria are more likely to use biological acids to penetrate into the mortar.Although the initial total porosity of AAF is the largest,its main characteristics after corrosion are the increase of 100-1000 nm pores and the decrease of 20-100 nm pores.Based on the results of the mortar tests in three stages,a deterioration corrosion model was established.The dependent variable surface p H,mass loss and compressive strength of mortar had a linear relationship with the independent variable corrosion time,but the change of AAF quality in the induction stage had a negative correlation with the corrosion time,which was contrary to the other groups of mortar.The service life of AAF is the longest when the failure standard is 5% mass loss rate,which can reach 2.8 times of OPC.Compared with OPC and AAS,the service life of AAF,alkaliactivated slag mortar(AAS1)and CAC in the microbial corrosion stage is longer.