Formation Of Microstructure Of Hardened Tricalcium Silicate Paste Under Coupling Of Hydration And Microbial Mineralization

With the development of society and economy,concrete is developing towards the trend to combine high durability and high appearance together while meeting the requirements of strength and durability.It is new method to densify surface layer from millimeter to centimeter using bio-mineralization,and then to improve durability of concrete.By changing the conditions such as the amount of microorganisms in the concrete and the carbon dioxide（CO₂）curing pressure through experiments,the gradient structure of the concrete surface can be adjusted to obtain a good material proportion,but this process requires a lot of time and material energy.Computer simulation can analyze the principles of concrete hydration and microbial mineralization,and predict the formation of microstructure of concrete under different initial conditions,thereby it’s a great method to save resources.This thesis mainly studies the mechanism of hydration of main cement mineral tricalcium silicate（C₃S）and microbial mineralization,and proposes the control equations of different processes and their mutual influence relationship from the principle,and constructs the hydration-microbial mineralization coupling model.The model is used to predict calcium hydroxide（Ca（OH）₂）,biological calcium carbonate（bio-Ca CO₃）,residual C₃S content and porosity distribution in hardened C₃S paste under different microbial dosage and CO₂ curing pressure.The hydration-microbial mineralization coupling model mainly includes the C₃S hydration process,microbial mineralization process and the transmission process of CO₂ and calcium ions(Ca²⁺)in the C₃S hardened slurry,and corresponding control equations are proposed for different processes.The hydration process uses the C₃S single particle hydration model to study the hydration rate constant in phase boundary control and diffusion control,to determine the relationship between the degree of hydration and time,and to determine the content of Ca（OH）₂ and C₃S and porosity through the quantitative relationship between reactants and products.The mineralization model analyzes the reaction rate of microorganisms in the three-step mineralization equation,and uses the Mie equation and the heterogeneous nucleation equation to determine the enzyme reaction process as a rate-limiting step,and determines the mineralization rate equation of microorganisms under different conditions.The transmission process describes the transmission and phase transition of CO₂ in the pores.Fick’s Second Law is used to determine the concentration distribution of CO₂ under different pore structures;the concentration distribution of Ca²⁺takes into account the dissolution of solid calcium phase and the diffusion in the pore solution applying Fick’s Second Law.The hydration-microbial mineralization coupling model also includes the interaction between the three processes.Mineralization process mainly affects the hydration rate constant,which affects the degree of hydration at different ages.Hydration process influences the microbial mineralization environment,which is described by the variables in the model.The hydration-mineralization coupling process influences the pore structure of the hardened paste,and affect the transmission of CO₂and Ca²⁺.The hydration-microbial mineralization coupled model predicts the Ca（OH）₂,bio-Ca CO₃ and C₃S content distribution and porosity distribution under different microbial dosage and CO₂ curing pressure,and compares it with the experiment results.The prediction results are in good agreement with the experiment results,which shows that the established coupling model can predict the microstructure of microbial mineralized hardened C₃S paste.