Preparation Of Microbial Active Functional Material And Its Application In Self-healing Mortar

As a multi-phase inhomogeneous material,concrete is prone to crack under the action of loads and deformations in engineering practice,which seriously affects the functionality and durability of concrete structures.Therefore,to develop the concrete with robust self-healing performance is of great significance to extend the service life of the structure.Inspired by the natural self-healing ability of natural organic life bodies after damage,researchers have proposed a variety of bionic self-healing methods for concrete cracks.Among them,the microbial self-healing method has received extensive attention from domestic and foreign researchers in recent years due to environmentally friendly and great self-healing potential.To solve the decline of microbial long-term activity and insufficient self-healing effect inside the crack in microbial self-healing concrete,the microbial active functional material was developed by encapsulating microbes in the artificial active functional carrier in this paper.The active functional carrier can release carbonate ions while protecting microorganisms,and the components of the carrier itself undergo a pozzolanic activity reaction to promote the repair of cracks.The main research contents and research conclusions are as follows(1)Based on the working principle of microbial self-healing concrete,microbial strain suitable for the self-healing of concrete cracks was selected,and the appropriate medium was determined according to the growth of microbial strain and urease activity.Moreover,the alkali resistance performance of the selected microbial strain and the mineralization ability under the action of different calcium sources were explored.The results showed that medium composed of yeast extract and urea was most suitable for the selected sporosarcina pasteurii strain.This strain has good alkali tolerance,but it is still difficult to grow under high alkali conditions(pH>12).In addition,when calcium chloride or calcium lactate was used as calcium source of the strain,the mineralized products formed were all calcite,but when calcium lactate was used as a calcium source,the mineralization deposition ability was better.(2)The active functional carrier encapsulated microorganisms was prepared by disc granulation technology,and the preparation process parameters of the active functional carrier were studied.The active functional carrier encapsulated microorganisms adopts a core-shell structure.The core material,including slag powder,bacteria-carrying calcium carbonate powder,sodium carbonate and yeast extract,were made into pellets by using sodium silicate solution as binder.Then the core pellets were double-layer coated by epoxy resin and sulphoaluminate cement.Moreover,the functional properties of the prepared active functional carrier such as microbial protection,slow release of carbonate ions and pozzolanic activity were investigated.The results showed that the intact active functional carrier had a good protective effect on microorganisms in the pore solution of the simulated cement-based material.When the active functional carrier ruptured,the carbonate ions were slowly released to compensate the lack of carbonate ions induced by microbial metabolism inside the crack and promoted the formation of calcium carbonate.In addition,the pozzolanic reactivity of active functional carrier could be activated to form C-S-H gel in the cement-based material(3)The active functional carrier encapsulated microorganisms and microbial mineralization substrates(urea and calcium lactate)were added to prepare microbial self-healing mortar.The compatibility of the active functional carrier encapsulated microorganisms and the mortar was explored.The results showed that the combined addition of active functional carrier encapsulated microorganisms and microbial mineralized substrates could improve the fluidity of cement mortar,but had a slight negative impact on the compressive strength of cement mortar.When the volume dosage of the carrier was 10%,the fluidity of the mortar had the greatest improvement,with an increase of 13.5%compared to the control group,and compressive strength of the mortar was slightly affected,the 28d compressive strength had only dropped by 5.9%.Moreover,crack self-healing effect of mortar with the active functional carrier encapsulated microorganisms(10%volume dosage)was studied by image method and water permeability test method,and the crack repair products were analyzed by X-ray diffraction analysis(XRD),thermogravimetric analysis(TG),and scanning electron microscope(SEM).The results showed that the active functional carrier encapsulated microorganisms significantly improved the self-healing effect of the mortar cracks.After healing for 56 d in water,for the cracks with a width of about 0.4mm,the area repair ratio reached 99.78%,and the water permeability coefficient dropped by 84.32%.The microscopic analysis results showed that the repair products on the crack surface were mainly calcite-type calcium carbonate,and bacterial imprints could be observed on the crystal surface,indicating that microorganisms were involved in mineralization.