Design And Preparation Of Core-shell Carrier For Microbial Healing Agent

In design,the material parameters,structural parameters and matching with the concrete matrix of the core-shell carrier based on the mechanical response mechanism were studied.A prediction model of the carrier load capacity on the crack surface based on probability distribution and surface function was constructed.The effects of different parameters on responsiveness and loadability were analyzed.Then,the responsive and loadable design method of the carrier was established.In preparation,the material selection range was determined through experimental tests,the design method of carrier material mix ratio was proposed,and the equipment parameters,process parameters,and product quality stability during the production capacity scale-up process were determined.In verification,the protective performance,durability,and motion characteristics of the healing agent particles,the effects of particle strengths and dosages on concrete strength,and the effects of particle dosages and crack widths on concrete self-healing performances were verified by experimental tests.The following four innovative achievements have been obtained.(1)The relationship between the tensile strength and the elastic modulus of the carrier and the concrete matrix is the key to restrict the mechanical responsiveness of the carrier.Methods for calculating elastic modulus,particle strength and size of carriers that are synchronous or slightly lagging the matrix response were successfully established.It is clarified that the larger the elastic modulus of the shell is,the higher the bearing stress is.The larger the"core"size,the simultaneous increase in shell and matrix stress.The increasing elastic modulus of the shell along the radial gradient of the particle can reduce the maximum stress concentration factor of the matrix.(2)The load capacity of the carrier is mainly related to the inner diameter and dosage of the core-shell type repair agent,and the design calculation formula is established.The probability distribution of particles on the crack surface is a binomial distribution,the Poisson approximation is suitable for small size carriers,and the normal approximation is suitable for large size carriers,and the critical size is 5.0 mm.Concrete with a larger proportion of coarse aggregate and a larger maximum particle size of coarse aggregate has a better carrier load capacity.(3)The fly ash/metakaolin composite sulfoaluminate cement can form a large elastic modulus adjustment range,which can meet the matching requirements of different strength grades of concrete.After the carrier is mixed into the concrete,it can produce gelatinity in an alkaline environment,and the strength will increase twice to meet the requirements of post-age matrix.Adding 0.6%lithium sulfate,the setting time of the shell material is greatly accelerated,and the maintenance process is greatly shortened.With the addition of 7.5%styrene-butadiene emulsion,the OH~-transportation in the shell is significantly inhibited,and the tensile strength of carrier is also greatly improved.The crack initiation toughness,instability toughness and fracture energy of the carrier-matrix interface can be determined by using nano-silica,and the suitable dosage is 3.2%.The rolling,stirring-rolling granulation process is suitable for the manufacture of core-shell structured particles.Equipment/process parameters for single batch10kg,50kg and industrial scale production were determined.The product quality stability of each production capacity level is good,and the process adaptability is strong.The world’s first fully automatic industrial production line for core-shell microbial healing agents has been built.(4)Under the protection of the shell,the physiological characteristics of the spore-loaded and germinated vegetative somatic cells were stable within 500 days,and the mineralization ability and mineralization product properties did not change significantly.The multi-ion coupled transport model predicts that the protection aging of 7.5%styrene-butadiene emulsion can reach 900d.The core-shell microbial healing agent has a mass loss rate of 1.6%under sulfate corrosion,can resist more than 60 freeze-thaw cycles,can withstand temperatures not higher than 80°C,and has good durability.The porosity of the shell tested by CT is 0.2%,the pore diameter is mostly less than 0.08mm,and the structure is dense.When the dosage of healing agent is 25kg/m~3,the repairing ratio of area at crack mouth surface and repairing ratio of crack against water permeating of cracks with a width of 0.5mm can reach more than 95%,and ultrasonic propagation velocity in cracked concrete after repair can reach 2.5km/s,and the concrete strength does not decrease.