Characterization Of Microorganisms And Mineralized Calcium Carbonate In Cement-based Materials

Considering the shortcomings of cement-based materials,such as brittleness,low tensile strength and early shrinkage,it is easy to produce micro cracks on the surface or inside of structures during service,which affects the service life of cement-based materials.Microbial induced calcium carbonate deposition（MICP）technology has attracted the attention of many scholars at home and abroad because of its green environment protection and the ability to produce mineralized calcium carbonate with good compatibility with concrete matrix.At present,there are few methods for the labeling of microorganisms in cement-based materials.Most of the labeling methods of microbial mineralized calcium carbonate in cement-based materials remain on the macro surface.In the process of the research on the distribution of mineralized products,though the mineralized products can be observed by X-ray computer fault scanning（X-CT）,However,because the density of mineralized products is not different from that of matrix material,the distribution of microbial mineralized products in self repairing concrete by X-CT is not recognized clearly and efficiently,which affects the characterization and analysis of microbial restoration effect of cement-based materials.Therefore,the study on the characterization of microorganisms and mineralized calcium carbonate in cement-based materials is of great significance to improve the repair effect and the way of fixing the microbial cement-based materials.In this paper,a method of microbial extraction from cement-based materials was studied,and the effect of extraction process on microbial extraction rate was explored.The methods of microbial staining,observation of survival status and the measurement of microbial quantity were studied.The methods of characterizing mineralized calcium carbonate,Cu²⁺adsorption and Eu³⁺doping were studied.The reaction time,temperature and the initial Cu²⁺concentration/the content of Eu³⁺were used to optimize the conditions.The properties of the products were analyzed by XRD,XRF,TG,SEM,EDS,TEM,X-CT and fluorescence spectra.The doping mechanism was analyzed by hybrid orbital theory and crystallization phase transition theory.The main results are as follows:（1）The extraction and analysis methods of microorganisms in cement-based materials were proposed.The cement-based materials were crushed by mechanical method,ground through 200 mesh sieve,and then the extract containing normal saline and nutrients was added.After soaking for 24h,changing the extract for three times,ultrasonic wave at 80k Hz for 5min,and 45℃,the extraction rate of microorganism was about 72%.When the dyeing time is 5min～30min,the dyeing temperature is30℃～45℃,the p H is alkaline,and the dye concentration is 1mg/m L～5mg/m L,the dyeing effect is better.Combined with inverted fluorescence microscope and flow cytometry,the"Crossgate"was set to distinguish the survival status and the number ratio of cells.（2）A direct observation and analysis method of Cu²⁺adsorption of mineralized product calcium carbonate was developed.When the initial concentration of Cu²⁺is12.5mg/m L,the temperature is 25℃and the adsorption time is 8h,the characterization effect of Cu²⁺adsorption method is the best.In the process of Cu²⁺adsorption by calcium carbonate,the adsorption capacity of biological calcium carbonate is more than that of chemical calcium carbonate,and the addition of nutrients has little effect on the adsorption capacity.The adsorption process of biological calcium carbonate for Cu²⁺conforms to the Langmuir model,and the maximum adsorption capacity is 108.60 mg/g.the adsorption process can be described by quasi second order kinetic equation.The adsorption rate of calcium carbonate for Cu²⁺is related to the surface active sites and the precipitation reaction of Cu²⁺in addition to physical adsorption.（3）A qualitative analysis method of mineralized product calcium carbonate with Eu³⁺doping labeling and X-CT was invented.When the content of Eu³⁺is 2%,the temperature is 45℃and the doping time is 48 h,the characterization effect of Eu³⁺doping method is the best.In the process of calcium carbonate doping Eu³⁺,the doping amount of biological calcium carbonate is more than that of chemical calcium carbonate,and the addition of nutrients has little effect on the doping amount.Eu³⁺had no significant effect on the number and activity of mineralizing microorganisms.The bonding ability and lattice distortion growth rate of Eu are analyzed by using hybrid orbital theory and phase transition theory of crystallization process.The feasibility of Eu doping into calcium carbonate lattice is further demonstrated theoretically.After Eu³⁺doping,Ca CO₃can be observed more clearly by X-CT.（4）The results showed that the number of living cells decreased rapidly in the early stage of cement-based materials,but it was relatively flat in the later stage;Compared with the results of thermogravimetric analysis of mineralized calcium carbonate in fracture area,the direct observation method of Cu²⁺adsorption and the X-CT analysis method of Eu³⁺doping have good accuracy in measuring the distribution of mineralized products and the repair depth in fracture area.