Gradient Mineralization Of Cement-based Materials By Microorganism And Its Effect On Anti-efflorescence

Cement based materials will be the most important structural materials in construction and civil engineering for a long time.However,the cement based material surface prones to cause the emergence of efflorescence and white spot,which seriously affects the appearance of exterior wall decoration and the constraints in actual engineering of large-scale application.At present,the treatment of efflorescence of cementitious materials is to add activated mineral admixtures to replace part of cement or coate protective layer on the surface of the cement based material.But these methods can not solve surface efflorescence of cement-based material problem in the root.This paper bases on the mechanism of surface efflorescence,using creatively microbial mineralization technology to formate mineralization products on the surface layer of concrete pores,high dense structure and durability.At the same time,change the efflorescence substances into insoluble minerals and dense surface structure to greatly reduce the efflorescence degree and probability through microbial mineralization.The main research conclusions and achievements of this thesis are as follows:（1）Determination of the formula of compound bacteria controlling gradient mineralization of the surface of cement based materialC bacteria and G bacteria were added into cement based materials.the concentration of Ca（OH）2 and the porosity of specimen can be decreased by 11.99%and 23.21%,and the maximum mineralization depth is 10-llmm when the C:G is 2:1,the content of compound bacteria is 0.4%,water cement ratio is 0.5 and the concentration of CO₂ is 80.68mol/L.Compared with single bacteria,the composite bacteria has stronger absorption ability of CO₂,better alkali resistance and high temperature resistance,which can control the depth range of cement based specimens more widely.（2）Revealation the mechanism of bacteria controlling cement based gradient mineralizationThrough the investigation of effect of bacterial on the CO₂ absorption,the conversion of CO₂,the adsorption of Ca2+ and the formation of CaCO₃.the mechanism of bacterial regulation of cement-based specimen gradient mineralization was revealated.Study shows that the enzymes produced by bacterias which can absorb the CO₂ in the air,CO₂ and H+ in solution reacted to HCO₃-under the action of bacteria.Because the enzyme produced by the two types of bacteria belongs to metal enzyme,which can adsorb Ca2+,and Ca2+ formed the site of CaCO₃ precipitation around bacteria.Because of the different culture methods of C bacteria and G bacteria,and their spore enzyme mechanism,which can impact the induction of CaCO₃ deposition process,the CaCO₃ induced by C was spherical,and the CaCO₃ induced by G was columnar.（3）Exploration the inhibition of the surface efflorescence of cement-based specimen by bacterial and product applicationSuppress the surface efflorescence of cement-based materials through the bacterial control of surface gradient mineralization.When the content of bacteria is 0.4%,water cement ratio is 0.45,the carbon dioxide concentration is 80.68mol/L,the cement specimen surface area can be reduced relative efflorescence from 31.23%to 87.56%.At the same time,according to the demand of enterprise products,the bacteria was used in the products producted by Nanjing Beilida Aojie,Xiamen kezhijie.The test results show the degree and probability of occurrence of efflorescence surface can be greatly reduced by adding compound bacteria in different types of cement based products.Which can improve product quality and reduce the cost of maintenance for enterprises.