Effect Of Biological Sulfuric Acid On Degradation And Chloride Ion Binding Of SAC Sea Sand Concrete

Microbial corrosion refers to the corrosion of material by microbial metabolism process,and the most typical one is biological sulfate corrosion.Compared to the corrosion of chemical sulfuric acid,biological sulfate is easier to cause concrete's cracking,strength loss and durability reduction.In this research,ordinary Portland cement(OPC)and sulphur aluminate cement(SAC)has been used to prepare sea sand concrete respectively,and T.t bacteria was adopted to simulate three kinds of biological sulfate corrosion conditions(pH=1.0,1.5,2.0).The concrete's quality,intensity,the pH of erosion solution and corrosion layer(5 mm from the surface of concrete),were measured,and the Chloride ion binding rate(hereinafter referred to as binding rate)was tested to analyze the degree of degradation caused by biological sulfate corrosion in the concrete,compared to the results of chemical sulfuric acid corrosion,By the methods of pore structure,SEM-EDS,XRD,NMR,the structure change of concrete corrosion layer and the corrosion products etc were studied,and the release of the binding chloride ion was analyzed.The results show that:1.The proportion of Q3 and Q4 in the hydration products and the polymerization degree of SAC sea sand concrete is higher than of OPC sea sand concrete,and the 28 d strength of SAC sea sand concrete is 70.5 MPa,which is higher than the OPC sea sand concrete.The average pore size of SAC sea sand concrete(21.6 nm)is smaller than that of OPC sea sand concrete(26.5 nm),leading to a compact structure and less affected by sulfuric acid corrosion degradation.In addition,the binding of chloride ions in SAC sea sand concrete is mainly chemical combination,whose chloride ion binding rate is 84.59%and the product F salt is relatively stable.But the binding of chloride ions in OPC sea sand concrete is less and mainly in the way of physical adsorption,thus the chloride ion is easy to release again.So under the conditions of sulfate,the degree of corrosion in OPC sea sand concrete is more serious than that in SAC sea sand concrete.2.Under the same conditions(pH=1.0,1.5,2.0),biological sulfate corrosion is different from chemical sulfuric acid corrosion.The pH value of erosion liquid after chemical sulfuric acid corrosion is increasing,and the degradation of concrete is weaken.But after biological sulfate corrosion,the erosion liquid pH value increases firstly and then decreases and eventually tends to a dynamic balance,which greatly influences the overall deterioration of concrete.Therefore,the degradation of both sea sand concretes under biological sulfate corrosion is worse than that under chemical sulfuric acid corrosion,and the decrease of chloride ion binding rate under biological sulfate corrosion is also more obvious than that under chemical sulfuric acid corrosion,When the chloride ion binding rate in sea sand concrete decreases to 0 under biological sulfate corrosion,the pH value is higher than that under chemical sulfuric acid corrosion.When entirely corrosion,the time required is less than that under chemical sulfuric acid corrosion.T.t bacterial is adsorbed on the rough,loose corrosion layer,which is full of gypsum and produces acid on the surface of concrete,and then the path that biological sulfate spreads into the concrete(bacteria effect)is shortened.Under the combined action of H+,SO42-and bacteria effect,the deterioration and the chloride ion release rate of sea sand concrete is accelerated.3.The sulfuric acid concentration affects the degradation degree of concrete.When the pH is high,the sediment filling effect of SO42-is greater than the dissolution of H1 on the concrete,and the degree of corrosion influence is not obvious;when the pH value is low,the H+ play a leading role on the dissolution of concrete,and the degree of corrosion is serious.With the decrease of the pH value,the time for chlorine ion binding rate of corrosion layer down to 0 becomes shorter.So,with the increase of H+ concentration in solution,the dissolution of sea sand concrete hydration products is more obvious;degradation degree of sea sand concrete is speeded up,and the chloride ion release speed is accelerated.